DNVGL-OS-C102 Structural design of offshore ship-shaped units

The electronic pdf version of this document, available free of chargefrom http://www.dnvgl.com, is the officially binding version.

DNV GL AS

OFFSHORE STANDARDS

DNVGL-OS-C102 Edition July 2018

Structural design of offshore ship-shapedunits

FOREWORD

DNV GL offshore standards contain technical requirements, principles and acceptance criteriarelated to classification of offshore units.

© DNV GL AS July 2018

Any comments may be sent by e-mail to [email protected]

This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of thisdocument. The use of this document by others than DNV GL is at the user's sole risk. DNV GL does not accept any liability or responsibilityfor loss or damages resulting from any use of this document.

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Offshore standards, DNVGL-OS-C102. Edition July 2018 Page 3Structural design of offshore ship-shaped units

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CHANGES – CURRENT

This document supersedes the July 2015 edition of DNVGL-OS-C102.Changes in this document are highlighted in red colour. However, if the changes involve a whole chapter,section or subsection, normally only the title will be in red colour.

Changes July 2018Topic Reference Description

Ch.3 Sec.1 [2] Introducing technical description of the additional classnotations FMS, R, FIELD and FAB.

Additional class notationincluded in Ch.3.

Ch.3 Sec.1 [2.4] New additional class notation FAB to cover extended NDT scopefor new building FSO/FPSOs operating in harsh locations.

Ch.2 Sec.1 Design principles in line with DNVGL-RU-SHIP Pt.3.

Design conditions applicable for offshore units included.

Ch.2 Sec.1 [2.2] Updated content of section and terms, abbreviations andsymbols in line with DNVGL-RU-SHIP Pt.3.

Ch.2 Sec.2 Design loads in line with the equivalent design wave (EDW)principle in DNVGL-RU-SHIP Pt.3.

Additionally input of direct site specific loads included,according to design conditions given in Ch.2 Sec.1.

Ch.2 Sec.3 Strength assessments in line with DNVGL-RU-SHIP Pt.3, basedon the site specific loads given in Ch.2 Sec.2 and with referenceto DNVGL-CG-0128 Buckling, and DNVGL-CG-0127 Finiteelement analysis.

Ch.2 Sec.4 Design fatigue principles in line with DNVGL-RU-SHIP Pt.3 andwith reference to DNVGL-CG-0129.

Ch.2 Sec.5 Hull equipments and supporting structure in line with DNVGL-RU-SHIP Pt.3.

Specific new subsections:

- support for permanently moored units

- support of offshore cranes.

Ch.2 Sec.6 Topside structure modified, in line with the structural principlesin DNVGL-RU-SHIP Pt.3.

Alignment with DNV GL rulesfor ships.

Ch.2 Sec.7 Special unit provisions:

— update and included loading conditions for the different unittypes

— FLNG and well intervention units included— conversion and lifetime extensions moved from previous

appendixes, and modified.

Application of fabricationand material standards incl.definition of FAB notation.

Ch.2 Sec.1 [5] Update material selection and inspection principles in line withthe DNVGL-RU-SHIP Pt.3.

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Topic Reference Description

Introducing documentationrequirements.

Ch.3 Sec.1 [1] Introducing document requirements.

Restructuring of technicalcontent between DNVGL-RP-C206 and DNVGL-OS-C102.

Ch.3 Sec.1 [2.1] Included the descriptions related to the FMS notation.

Editorial corrections

In addition to the above stated changes, editorial corrections may have been made.

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CONTENTS

Changes – current............................................................3

Chapter 1 Introduction..................................................... 7Section 1 General................................................................................................................ 7

1 General.................................................................................................................7

2 Definitions............................................................................................................8

Chapter 2 Technical provisions....................................... 12Section 1 Design principles............................................................................................... 12

1 General...............................................................................................................12

2 Design conditions...............................................................................................13

3 Design load scenarios........................................................................................ 16

4 Arrangements.....................................................................................................17

5 Material selection and inspection principles...................................................... 18

6 Net scantling and corrosion protection.............................................................. 23

Section 2 Design loads...................................................................................................... 25

1 General...............................................................................................................25

2 Static loads........................................................................................................ 26

3 Dynamic loads....................................................................................................27

4 Design load scenarios and design loading conditions........................................ 39

Section 3 Strength assessment......................................................................................... 40

1 General...............................................................................................................40

2 Hull girder nominal strength check....................................................................40

3 Hull local scantling.............................................................................................41

4 Finite element analyse.......................................................................................42

5 Welding connections.......................................................................................... 44

Section 4 Fatigue............................................................................................................... 46

1 Principles and methodology...............................................................................46

Section 5 Hull equipment, supporting structures and appendages.................................... 51

1 Anchor and anchor mooring equipment............................................................. 51

2 Support structure of deck fittings for mooring and towing................................ 51

3 Support structure for permanent mooring systems........................................... 52

4 Support of equipments, winches and pulling accessories...................................54

5 Support of topside structures............................................................................ 55

6 Support structure for inboard cranes, davits and lifting masts.......................... 55

7 Support of offshore cranes................................................................................ 56

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8 Bulwarks, protection of crew and appendages.................................................. 63

Section 6 Topside structures requirements....................................................................... 65

1 Application......................................................................................................... 65

2 Material and inspection principles..................................................................... 65

3 Design principles................................................................................................66

4 Design loads...................................................................................................... 66

5 Local design requirements.................................................................................69

6 Primary supporting members.............................................................................71

Section 7 Special provisions for unit types, conversions and lifetime extensions.............. 74

1 General...............................................................................................................74

2 Drilling units...................................................................................................... 74

3 Well intervention units...................................................................................... 78

4 Floating production and storage units............................................................... 79

5 Conversion of units............................................................................................98

6 Life time extension.......................................................................................... 103

Chapter 3 Classification and certification......................105Section 1 Classification and certification requirements................................................... 105

1 General.............................................................................................................105

2 Additional class notations - structural strength............................................... 111

Changes – historic........................................................119

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CHAPTER 1 INTRODUCTION

SECTION 1 GENERAL

1 General

1.1 IntroductionThe requirements given in this standard gives supplementary requirements above the basic hull strengthrequirements in DNV GL rules for classification of ships, DNVGL-RU-SHIP Pt.3.For items or strength requirements not specific given in this standard, the general requirements in DNVGL-RU-SHIP Pt.3 applies.

1.2 ObjectivesThe objectives of this standard are to:

— provide an internationally acceptable standard for design of offshore ship-shaped units— serve as a technical reference document in contractual matters between purchaser and manufacturer— serve as a guideline for designers, purchaser, contractors and regulators— provide, as far as possible, consistent loads for both topside and hull design.

1.3 Scope and applications

1.3.1 This standard cover the following ship shaped units constructed in steel:

— production and storage (FPSO/FLNG/FSO)— drilling— well intervention

for the following structural items:

— material selection and inspection principles— design conditions and design loads— hull strength assessment— fatigue requirements— topside structure— topside and turret interface to hull structure— specific units requirements— procedures and requirements for units subject to DNV GL classification services.

1.3.2 Serviceability (SLS) condition is not covered in this standard.

1.3.3 Strength requirements are given for restricted and non-restricted transit and operation. Units withoutany restrictions may operate world wide, except in Polar areas. For operation in Polar areas additionallyrequirements associated with such operation shall be complied with.

1.3.4 For novel designs or unproven applications where limited experience are available, global FE-analysisand model tests may be required to demonstrate the overall strength and fatigue capacity.

1.3.5 In case of conflicts between requirements given in this standard and other DNV GL documents, therequirements given in this standard prevail.

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1.3.6 For application of this standard as technical basis for classification see Ch.3 Sec.1.

1.3.7 Flag and shelf state requirements are not covered by this standard.Guidance note:

Governmental regulations may include requirements in excess of the provisions of this standard depending on the type, locationand intended service of the offshore unit or installation.

---e-n-d---o-f---g-u-i-d-a-n-c-e---n-o-t-e---

2 Definitions

2.1 Verbal forms

Table 1 Definition of verbal forms

Term Definition

shall verbal form used to indicate requirements strictly to be followed in order to conform to the document

shouldverbal form used to indicate that among several possibilities one is recommended as particularly suitable,without mentioning or excluding others, or that a certain course of action is preferred but not necessarilyrequired

may verbal form used to indicate a course of action permissible within the limits of the document

2.2 Terms, abbreviations and symbols

2.2.1 The following terms are used in this standard. Typical ship specific terms are given in DNVGL-RU-SHIPPt.3 Ch.1 Sec.4 [3.8].

Table 2 Definition of terms

Term Definition

accidental limit state(ALS)

a limit where the structure no longer resists accidental loads and maintain structural integritydue to local damage

design life the defined period the unit is designed to operate

design temperature the reference temperature in air for assessing areas where the unit can be transported,installed and operated

drilling unita unit used for drilling in connection with exploration and/or exploitation of oil and gasThe unit is generally operating on the same location for a limited period of time and isnormally equipped with dynamic positioning system with several thrusters.

design fatigue life design life × design fatigue factor (DFF)

fatigue limit state (FLS) a limit where the structure not longer satisfy the requirement related to damage from cyclicloading

floating liquid natural gas(FLNG)

a unit for processing hydrocarbons and refrigerate gas to produce liquefied gas, storage andoffloadingThe unit is typically permanently moored, and equipped with a side by side offloadingsystem.

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Term Definition

floating storage andoffloading unit (FSO)

a unit used for storage of oil with arrangement for offloading to a shuttle tankerThe unit is typically permanently moored at one location using a turret or spread mooringsystem.

floating production,storage and offloadingunit (FPSO)

a unit used for production and storage of crude oil, with arrangement for offloading to ashuttle tankerThe unit is typically permanently moored at one location using a turret or spread mooringsystem.

serviceability limit state(SLS) a limit where the structure no longer satisfy the criteria related to normal use or durability

temporary mooring anchoring in sheltered waters or harbours exposed to moderate environmental loads

turreta device providing a connection point between the unit and the combined riser- andmooring- systems, allowing the unit to freely rotate (weather vane) without twisting therisers and mooring lines

ultimate limit state (ULS) a limit related to the maximum load carrying resistance of the structure

2.2.2 Unless otherwise specified, the following abbreviations are used in this standard.

Table 3 Abbreviations

Abbreviation Description

AP after perpendicular

CL centreline

COG centre of gravity

DFF design fatigue factor

DP dynamic positioning

EDW equivalent design wave

FE finite element

FP fore perpendicular

GM meta-centric height

KL keel line

KB vertical centre of buoyancy

LC longitudinal condition

LCB longitudinal centre of buoyancy

LMDAT lowest mean daily average temperature in air

MT magnetic particle testing, see DNVGL-RU-SHIP Pt.2 Ch.4 Sec.7

NDT non-destructive testing, see DNVGL-RU-SHIP Pt.2 Ch.4 Sec.7

PSM primary supporting member

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Abbreviation Description

PT penetrant testing, see DNVGL-RU-SHIP Pt.2 Ch.4 Sec.7

RT radiographic testing, see DNVGL-RU-SHIP Pt.2 Ch.4 Sec.77

SCF stress concentration factor

UT ultrasonic testing, see DNVGL-RU-SHIP Pt.2 Ch.4 Sec.7

2.2.3 Unless otherwise specified, the following symbols and their unit are used in this standard. Generalsymbols applicable for all ships are given in DNVGL-RU-SHIP Pt.3 Ch.1 Sec.4 [2].

Table 4 Primary symbols

Symbol Definition Units

L rule length as defined in DNVGL-RU-SHIP Pt.3 Ch.1 Sec.4 m

LPP length between perpendiculars m

φ pitch angle deg

θ roll angle m

Table 5 Symbols for material


E Young’s modulus N/mm2

ReH specified minimum yield strength as given in DNVGL-RU-SHIP Pt.3 Ch.3 Sec.1 N/mm2

Table 6 Symbols for loads


aX longitudinal acceleration m/s2

aY transverse acceleration m/s2

aZ vertical acceleration m/s2

Mwh horizontal wave bending moment KNm

Mwv vertical wave bending moment KNm

Qwv vertical wave shear force KN

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Table 7 Symbols for scantlings

Term Definition Units

t net required thickness mm

tc corrosion addition mm

tgr gross thickness mm

tres reserve thickness mm

Z hull section modulus m3

2.3 ReferencesThe following other DNV GL service documents given in Table 8 are referred to in this standard.

Table 8 DNV GL documents

Documet code Title

DNVGL-RP-C205 Environmental conditions and environmental loads

DNVGL-OS-C401 Fabrication and testing of offshore structures

DNVGL-CG-0127 Finite element analysis

DNVGL-CG-0128 Buckling

DNVGL-CG-0129 Fatigue assessment of ship structures

DNVGL-OS-C301 Stability and watertight integrity

DNVGL-OS-E401 Helicopter decks

DNVGL-RU-SHIP Pt.3 DNV GL rules for classification: Ships, Pt.3 Hull

DNVGL-RU-SHIP Pt.2 DNV GL rules for classification: Ships, Pt.2 Materials and welding

DNVGL-RU-SHIP Pt.6 Ch.6 DNV GL rules for classification: Ships, Pt.6 Additional class notations - Cold climate

DNVGL-ST-0378 Standard for offshore and platform lifting appliances

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CHAPTER 2 TECHNICAL PROVISIONS

SECTION 1 DESIGN PRINCIPLES

1 General

1.1 Limit state design

1.1.1 The standard is based on the principles of limit state design. Limit state design is a systematicapproach where each structural element is evaluated with respect to possible failure modes related torelevant design load scenarios. For each retained failure mode, one or more limit states may be relevant. Byconsideration all relevant limit states, the limit load of structural elements are the limit load considering allrelevant limit states.

1.1.2 The limit states are divided into the four categories:- serviceability limit states (SLS)- ultimate limit states (ULS)- fatigue limit states (FLS)- accidental limit states (ALS).

Guidance note:

Requirements related to SLS condition is not specifically given in the standard. However, for high or slender structures like highcrane pedestals, boom rest structure, etc. deflections should be considered.


1.2 Design methods

1.2.1 Working stress design methodIn the working stress design (WSD) method, also known as the allowable stress method, the target safetylevel is achieved by comparing the calculated design loads (W) with the characteristic structural capacity (R),including a permissible utilization factor (η) as following:

W ≤ η ∙RThe calculated response (W) contains static and dynamic loads as found applicable, and (R) represents thelimit states defined in [1.1.2].WSD method is general used for yield and buckling control, except for the hull girder ultimate strength wherethe PSF method is used, see [1.2.2].The η factor is based on actual design load scenario and criteria considered.

1.2.2 Partial safety factor (load and resistance factor design) methodIn the partial safety factor (PSF) method, also known as load and resistance factor design method (LRFD),the target safety level is obtained by applying the load with a load factor, together with a material factor.The design load (W) is found by multiply the permanent static loads (Wstat) and dynamic loads (Wdyn), withgiven partial load factors (γ). The design load (W) is then compared with the characteristic structural capacity(R), including a material factor (γR).

γstat ∙Wstat + γdyn ∙Wdyn ≤ R/γR

The PSF method shall be used for the hull girder ultimate strength control as described in Sec.3 [2.3].

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2 Design conditions

2.1 General

2.1.1 The following design conditions shall be considered:

— transit condition— operating condition— survival condition— accidental condition— inspection and maintenance condition.

2.1.2 The correlation between limit states and design conditions are:

Table 1 Design conditions and limit states

Design conditions

Site specific operationLimitstate Description

TransitOperating Survival Accidental 1) Inspection 2)

ULS Maximum static/maximum combined staticand dynamic loads X X X X

FLS Dynamic cyclic loads X X

ALS Accidental loads X X1) Accidental condition are related to project specific events and shall be specifically considered as applicable, see [2.7].2) Inspection and maintenance conditions are related to project specific operation philosophy, and shall be specificallyconsidered as applicable, see [2.5].

2.2 Transit condition

2.2.1 Unrestricted transitUnrestricted transit is defined as a condition when the unit moves, using own propulsion, between anygeographical locations, expect in polar areas. Design loads shall be based on prescriptive rule loads givenin DNVGL-RU-SHIP Pt.3 Ch.4, which is based on a probability level of 10-8, which again corresponding to 25years design life. Exemption is for sloshing loads where 10-4 probability level is used, see DNVGL-RU-SHIPPt.3 Ch.1 Sec.2 [5].Topside accelerations may alternatively be based on direct analysis according to the principles in Sec.2 [3.9].

2.2.2 Restricted transitRestricted transit is defined as a condition when the unit is restricted to move, using own propulsion, withinspecific geographical locations. Design loads shall be based on site specific information (scatter diagrams)used for transit, according to the principles given in Sec.2 [3.9].

Guidance note:

Classed units with propulsion having restricted transit will be assigned the additional class notation R (restricted in use), see Ch.3Sec.1 [2.2].


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2.3 Operating conditionOperating condition is defined as a condition where the unit is operating on location for the purpose the unitis built for (e.g. drilling). The unit will normally have limitations of how it can operate when at location(s).There will typically be a maximum sea state (Hs) to which the unit has to suspend normal operations,as motions or forces exceed the operational design limits. The maximum design sea state (Hs) for theoperational condition shall reflect a minium 1 year response level.Relevant combination of environmental wave and wind loads, and operational loads, shall be consideredas applicable. Operational limitations shall be clearly specified in the design basis documentation, see Ch.3Sec.1 [1.4].

2.4 Survival condition

2.4.1 Survival condition is defined as the condition for the most severe environmental loads the unit isexposed to at location, and is related to the 100 year response level. The location may be site specific, orworldwide.

2.4.2 Harsh locationA harsh location is defined as a location at which the unit's vertical wave bending response at location is:

MwDir-100year > MwRule

where:

MwDir-100year = 100 years direct calculated characteristic vertical wave bending moment according to theprinciples defined in Sec.2 [3.9.2], including non-linear correction defined in Sec.2 [3.9.3].

MwRule = Vertical rule wave bending moment as defined in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.4 [3.1].

2.4.3 Restricted location - benign locationA restricted location (benign location) is defined when the unit's vertical wave bending response at givenlocation is:

MwDir-100year < MwRule

Restricted area for site operation is normally applicable for unit's permanently moored at one location wherethe environmental condition is calm or moderate, or intend abort operation and seek sheltered waters inextreme weather.

Guidance note:

Benign water area is also defined when the significant 100 years wave height Hs100 year at the location is documented to be lessthan 8.0m - 10.0m, depending on the units length Lpp. Between L = 100 m and L = 200 m, linear interpolation may be used.

100 < Lpp < 200 m Lpp > 200 m

HsDir-100 year ≤ 8.0 m HsDir-100 year ≤ 10.0 m


2.4.4 For units designed for leaving location in case of an extreme weather condition (e.g. forewarnhurricanes, iceberg, etc.), an approved system/procedure for the disconnecting shall be provided. The unitshall anyhow be checked for the regular site specific 100 years environmental condition (storm excludinghurricanes) at the location.

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Guidance note:

Class approved units intended leaving location in case of extreme weather condition, will be assigned the additional class notationR (restricted in use), see Ch.3 Sec.1 [2.2].


2.5 Inspection and maintenance conditionInspection and maintenance condition is defined as conditions at which inspection and maintenance arecarried out. There will typically be environmental restrictions to this condition. All actual drafts and tank fillingconfigurations shall be considered. The environmental conditions and relevant filling configuration shall bespecified by the project, and shall be part of the unit's design basis documentation, see Ch.3 Sec.1 [1.4]. Anyrestriction related to a maximum design sea state (Hs) for the inspection and maintenance condition shouldreflect a minimum 1 year response level.

Guidance note:

Inspection and maintenance condition may be omitted for strength check, provided it can be demonstrated that transit or survivalconditions are governing.


2.6 Wet tow to locationWet tow to location is defined as one single voyage within a defined towing route, typically from the shipyardto site a specific location where the unit shall operate. For hull structure the requirements to the transitcondition as given in [2.2] applies. The hull strength may be based on 1 year direct loads for the definedtowing route.

Guidance note:

Wet tow to location is defined to have short duration (normally within 30 days), and is general applicable for storage units withoutpropulsion, i.e. class notation OI (offshore installation). The towing execution itself is not covered in the standard class scope, butis normally covered by the rules from recognized Marine Warranty.


2.7 Accidental condition

2.7.1 Accidental condition are events caused by abnormal operation or technical failure. The relevantaccidental loads depend on the unit's function, arrangements, operational procedures, safety systems, etc.The accidental loads shall normally be based on a risk assessment study. Generic design accidental loads arespecified in DNVGL-OS-A101.

Guidance note:

Environmental events applicable for the hull structure are covered by the conditions given in [2.2] to [2.6]. For units moored athurricane locations or in polar areas, extreme environmental events shall be special considered.

Statutory authorities may have requirements in excess of the design accidental loads and safety principles given in DNVGL-OS-A101.

Collision with supply boats are normally not considered affecting the structural integrity as long as the unit complies with stabilityrequirements from the national or international bodies.

Dropped objects are applicable in areas where a potential object may lead to critical failure or damage to the unit's process orsafety system. Safety critical equipment shall be protected from dropped objects, and the protecting structure shall resist theactual impact energy.


2.7.2 For accidental events found applicable for the project, the acceptance criteria for FE-analysis yieldcontrol (DNVGL-RU-SHIP Pt.3 Ch.7) and buckling (DNVGL-RU-SHIP Pt.3 Ch.8) shall be based on criteria AC-III defined in the DNVGL-RU-SHIP Pt.3 Ch.1 Sec.2 [5.4].

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Non-linear FE analysis may be applied for the strength calculation, considering all relevant failure modes(e.g. strain rate, local buckling, joint overloading). Local overloading of the structure is acceptable, providedredistribution of forces is possible.

3 Design load scenariosThe design load scenarios are similar the principles as defined in DNVGL-RU-SHIP Pt.3 Ch.1 Sec.2 [4.2]. Thegoverning loads related to transit or site specific operation, shall be used for the design load scenarios asfound applicable.

Table 2 Design load scenarios

Load calculation method Acceptancecriteria 2)

Limitstate Scenario Type Description

Prescriptiverule loads

Direct loadcalculation

Transit seagoing or site specific operational scenario

ULS S + D Static +dynamic load

Static loads and governing dynamicload from seagoing transit condition,or from site specific operation

x x 1) AC-II

ULS I Impact load Impact loads as slamming, bow impact x AC-IV

ULS SL Sloshing Sloshing in tanks for seagoingcondition x AC-I

FLS F Fatigue Fatigue design load scenario x x -

Harbour or static loads scenario

ULS S Static loadMax static loads due to loading andunloading tanks in harbour or withoutany dynamic loads

AC-I

ULS S Static loadMax static loads related tomaintenance or inspection condition insheltered waters

N/A 4)

AC-I

Overfilling of ballast water tanks and testing scenario

ALS A Accidental Overfilling of ballast tanks through airpipe x AC-III

ALS T Testing Tank testing of liquid tanks x AC-III

Flooding scenario

ALS A Accidental Max loads on watertight bulkheads x AC-III 3)

1) The required load calculation method depends of site specific operation criteria, see Sec.1 [2.4] and Sec.2 [3.2].2) See DNVGL-RU-SHIP Pt.3 Ch.1 Sec.2 [5.4] for applicable acceptance criteria.3) For collision bulkhead, acceptance criteria AC-I shall be used.4) Not applicable as only static loads are considered.5) Pressure in flooding condition is given in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.6 [1.2.7].

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4 Arrangements

4.1 General

4.1.1 The requirements to arrangements of bulkheads and compartments shall follow the requirements givenin DNVGL-RU-SHIP Pt.3 Ch.2 Sec.2 and DNVGL-RU-SHIP Pt.3 Ch.2 Sec.3, unless otherwise is specific agreedby the class.

4.1.2 The overall principles are based on the following:

— Safety of the structure can be demonstrated by addressing the potential structural failure mode(s) whenthe unit is subjected to loads scenarios encountered during transit, operation and in harbour.

— Structural requirements are based on a consistent set of loads that represent typical worst possibleloading scenarios.

— The unit has inherent redundancy. The unit’s structure works in a hierarchical manner and as such, failureof structural elements lower down in the hierarchy should not result in immediate consequential failure ofelements higher up in the hierarchy.

— Structural continuity is ensured. The hull structure should have uniform ductility.

4.2 Access arrangements

4.2.1 Permanent means of access (PMA) is related to means of safe access for service and periodic surveys,in order to ensure that the unit is maintained within applicable requirements throughout its operational life.

4.2.2 The requirements for access arrangement are given in DNVGL-RU-SHIP Pt.3 Ch.2 Sec.4.Guidance note:

Relevant parts of the PMA requirements should be embedded in the early design phase, considering:

— Access arrangement and structural arrangement of stairs, ladders, platforms and handrails.

— Number of openings, accessibility, types, sizes and positions wrt fatigue sensitive areas.

— Location of horizontal stiffeners, girders ans stringers such that they may be used as access platforms.


4.2.3 All spaces shall be accessible for easy inspection, see DNVGL-RU-SHIP Pt.3 Ch.2 Sec.4 [2].Guidance note:

PMA requirements are also specified in SOLAS Regulation II-1/3-6 for oil tankers and bulk carriers, and in the code for mobileoffshore drilling units (MODU) Ch.2 [2.2], and are applicable for the unit as required by the flag. An access manual plan and/ordrawings showing the access arrangement and access openings shall normally be prepared, see Ch.3 Sec.1 [1.4].


4.3 Structural arrangements and detail design

4.3.1 The requirements to structural arrangements shall follow DNVGL-RU-SHIP Pt.3 Ch.3 Sec.5.

4.3.2 The requirements to structural detail design and structural idealization of members are given inDNVGL-RU-SHIP Pt.3 Ch.3 Sec.6 and DNVGL-RU-SHIP Pt.3 Ch.3 Sec.7.

4.3.3 Documentation using direct strength calculation as alternative to the strength requirements given inDNVGL-RU-SHIP Pt.3 Ch.3 Sec.5, DNVGL-RU-SHIP Pt.3 Ch.3 Sec.6 and DNVGL-RU-SHIP Pt.3 Ch.3 Sec.7 maybe accepted, using the criteria given in Sec.3.

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5 Material selection and inspection principles

5.1 General

5.1.1 This subsection describes the application of structural materials and inspection principles to be appliedfor hull structure including superstructure and deckhouses.

5.1.2 Requirements to fabrication, testing, qualification of welders, welding procedures etc. are covered inDNVGL-RU-SHIP Pt.2 Ch.4.

5.1.3 Topside structure contributing to the hull global strength of the unit, typically drillfloor structure, shallfollow the requirements in this subsection. Otherwise, topside structure is covered in Sec.6.

Guidance note:

Material for topside structure may be selected according to e.g. DNVGL-OS-E101 for drilling plant, and DNVGL-OS-E201 for topsideprocessing system.


5.1.4 The materials shall be suitable for their intended purpose and have adequate properties in all relevantdesign conditions.

5.2 Design temperature

5.2.1 Design temperature is the lowest mean daily average temperature in air (LMDAT), and is the referencetemperature for the area where the unit shall be transported, installed and operated. For season restrictedoperations, LMDAT for actual season may be applied.

5.2.2 The material grade shall be selected according to the DNVGL-RU-SHIP Pt.3 Ch.3 Sec.1 for designtemperature above -20°C (warmer than -20°C) related to LMDAT, see also DNVGL-RU-SHIP Pt.3 Ch.1 Sec.2[3.5.4].

5.2.3 For design temperatures (LMDAT) below and including -20°C, the requirements to material class aregiven in DNVGL-RU-SHIP Pt.6 Ch.6 Sec.4.

Guidance note:

Design temperature equal and below -20°C is normally only applicable in Polar regions. For unit's operating in Polar regions, theexternal structure below lowest ballast waterline, permanently heated areas, oil storage tanks, and internal structure 0.6m fromshell plating are normally not exposed to colder (LMDAT) than -20°C, and the material in these areas may follow DNVGL-RU-SHIPPt.3 Ch.3 Sec.1.


5.2.4 Structural parts where the temperature is reduced below -20°C, e.g. by localised cryogenic or othercooling conditions, shall be specially considered using the actual local temperature.

5.3 Material class and grades

5.3.1 Structural material/member categories and corresponding material class/grades shall follow therequirements as given in DNVGL-RU-SHIP Pt.3 Ch.3 Sec.1 [2].

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5.3.2 Additional offshore specific material/members categories with corresponding material classes forstructural members shall follow Table 3. Requirement to material grade for the material classes defined inTable 3, are given in DNVGL-RU-SHIP Pt.3 Ch.3 Sec.1 Table 9.Structural members exposed to high stresses not specified in Table 3, shall be special considered, but aregeneral defined to be in material category primary.

Table 3 Material classes applicable for offshore specific members

Materialcategory Structural member Material class

Secondary

— Laydown platforms.— Mezzanine decks, platforms.— Outfitting steel.— Pipe support structure.— Stair towers.— Hull structure support below the main deck where the weight of equipment < 50 ton.— Hull structure support below other decks where the weight of equipment > 50 ton.

Class I

Primary

— Shipboard crane pedestal.— Hull structure support below the main deck where the weight of equipment > 50 ton.— Main structures in drillfloor.— Main supporting structures (substructure) for helideck pancake.— Mating ring for STL/STP structure.— Riser balcony and pull in structure.— Shipboard crane pedestal supports.— Offshore crane boom rest and supporting structures.— Hull support structures of heavy machinery and equipment typically; thrusters, gantry

and rails, winches, davits, towing brackets, hawser winch, etc.— Davits and support of appliances for lifesaving equipments.— Topside support stools and supporting structures.— Moonpool bulkheads.

Class II

Special

— Offshore crane pedestal.— Deck and bottom plates in way of 0.5m from the moonpool corners.— Support structures for offshore crane pedestals.— Support structures for flare tower, anchor line fairleads and chain stoppers, riser

fairleads.— Support structures for turret.— Support structures for derrick and drillfloor.

Class III

Note;

Area for the support structures should minimum extend 0.5 m surrounding the connection (below deck), but may berequired extended based on girder arrangement or if high stress level extend the 0.5 m zone.

5.3.3 The material for the connection (doubler) between the modules/equipment support and hull structuresshall follow the material requirement as for the hull structural member. Doublers shall not be used whereuplift forces are present, i.e. additional brackets with backing supports are required.Doublers supporting minor structure such as pipe supports, minor foundations, fittings, etc. are generaldefined in category secondary. For support of doubler connections, see Figure 1.

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Figure 1 Doubler connections

5.4 Through thickness properties

5.4.1 In structural cross-joints where tensile stresses are acting perpendicular to the plane of the plate,through thickness properties of the material as given in the DNVGL-RU-SHIP Pt.3 Ch.3 Sec.1 [2.5] shall beused (Z-quality).

5.4.2 Continuous deck plate under crane pedestal shall have Z-quality steel with minimum extension of 500mm. If the pedestal is continuous through the deck plate, the pedestal plate shall have Z-quality steel withminimum extension of 500 mm above and below the deck, see Figure 2.

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Figure 2 Crane pedestal through thickness properties extension area

5.5 Inspection principlesThe requirements to fabrication and testing are given in DNVGL-RU-SHIP Pt.2 Ch.4. Requirements to non-destructive testing (NDT) are given in Table 4, and is based on the principles given in DNVGL-RU-SHIP Pt.2Ch.4 Sec.7. For members not listed in Table 4, the NDT requirements given in DNVGL-RU-SHIP Pt.2 Ch.4Sec.7 prevail.Welds in areas not accessible and not planned to be inspected in service, shall follow the NDT requirementsfor the inspection category I.All welds are generally subject to 100% visual inspection by the builder's qualified personal and to beaccepted before NDT is applied.The weld connection between members of different category shall be assigned the NDT extent according tothe strictest.

Guidance note:

— The NDT scope should focus of fatigue critical details (calculated fatigue damage < 0.5), where welding assembly may bechallenging (block joints), and welds performed using specific required welding methods.

— New-building of storage and/or production units operating at harsh locations ([2.4.2]), will be assessed the additional classnotation FAB . See Ch.3 Sec.1 [2.4] for details.

— DNVGL-OS-C401 or other international standards (e.g. NORSOK) may be accepted as alternative standards, but should beaccepted by all involved parties in the project (owner/operator, yard, DNV GL).


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Table 4 NDT scope for hull and offshore interface structure

Test method 1)Inspectioncategory Inspection member Weld connection

MT/PT RT/UT

III

— General hull structural details not specific listed.— Laydown platforms.— Mezzanine decks, platforms.— Outfitting steel.— Pipe support structure.— Stair towers.— Hull structure support below the main deck where the

weight of equipment < 50 ton.— Hull structure support below other decks where the weight

of equipment > 50 ton.

Butt and T-joints, full pen.

T-joints, partly pen.

Fillet welds.

2%

2%

-

2%

-

-

II

— Sheer strake at strength deck within 0.4L amidship.— Stringer plate in strength deck within 0.4L amidship.— Deck strake at longitudinal bulkhead within 0.4L amidship.— Bilge strake.— All watertight bulkheads independent of location.— Shipboard crane pedestal.— Hull structure support below the main deck where the

weight of equipment > 50 ton.— Main structures in drillfloor.— Mating ring for STL/STP structure.— Riser balcony and pull in structure.— Shipboard crane pedestal supports.— Offshore crane boom rest and main supporting structures.— Hull support structures of heavy machinery and equipment

typically; thrusters, gantry and rails, winches, davits,towing brackets, hawser winch, etc.

— Davits and support of appliances for lifesaving equipments.— Topside support stools and main supporting structures.— Moonpool bulkheads.



Fillet welds.

5%

5%

-

5%

-

-

I

— Areas where the likelihood of occurrence of detrimentaldefects are considered to be extra high 2).

— Offshore crane pedestal.— Support structures (substructure) for helideck pancake.— Deck and bottom plates in way of 0.5m from the moonpool

corners.— Support structures for offshore crane pedestals.— Support structures for flare tower, anchor line fairleads and

chain stoppers, riser fairleads.— Support structures for turret.— Support structures for derrick and drillfloor.



Fillet welds.

20%

20%

20%

20%

-

-

1) See DNVGL-RU-SHIP Pt.2 Ch.4 Sec.7 [4] for specifications.2) Welds produced by yards with limit experience of required welding method, or welds produced by high heat input (>50 KJ/cm) .

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6 Net scantling and corrosion protection

6.1 Net scantling approach

6.1.1 The net scantling approach shall be according to the principles given in the DNVGL-RU-SHIP Pt.3 Ch.3Sec.2, based on the corrosion addition given in DNVGL-RU-SHIP Pt.3 Ch.3 Sec.3.

Guidance note:

The corrosion addition given in DNVGL-RU-SHIP Pt.3 Ch.3 Sec.3 accounts for corrosion that is likely to occur during the units basicdesign life time of 25 year. For units where the design life is longer than the basic 25 year, no specific change in the corrosionaddition is required by DNV GL, but additional owner/operator specific corrosion margin may be added.


Gross scantling: tgr = t + tcwhere:t = net required thickness in mmtc = tc1 +tc2 + tres

tc1,tc2 = corrosion addition in mm, for each side, depending on actual compartment typetres = 0.5 mm and is a minimum value independent on the compartment type.

6.1.2 The corrosion additions tc that shall be applied for the structural assessments are as following:

Table 5 Corrosion addition to be applied for structural assessments

Structural requirements Analysis type Reference Corrosionaddition part of tc

Minimum thickness, incl. primarysupport members (PSM) Thickness Sec.3 [3.4] tc

Thickness/section properties Sec.3 [3.4] tcLocal strength (plate, stiffenersand frames) Proportions/buckling capacity Sec.3 [3.2] tc

Grillage analysis Sec.3 [3.4] 0

Sectional properties Sec.3 [3.4] 0Primary support membersProportions of web and flange, bucklingcapacity Sec.3 [3.2] tc

Global FE model Sec.3 [4.2] 0

Cargo hold/midship FE model Sec.3 [4.3] 0

Buckling control Sec.3 [3.2] tcStrength assessment by FEM

Local fine mesh model Sec.3 [4.4] 0

Section properties Sec.3 [2.1] 0.5 tc

Vertical hull girder bending and shear check Sec.3 [2.2] 0Hull girder strength

Buckling control Sec.3 [2.2] tc

Hull girder ultimate strength Section properties Sec.3 [2.1] 0.5 tc

Hull girder ultimate strength Buckling/collapse capacity Sec.3 [2.3] 0.5 tc

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Structural requirements Analysis type Reference Corrosionaddition part of tc

Prescriptive analysis (simplified analysis)Hull girder section properties

Local supporting memberSec.4 [1.2] 0.5 tc

Component stochastic fatigue analysisHull girder section properties

Local supporting memberSec.4 [1.2] 0.5 tc

FE stress analysis (hot spot stress analysis) Sec.4 [1.2] 0

Fatigue assessment

Full stochastic analysis Sec.4 [1.2] 0

6.2 Corrosion additions

6.2.1 The requirements to corrosion addition (tc1, tc2) for one side of structural member is given in DNVGL-RU-SHIP Pt.3 Ch.3 Sec.3.

6.2.2 Project specific corrosion margin based on information of the tank content properties (sourness), maybe used, provided documented.

6.2.3 The moonpool follow the corrosion addition similar corrosion as the side shell.

6.3 Corrosion protectionCorrosion protection shall be according to DNVGL-RU-SHIP Pt.3 Ch.3 Sec.4.

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SECTION 2 DESIGN LOADS

1 General

1.1 Application

1.1.1 GeneralThis section provides the design loads for strength and fatigue assessments. The concept of design loadscenarios as described in [4] are used to specify consistent design load sets, which cover the appropriateoperating modes of the unit in question.

1.1.2 Equivalent design waveThe dynamic loads associated with each dynamic load case are based on the equivalent design wave (EDW)concept, and is a consistent set of dynamic loads to the unit such that the specified dominant load responseis equivalent to the required long term response value.

1.1.3 Dynamic load cases and load combination factorsAll dynamic load components for each dynamic load case are applied as simultaneously, using the loadcombination factors for strength and fatigue assessment as given in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.2.

Figure 1 Dynamic load cases for strength and fatigue assessment

EDW Index Description

HSM 1,2 = Head sea, maximize vertical wave bending moment amidships

FSM 1,2 = Following sea, maximize vertical wave bending moment amidships

BSR 1P, 1S 2P, 2S = Beam sea, maximize roll motion

BSP 1P, 1S 2P, 2S = Beam sea, maximize dynamic sea pressure at the waterline amidships

OSA 1P, 1S 2P, 2S = Oblique sea, maximize pitch motion

OST 1P, 1S 2P, 2S = Oblique sea, maximize torsion moment

1= Sagging condition2= Hogging conditionP= Port sideS= Starboard side

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1.1.4 Specific loads for offshore unitsUnits operating in harsh locations shall be based on direct site specific loads, while units operating inrestricted locations may follow the prescriptive rule based loads as given in DNVGL-RU-SHIP Pt.3 Ch.4. Thedynamic loads shall be based on principles given in [3.2].

2 Static loads

2.1 General

2.1.1 The still water loads consist of the permanent and variable functional loads.Permanent functional loads includes:

— Mass of the steel of the unit including permanently installed modules and equipment, such asaccommodation, helicopter deck, cranes, drilling equipment, flare and production equipment.

— Mass of mooring lines and risers.

Variable functional loads are loads that vary in magnitude, position and direction during the period underconsideration, typically:

— hydrostatic pressures resulting from buoyancy— crude oil, fuel oil and ballast water— mud, brine and drill water— consumables and personnel— general cargo— riser tension and mooring forces.

2.1.2 The variable functional loads utilised in structural design shall normally be taken as either the lower orupper design value, whichever gives the more unfavourable effect.

2.2 Still water hull girder loads

2.2.1 All relevant still water load conditions shall be defined and permissible limit curves for hull girderbending moments and shear forces shall be established. Different permissible limit curves for different designconditions may be applied, but for practical purpose the set of limit curves should be minimized.

2.2.2 The permissible limits for hull girder stillwater bending moments and hull girder still water shear forcesshall be specified, at least at each transverse bulkhead position. The limit curves shall be reflected in theunits loading manual. Limits for both stillwater sagging and hogging moments, together with positive andnegative stillwater shear forces shall be included.

2.2.3 The stillwater hull girder loads values and distribution should be based on the (preliminary) loadingmanual. The stillwater distribution given in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.4 [2] may alternatively be used, ifa (preliminary) loading manual not is available.

Guidance note:

An extra margin of 5% -10% for uncertainly of mass distribution and possible additionally loading conditions should be consideredin feed phase of the project.

Correlation between the limit curves for stillwater hull girder bending moments and hull girder shear forces may be considered,provided all loading conditions are ensured.


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2.3 Hydrostatic sea pressure and tank pressure

2.3.1 Hydrostatic sea pressure shall be based on actual draft as specified in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.5[1.2].

2.3.2 Static pressure due to liquid in the tanks includes requirements for overfilling, tank testing and floodingbased on tank filling height and density of the liquid, and shall be based on DNVGL-RU-SHIP Pt.3 Ch.4 Sec.6[1.2].

3 Dynamic loads

3.1 IntroductionEnvironmental loads are loads caused by environmental phenomena, typically:

— wave induced loads— wind loads— current loads— snow and ice loads, when relevant— green sea on deck— sloshing in tanks— slamming and bow impact loads.

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3.2 Dynamic loads related to design conditions

3.2.1 Dynamic global and local loads for different design conditions for strength assessment (ULS) are givenin Table 1. Depending of the units operation philosophy, the loads from either transit or at site location(s)shall be used for the strength assessments.

Table 1 Dynamic loads for different design conditions for strength assessment (ULS)

Design condition

Transit Offshore condition at site

SurvivalDesign load

Unrestricted Restricted 3) Operation 4)

Harsh Restricted 2)

Inertia loadsfrom motion andaccelerations

DNVGL-RU-SHIP Pt.3 Ch.4

Sec.3, or accordingto Table 3 1)

Table 3 Table 3DNVGL-RU-SHIP Pt.3 Ch.4Sec.3, or according toTable 3

Wave bendingmoments and shearforce

DNVGL-RU-SHIPPt.3 Ch.4 Sec.4 [3] Table 4 Table 4 Table 4

External seapressure

DNVGL-RU-SHIP Pt.3Ch.4 Sec.5 [1.3] Table 5

DNVGL-RU-SHIP Pt.3 Ch.4Sec.5 [1.3], or accordingto Table 5

Green sea pressure [3.5.2]

Slamming and bowimpact pressure [3.5.3]

Dynamic tankpressure [3.6.1]

Tank sloshing andliquid impact [3.6.2]

1) Direct calculated values may be applied.2) Direct calculation of dynamic loads may alternative be used for restricted operation.3) Wet tow condition may be considered similar as restricted transit condition.4) Inspection and maintenance condition may be considered similar as operation condition.

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3.2.2 Dynamic global and local loads for different design conditions for fatigue assessment (FLS) shall beaccording to Table 2. The calculation methods for fatigue check are described in Sec.4 [1.2].

Table 2 Dynamic loads for fatigue assessment (FLS)

Design condition 3)

Transit Operating at siteDesign load

Unrestricted Restricted Harsh Restricted 2)

Motion andaccelerations

DNVGL-RU-SHIP Pt.3 Ch.4

Sec.3, or accordingto Table 3 1)

Table 3 Table 3DNVGL-RU-SHIP Pt.3 Ch.4Sec.3, or according toTable 3

Wave bendingmoments and shearforce

DNVGL-RU-SHIPPt.3 Ch.4 Sec.4 [3] Table 4 Table 4

DNVGL-RU-SHIP Pt.3 Ch.4Sec.4 [3], or according toTable 4

External sea pressure DNVGL-RU-SHIP Pt.3Ch.4 Sec.5 [1.4] Table 5 Table 5

DNVGL-RU-SHIP Pt.3 Ch.4Sec.5 [1.4], or accordingto Table 5

Dynamic tank pressure [3.6.1]

1) Direct calculated values may be applied.2) Direct calculation of dynamic loads may alternative be used for restricted operation.3) See Sec.7 for fatigue contribution in transit and operation for the different unit types.

3.3 Ship motion and accelerations

3.3.1 When direct calculated values are requested as specified in [3.2], the principles given in [3.9] shall beapplied.Both loaded and ballast condition for the relevant design conditions shall be considered. The direct calculatedvalues of motion and accelerations shall be calculated at the units centre of gravity, see DNVGL-RU-SHIP Pt.3Ch.4 Sec.3 [2.2].

Table 3 Accelerations and motion angles for direct load assessment

Load component Description

asurge longitudinal acceleration due to surge motion in m/s2

asway transverse accelerations due to sway motion in m/s2

aheave vertical acceleration due to heave motion in m/s2

apitch pitch accelerations in rad/s2

φ pitch angle in degree

aroll roll accelerations in rad/s2

θ roll angle in degree

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3.4 Dynamic hull girder loads

3.4.1 When direct calculated values are requested as specified in [3.2], the principles given in [3.9] apply.The prescriptive rule values shall be replaced or adjusted based on direct load calculations as given in Table4, and are applicable at any longitudinal position for loaded and ballast conditions.

Table 4 Dynamic hull girder loads for direct load assessment

Dynamic response Load component Strength assessment (ULS) Fatigue assessment (FLS)

Vertical wave bending moment Mwv Mwv-Dir-uls Mwv-Dir-fls

Vertical wave shear force Qwv Qwv-Dir-uls Qwv-Dir-fls

Horizontal wave bending moment Mwh Mwh* fwv-uls Mwh* fwv-fls

Wave torsional moment Mwt Mwt * fwv-uls Mwt * fwv-fls

where:

Mwv-Dir-uls = 100 years direct calculated characteristic vertical wave bending moment for loaded(sagging) and ballast (hogging) according to [3.9.2]. Non-linear correction factors specifiedin [3.9.3] shall be considered.

Mwv = Vertical rule wave bending moment for sagging and hogging condition, for strength andfatigue assessment as defined in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.4 [3.1].

Mwv-Dir-fls = Direct calculated linear vertical wave bending moment for fatigue assessment based on[3.9.2].

Qwv-Dir-uls = 100 years direct calculated characteristic vertical wave shear force according to [3.9.3].Non-linear correction factors as given in [3.9.3] shall be considered.

Qwv-uls = Vertical rule wave shear force for sagging and hogging condition for strength and fatigueassessment as defined in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.4 [3.2].

Qwv-Dir-fls = Direct calculated vertical wave shear force for fatigue assessment based on [3.9.2].

Mwh = Horizontal rule wave bending moment for sagging and hogging condition for strength andfatigue assessment as defined in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.4 [3.3].

Mwt = Torsional rule wave moment for strength and fatigue assessment as defined in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.4 [3.4].

fwv-uls = Coefficient for strength assessment.

fwv-fls = Coefficient for fatigue assessment.

3.4.2 For units operating in harsh location (Sec.1 [2.4.2]) the dynamic hull girder loads shall not be lessthan the prescriptive ship rule values (distribution) for Mwv and Qwv given in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.4[3]. For units operating in restricted location (Sec.1 [2.4.3]) and with restricted transit (Sec.1 [2.2.2]), thedynamic hull girder loads shall not be less than 50% of the prescriptive ship rule values (distribution) for Mwvand Qwv, i.e. rule fr factor of 0.5.20-25 positions evenly distributed along the ship length are normally required for Mwv-Dir and Qwv-Dir.

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3.5 External dynamic pressure loads

3.5.1 Sea pressureWhen direct calculated values are requested as specified in [3.2], the dynamic external sea pressure shallbe calculated at the midship waterline according to the principles given in [3.9] for the loaded and ballastconditions. The prescriptive rule sea pressure shall be replaced and adjusted based on the direct values whenrequested as given in Table 5.

Table 5 Dynamic sea pressure for direct load assessment

Dynamic load case EDW Strength assessment (ULS) Fatigue assessment (FLS)

Head sea HSM-1, HSM-2 PW * fP-uls PW * fP-fls

Head sea HSA-1, HSA-2 PW * fP-uls PW * fP-fls

Follow sea FSM-1, FSM-2 PW * fP-uls PW * fP-fls

Beam sea, max. roll BSR-1P, BSR-2P,BSR-1S, BSR-2S PW * fP-uls PW * fP-fls

Beam sea, max. pressure BSP-1P, BSP-2P,BSP-1S, BSP-2S PW * fP-uls PW * fP-fls

Oblique sea, max. torsionalmoment

OST-1P, OST-2P,OST-1S, OST-2S PW * fP-uls PW * fP-fls

Oblique sea, max. pitchacceleration

OSA-1P, OSA-2P,OSA-1S, OSA-2S PW * fP-uls PW * fP-fls

where;

fP-uls =

Coefficient for strength assessment based on relation betweendirect calculated wave pressure for strength assessment, andrule wave pressure for the beam sea scenario at the actualwaterline.

fP-fls =Coefficient for fatigue assessment based on relation betweendirect wave pressure for fatigue assessment, and rule wavepressure for the beam sea scenario at the actual waterline.

PDir-WL-uls = Direct calculated dynamic sea pressure in water line at midship according to [3.9.2] for theloaded condition as applicable.

PDir-WL-fls = Direct calculated dynamic sea pressure in water line at midship according to [3.9.4] for theloaded condition, as applicable.

PW = Rule wave pressure for the actual EDW considered

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Figure 2 Typical dynamic sea pressure distribution rule and direct values for HSM, HSA and FSM

3.5.2 Green sea pressureThe green sea is the over-topping by sea in severe wave conditions. The forward part of the deck and areasaft of midship will be particularly exposed to green sea. Green sea pressure is considered as a local load. Thegreen sea pressure load of exposed decks shall be according to DNVGL-RU-SHIP Pt.3 Ch.4 Sec.5 [2.2]. Forproduction and storage unis, see specific requirement given in Sec.7 [4.2].For units operating in restricted locations (Sec.1 [2.4.3]) and with restricted transit (Sec.1 [2.2.2]), theexternal pressure values PSI and PA given in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.5 [3] for superstructure anddeckhouses, may be reduced with wave factors fSI-uls and fA-uls = fwv-uls.Reduction of green sea pressure due to shadow effects from green water protection panels, wave breakers,or other structure is in general not accepted for hull scantling requirements. For topside structure andequipments the effect of green sea protection arrangement may be considered, provided documented.

Guidance note:

Appropriate measures should be considered to avoid or minimise the green sea effects on the hull structure, accommodation,deckhouses, topside modules and equipment. These measures include bow shape design, bow flare, bulwarks and other protectivestructure. Adequate drainage arrangements shall be provided.


3.5.3 Slamming and impact pressureSlamming and impact pressure loads are considered as local loads, and shall be based on the prescriptiverule pressure given in DNVGL-RU-SHIP Pt.3 Ch.10. For production and storage unis, see specific requirementgiven in Sec.7 [4.2].For units operating in restricted locations (Sec.1 [2.4.3]) with restricted transit (Sec.1 [2.2.2]) the pressurevalues for bow impact given in DNVGL-RU-SHIP Pt.3 Ch.10 Sec.1 [2] and stern slamming as given in DNVGL-RU-SHIP Pt.3 Ch.10 Sec.3 [2], may be reduced with wave factors ( fFB-uls and fSS-uls = fwv-uls).The input to service speed V given in formulas in DNVGL-RU-SHIP Pt.3 Ch.10 Sec.1 shall be minimum 8knots.

3.5.4 Pressure inside moonpool areaDynamic sea pressure inside moonpool opening shall be based on the external dynamic sea pressure at thebottom plate edge corner of the moonpool, and at the moonpool longitudinal centre, for each dynamic loadcase defined in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.5 [1.3]. For circular and un-regular moonpool openings, thedynamic bottom pressure at the edge corner at the largest distance from the units centre line, shall be usedfor the whole moonpool area.

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Above the actual draught considered, a quasi-static assumption up to main deck level may be used for eachEDW load case, see Figure 3 below. Static sea pressure shall be according to [2.3.1].

Figure 3 Static and dynamic sea pressure inside moonpool structure

3.6 Internal dynamic loads

3.6.1 Dynamic liquid pressureDynamic pressure due to liquid in the tanks shall be based on the principles given in DNVGL-RU-SHIP Pt.3Ch.4 Sec.6 [1.3], using the accelerations as specified in [3.3].

3.6.2 Sloshing and impact loads in tanksSloshing and impact pressure loads are local loads due to partly filled tanks. Factors relevant for theoccurrence of sloshing are:— tank dimensions— tank filling level— structural arrangements inside the tank (wash bulkheads, web frames etc.)— transverse and longitudinal metacentric height (GM)— draught— natural periods of unit and cargo in roll (transverse) and pitch (longitudinal) modes.Sloshing and impact pressure loads shall be based on the prescriptive rule values given in DNVGL-RU-SHIPPt.3 Ch.10 Sec.4 [2].

3.7 Design density of fluids

3.7.1 The following minimum design density of tanks shall be used for the strength and fatigue analysis,unless otherwise is agreed:

— ballast: 1.025 t/m3 (seawater)— base oil: 0.9 t/m3

— brine: 2.2 t/m3

— cargo: 0.9 t/m3

— drill water: 1.0 t/m3

— fresh water/potable water/black water/drain: 1.0 t/m3

— fuel oil/diesel oil: 0.9 t/m3

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— glycol (MEG): 1.1 t/m3

— liquid mud: 2.5 t/m3

— urea: 1.35 t/m3.

3.7.2 Higher design densities than given above shall be used if specified by the project, and shall bespecified on the tank plan drawing.

3.7.3 For tank testing design load scenario, see DNVGL-RU-SHIP Pt.3 Ch.4 Sec.7 [2], the density ofseawater 1.025 t/m3 shall be used for all tanks with density lower than 1.025 t/m3.

3.8 Wind loads

3.8.1 Wind loads are applicable for the topside and topside support structure. The mean wind speed over1 minute period at actual position above the sea level shall be used as basis. The wind profiles are given inDNVGL-RP-C205, but minimum wind pressure should not be less than 2.5 kN/m2.For slender member, e.g. helideck substructure and members in a flare tower structure, Vortex-Sheddingshall be considered according to the principles in DNVGL-RP-C205

3.8.2 The following wind velocity for the design conditions shall be used, unless otherwise documented:

— Transit condition: v1min10m = 36 m/s (1 minute period at 10 m above sea level, corresponds to aprobability level of 10-8).

— Operation conditions: site specific defined by the project, but v1min10m =36 m/s (1 minute period at 10 mabove sea level) will generally cover world wide operation.

— Survival condition: site specific.Guidance note:

For units intended for world wide operation (unrestricted service) winds speed of v1min10m = 51.5 m/s for the survival condition(100 year) will cover most locations. Typical wind speed values for other locations are given in DNVGL-OS-E301 Ch.2 Sec.1 [2.3].Correlation between different average time for the wind speed and elevation above sea level are as following:

Elevation abovesea level (z)

Average time [sec]

3 sec 5 sec 15 sec 1 min. 10 min. 60 min.

1 m 0.934 0.910 0.858 0.793 0.685 0.600

5 m 1.154 1.130 1.078 1.013 0.905 0.821

10 m 1.249 1.225 1.173 1.108 1.000 0.916

20 m 1.344 1.320 1.268 1.203 1.095 1.011

30 m 1.400 1.376 1.324 1.259 1.151 1.066

40 m 1.439 1.415 1.363 1.298 1.190 1.106

50 m 1.470 1.446 1.394 1.329 1.220 1.136

60 m 1.494 1.470 1.419 1.354 1.245 1.161

100 m 1.564 1.540 1.489 1.424 1.315 1.231

The values in the table above are based on the following expression given in DNVGL-RP-C205:

U(T,z) =U10· (1+0.137·ln(z/H) -0.047·ln(T/T10).


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3.9 Direct calculation of wave load responses

3.9.1 When dynamic site specific load calculations are required as specified in [3.2], a hydrodynamic waveload analysis using three dimensional sink source (diffraction) formulation shall be performed.The effect of free water surface (FSE) of tank liquids shall be considered for the hull motion and accelerationresponses for the survival condition.

Guidance note:

Correction of FSE is mostly relevant for wide tanks (loaded cargo tanks), and may be accounted for in the hydro programs bychanging the KG value based on input from hydro stability calculations for the actual conditions.


3.9.2 Ultimate limit stateWave load analysis for the hull strength assessments shall follow the design basis as specified in Table 6. Thedesign basis are related to long-term response analysis.If short term response analysis are applied, the 100 years significant wave heights (Hs) with correspondingperiods (T) at the contour line for the 90% percentile fractal value. The highest response from each individualwave directions according to Table 6 shall be considered.

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Table 6 Design basis for wave load analysis - hull strength assessment (ULS)

Design condition7)

Transit

UnrestrictedDesign conditions at siteWave parameter

Hull Topside 1)Restricted

Operation Survival

Wave environment N/A North Atlanticscatter diagram Defined area 5) Defined sea state Site specific 3)

Probability/annual ofexceedance N/A 10-8 1 year 4) 100 year

Wave spectrum N/A PM 2) Jonswap 2) Jonswap 2)

Wave spreading N/A Cos 2 Cos 2 None

Wave response Heading profile for wave load response - turret moored units

Sectionloads MWV, QWV N/A Head sea, 180°


asurge ,asway ,aroll

aheave ,apitch,φ,θAll headings 0° - 360°,

equal probability 6)

Head sea: 60%± 15° of head: 30%

± 30° of head: 10%

Seapressure PW

DNVGL-RU-SHIPPt.3 Ch.4

N/AHead sea: 60%

± 15° of head: 30%

± 30° of head: 10%

Wave response Heading profile for wave load response - dynamicpositioned units or units with spread mooring

Sectionloads

MWV

QWVN/A Head sea, 180°


asurge ,asway ,aroll

aheave ,apitch,φ,θAll headings 0° - 360°,

equal probability 6)

Agreed defined project specificationaccounting for correlation

between waves, current and wind.

Seapressure PW

DNVGL-RU-SHIPPt.3 Ch.4

N/AAll headings 0° - 360°, equal probability,or agreed defined project specific profile

1) Optional when direct values of motion and accelerations for topside interface analysis are used, as substitute to theaccelerations given in the DNVGL-RU-SHIP Pt.3 Ch.4 Sec.3.

2) Other spectrum may be used if specified by the project, see e.g. DNVGL-RP-C205 for details.3) For units intended for unrestricted service (world wide operation), North Atlantic scatter diagram shall be used.4) Restriction for operation, typically a maximum sea state for a drilling operation, a stand-by condition, etc. Restricted

operation condition may be based on site specific scatter diagram, where all wave heights above the restrictedallowable wave height (Hs) are removed. The 1 year response shall minimum be used, considering the mostrelevant severe heading or wave direction.

5) For restricted transit, actual scatter diagram for the restricted areas shall be used.6) For units with redundant propulsion system (DP), heading profile similar as for operation and survival condition

may be applied. All headings 0° - 360° with equal probability should to be used, if no other relevant heading profileinformation is available.

7) For wet towing condition and for inspection and maintenance condition, see [3.2.1].

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3.9.3 Non-linear effectGeneralNon-linear effect is here related to the effect from Froude-Kriloff and restoring forces from wave elevationand hull shape form up to actual wetted surface, and shall be considered for the vertical wave bendingmoments and the vertical wave shear force.The non-linear factors for the sagging (loaded) condition given in Table 7 are applicable for drilling and wellintervention units operating both in restricted and/or worldwide locations, and for production and/or storageunits operating in restricted locations.

Table 7 Non-linear correction factors for survival sagging (loaded) condition

Sagging (loaded condition)Position

Vertical wave bending moment Vertical wave shear force

Aft part behind 0.25 Lpp 1.0 1.0

Midship (0.5 Lpp) and fwd 1.1 1.1

Linear interpolation shall be used between the positions.

Non-linear correction need not be considered for the hogging (ballast) condition, and for the following:

— transit conditions as specified in Sec.1 [2.2]— operation conditions as specified in Sec.1 [2.3]— restricted operation as specified in Sec.1 [2.4.3]— fatigue calculations, see Sec.4.

Production and/or storage units - harsh locationFor production and/or storage units moored at harsh locations (Sec.1 [2.4.2]), the non-linear response issignificant in extreme sea states and the response strongly depends of the units hull form. The non-lineareffect shall thus be calculated specific for each unit, and a non-linear wave load analysis for both sagging (fullload) and hogging (ballast) condition is required.

Guidance note:

The non-linear DNV GL hydrodynamic program WASIM may be used for calculating non-linear wave responses.


3.9.4 Fatigue limit stateThe basis when using direct calculated dynamic loads for fatigue assessments are given in Table 8 below, andis related to long-term response analysis.Short term response analysis may alternatively be used, using significant wave heights (Hs) equal to theprobability of exceedance of 10-2 with corresponding periods (T). The direction giving the highest responsefrom each individual wave direction according to Table 8 should be considered. For fatigue calculationmethods using direct loads, see Sec.4 [1.2].

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Table 8 Design basis for wave load analysis - fatigue assessment (FLS)

Design condition

Location at siteWave parameter Unrestricted andrestricted transit Turret moored No turret or spread moored

Wave environment World wide scatter diagram Site specific 1)

Probability of exceedance 10-2 10-2

Wave spectrum PM spectrum PM spectrum

Wave heading profileAll headings included

0° - 360° 2)

Head sea: 60%± 15° of head: 30%

± 30° of head: 10%

All headings 0° - 360° withequal probability, or agreedproject specific heading profile

Wave spreading Cos 2 Cos 2

1) For units intended for unrestricted service (world wide operation), the world wide scatter diagram should be used,see DNV-RP-C205. Units designed for site specific service locations shall base the fatigue assessment on site specificscatter diagram.

2) For units with redundant propulsion system (DP), a head sea dominated heading profile similar as for a turretmoored units may be applied.

3.10 Wheel loadingWheel loads from cargo handling vehicles or other transporting vehicles shall follow DNVGL-RU-SHIP Pt.3Ch.10 Sec.5.

3.11 Loads from topside structuresLoads from topside shall be considered for all relevant design conditions as given in Sec.1 [2] by either:

1) Combine the accelerations at the topside modules centre of gravity (COG) with the units hull responsesaccording to the principles in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.3 [3.2], or

2) apply the topside loads using envelope accelerations and the combination with fraction of responsesaccording to Table 9.

Table 9 Combination of dynamic responses

Combination with fraction of responses

Global hull girder loads AccelerationDesign condition LC

MWv QWv aZ aY aX

Hogging - max. MWv, QWv, aZ 1a 1 1 +/- 1.0 +/- 0.4 +/- 0.8

Sagging - max. MWv, QWv, aZ 1b -1 1 +/- 1.0 +/- 0.4 +/- 0.8

Hogging - max. aX 2a 0.3 0.5 +/-0.5 +/- 0.6 +/-1.0

Sagging - max. aX 2b -0.3 0.5 +/-0.6 +/- 0.6 +/-1.0

Hogging - max. aY 3a 0.7 0.7 +/- 0.9 +/- 1.0 +/- 0.7

Sagging - max. aY 3b -0.7 0.7 +/- 0.9 +/- 1.0 +/- 0.7

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— Positive longitudinal acceleration (ax) is along positive x-axis (forward).— Positive transverse acceleration (ay) is along positive y-axis (towards port side of the unit).— Positive vertical acceleration (az) is along positive z-axis (upwards).

— Positive vertical bending moment (Ms, MWv)is hogging moment, and negative is saggingmoment.

— Vertical shear force defined positive (absolutevalue).

4 Design load scenarios and design loading conditions— The design loading scenarios shall follow the principles given in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.7.— Loads from topside modules, drillfloor and turret structure shall be included, as found applicable.— Design load combinations for the FE-analysis for the different unit types are specified in Sec.7.

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SECTION 3 STRENGTH ASSESSMENT

1 GeneralThe strength assessment applicable for design conditions and software tool are present in Table 1.

Table 1 Structural analysis applicable for design conditions and applicable software tools

Applicable for design condition

Analysis Ref.Transit 2) Operation2) Survival 2)

Inspectionand

maintenance

Wettowing Accidental

Applicable software

Limit curvesfor still waterbendingmoments andshear forces 1)

Sec.2[2.2] X X X X X N/A Stability analysis

calculation

Hull girdersectionmodulesrequirement

[2.1] X N/A X N/A N/A N/A

Hull girdernominal yieldand bucklingcheck

[2.2] X N/A X N/A N/A N/A

Hull girderultimate check [2.3] X N/A X N/A N/A N/A

Hull localscantling [3] X N/A X N/A N/A N/A

DNV GL Nauticus Hull rulecheck program, or similarsoftware tool

Finite elementanalysis [4] X X3) X X3) X3) N/A4) DNV GL Sesam GenieE or

similar FE programs

1) The number of limit curves should be minimized, see Sec.2 [2.2.1].2) See Sec.2 [3.2.1] for the applicable loads.3) As found applicable, see Sec.1 [2.3], Sec.1 [2.5] and Sec.1 [2.6].4) Normally not applicable, see Sec.1 [2.7].

2 Hull girder nominal strength check

2.1 Minimum requirements to hull girder section

2.1.1 The requirements to the section modules Zgr as given in DNVGL-RU-SHIP Pt.3 Ch.5 Sec.2 [1.4], shallbe based on the vertical wave bending moment specified in Sec.2 [3.2].

2.1.2 The shear strength capacity requirements given in DNVGL-RU-SHIP Pt.3 Ch.5 Sec.2 [2], shall be basedon the wave shear force as specified in Sec.2 [3.2].

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2.1.3 The minimum requirement to the section modules at midship ZR-gr given in DNVGL-RU-SHIP Pt.3Ch.5 Sec.2 [1.3] and the moment of inertia IyR-gr given in DNVGL-RU-SHIP Pt.3 Ch.5 Sec.2 [1.5], shall becomplied with.The factor fr= fr-ULS need not to be taken larger than 1.0, but shall not be taken less than 0.5.

2.2 Hull girder longitudinal yield and bucklingThe yield criteria given in DNVGL-RU-SHIP Pt.3 Ch.5 Sec.3 and the buckling criteria given in DNVGL-RU-SHIPPt.3 Ch.8 Sec.3, shall be based on the wave bending moment and wave shear force as specified in Sec.2[3.2].

2.3 Hull girder ultimate strengthThe hull girder strength criteria given in DNVGL-RU-SHIP Pt.3 Ch.5 Sec.4, shall be based on the vertical wavebending moment as specified in Sec.2 [3.2] for both hogging and sagging condition.

2.4 Irregular hull formsFor units with irregular midship or novel design, where there are frequent changes in cross-sectionalproperties, a FE-calculation as specified in [4] shall be performed. The requirements in [2.1], [2.2] and [2.3]may then be waived and replaced by FE-calculation, as found applicable.

3 Hull local scantling

3.1 General

3.1.1 The loads for hull local scantlings as specified below are given in Sec.2.

3.1.2 Hull local scantlings and requirements shall follow DNVGL-RU-SHIP Pt.3 Ch.6 including:

— load application

— minimum thickness of plates, stiffeners and primary supporting members (PSM)

— plating, stiffeners, PSM and pillars

— intersection of stiffeners and PSM

— superstructure and deckhouse

— simple beam and grill analysis of stiffeners and girders.

3.1.3 Moonpool shall follow:

— The design load set Sea-1 and Sea-2 as defined in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.2 Table 1 for theexternal shell, considering the static and dynamic pressure as defined in Sec.2 [3.5.4].

— The minimum requirements to plating, stiffeners and primary supporting members similar to side shellstructure as defined in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.3.

— The requirements to plating given in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.4 [1].— The requirements to stiffeners given in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.5 [1].— The requirements to PSM given in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.6 [2].

3.1.4 In general plate thickness used in hull structure, superstructure, deckhouse, integrated ventilationducts, etc. shall not be less than 4.0 mm (net scantling).

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3.2 Buckling

3.2.1 Net scantlings shall be used for the buckling control.

3.2.2 Requirements to slenderness of plate, stiffeners, PSM, pillars, brackets and edge reinforcement in wayof openings shall be according to DNVGL-RU-SHIP Pt.3 Ch.8 Sec.2.

3.2.3 Requirements to prescriptive buckling requirements of plate and stiffeners shall be according toDNVGL-RU-SHIP Pt.3 Ch.8 Sec.3.

3.2.4 Buckling requirements based on stresses from FE-stress analysis of plate, stiffened panel, stiffeners,pillars, struts, cross ties shall be according to DNVGL-RU-SHIP Pt.3 Ch.8 Sec.4.

3.2.5 Allowable buckling utilization factors for different design load scenario shall be according to DNVGL-RU-SHIP Pt.3 Ch.8 Sec.1 [3.4].

3.3 Local strength of impact and slamming loadsLocal impact and slamming loads as:

— bow impact given in Sec.2 [3.5.3]

— bottom and stern slamming given in Sec.2 [3.5.3]

— sloshing and liquid impact in tanks given in Sec.2 [3.6.2]

shall follow the strength requirements given in DNVGL-RU-SHIP Pt.3 Ch.10.

3.4 Special hull structure elementsSpecial hull structure elements such as plate stem, breast hooks, stern frames, propeller posts, sea chest,thruster tunnels, machinery foundations, box coolers, berthing impact and tug contact and wave breakersshall follow DNVGL-RU-SHIP Pt.3 Ch.10 Sec.6.

4 Finite element analyse

4.1 General

4.1.1 FE-analyse is here related to complex analyse for hull strength control by use of plate/shell elements,or in combination with beam elements. Simple beam and grillage analyse is general only accepted for hulllocal scantling control as given in [3], or for simple topside modules as described in Sec.6.

4.1.2 The requirements to modelling principles, extension of model, boundary conditions and acceptancecriteria for the FE-analyse are given in DNVGL-RU-SHIP Pt.3 Ch.7 and in DNVGL-CG-0127.

4.1.3 The loads for finite element (FE) analysis are given in Sec.2.

4.1.4 Gross scantlings shall be applied.

4.1.5 Topside structures, e.g. drillfloor substructure and main support stools for topside process, which willhave significant impact of the hull girder stiffness, shall be part of the hull strength model.

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4.2 Global strength analysse

4.2.1 Global strength analyses are normally not required. However, for units with large discontinuities andtorsional sensitive structures, like large deck openings, a global FE model may be requested in order toevaluate the stress distribution properly.

4.2.2 The following yield and buckling criteria shall general be used:

— Von Mises yield check coarse mesh size using gross scantlings: DNVGL-RU-SHIP Pt.3 Ch.7 Sec.2 [4.2].— Buckling check using net scantlings: DNVGL-RU-SHIP Pt.3 Ch.8 Sec.1 [3.4].

4.2.3 For operation condition (Sec.1 [2.3]) and for inspection and maintenance condition (Sec.1 [2.5]), thefollowing yield and buckling criteria shall be used, as applicable:

— Von Mises yield check coarse mesh size, λyperm= 0.8.— Buckling check using net scantlings, ηall=0.8.

4.3 Part ship structural analyse

4.3.1 Partial ship analyse (cargo hold analyse) shall be performed as part of the hull strength documentationaccording to the requirements given in DNVGL-RU-SHIP Pt.3 Ch.7 Sec.3 [2], and the unit specificrequirements given in Sec.7.

4.3.2 All relevant tank filling configuration and topside loads shall be considered.

4.3.3 The following yield and buckling criteria shall general be used for part ship FE analysis:

— Von Mises yield check coarse mesh size using gross scantlings: DNVGL-RU-SHIP Pt.3 Ch.7 Sec.3 [4.2.4].

— Buckling check using net scantlings: DNVGL-RU-SHIP Pt.3 Ch.8 Sec.1 [3.4].

4.3.4 For operation condition (Sec.1 [2.3]) and for inspection and maintenance condition (Sec.1 [2.5]), thefollowing yield and buckling criteria shall be used, as applicable:

— Von Mises yield check coarse mesh size, λyperm= 0.8.— Buckling check using net scantlings, ηall=0.8.

4.4 Local structural strength analyse

4.4.1 The purpose of a local fine mesh analyse is:

— to perform a local strength check of details where the stress results cannot be adequately representedusing normal coarse mesh size

— to find local hot spots relevant for fatigue assessments for details listed in Sec.4, when tabulated hotspots not are available.

4.4.2 Where global stress concentrations are present due to discontinuities and large openings (e.g.moonpool opening), local stresses shall be evaluated using local FE analysis.

4.4.3 Structural modelling shall follow the principles as given in DNVGL-CG-0127 Sec.4.

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4.4.4 Local peak stress may be accepted for small local areas, provided redistribution of stresses to theadjacent area is possible without developing a mechanism. Where peak stress is dominated by dynamicloads, fatigue shall additionally be documented.

4.4.5 Local yield stress criteria for fine mesh analysis shall follow the requirements given in DNVGL-RU-SHIPPt.3 Ch.7 Sec.4 [4].Non-linear analysis using recognized finite element program may alternatively be used. For non-linearanalysis the plastic strain criteria may, on agreement, replace the local yield stress criteria.

Guidance note:

A local strain of maximum 5% may be accepted, provided redistribution of loads is possible.


5 Welding connections

5.1 General

5.1.1 The technical requirements for the welding and weld connections shall, as a minimum, comply with theDNVGL-RU-SHIP Pt.3 Ch.13.

5.1.2 For areas not specified in the DNVGL-RU-SHIP Pt.3 Ch.13 Sec.1 [2.5], a fweld factor of 0.4 should beused, unless the weld connection is documented according to [5.3].

5.2 Partial and full penetration welds

5.2.1 In addition to the requirements specified in DNVGL-RU-SHIP Pt.3 Ch.13 Sec.1 [2.4], partial or fullpenetration welds shall be used for the following connections:

— crane pedestal to deck plating— topside support stools to main deck— flare to hull structure— drill floor support structure to main deck— turret/yoke support structure to hull structure.

5.2.2 In structural parts where dynamic stress or high tensile stress act through an intermediate plate, seeFigure 1, full penetration weld or partly penetration weld should be used.

Figure 1 Weld root face

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5.3 Direct calculation of weldsWelds exposed to hight tensile stress shall be based on the requirements given in the DNVGL-RU-SHIP Pt.3Ch.13 Sec.1 [2.4.5].

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SECTION 4 FATIGUE

1 Principles and methodology

1.1 Assessment principles

1.1.1 DNVGL-CG-0129 Fatigue of ship structures shall be used for the fatigue evaluation.

1.1.2 Additional stress concentration shall be considered when fabrication imperfections exceed the valuesincluded in the design SN-curves.

1.1.3 Fatigue life shall be calculated combining global and local responses.

1.1.4 Repeated yield (low cycle fatigue) due to the repetitive loads from loading and unloading tanks shallbe considered according to principles given in DNVGL-CG-0129. However, information of actual tank fillingpattern and sequence during loading and unloading may be accounted for in the calculation.

1.1.5 The accumulated fatigue damage from transit and location at site shall be calculated with appropriatefraction of time in each loading condition, see also unit specific sub chapters in Sec.7.

1.1.6 Corrosion addition shall be considered for the fatigue assessment as described in Sec.1 [6.1].

1.2 Fatigue calculation methods

1.2.1 Fatigue calculations shall be based on either prescriptive rule loads as given in DNVGL-RU-SHIP Pt.3Ch.4, or by direct loads as required in Sec.2 [3.2.2]. Load combination factors given in DNVGL-RU-SHIP Pt.3Ch.4 Sec.2 [3] should be applied, if not the load combinations are derived from a wave load analysis.

1.2.2 Stress concentration factors (SCF) of local details given in DNVGL-CG-0129 may be applied. For detailsnot covered in DNVGL-CG-0129, or documented in other recognised publications, a local FE analysis shall beperformed to determine actual SCF.

1.2.3 Fatigue calculation method 1 and 2 as listed in Table 1 should be applied, unless project specificrequirements are given, or additional fatigue class notation is requested, see also DNVGL-CG-0129 fordescription of the methods.

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Table 1 Fatigue calculation methods

Method Description Applicable for Loads Combinationof loads

Stress calc.method

1a Beam model

1b

Prescriptiveanalysis Drillships for unrestricted transit Prescriptive (EDW) Rule

combination FE-analysis

2a Beam model

2b

Prescriptiveanalysis

Rulecombination FE-analysis

3a Componentstochastic Beam model

3b Fullstochastic

Units for unrestricted orrestricted transit and sitespecific operation

Direct - Sec.2 [3.9.4]Stochastic, waveload analysis

FE-analysis

Method 3 is required for units applying the additional class notation FMS (fatigue methodology specification),see Ch.3 Sec.1 [2.2].

1.3 Acceptance criteria

1.3.1 The design fatigue life TDF of new units shall be minimum 25 years. For conversions, see Sec.7 [5].

1.3.2 Design fatigue factors (DFF) given in Table 2 depending of the inspection interval, accessibility andrepair of any cracks, and shall be considered in the required design fatigue life TF as following: TF > TDF*DFF.

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Table 2 DFF’s for structure areas wrt inspection interval, accessibility for inspection and repairs

Structure Example areas5-year inspectioninterval carried

out in dry docking

5-year inspectioninterval, carried

out afloat

External structure, accessiblefor regular inspection and repairin dry and clean conditions ispossible.

Main deck plate, topside andequipments connections to main deckplate.

1 1

External structure where accessfor inspection is limited, andwhere repair in dry and cleanconditions not is possible.

Side shell and bottom plate, includingbilge keel, fairlead structure, risertubes.

1 2

Internal structure, accessible andnot welded directly to submergedpart.

Transverse frames, transverse BHD,longitudinal BHD, stringers, cross ties. 1 1

Internal structure, accessible andwelded directly to the submergedpart.

Longitudinals, transverse frames,transverse BHD’s welded to thebottom plate or side shell plate belowthe scantling draft.

1 2

Non-accessible structure, notplanned to be accessible forinspection and repairs duringoperation.

Void spaces, sea chests, smallcofferdams, and topside supportsequipped with passive fire protection.

3 3

Guidance note:

The DFFs are based on the principle that a fatigue crack in a ship-shaped structure is not critical, i.e. will not lead to substantiationfailure of the unit.


Figure 1 Example of design fatigue factor in bottom area for units not intended for dry dockingintervals

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1.4 Details to be assessed

1.4.1 As a minimum the details as listed in Table 3 shall be documented with respect to fatigue. Additionaldetails may be required documented, based on the complexity and design.

Guidance note:

For units holding the additional class notation FMS (fatigue methodology specification), see Ch.3 Sec.1 [2.1].


Table 3 Fatigue details to be checked for normal class scope

No. Hot spot detail Description

1 Bracket toe of typicaltransverse web frame

2 Toe and heel of horizontalstringer

3

Longitudinal stiffener endconnections to transverseweb frame and bulkhead.Shell plate connection tolongitudinal stiffener andtransverse frames.

SCF defined in DNVGL-CG-0129 App.A may be applied.

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No. Hot spot detail Description

4 Hopper knuckles

SCF defined in DNVGL-CG-0129 App.A may be applied.

5 Moonpool corners

6 Openings andpenetrations in main deck

Allowable stress concatenation (SCF) at different longitudinal position should first becalculated, and second the actual penetration/opening SCF can be controlled againstallowable SCF.

7Crane pedestalconnections to hullstructure

8 Turret or turret yokeinterface to hull structure

9 Topside interface to hullstructure

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SECTION 5 HULL EQUIPMENT, SUPPORTING STRUCTURES ANDAPPENDAGES

1 Anchor and anchor mooring equipment

1.1 General

1.1.1 The requirements for anchor and mooring equipments and their arrangements are given in DNVGL-RU-SHIP Pt.3 Ch.11 Sec.1.

1.1.2 The requirements for support of anchor mooring equipments, like chain stoppers and windlasses, aregiven in DNVGL-RU-SHIP Pt.3 Ch.11 Sec.2 [2].

Guidance note:

Anchor equipments for temporary mooring may be excluded for units without propulsion intended for permanent mooring at sitespecific location, or for units with redundant propulsion system, see specific requirements given in DNVGL-RU-OU-0101, DNVGL-RU-OU-0102 and DNVGL-RU-OU-0103, as applicable.


2 Support structure of deck fittings for mooring and towing

2.1 General

2.1.1 Design and construction of shipboard fittings and support structure for towing and quayside mooringshall follow DNVGL-RU-SHIP Pt.3 Ch.11 Sec.2 [5].

2.1.2 A towing and quayside mooring arrangement plan for the fittings type, purpose (towing services,quayside mooring), safe towing load (TOW) or safe working loads (SWL) with angles, etc. shall be submittedas specified in DNVGL-RU-SHIP Pt.3 Ch.11 Sec.2 [5.7.3].

2.1.3 Calculation of the support structure for different towing services shall follow the safe towing load(TOW) as given in Table 1.

Table 1 Towing services

Towing services Definition Safe towing load (TOW)

Canal towing Towing service for units transiting canals(e.g. Panama canal).

Maximum towline load, e.g. static bollard pullaccording to [2.1.2].

Escort towing Towing service as defined in DNVGL-RU-SHIP Pt.3 Ch.11 Sec.2 [5.1.4].

Tow to location Towing assistance from ship yard tolocation (marine warranty).

Emergency towing Emergency towing in case of failure ofpropulsion.

80% of the maximum defined towing load, but not lessthan the minimum breaking strength of the towing lineaccording to the units equipment number.

2.1.4 For quayside mooring the calculation of the support structure shall apply the following safe workingload (SWL).

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Table 2 Quayside mooring equipments

Definition Safe working load (SWL)

Mooring at quay 1.15 times the minimum breaking strength of the mooring line, see DNVGL-RU-SHIP Pt.3 Ch.11Sec.2 [5.5.1].

2.1.5 If a higher TOW or SWL specified on the fittings exceed the design loads given in [2.1.3] and [2.1.4],the design loads for the support structure shall be increased accordantly.

2.1.6 Support of fittings intended for different purpose (normal towing, emergency towing, quaysidemooring) shall be controlled using the largest design load (TOW or SWL) according to [2.1.3] and [2.1.3].

2.1.7 The acceptance criteria for yield shall follow DNVGL-RU-SHIP Pt.3 Ch.11 Sec.2 [5.6]. For bucklingcontrol the utilization factors given for AC-III in DNVGL-RU-SHIP Pt.3 Ch.8 Sec.1 [3.4] shall be applied.

3 Support structure for permanent mooring systems

3.1 General

3.1.1 This standard covers supporting structure for the following mooring systems:

— An internal turret system using a cylinder or a submerged turret loading system installed inside theforward part of the unit.

— An external turret system using a turret installed in front of the unit, i.e. mounted to external yokestructure.

— Spread mooring system.

Figure 1 Turret systems

3.1.2 The DNVGL-OS-E301 shall be used as basis for the:

— requirements for the mooring components— design reaction loads from the mooring system.

3.2 Design loads

3.2.1 Units with internal or external turret structureFor hull strength control, the extreme 100 years restoring loads from the turret as provided by the turretdesigner, shall be combined with hull girder loads and local loads from tank and sea pressure as specified inSec.2.

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Guidance note:

As turret moored units weathervane, the turret loads acting on the hull support structure need normally only be consider directionsfrom the bow area. For oblique sea conditions, the turret loads may be applied at 45° of heading. The loads shall be applied to theFE hull model as distributed loads at the turret roller, or at relevant contact areas.

For the fatigue control, the dynamic load blocks and cycles related to a defined period (e.g. 1 year) may be applied.

Figure 2 Main turret load directions


3.2.2 Spread moored unitsThe characteristic breaking load for mooring line shall be used for the most unfavourable relative anglebetween the unit and the anchor lines.Loads from mooring shall be combined with global and local hull loads as found relevant.

Figure 3 Fairlead with vertical inlet angle (γ) and horizontal working angle (φ)

Guidance note:

If the hull connection of the mooring lines are positioned aft of 0.1LPP from AP, or forward of 0.9LPP from AP, the contribution fromhull girder loads may be excluded in the support structure calculation.


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3.3 Strength assessmentStrength assessment of support structure for mooring devices shall normally be controlled using a FE-analyseusing the corrosion addition as given in Sec.1 Table 5.

The permissible utilization factor for Von Mises coarse mesh yield check is: λyperm= 0.8.The permissible utilization factor for buckling capacity is: ηall = 0.8In case local fine mesh analysis is required (Sec.3 [4.4.1]), the strength requirements given in Sec.3 [4.4]shall be applied.

3.4 Fatigue assessment

3.4.1 Units with internal or external turret structureFatigue damage for the turret support structure may be calculated using time simulation of the combinedstress process from the hull motions and the mooring loads. Alternatively, the fatigue damage from hullmotions and mooring may be calculated separately and combined using the following formula:

where:D 1 = calculated fatigue damage for the high cycle fatigue (hull motions)D 2 = calculated fatigue damage for the low cycle fatigue (mooring loads)ν1 = mean zero up crossing frequency for the high cycle fatigue (hull motions)ν2 = mean zero up crossing frequency for the low cycle fatigue (mooring loads)m = negative inverse slope of the S-N curve.

Guidance note:

— The formula is based on that a one slope SN-curve is used for the fatigue damage calculations. If a two-slope SN-curve is usedfor the fatigue calculations the strictest m-factor in the SN-curve (m = 5) should be used in the formula, or the fatigue damagecalculation for the mooring load process should be based on the lowest m-factor in the relevant SN-curve.

— ν1 is either to be calculated by wave load analysis or taken from DNVGL-CG-0129.

— ν2 may be calculated by dividing number cycles for the mooring loads over the period.


3.4.2 Spread mooring unitsFatigue documentation of supporting structures is not required, provided the following criteria fulfilled:

— the strength is in accordance with [3.3]— the area is accessible for inspection— the material and inspection principles given in Sec.1 are complied with.

4 Support of equipments, winches and pulling accessories

4.1 General

4.1.1 The strength requirements to support of winches and pulling accessories other than used for mooringand towing, shall follow the requirements given in DNVGL-RU-SHIP Pt.3 Ch.11 Sec.2 [3].

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4.1.2 Equipments are generally defined as heavy when the static weight is above 50 KN, or if the staticbending moment at deck exceeds 100 KNm. The strength requirements to support of heavy equipments shallfollow the requirements given in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.6.In general and independent of the design loads, all deck equipments shall generally be properly supported.

4.1.3 Hull strength support related to special equipments shall follow the load and acceptance criteria aslisted in Table 3.

Table 3 Design principles for foundations and supporting structures of hull equipment andmachinery

Hull support structure of: Load Acceptance criteria

Thrusters DNVGL-RU-SHIP Pt.3 Ch.10 Sec.6 [6.3]

Helicopter substructure (including pancake) 1) DNVGL-OS-E401 Ch.2 Sec.2 DNVGL-OS-E401 Ch.2 Sec.31) Only stowed condition to be considered.

5 Support of topside structures

5.1 General

5.1.1 For topside loads, see Sec.2 [3.11].

5.1.2 Topside weight should consider a contingency factor of 1.1.Guidance note:

The contingency factor accounts for the uncertainly of topside weight and should be considered in feed phase of the project.


5.1.3 Topside support shall be controlled using a FE-analysis according to Sec.3 [4].

6 Support structure for inboard cranes, davits and lifting masts

6.1 General

6.1.1 Support structure for inboard cranes where lifting is performed within the unit, davits and lifting mastsshall follow DNVGL-RU-SHIP Pt.3 Ch.11 Sec.2 [4].

6.1.2 Design loads shall be provided by the crane designer and shall consider the crane self weight and theworking load, including corresponding dynamic factors as applicable.

6.1.3 Design loads for davits used for life saving appliances shall include an additional load factor of 2.2times SWL as specified in DNVGL-RU-SHIP Pt.3 Ch.11 Sec.2 [4.5.2].

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7 Support of offshore cranes

7.1 General

7.1.1 This subsection covers requirements to support structure of offshore cranes. An offshore crane is alifting appliance on board the unit intended for handling loads outside the unit while at sea.

Figure 4 Typical crane arrangement

Guidance note:

Supporting structure is here defined as the structure below the sleewing bearing (sleewing ring), as the sleewing bearing normallydefines the boundary of scope between the crane designer and the hull designer/yard.

For crane mounted on high pedestals, deflection should be considered


7.1.2 The strength requirements given to the crane pedestal and the crane pedestal support structure shallbe based on crane reaction loads, with corresponding load factors and dynamic factors as given in DNVGL-ST-0378.

7.2 Design conditions

7.2.1 The operational modes of the crane related to design conditions are given below. See Sec.2 [4] fordefinition of design conditions.

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Table 4 Design conditions for offshore cranes

Design conditionOperational mode

Operational Transit Survival

Crane in operation (in use) X

Crane in stowed position (parked in a cradle) X X

7.3 Crane working loadsThe design crane reaction loads at the sleewing bearing shall be based on DNVGL-ST-0378, and the cranereaction loads listed below shall be provided by the crane designer, see Ch.3 Sec.1 [1.4].

— Working load (W) and dynamic factor Ψ used as basis for the design cases.— In plane and vertical loads, and bending moment at the slewing ring considering wind and accelerations as

applicable.— The wind speed, Vw.— Crane dead weigh, SG , including weight of the crane components and the centre of gravity in stowed

condition.— Classification of the crane, including number of cycles, spectrum factor (load spectrum class), or lifting

cycles.— Design loads at top of crane cradle in stowed condition.

The in-plane forces and moments of Y and X axis are normally identically as the crane normally will operatein all directions, The design loads from the crane are forces (KN) and moments (KNm) as following:

F z = vertical force

Fxy = horizontal in-plane forces

Mxy = overturning moments

M z = slewing moment.

Guidance note:

When crane operator cabin is located above the sleewing bearing, additional safety factors shall be considered as specified inDNVGL-ST-0378 Sec.8 [8.2.2.4]


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7.4 Hull girder deflection, δx

7.4.1 The hull girder deflection δx from vertical wave bending moment VBM shall be considered.Guidance note:

The δx may be estimated using the following simplified formula:

where:

σg = maximum hull girder stress at actual position for the given condition

Lm = longitudinal extent of the FE-model

E = Young’s modulus (taken as 210 GPa for steel

VBM = Msw + Mww, = total vertical hull girder moment at position for actual design condition (loaded/ballast)

Z = section modulus of hull girder at deck level at the crane position.


7.4.2 When the crane is in operation (in use), the hull girder deflection shall be considered using:

— M sw according to Sec.2 [2.2]— M wv according to Sec.2 [3.2] using specified operation limitation (Hs), or alternatively using 50% of the

Mww as given in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.4 [3.1].

7.4.3 When the crane is stowed in the cradle, the hull girder deflection shall be considered using:

— M sw according to Sec.2 [2.2]— M wv according to Sec.2 [3.2].

Below the hull girder deformations are shown as prescribed deformation to the left and end moment at right.

7.5 Inertia loads, Fa

7.5.1 For use of the crane , the relevant operational hull motions shall be covered in the reaction forcesgiven in Sec.7 [3.2].

7.5.2 In stowed condition, the inertia loads Fa from ship motions (accelerations) shall be considered basedon the cranes self weight SG acting at the centre of gravity in stowed condition. The accelerations shall be

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based on Sec.2 [3.3], and the combination of responses may be based on Sec.2 Table 9, or directly from awave load analysis.

7.6 Wind (SW) and green sea loads (PSI)

7.6.1 For use of the crane, the relevant operational wind loads shall be covered in reaction loads given inSec.7 [3.2].

7.6.2 In stowed condition, wind loads (SW) shall be considered based on actual wind speed and projectedcrane pedestal wind area, see wind speeds given in Sec.2 [3.8].

7.6.3 Green sea pressure (PSI) as defined in Sec.2 [3.5.2] may be considered as a local load case in stowedcondition, when found relevant.

Guidance note:

Pedestals are normally stocky constructions, and green sea load is normally not a governing load for the strength.


7.7 Combination of loads

7.7.1 Combination of loads shall be considred for the strength and fatigue control according to Table 5.

Table 5 Load combination for offshore crane pedestal and support structure

Crane reaction loadat the slewing ring Hull deflection, inertia and wind loads

Loadcomb.

Limitstate Design condition F z F xy M xy M z S G δ x F a S W P SI

1a ULS 1) Operational condition, crane inuse x x x x x

1b FLS 1) Operational condition, crane inuse x x x x x

2a Crane stowed - transit x x x x (x)3)

2bULS 2)

Crane stowed - survival x x x x (x)3)

3a Crane stowed - transit x x

3bFLS 2)

Crane stowed - survival x x

1) Minimum every 45 degree of the operating sector of the crane shall be controlled. Hull deflection may be based onthe head sea condition for all operating sectors, or the hull deflection may account for each individual operatingsector.

2) Based on unit restrictions, see Sec.2 [3.2], either transit or survival condition is governing.3) May be applied as a separate load case, if relevant.

7.8 Finite element analysis

7.8.1 A FE-analysis shall normally be carried out, and shall include the interaction with hull structure. A localFE-model is acceptable, provided the boundary conditions do not influence of the stress results.

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7.8.2 The hull deflection loads specified in [7.4] may be applied on the FE-model as prescribed deformation,or applied as end moments. If prescribed deformations are applied, different boundary conditions shall beconsidered for the prescribed deflection and the crane loads. Alternatively, the deflection may be consideredas applied bending moment on a larger FE-model as shown in [7.4.3].

7.8.3 The crane reaction loads and inertia loads shall be applied by a multiple point constraint at the slewingring, and the wind load may be applied on the pedestal as pressure or line load.

7.9 Yield and buckling control

7.9.1 Allowable usage factor is ηall = 0,75ReH for Von Mises yield criteria. For buckling control ηall = 0,75,using DNVGL-CG-0128 in general, and DNVGL-RP-C202 for shell buckling, as applicable.

Guidance note:

The usage factor (ηall = 0,75ReH) is based on that load case II given in DNVGL-ST-0378 Sec.4.3 Table 4-2 is found governing.When other load cases (I or III) are found relevant, the allowable usage factor as given in DNVGL-ST-0378 Sec.4.3 Table 4-2 shallbe applied.


7.9.2 When local fine mesh analysis is applied, a 50 x 50 mm mesh size shall be used, together with theacceptance criteria as given in DNVGL-RU-SHIP Pt.3 Ch.11 Sec.2 [4.6].

7.10 Fatigue control

7.10.1 GeneralFatigue capacity of the crane pedestal and it's support structure depends on:

— The dynamic factor, number of load cycles and load spectrum due to lifting (hoisting), when the crane is inuse.

— Inertia loads from hull girder deflection and vessel motion (accelerations) with corresponding cycles, whenthe crane is in stowed position.

— The actual detail (hot spot) to be considered, including weld type.— Relation between maximum and minimum stress range in a stress cycle.

Fatigue damage from crane operation DO, and fatigue damage when the crane is stowed DS, may beassumed uncorrelated. I.e. total calculated fatigue damage DF is:

D F = DO + DS

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7.10.2 Fatigue damage - crane operationCranes are subject to different design cycles (class of utilization, Ν) and load spectra (load spectrum class,kp) depending on crane type and the intended operation. This information should be specified by the cranedesigner.Guidance for selection of these parameters is given in Table 6. Alternatively the crane specific spectrum maybe directly calculated as:

where the load spectrum is divided into successive blocks with particular load levels and where:N = total number of design loads for the craneni = number of lifts in the block for the maximum load Li

Li = maximum load of all lifts in the blockLMax = maximum load of all cycles.

Guidance note:

Table 6 Typical cycles and load spectrum for common crane types

Crane type Number of cycle (Ν) Spectrum (kp)

Jib crane for container service 200 000 0.66

Shipboard crane 200 000 0.66

Offshore crane whip hoist 200 000 0.66

Offshore crane main hoist 63 000 0.33

Provision crane 63 000 0.33

If the crane is categorized according to F.E.M. standard (Federal Europeenne de la Manutention), EN13001-3-1, the correspondingupper bound of kp for the particular load spectrum class (Q1-Q4) may be used directly. kp and the number of cycles N may then betaken as the upper bound for the particular class of utilization (U0-U9).


Based on the defined Ν and kp, the fatigue damage due to crane loads may be calculated as:

where:a1 = intercept of the applicable SN curve given in DNVGL-CG-0129σmax = maximum stress range at the hotspot to be considered.

Guidance note:

As the dominating turning angle for crane operation is normally limited to 130o (not 180o) and that the reaction loads for liftingnormally consists of lifting load, crane boom weight and dynamic amplification factor, the hotspot stress from the crane loads givenin Sec.7 [3.2] may be applied as the stress range σmax in the fatigue calculations.


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7.10.3 Fatigue damage - crane stowedFatigue damage from the inertia loads due to ship motions and hull girder deflection may be calculated byusing a long term Weibull shape parameter of the stresses found from a wave load analysis. Alternativelya Weibull shape parameter of 1.0 may be used. When assuming linear cumulative fatigue damage, theexpression for the fatigue damage is given as:

where:Td = design life in secondsa1 = intercept of SN curve as given in DNVGL-CG-0129T0 = zero-crossing period, may be estimated assuming T0=4*LOG(L)L = ship rule lengthΔσ0 = maximum stress range (MPa) from n0 cyclesn0 = number of cycles for actual stressm = slope of SN-curve, for most curves m = 3Γ = gamma function, Γ(4) = 6.0.For combination of inertia loads, see [7.5].

Fatigue damage contribution for the transit condition may be excluded if time in transit is expected to be lessthan 5% of the total design fatigue time, see also Sec.7 [4.5.3].

7.10.4 Calculation of hot spot stressesThe relevant hot spots may be based on tabulated values when applicable, or by local fine mesh FE analysis.See DNVGL-CG-0129 for details.

Figure 5 Crane pedestal fine mesh for hot spot calculation

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7.11 Crane boom rest structure

7.11.1 For cranes resting in a crane cradle when not in use, the crane cradle loads are normally to besupplied by the crane designer in longitudinal, transverse and vertical direction. Wind loads shall beconsidered as found applicable. The loads shall be applied simultaneously, unless otherwise documented.

Guidance note:

If reaction forces not are specified by the crane designer, the wind speed as defined in Sec.2 [3.8], together with inertia loads fromaccelerations onthe crane boom as specified in Sec.2 [3.3] shall be considered. Using 0.35g in longitudinal (ax) and vertical (az)direction, and 0.5g in transverse direction (ay) will normally be a conservative approach, when applied simultaneously.


7.11.2 Inertia and wind loads acting on the boom rest support structure itself, and the hull girder deflection,may normally be excluded.

7.11.3 Structural documentation of the crane boom rest including support structure shall be performed by aFE or beam model, using the reaction loads provided by the crane designer.

Figure 6 FE-model crane boom rest

7.11.4 Acceptance criteria are given in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.6.

8 Bulwarks, protection of crew and appendages

8.1 Bulwark and protection of crew

8.1.1 Requirements to construction of bulwark are given in DNVGL-RU-SHIP Pt.3 Ch.11 Sec.3 [2].

8.1.2 Requirements to guard rails, gangways, walkways and passageways are given in DNVGL-RU-SHIP Pt.3Ch.11 Sec.3 [3], as found applicable.

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8.2 Bilge keel

8.2.1 The requirements to bilge keel are given in DNVGL-RU-SHIP Pt.3 Ch.11 Sec.4 [2].The bilge keel should be made using doubler plate to prevent potential fatigue crack to propagate into theshell plate, and the bilge keel shall have soft terminations.

Figure 7 Bilge keel soft termination

8.2.2 When the bilge keel web height exceeds 500 mm, supporting brackets at each frame position shouldbe considered. Supporting brackets shall be of the same material class as the bilge strake, and soft detailsshould be used in order minimize fatigue critical hot spots. Full penetration weld should be used between thebilge plate and the support bracket, and should also be provided for the welds inside the hull (between theframe and the bilge plate).

Figure 8 Bilge keel with support brackets

8.3 Propeller nozzles, shaft brackets and stern tubesRequirements shall follow DNVGL-RU-SHIP Pt.3 Ch.11 Sec.4, as applicable.

8.4 Rudders and steeringOffshore ship-shaped units equipped with rudder shall comply with the requirements given in DNVGL-RU-SHIP Pt.3 Ch.14.

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SECTION 6 TOPSIDE STRUCTURES REQUIREMENTS

1 ApplicationThe requirements in this section may be applied for design selection of material, inspection principles, andstructural strength of topside structures.

Guidance note:

Topside structures are not part of DNV GL main class scope, but are part of additional class notations, e.g. DNVGL-OS-E101 forDrilling plant, and DNVGL-OS-E201 for topside processing.


2 Material and inspection principlesSelection of material and NDT scope for typical topside structures are based on the principles given in Sec.1[5]. All main load bearing members (girders and pillar and columns) should follow the requirements forstructure category primary. Plates and stiffeners are generally defined as secondary members.Topside members contributing in the units global longitudinal strength are defined in structure categoryprimary.

Table 1 Material category and corresponding material classes for typical topside members

Materialcategory

Inspectioncategory Structural member Material

class

Secondary III — Pipe rack structure.— Main load bearing structure of modules where the weight < 50 ton.

Class I

Primary II

— Main load bearing structure of modules where the weight > 50 ton.

— local support of equipment where the equipment weight is above 20 ton or— where the resulting (static + dynamic) overturning moment is above 40

tonm.

— Flare tower structure.

Class II

Inspection principles (NDT) for topside structures shall follow DNVGL-OS-C401, unless otherwise agreed.

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Figure 1 Typical main bearing structure for topside module

3 Design principlesThe topside structures shall be designed to withstand the relevant design limit states as described in Sec.1[1.1.2].

4 Design loads

4.1 General

4.1.1 Design loads for topside module structures shall in general follow the principles applicable for the hullstructure, see Table 2 below.

Table 2 Design loads for different design conditions

Design condition

Transit Offshore condition at site

SurvivalDesign load

Normal Restricted OperatingHarsh Restricted

Accidental

Inertia loadsfrom motion andaccelerations

DNVGL-RU-SHIPPt.3 Ch.4 Sec.3,or Sec.2 Table 3

Sec.2 Table 3 Sec.2 Table 3DNVGL-RU-SHIPPt.3 Ch.4 Sec.3, orSec.2 Table 3

Hull girder deflectionfrom vertical bendingmoments

[4.3]

Green sea load Sec.2 [3.5.2]

Wind loads Sec.2 [3.8]

Internal deck loads [4.2]

N/A

Explosion and fire N/A [4.1.5]

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4.1.2 Simultaneous acting static loads (mass of modules), and correlation between responses as described inSec.2 [3.11] may be applied.

4.1.3 Topside structure exposed to green sea loads shall be checked using the green sea pressure defined inSec.2 [3.5.2]. Green sea load is considered as a local load scenario.

4.1.4 Wind loads specified in Sec.2 [3.8] shall be included for large modules and equipments (e.g. flaretower, derrick structure) in the strength control of primary support members (PSM), see [6].

4.1.5 Explosion and fire events shall be considered, see also Sec.1 [2.7].

4.2 Deck loads

4.2.1 Local static pressure distribution Pdl-s and static point load Fdl-s to be used for decks and platforms intopside modules are given in Table 3 below.

Total distributed pressure loads Pdl on deck or platforms is given as following:

and the total point load Fdl is given as following:

where:Pdl-s = static pressure distributionFdl-s = static point loadaz = vertical acceleration for the position considered as given in Table 2 above.

Table 3 Static deck loads in topside modules

For local design (plates, stiffeners)

Decks Distributed load, Pdl-s

[KN/m2]Point load2),

Fdl-s [KN]

For primary design(girders and columns), Pdl-s

[KN/m2]

Storage areas in modules 1) Pdl-s 1.5 × Pdl-s Pdl-s

Lay down areas 1) Pdl-s 1.5 × Pdl-s Pdl-s × f 3)

Area between equipment 5.0 5.0 5.0 × f 3)

Walkways, staircases andplatforms, crew spaces 4.0 4.0 4.0 × f 3)

Walkways and staircases forinspection only 3.0 3.0 3.0 × f 3)

Minimum values for areas notspecified above 2.5 2.5 2.5

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For local design (plates, stiffeners)

Decks Distributed load, Pdl-s

[KN/m2]Point load2),

Fdl-s [KN]

For primary design(girders and columns), Pdl-s

[KN/m2]

1) Pdl-s to be evaluated on case by case, but should not be less than 15 kN/m2.2) Point load may be applied on an area 100 × 100 mm at the most severe position, but need not be combined with

wheel loads or distributed loads.3) Factor f:

where A is the loaded area in m2.

4.2.2 Wheel loads shall be added to the distributed loads Pdl-s when relevant. Individual wheel loads may beapplied over an area of 300 × 300 mm, if not otherwise specified.

4.2.3 If the deck is part of a tank boundary, the pressure from the tank shall be considered.

4.3 Hull girder deflectionThe hull girder loads will impose horizontal and vertical deformation loads to the topside modules, and shallbe considered.

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Guidance note:

The horizontal hull girder deformation may be estimated by using the following simplified formula:

δ = longitudinal deformation between sections 1 and 2

M = design vertical bending moment at sections 1 and 2 for the design condition to be considered

Z = section modulus at the deck at the interface with topside structure

E = Young’s modulus of elasticity

l 1 = distance between sections 1 and 2.

For topside support connections of sliding bearing type, the horizontal deformation may be excluded.


5 Local design requirements

5.1 General

5.1.1 The following general symbols are used in this subsection.

k = material factor as defined in DNVGL-RU-SHIP Pt.3 Ch.3 Sec.1 [2.2]

lbdg = effective bending stiffener or girder span in mm as defined in DNVGL-RU-SHIP Pt.3 Ch.3 Sec.7

lshr = effective shear span or girder span in mm

Pdl = total pressure loads, including static and dynamic contribution

PD = green sea pressure in KN/m2

ReH = specified minimum yield stress of the material in N/mm2

τeH = specified yield shear stress in N/mm2, .

Guidance note:

For permanently manned areas like superstructure, the requirements given in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.8 are applicable.


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5.1.2 The local requirements of intersections between stiffeners and primary support members are given inDNVGL-RU-SHIP Pt.3 Ch.6 Sec.7.

5.2 Plates

5.2.1 The plate thickness [mm], normal and corrugated, should not to be less than:

5.2.2 The thickness of plating [mm], subjected to lateral pressure shall not be less than:

where:a = ength of plate panel in mmb = breadth of the plate panel in mmηall-p = allowable usage factor for plate =0.9αP = correction factor for aspect ratio of plate field, 1.2 -b/(2.1a), need not to be taken larger than 1.0.

5.2.3 Plates exposed for green sea loads shall be checked using the loads defined in Sec.2 [3.5.2], and theplate thickness [mm] shall not be less than:

5.3 Stiffeners

5.3.1 The section modulus for longitudinals, beams, frames and other stiffeners subjected to lateral loadshall not be less than:

where:fbdg = bending moment factor for stiffeners

12 for continues stiffeners fixed at both ends8 for non-continues and continues stiffener, with one or both ends simply supported

fu = factor due to unsymmetrical profiles1.0 for flat bars and symmetrical profiles (T-profiles)1.03 for bulb profiles1.15 for unsymmetrical profiles (L-profiles)

ηall-S = stiffener spacing in mm= permissible usage factors for stiffeners = 0.8.

5.3.2 Stiffeners with sniped ends may be accepted where dynamic stresses are low (< 30 MPa), providedthat the thickness of the plate supporting the stiffener is not less than:

5.3.3 Stiffeners exposed for green sea loads shall be checked using the loads defined in Sec.2 [3.5.2] andthe section modulus shall not be less than:

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6 Primary supporting members

6.1 Scantling requirements

6.1.1 The requirements in this subsection apply to simple PSM subject to lateral loads and concentratedloads, and pillars subject to axial loads.

6.1.2 For PSM part of a complex grillage system, where boundary conditions for individual girders are notpredictable by using simple beam theory, a grillage analysis as explained in [6.2] shall be used.

6.1.3 The net thickness of web and flange of girders should not be less than 5.0 mm

6.1.4 The effective flange of girders is given in DNVGL-RU-SHIP Pt.3 Ch.3 Sec.7 [1.3].

6.1.5 The effective of cut outs and openings shall be considered.

6.1.6 Minimum section modulus of simple girders subject to lateral pressure shall not be less than:

6.1.7 Minimum web area after deduction of cut-outs:

where:fbdg-psm = bending moment factor for PSM as defined in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.6 [2]fshr-psm = shear force factor for PSM as defined in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.6 [2]S = PSM spacing in m as defined in DNVGL-RU-SHIP Pt.3 Ch.6 Sec.7 [1.2]ηall-PSM = permissible usage factors for PSM = 0.8.

6.2 Complex girder system

6.2.1 For large topside modules containing complex girder grillage system, beam or FE-analysis shall beperformed.

6.2.2 The model shall account for the actual support structure (boundary conditions). For modellingtechniques see DNVGL-CG-0127.

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6.2.3 Equipment deck loads, wind loads and global hull deflections shall be included, assuming the mostsevere combination of the loads.

6.2.4 Simultaneous acting static deck loads shall be considered, unless otherwise documented:

where:M = static global weight of the moduleFs = total steel weight of the moduleFe = weight of equipment including tank loads when relevantn = total number of equipmentsK = 0.6, reduction factor to account for simultaneous acting weight, if Mdl-s is used for distributed weightMdl-s = Pdl-s/g, evenly distributed design weight according to Table 3, unless otherwise is specifiedm = total number of decksA = loaded area of deck considered (area occupied by equipments shall not be included).

6.2.5 The global dynamic loads shall be based on the accelerations as specified in Sec.2 [3.3].

6.2.6 The loads may be combined using the EDW principle as specified in Sec.2 [1], or the loads may becombined as shown in Table 4.

Table 4 Combination of dynamic responses for topside structures

Combination with fraction of responses

Global hullgirder deflection Accelerations (topside loads)Design condition LC

δ aZ (FZ) aY (FY) aX (FX)

Windloads (Fw)

Hogging - max. δ, az (Fz) 1a 1 +/- 1.0 +/- 0.4 +/- 0.8 1.0

Sagging - max. δ, az (Fz) 1b -1 +/- 1.0 +/- 0.4 +/- 0.8 1.0

Hogging - max. ax (Fx) 2a 0.3 +/-0.5 +/- 0.6 +/-1.0 1.0

Sagging - max. ax (Fx) 2b -0.3 +/-0.6 +/- 0.6 +/-1.0 1.0

Hogging - max. ay (Fy) 3a 0.7 +/- 0.9 +/- 1.0 +/- 0.7 1.0

Sagging - max. ay (Fy) 3b -0.7 +/- 0.9 +/- 1.0 +/- 0.7 1.0

δ = hull girder longitudinal deflection from vertical hull girder bending moment (Ms + Mw)

M = mass of the topside unit

g = gravity acceleration

aZ (FZ) = vertical accelerations (vertical forces)

aY (FY) = transverse accelerations (transverse forces)

aX (FX) = longitudinal acceleration (longitudinal forces)

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Fw = wind loads (assumed acting in the same direction as the incoming waves, unless otherwisespecified by the project).

6.2.7 All relevant design conditions given in Sec.1 [2] shall be considered.

6.2.8 In-plane hull girder deformation may be excluded if sliding supports are used, but hull girder verticaldeformation shall be evaluated.

6.3 Yield and buckling control

6.3.1 Permissible factor for yield control is ηall-yield = 0,8ReH, using Von Mises yield criteria.

6.3.2 Permissible usage factor for buckling control ηall, shall follow the requirements given in DNVGL-RU-SHIP Pt.3 Ch.8 Sec.1 [3.4].

6.4 Fatigue

6.4.1 Topside structures shall be evaluated for fatigue according to the principles given in Sec.4

6.4.2 Vortex induced vibrations shall be considered for slender members, e.g. flare tower and derrickstructure, see DNVGL-RP-C205 for details.

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SECTION 7 SPECIAL PROVISIONS FOR UNIT TYPES, CONVERSIONSAND LIFETIME EXTENSIONS

1 GeneralThis section specifies requirements specific for the different unit types, and requirements applicable forconversions and lifetime extensions.

1.1 Principles of finite element load combinations

1.1.1 Each design load combination consists of a loading pattern, dynamic loads, structural weight,internal and external pressures, and hull girder loads. For seagoing condition, both static and dynamic loadcomponents (S+D) shall be applied. For harbour and tank testing condition, only static load components (S)need to be considered.

1.1.2 The following symbols are used within this section:

CBM-LC = Percentage of permissible stillwater moment Msw for the load combination considered. Fordetails see DNVGL-CG-0127 [6.2.1].

CSF-LC = Percentage of permissible stillwater shear force Qsw. for the actual load combinationconsidered. For details see DNVGL-CG-0127 [6.2.2].

Vertical stillwater bending moment Msw:

100% Msw = 100% of the permissible vertical stillwater bending moment, for details see DNVGL-CG-0127Sec.3 [6.3.8]and DNVGL-CG-0127 Sec.3 [6.3.9].

50% Msw = 50% of the permissible vertical stillwater bending moment, for details see DNVGL-CG-0127Sec.3 [6.3.8] and DNVGL-CG-0127 Sec.3 [6.3.9].

Vertical stillwater shear force Qsw:

100%Qsw

= 100% of the permissible vertical stillwater shear force, for the given load combination, Thetotal shear force to be adjusted to reach the target value at forward bulkhead and aft bulkheadof the mid-hold. For details see DNVGL-CG-0127 Sec.3 [6.3.5].

100%and 75%

= 100% or 75% of the permissible vertical stillwater shear force. The vertical shear force in theFE is not request adjusted to reach the target value, when the shear forces at both forwardand aft bulkheads are not higher than the target value. For details see DNVGL-CG-0127 Sec.3[6.3.5].

2 Drilling units

2.1 Design conditions and design loads

2.1.1 The relevant design load conditions are given in Sec.1 [2].

2.1.2 The operating condition as specified Sec.1 [2.3] shall be specially considered for drilling units. Anylimiting operational condition shall be clearly specified in the structural design basis document. The followingshall in addition be specified:

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— Wave scatter diagram for the operational locations, together with information of any restricted waveheight criteria (Hs) during operation. Alternatively, information of restricted wave height (Hs) andresponding up-crossing periods.

— Limiting wind speed.

2.1.3 Design loads are generally given in Sec.2. The most governing design loads for the design conditions intransit, operating and survival condition shall be used, see Sec.2 [3.2]. Non-linear correction factors shall beconsidered as specified in Sec.2 [3.9.3].

2.2 Design load scenarios and design loading combinations

2.2.1 The following structural areas shall normally be considered:

— machinery space area— moonpool/drillfloor area— riser hold area— mud tank area.

Loading patterns need to be specially considered for each unit, as the arrangement for drilling units differ.In Table 1 typical design combinations are presented, but other design combinations may also have to beconsidered depending of the unit's arrangement. Full load and ballast condition should be considered withcorresponding limit stillwater loads for the most severe tank filling configurations. The design load scenariosand design load combinations shall be clearly explained in the structural design basis document. See [1.1.2]for symbols used in Table 1.

Table 1 Typical design load combinations for FE-analysis of drilling units

Stillwater loads Dynamic load casesNo.

Draught CBM-LC CSF-LC Head sea Beam sea Oblique sea Comment

Design scenario - seagoing condition

Typical normalloaded condition.Full riser stack.

100% Msw Sagging 100% HSM-1 BSP-1P/S

A1

1.0 TSs100% Msw Hogging 100% HSM-2 FSM-2 BSP-1P/S OST-2P/S

OSA-1P/S

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Stillwater loads Dynamic load casesNo.

Draught CBM-LC CSF-LC Head sea Beam sea Oblique sea Comment

Design scenario - seagoing condition

No filling in doublebottom or doubleside tanks.Full riser stack.


A2

1.0 TSC100% Msw Hogging 100% HSM-2 FSM-2 BSP-1P/S OST-2P/S

OSA-1P/S

Typical normalballast condition.Empty riser stack.


A3

1.0 TBal100% Msw Hogging 100% HSM-2 FSM-2 BSP-1P/S OST-2P/S

OSA-1P/S

Typical normalballast condition.No fuel tanks.Empty riser stack.


A4

1.0 Tbal100% Msw Hogging 100% HSM-2 FSM-2 BSP-1P/S OST-2P/S

OSA-1P/S

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2.3 Strength assessment

2.3.1 Requirements to the hull strength are given in Sec.3.

2.3.2 Part ship finite element analyseIn order to account for all heavy loads and variation of the structure in structure arrangement, a part shipFE-analysis including moonpool area with drillfloor structure, riser and drill hold section area and machineryarea for the typical design load combinations as presented in Table 1, is normally required.In fore-part and aft-part area where the longitudinal elements are not continuous with adjacent structure,e.g. discontinuity in longitudinal bulkheads or when changing from longitudinal to transverse stiffening, theseareas shall be included in the FE-analysis.

Figure 1 Typical drillship arrangement

2.3.3 Local finite element modelsLocal analysis for the topside interface areas as listed below are normally required. Other details may berequired to be analysed based on the topside arrangement and complexity.

— Drillfloor substructure and supporting structure (included in part ship FE model).

— Topside stools and support for heavy topside structure.

— Crane pedestal foundation and support structure.

— Foundation and support structure for gantry crane rail.

The local FE-models may be performed as separate FE-models, where the loads from the topside structureare combined with global hull girder stress and local tank pressure as found relevant.


2.4.1 Fatigue shall be documented in accordance with the principles given in Sec.4.

2.4.2 The fraction of the total design life spent in transit and operating conditions shall be reflected in thefatigue calculation.

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Guidance note:

The fraction of the total design life using 80% in operation and 20% in transit may be used if no other information is available.


2.4.3 A design fatigue factor (DFF) of 1.0 is acceptable for all structural elements that follow the 5-yearinspection interval in dry-dock. For units not intended to be dry-docked, Sec.4 Table 2.

3 Well intervention units


3.1.1 Well intervention units may be based on the prescriptive ship rule loads as given in DNVGL-RU-SHIPPt.3 Ch.4 , including topside loads as found applicable.

3.1.2 Well intervention units that shall comply with the MODU code requirements for hull strength shallbe based on the design loads as specified in Sec.2 [3]. Non-linear correction factors shall be considered asspecified in Sec.2 [3.9.3].

Guidance note:

The 100 year environmental loads may be replaced with 50 year environmental loads as defined in the MODU code.


3.1.3 The operating condition as specified Sec.1 [2.3] shall be specially considered for drilling units. Anylimiting operational condition shall be clearly specified in the structural design basis document. The followingshall in addition be specified:

— Wave scatter diagram for the operational locations, together with information of any restricted waveheight criteria (Hs) during operation. Alternatively, information of restricted wave height (Hs) andresponding up-crossing periods.

— Limiting wind speed.Guidance note:

A reduction below the prescriptive rule loads given in DNVGL-RU-SHIP Pt.3 Ch.4, shall be documented by means of a wave loadanalysis using the principles given in Sec.2 [3].


3.2 Design load scenarios and design loading combinations

3.2.1 The following areas shall typically be considered:

— machinery space area— moonpool area— mud and cement storage areas.

Full load and ballast conditions for the most severe tank filling configurations shall be considered togetherwith stillwater limit curves. All design scenarios and load combinations shall be clearly explained in thestructural design basis.


3.3.1 Requirements to the hull strength is generally given in Sec.3.

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3.3.2 Part ship finite element analyseIn order to account for all heavy loads and variation of the structure in structure arrangement, a part shipFE-analyse including moonpool areas considering the loads from drill tower as applicable, and machineryarea, is normally required.In fore-part and aft-part area where the longitudinal elements are not continuous with adjacent structure,e.g. discontinuity in longitudinal bulkheads or when changing from longitudinal to transverse stiffening, theseareas shall be included in the FE-analysis.

3.3.3 Local analysis like drill tower support, crane pedestal supports, etc. will normally be required based onthe unit's arrangement and complexity.



3.4.2 The fraction of the total design life spent in transit and operating conditions shall be reflected in thefatigue calculation.

Guidance note:

The fraction of each loading condition may be taken similar as for multi purpose vessels (MPV) as defined in DNVGL-RU-SHIP Pt.5Ch.9 Sec.4.


3.4.3 A design fatigue factor (DFF) of 1.0 is acceptable for all structural elements provided the unit follow 5-year inspection interval for dry-docking. For units not intended to be dry-docked, Sec.4 Table 2.

4 Floating production and storage units

4.1 General

4.1.1 Floating production and storage units are here defined as:

— FPSO: floating production, storage and offloading units— FSO: floating storage and offloading units— FLNG: floating liquified natural gas units.

4.1.2 The design load combinations given in [4.3] are applicable for FPSOs and FSOs.

4.1.3 For FLNG units the structural requirements to the LNG containment is given in DNVGL-RU-SHIP Pt.5Ch.7 and in DNVGL-RU-SHIP Pt.5 Ch.8, as applicable. The strength requirements given in this standard coveronly the hull structure, excluding the LNG containment.

Guidance note:

FLNG units are normally moored in restricted location, see Sec.1 [2.4.3]. The hull strength requirements and accelerations used fortopside strength are then normally governed by the transit condition (see Sec.1 [2.2]) or the wet tow to location (see Sec.1 [2.6]),as applicable.



4.2.1 The applicable design conditions are given in Sec.2 [4].

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Guidance note:

Operating condition as specified Sec.1 [2.3] is normally not considered applicable for conventional production and storage units,as the survival condition will be the governing condition. For units intend to disconnect and move from location in case of extremeweather like a hurricane, such operational condition shall be evaluated.


4.2.2 Design loads are given in Sec.2 for the different design conditions. Non-linear correction as defined inSec.2 [3.9.3] shall be considered, as applicable.

4.2.3 Green sea pressureFor superstructure and deckhouses structure the external pressure PSI for sides of superstructure given inDNVGL-RU-SHIP Pt.3 Ch.4 Sec.5 [3.3.1], shall include a wave factor fSI-uls as following:fSI-uls= fwv-uls

For end bulkheads and front wall pressure the PA as specified in DNVGL-RU-SHIP Pt.3 Ch.4 Sec.5 [3.4.1] awave factor fA-uls shall be included as following:

for fwv-uls< 1.0; fA-uls= fwv-uls

for 1.0 > fwv-uls< 1.2; fA-uls= 2.5fwv-uls-1.5

for fwv-uls>1.2; fA-uls= 1.5

fwv-uls is given in Sec.2 [3.4.1].

For units operating in restricted locations (Sec.1 [2.4.3]) with unrestricted transit (Sec.1 [2.2.1]), the PSLand PA shall be according to DNVGL-RU-SHIP Pt.3 Ch.4 Sec.5 [3.3.1] and DNVGL-RU-SHIP Pt.3 Ch.4 Sec.5[3.4.1] respectively.

4.2.4 Slamming and impact pressureSlamming and impact pressure loads shall be based on the prescriptive rule pressure requirements inDNVGL-RU-SHIP Pt.3 Ch.10, with the following additional requirements:

— The bow impact pressure load given in the DNVGL-RU-SHIP Pt.3 Ch.10 Sec.1 [2] shall include a wavefactor fFB-uls as following:fFB-uls=fWv-uls, where fwv-uls is given in Sec.2 [3.4.1].

— The stern slamming pressure load given in the DNVGL-RU-SHIP Pt.3 Ch.10 Sec.3 [2] shall include a wavefactor fSS-uls as following:fSS-uls=fWv-uls, where fwv-uls is given in Sec.2 [3.4.1].

For units operating at restricted locations (Sec.1 [2.4.3]) with unrestricted transit (Sec.1 [2.2.1]), the valuesfor bow impact pressure given in DNVGL-RU-SHIP Pt.3 Ch.10 Sec.1 [2] and stern slamming pressure given inDNVGL-RU-SHIP Pt.3 Ch.10 Sec.3 [2] shall be used.

4.3 Design load scenarios and design load combinationsThe design load scenario and design load combinations for the FE-analysis are given in the tables below fordifferent arrangements. The principles are based on oil tankers defined in the IACS Common structural rules(CSR) for bulk and oil tankers Pt.1 Ch.4 Sec.8 [3]. Units specific arrangement shall be considered togetherwith topside and turret loads, as applicable.

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Figure 2 Typical hull areas to be analysed for production and storage units

4.3.1 The inertia forces from topside structure and turret shall follow the dynamic EWD load cases similar tothose for the hull structure, and combined together with the dynamic load cases present in [4.3.2].

4.3.2 For units with two longitudinal oil tank bulkheads, the dynamic load cases for seagoing and for harbourand testing conditions are given in Table 2 and Table 3 below. See [1.1.2] for symbols used in the tables.

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Table 2 Load combinations for FE analysis - seagoing conditions - oil storage units with two oiltight BHDs

Permissible stillwater loads

Dynamic load cases (EDW)

Foremost areaNo. Draft

Aftmost area Midship areaInternal turret system No or external turret

CBM-LC CSF-LC CBM-LC CSF-LC CBM-LC CSF-LC CBM-LC CSF-LC

Sagging

100%Msw 100% 100%Msw 100% 100%Msw 100% 100%Msw 100%

HSM-1, FSM-1,BSP-1PS HSM-1, BSP-1PS HSM-1, FSM-1, BSP-1PS,

BSR-1PS, OSA-2PS, OST-1PS

HSM-1, FSM-1,BSP-1PS, BSR-1PS,OSA-2PS, OST-1PS

Hogging

100%Msw

100% 100% Msw 100%

A1 0.9TSC

HSM-2, BSR-1PS,BSP-1PS, OSA-1PS

HSM-2, FSM-2, BSP-1PS,OSA-1PS, OST-2PS

N/A N/A


Sagging

100%Msw 100%Msw 100%Msw 100% 100%Msw 100% 100% Msw 100%

HSM-1, FSM-1,BSR-1PS, OST-1PS

HSM-1, BSR-1PS,BSP-1PS HSM-1, OSA-2PS HSM-1, OSA-2PS

Hogging

100% Actual

100%

A2 0.9TSC

HSM-2, FSM-1,FSM-2, OSA-1PS

HSM-2, FSM-2,BSR-1PS, BSP-1PS

N/A N/A

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N/A


Sagging

100%Msw 100%Qsw 100%Msw 100% 100%Msw 100%

HSM-1, FSM-1 HSM-1, OSA-2PS HSM-1, OSA-2PS

100%Msw 100%

BSP-1PS

N/A

N/A

Hogging

100%Msw 100%Qsw

A3a 0.65TSC

HSM-2, FSM-2N/A


Sagging

100%Msw 100% 0% 100%Qsw 100%Msw 100% 100%Msw 100%Qsw

HSM-1, FSM-1 HSM-1 HSM-1 HSM-1

100% 100%Qsw

0% 100% 100% Msw 100% 100% Msw 100%

A3b 0.65TSC

BSP-1PS, OST-1PS BSP-1PS OSA-2PS OSA-2PS

Hogging

100%Msw 100%Qsw 100%Msw 100%Qsw 0% 100%Qsw 0% 100%Qsw

HSM-2 HSM-2 HSM-2 HSM-2

100%Msw

100% 100% Msw 100% 0% 100% 0% 100%

A3b 0.65TSC

BSP-1PS, OSA-1PS BSP-1PS BSP-1PS, OSA-2PS BSP-1PS, OSA-2PS

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Sagging

100%Msw 100% 100%Msw 100% 50%Msw 100% 50%Msw 100%

HSM-1, BSP-1PS HSM-1, BSR-1PS,BSP-1PS, OSA-2PS N/A N/A

Hogging

100%Msw 100% 50%Msw 100% 100%Msw 100%

A4 0.6TSC

HSM-2, FSM-1,BSP-1PS,

OSA-1PS, OSA-2PS

N/AFSM-1, BSP-1PS, OSA-2PS FSM-1, BSP-1PS,

OSA-2PS


Sagging

0% 100%Qsw 100%Msw 100%Qsw 0% 100%Qsw 0% 100%Qsw

HSM-1,HSM-2, FSM-1 HSM-1 HSM-1 HSM-1

100% Msw 100%N/A

BSP-1PSN/A N/A

Hogging

100%Msw 100%Qsw 0% 100%Qsw 100%Msw 100%Qsw 100%Msw 100%Qsw

HSM-2, FSM-1 HSM-2 HSM-2 HSM-2

100%Msw 100% 0% 100% 100%Msw 100% 100%Msw 100%

A5a 0.65TSC

BSP-1PS BSP-1PS BSP-1PS BSP-1PS

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CBM-LC CSF-LC

Sagging

0% 100%Qsw

HSM-1, HSM-2

0% 100%

BSP-1PS, BSR-1PS

Hogging

100%Msw 100%Qsw

A5b 0.65TSC

HSM-2, FSM-2

N/A


Hogging

100%Msw 100% 100%Msw 100% 50%Msw 100% 50%Msw 100%

A6 0.6TSC

HSM-2, FSM-1,BSR-1PS, BSP-1PS,OSA-1PS

HSM-2, BSR-1PS,BSP-1PS, OSA-1PS OSA-2PS OSA-1PS


Sagging

100%Msw 100% 100%Msw 100%

A7a TLC

N/A N/A HSM-1, HSA-1, FSM-1, BSP-1PS,BSR-1PS, OST-1PS, OSA-2PS

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Hogging

100%Msw 100% 100%Msw 100%A7a TLC HSM-2, FSM-1,

BSP-1PS,BSR-1PS, OSA-1PS

HSM-2, FSM-2, BSR-1PS,BSP-1PS, OST-2PS,OSA-1PS, OSA-2PS

N/A N/A


Sagging

100%Msw 100% 100%Msw 100%

N/A N/A HSM-1, HSA-1, FSM-1, BSP-1PS,BSR-1PS, OST-1PS, OSA-2PS

Hogging

100%Msw 100% 100%Msw 100% 100%Msw 100% 100%Msw 100%

A7b TLC

HSM-2, FSM-1,BSP-1PS,

BSR-1PS, OSA-1PS

HSM-2, FSM-2, BSR-1PS,BSP-1PS, OST-2PS,OSA-1PS, OSA-2PS

N/A N/A

N/A

N/A N/A

Sagging

100%Msw 100%

A8 TBal

N/A HSM-1, BSR-1PS,BSP-1PS, OSA-2PS

N/A N/A

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Table 3 Load combinations for FE analysis - harbour and test conditions - oil storage units withtwo oil tight BHDs






Sagging

N/A 100%Msw 100% N/A

Hogging

A9 0.25TSC

100%Msw 100% N/A 100%Msw 100% 100%Msw 100%


Sagging

N/A 100% Msw 100% N/A

Hogging

A10 0.25TSC

100%Msw 100% N/A 100%Msw 100% 100%Msw 100%


Sagging

N/A 100%Msw 100%Qsw N/A

Hogging

A11a

100%Msw 100%Qsw N/A 100%Msw 100%Qsw 100%Msw 100%Qsw

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N/A N/A N/A


Hogging

A11b 0.6TSC


A12a 0.33TSC

N/A - testing condition

A12b 0.33TSC

N/A - testing condition


Sagging

N/A N/A 100%Msw 100%Qsw 100%Msw 100%Qsw

Hogging

A13a 0.7TSC

100%Msw 100%Qsw 100%Msw 100%Qsw N/A

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CBM-LC CSF-LC

Sagging

100%Msw 100%Qsw

Hogging

A13b 0.7TSC

100%Msw 100%Qsw

N/A


Sagging

100%Msw 100% N/A 100%Msw 100% 100%Msw 100%

Hogging

A14 TSC

100%Msw 100% 100%Msw 100% N/A

4.3.3 For units with one longitudinal centreline oil tank bulkhead, the dynamic load cases for seagoing andfor harbour and testing conditions are given in Table 4 and Table 5 below.

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Table 4 Load combinations for FE analysis - seagoing conditions - oil storage units with onecentreline oil tight BHD






Sagging

100%Msw 100% 100%Msw 100% 100%Msw 100% 100%Msw 100%

HSM-1, FSM-1,BSP-1PS, BSR-1PS HSM-1, HSA-1, BSP-1PS HSM-1, BSP-1PS, OSA-2PS

Hogging

100%Msw 100% 100%Msw 100%

B1 0.9TSC

HSM-2, BSP-1PS,OSA-1PS

HSM-2, FSM-2, BSR-1P,BSP-1P, OST-2P

N/A N/A


Sagging

100%Msw 100% 100%Msw 100% 100%Msw 100% 100%Msw 100%

HSM-1, FSM-1,BSP-1PS, BSR-1PS HSM-1, HSA-1, BSP-1PS HSM-1, BSP-1PS, OSA-2PS

Hogging

100%Msw

100% 100% Msw 100%

B2


HSM-2, FSM-2, BSR-1PS,BSP-1PS, OST-2S

N/A N/A

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Sagging

100% 100%Qsw 0% 100%Qsw

HSM-1, FSM-1N/A

100%Msw 100% 100%Msw 100% 100%Msw 100% 100%Msw 100%

BSP-1PS HSM-1, BSP-1S, OSA-2PS

Hogging

100%Msw 100%Qsw 100%Msw 100%Msw

HSM-2 HSM-2, FSM-2

100%Msw 100% 100%Msw 100%

B3a 0.9TSC

BSP-1PS

N/A

CBM-LC CSF-LC CBM-LC CSF-LC

Sagging Sagging

100%Msw 100%Qsw 100%Msw 100%Qsw

HSM-1, FSM-1 HSM-1, FSM-1

100%Msw 100% 100%Msw 100%

BSP-1PS BSP-1PS,OST-1PS, OSA-2PS

Hogging Hogging

100%Msw 100%Qsw 0% 100%Qsw

HSM-2, FSM-2 HSM-2

100%Msw 100% 100%Msw 100%

B3b 0.9TSC

BSP-1PS, OSA-1PS

N/A

BSP-1PS, OSA-2PS

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Sagging

100% 75%N/A

HSM-1, BSP-1P, OSA-2PSN/A

Hogging

100%Msw 75% 100%Msw 75% 100%Msw 75%

B4 0.6TSC


N/ABSP-1PS, OSA-2PS


Sagging

100% 75%N/A

HSM-1, BSP-1P, OSA-2PSN/A

Hogging

100%Msw 75% 100%Msw 75% 100%Msw 75%

B5 0.6TSC


N/ABSP-1PS, OSA-2PS

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Sagging

0% 100%Qsw 100%Msw 100%Qsw 0% 100%Qsw 0% 100%Qsw

HSM-1 HSM-1 HSM-1

100% 100%Qsw 100% 100%Qsw 100%Msw 100%N/A

BSP-1PS OSA-2PS

Hogging

100%Msw 100%Qsw 0% 100% 100%Msw 100%Qsw 100%Msw 100%Qsw

HSM-2 HSM-2 HSM-2, FSM-2

100%Msw 100% 100%Msw 100%

B6a 0.6TSC

N/A N/AOSA-2PS

CBM-LC CSF-LC

Sagging

0% 100%Qsw

HSM-1

Hogging

100%Msw 100%Qsw

HSM-2

100%Msw 100%

B6b 0.6TSC

HSA-2, BSR-1PS

N/A

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CBM-LC CSF-LC CBM-LC CSF-LC

Sagging

100%Msw 100% 100%Msw 100%

B7 TBal N/A

HSM-1, BSP-1PS

N/A

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Table 5 Load combinations for FE analysis - harbour and test conditions - oil storage units withone CL oil tight BHD






Sagging

N/A 100%Msw 100%Qsw N/A

Hogging

B8a 0.33TSC


CBM-LC CSF-LC

Sagging

100%Msw

100% Qsw

Hogging

B8b 0.33TSC

100%Msw

100% Qsw

N/A


Sagging

N/A 100%Msw 75% N/A

Hogging

B9 0.33TSC

100%Msw 75% 100 Msw 75% 100%Msw 75% 100%Msw 75%

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Sagging

N/A 100%Msw 75% N/A

Hogging

B10 0.33TSC

100%Msw 75% N/A 100%Msw 75% 100%Msw 75%


Sagging

100%Msw 100%Qsw N/A 100%Msw 100% 100%Msw 100%

Hogging

B11a TSC

100%Msw 100%Qsw 100%Msw 100%Qsw N/A


Sagging

100%Msw 100%Qsw 100%Msw 100%Qsw

Hogging

B11b

100%Msw 100%Qsw

N/AN/A

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4.4.1 Requirements to the hull strength are given in Sec.3.

4.4.2 A part ship FE-analyses covering the areas and relevant design load combinations as shown in Figure 2and in the tables above, are normally required.It shall be noted that:

— In fore-part and aft-part area where the longitudinal elements are not continuous with adjacent structure,e.g. discontinuity in longitudinal bulkheads or when changing from longitudinal to transverse stiffening,these areas shall be included in the part ship FE-analysis.

— where an external turret/yoke introduce large forces effecting the global bending moment and shearforces, the fore ship structure shall be included in the foremost part ship FE-analysis.

4.4.3 The shear force correction shall be considered as following:

where:QR = total vertical hull girder shear force capacity in KNqvi-gr = unit shear flow for hull girder vertical shear force, in mm-1, for the plate i based on gross

thickness ti-gr, in mmti-gr-eff = effective gross thickness of plate i, in mm, accounting for tsfi-gr and tsti-gr

tsfi-gr = effective gross plate thickness accounting for shear force correction from the bottom structureaccording to CSR rules for oil tankers Ch.5 Sec.1 [3.4.1], where net scantlings used in theformulas to be replaced with gross thickness

tsti-gr = effective gross plate thickness accounting for shear force correction due to loads from transversebulkhead stringers according to CSR rules for oil tankers Ch.5 Sec.1 [3.5.1], where netscantlings used in the formulas to be replaced with gross thickness

τi-perm = permissible hull girder shear stress for plate given in CSR rules for oil tankers Ch.5 Sec.1, to bereplaced with permissible gross shear stress for plate according to DNVGL-RU-SHIP Pt.3 Ch.5Sec.2, i.e τi-perm= 110/k.

4.4.4 Limit curves for harbour conditions as given in DNVGL-RU-SHIP Pt.3 Ch.5 Sec.2 [1.7]] and DNVGL-RU-SHIP Pt.3 Ch.5 Sec.2 [2.3] may be omitted, but relevant limit curves for inspection and maintenanceconditions may be applicable.

4.4.5 Local finite element modelsLocal analysis for the topside interface areas as listed below are normally required. Other details may berequired to be analysed based on the topside arrangement and complexity.

— topside stools and support for heavy topside structure

— turret support and interface structure

— crane pedestal foundation and flare tower support structure

— riser interface and fairlead support structure.

The local FE-models may be performed as separate FE-models, where the loads from the topside structureare combined with global hull girder stress and local tank pressure as found relevant.

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4.5.2 The fraction of the total design life spent in loaded and in ballast for the operating condition shall beconsidered in the fatigue calculation.

Guidance note:

For tankers, 50% in full load and 50% in ballast may be applied for the operation, unless otherwise documented. Partial loadedcondition should be considered if the difference in the draft between full load and ballast exceed 8 m. 33% in each draft may thenbe used, unless otherwise documented.


4.5.3 The transit condition may be omitted if the estimated time in transit is lower than 5% of the unitsdesign life time.

5 Conversion of units

5.1 Scope

5.1.1 The principles given in DNVGL-CG-0156 shall in general be used, together with the requirements listedbelow.

5.1.2 The basis of conversion is a unit that complies with the material, fabrication and structuralrequirements, from the date the unit was built.

5.1.3 Prior to conversion the unit shall be surveyed and evaluated for the following:

— identification of steel wastage by thickness measurements— identification of fatigue cracks or damage.

5.1.4 Major change of the unit's main parameters such as e.g. lengthening or conversion to another unittype, will normally require new global and local scantling checks.

5.1.5 New permissible stillwater bending and shear force limit curves for all operational modes shall beprovided as part of an updated loading manual, and the loading instrument when relevant.

5.2 Material, extent of non-destructive testing and tank testing

5.2.1 Renewed structural materials shall be replaced with material of same or greater scantling as existingmaterial, and of the same or higher material grade.

5.2.2 All new structures shall as a minimum comply with the requirement given in Sec.1. Welds betweennew and existing structure shall follow the requirement to inspection for structural category primary, seeSec.1 [5.5.1].

5.2.3 For minor modifications in existing tanks, new structural tank testing may be omitted, but shall beconsidered on a case by case basis.

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5.3 Hull strength

5.3.1 Existing hull structure prior to conversion is accepted as is, provided any steel wastage from corrosionis within the minimum thickness list provided as a tanker (net scantling), and possible fatigue cracks or anyother hull defects are repaired.If existing loading conditions do not cover all new loading configurations, or are filled with liquid of higherdensity than used as basis for the original strength approval, the local structure shall be checked according tothe strength requirements in Sec.3 [3].

5.3.2 For units intended for operation at harsh locations, see Sec.1 [2.4.2], or if new loading conditions areincluded, additional nominal hull girder strength check according to Sec.3 [2] shall be performed.

5.3.3 All new structure and existing hull structure supporting new equipments, shall comply with therequirements in this standard. This will typically include, but is not limited to:

— new bulkheads— installation of turret or mooring arrangement— modification of super-structure— installation of topside modules and equipments— installation of helideck, lifeboat davits, cranes, etc.

5.4 Topside and topside interface to hull structure

5.4.1 Topside structure shall be calculated according to Sec.6.

5.4.2 Topside interface to hull structure shall be calculated according to Sec.2 [3.11].

5.4.3 The following approach should be taken to evaluate the suitability of the hull structure for the expectedtopside loads:

— Determine the condition of the unit with respect to corrosion and cracks.— Identify the weight of the topside loads.— Identify positions of topside modules and strength of hull support structure.— Uplift of the topside structure may introduce high tensile stresses perpendicular to the plate of the deck

plate and replacing existing plate with z-quality steel may be required.— Due to fatigue, existing fillet welds between transverse frame/bulkhead and deck plate may be increased

or replaced with full penetration welds when topside support structure is mounted.

5.5 Fatigue calculation

5.5.1 GeneralAccumulated and future fatigue damage shall be evaluated in accordance with Sec.4, and depends of thefollowing parameters:

— results from survey and previous repair history— service history of the unit— duration and environmental conditions for the new site specific location.

Previous repair and crack damage history should be considered in the total fatigue evaluation, in order tominimized potential fatigue failures in future operation.The fatigue calculation methods described in Sec.4 [1.2] shall be used for the fatigue calculation.The corrosion addition principles as given in Sec.1 [6.1.1] shall be applied for the fatigue calculations.

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5.5.2 Previous tradingFatigue damage from historical trading shall be calculated, using trading route history if applicable, or usingworld wide scatter diagram if tanker trading history not is available.Design fatigue factor (DFF)=1 may be applied for the previous trading phase.Gross scantlings and SN curves for air may be applied for the past trading period (no time in corrosiveenvironment), provided the corrosion protection system (e.g. painting, anodes) is intact.For details fully repaired and inspected (NDT), the historical fatigue damage may be excluded and only thefatigue damage calculation from future operation should be considered.

5.5.3 Future operationMinimum 10 years fatigue life should be applied for the future operation (TDO).Design fatigue factors (DFF) as specified in Sec.4 [1.3.2] shall be used.The time in corrosive environment (TC) shall be calculated according to the principles given in DNVGL-CG-0129 Sec.3 [4], where:Design fatigue life TDF = Previous trading time (TDT) + future operation time (TDO).TD = 25 years.TC,25 according to DNVGL-RU-SHIP Pt.3 Ch.9 Sec.4 [4.4].

5.5.4 Areas to be calculatedFatigue sensitive details in existing hull structure and new structures shall be documented to validatesufficient fatigue strength. Details given in Sec.4 [1.4] to be considered.

Guidance note:

For conversion of tankers to production and/or storage units intended to operate in harsh environment, the side shell platethickness above the stiffener spacing should not be less than 1/46 due to plate fatigue.


5.5.5 Design fatigue factors and acceptable fatigue damageThe design fatigue factors (DFF) specified in Sec.4 [1.3.2] shall be applied for the future operation. For thehistorical trading phase, DFF equal 1.0 should be used.

Table 6 Design fatigue factors for past trading and future operation phases

Fatigue damage for past tanker trade Fatigue damage for future operation Total fatigue damage

D1 D2 x DFF D1 + D2 x DFF < 1.0

The calculated total fatigue damage should be above 1.0. However, upon special consideration lowercalculated fatigue damage may be accepted providing the following is considered:

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Items relevant for total fatigue evaluation Explanation

No or few fatigue cracks are reported for the past tradinghistory.

Conservative assumptions used in the fatigue calculationmethod.

Calculated fatigue damage for future operation is low.Dynamic loads are small for new location compared withdynamic loads used as basis for the past tanker trading.Low possibility for future cracks at location.

Inspection program is created or extended.Details in areas with fatigue damage > 1 are inspectedmore frequently. Possible fatigue cracks will be discoveredand stooped before found critical.

Criticality of possible cracks is low.Possible cracks appear in areas not found critical for hullstrength, not lead to leakage, and will likely not continuefurther crack propagation after initiation is discovered.

5.5.6 Environmental reduction factorsThe environmental reduction factor, fe, is defined as the difference in vertical wave bending momentresponse, calculated by wave load analysis for North Atlantic scatter diagram and actual site specific scatterdiagram as following:For world wide operation the fe-factor of 0.8 should be used. For units that are operating in North Atlantic orin harsh environments, the fe-factor of 1.0 should be used.The fe factor may alternatively be estimated using the predefined values given in Table 3. Interpolationbetween the ship lengths may be used. For units traded in different areas, weighing between the areas maybe applied to calculate the total fe-factor for the past trading phase.

Figure 3 Nautical zones for estimation of fatigue reduction factors, fe

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Table 7 Environmental reduction factor fe related to unit length and nautical zones

LBP 300 m 200 m 100 m LBP 300 m 200 m 100 m

Zone no. fe- factor Zone no. fe- factor

1 0.79 0.88 0.92 53 0.58 0.67 0.72

2 0.64 0.73 0.78 54 0.50 0.59 0.63

3 0.95 1.00 1.00 55 0.37 0.46 0.50

4 0.85 0.92 0.94 56 0.49 0.58 0.62

5 0.38 0.47 0.52 57 0.43 0.52 0.57

6 0.88 0.95 0.97 58 0.35 0.44 0.49

7 0.90 0.96 0.99 59 0.47 0.56 0.60

8 1.00 1.00 1.00 60 0.60 0.69 0.74

9 1.00 1.00 1.00 61 0.48 0.57 0.61

10 0.81 0.90 0.94 62 0.50 0.59 0.64

11 0.79 0.88 0.93 63 0.44 0.53 0.58

12 0.98 1.00 1.00 64 0.48 0.57 0.61

13 0.90 0.96 0.99 65 0.45 0.54 0.58

14 0.81 0.90 0.94 66 0.47 0.57 0.61

15 0.95 1.00 1.00 67 0.49 0.58 0.62

16 1.00 1.00 1.00 68 0.49 0.58 0.63

17 0.91 0.98 1.00 69 0.50 0.60 0.64

18 0.69 0.78 0.83 70 0.55 0.64 0.69

19 0.83 0.92 0.97 71 0.41 0.50 0.55

20 0.98 1.00 1.00 72 0.55 0.64 0.68

21 0.81 0.88 0.90 73 0.56 0.65 0.70

22 0.57 0.66 0.70 74 0.57 0.66 0.70

23 0.71 0.80 0.85 75 0.71 0.80 0.85

24 0.92 0.99 1.00 76 0.71 0.80 0.84

25 0.84 0.90 0.93 77 0.76 0.82 0.85

26 0.60 0.69 0.73 78 0.67 0.76 0.80

27 0.58 0.67 0.71 79 0.60 0.70 0.74

28 0.61 0.70 0.75 80 0.65 0.75 0.79

29 0.74 0.83 0.88 81 0.73 0.86 0.82

30 0.93 1.00 1.00 82 0.65 0.74 0.78

31 0.64 0.73 0.78 83 0.62 0.71 0.76

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LBP 300 m 200 m 100 m LBP 300 m 200 m 100 m

Zone no. fe- factor Zone no. fe- factor

32 0.49 0.58 0.63 84 0.63 0.72 0.76

33 0.56 0.65 0.69 85 0.79 0.86 0.88

34 0.63 0.72 0.77 86 0.88 0.94 0.97

35 0.60 0.69 0.73 87 0.78 0.87 0.92

36 0.54 0.64 0.68 88 0.88 0.94 0.97

37 0.39 0.48 0.53 89 0.96 1.00 1.00

38 0.36 0.45 0.49 90 0.97 1.00 1.00

39 0.51 0.60 0.64 91 0.97 1.00 1.00

40 0.73 0.82 0.87 92 0.93 1.00 1.00

41 0.72 0.81 0.86 93 0.86 0.92 0.95

42 0.74 0.83 0.87 94 1.00 1.00 1.00

43 0.69 0.78 0.82 95 0.89 0.95 0.98

44 0.59 0.68 0.72 96 0.81 0.90 0.95

45 0.56 0.65 0.69 97 1.00 1.00 1.00

46 0.52 0.61 0.65 98 0.94 1.00 1.00

47 0.54 0.63 0.68 99 1.00 1.00 1.00

48 0.52 0.61 0.65 100 1.00 1.00 1.00

49 0.52 0.61 0.65 101 0.94 1.00 1.00

50 0.72 0.81 0.85 102 0.88 0.94 0.97

51 0.50 0.59 0.63 103 1.00 1.00 1.00

52 0.61 0.70 0.75 104 0.88 0.94 0.97

6 Life time extension

6.1 Scope

6.1.1 This subsection describes life time fatigue calculations for units intended to continue operation at theexisting location, above the basic original design fatigue life.

6.1.2 For units that shall operate at a new location, the requirements given in Sec.5 apply.

6.1.3 Any new structures or modifications shall comply with the requirements given in given in Sec.5.

6.1.4 Renewed structural material shall be replaced with material of same or greater scantling as existingmaterial, and of the same or higher material grade.

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6.1.5 Prior to the life time extension the unit should be evaluated for the following:

— identification of steel wastages by thickness measurements— identification of fatigue cracks or damage.

6.2 Fatigue calculations

6.2.1 The past trading, the past time in operation and the future operation at the specific location shall beconsidered for the fatigue calculations. World wide scatter diagram may be used for the historical tradinghistory, if no other information is available.

6.2.2 The fatigue calculation methods described in Sec.4 [1.2] shall be used for the fatigue calculation.

6.2.3 Gross scantlings and SN curves for air may be applied for the past trading and the past operationphases, provided the corrosion protection system (e.g. painting, anodes) is intact.For details fully repaired and inspected (NDT), the historical fatigue damage may be excluded and only thefatigue damage calculation from future operation should be considered.

6.2.4 The time in corrosive environment (TC) shall be calculated according to the principles given in DNVGL-CG-0129 Sec.3 [4], where:Design fatigue life TDF = Previous trading/operation time (TDT) + future operation time (TDO).TD = 25 years.TC,25 according to DNVGL-RU-SHIP Pt.3 Ch.9 Sec.4 [4.4].

6.2.5 Fatigue sensitive details given in Sec.4 [1.4] shall be considered for the fatigue calculations.

6.2.6 For historical trading and operation until the life time extension, design fatigue factor (DFF) of 1.0 maybe applied. For the extended operation the DFF’s as specified in Sec.4 [1.3.2] are applicable.

Table 8 Design fatigue factors for trading, past operation and future operation

Operation phasePrevious trade

Past operation Future operationTotal fatigue damage

D1 D2 D3 x DFF D1 + D2 + D3 x DFF < 1.0

6.2.7 For evaluation of details where calculated total fatigue damage is below 1.0, see [5.5.5] .

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CHAPTER 3 CLASSIFICATION AND CERTIFICATION

SECTION 1 CLASSIFICATION AND CERTIFICATION REQUIREMENTS

1 General

1.1 Introduction

1.1.1 As well as representing DNV GL’s recommendations on safe engineering practice for general use bythe offshore industry, the offshore standards also provide the technical basis for DNV GL classification,certification and verification services.

1.1.2 This section specifies the design documentation, certification, fabrication and survey requirements tobe applied when using this standard for certification and classification purposes.

1.1.3 The requirements to stability and watertight integrity are given in DNVGL-OS-C301.

1.1.4 A complete description of principles, procedures, applicable class notations and technical basis foroffshore classification is given by the DNV GL Rules for classification of offshore units as listed in Table 1.

Table 1 DNV GL rules for classification - offshore units

Document code Title

DNVGL-RU-OU-0101 Offshore drilling and support units

DNVGL-RU-OU-0102 Floating production, storage and loading units

DNVGL-RU-OU-0103 Floating LNG/LPG production, storage and loading units

1.2 Application

1.2.1 DNV GL may accept alternative solutions found to represent an overall safety level equivalent to therequirements given in Ch.2 of this standard.

1.2.2 Any deviations and exceptions to the design codes and standards given as recognised reference codesshall be approved by DNV GL.

1.2.3 Structural requirements related to conversions of tankers to floating offshore units shall follow thespecifications given in Ch.2 Sec.7 [5].

1.3 Basic hull classification scope

1.3.1 The basic classification requirements for the hull strength are given in Ch.2 of this standard. Thestructural requirements are based on the principle of mitigating the risk of major structural failure related tothe safety of life, property and to contribute to the durability of the hull structure for the unit's design life.

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Guidance note:

The following structure are not covered in the main scope unless specially agreed, or if additional class notations are requested.

— Topside structures, derrick structure, offloading equipment, pipe rack structure, independent tanks, etc. These structures arepart of DNV GL class scope when additional DNVGL class notation is requested (e.g. PROD, DRILL), see DNV GL rules forclassification of offshore units as listed in [1.1.4] for description of class notations

— Railways and trolley beams for transport of equipments

— Access platforms, stairs and ladders

— Lifting lugs


1.4 Documentation requirements

1.4.1 The documents (Docreq) for structure that shall be submitted are specified in Table 2 for the differentunit types. The document list cover the basic class notation 1A and OI, and is a generic list that needs to betuned for each specific project. Meaning, some of the required documentation may not be applicable for theproject, or additional documents might be applicable and shall be submitted.The following status codes are used:

AP = drawing is reviewed and stamped “For approval”

FI = document is reviewed and stamped “For information”

L = the document is handled locally (at site).

Further descriptions and definitions of the document types are given in DNVGL-RU-SHIP Pt.1 Ch.3.

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Table 2 Documents to be submitted for offshore ship-shaped units - hull part

Funct. code Object Documentationtype Description/comments Info

M050 - cathodicprotectionspecification,calculation anddrawings

FI

Z030 -Arrangement plan

In ballast tanks.

AP

102.1 Sacrificialnodes

C030 - Detaileddrawing Fastening of anodes in ballast tanks. AP

103 Structuralfabrication

H131 - Non-destructive testing(NDT) plan

Overall plan showing inspection category,For details, see Ch.2 Sec.1 [5.5].

AP, L

103.1 Welding H140 - Weldingtables Alternatively, welds are shown on drawings AP

111 Design basis H010 - Structuraldesign brief FI

111 Designloads

H084 - Wave loadanalysis

May be excluded for units with restricted operation.

For well intervention, only required for MODU compliance.

For details, see Ch.2 Sec.2 [3.9].

FI

H020 - Design loadplan FI

H030 - Tank andcapacity plan FI

H050 - Structuraldrawing Decks and inner bottom. AP

H050 - Structuraldrawing Transverse bulkhead. AP

H050 - Structuraldrawing Longitudinal bulkheads. AP

111 Ship hullstructure

H050 - Structuraldrawing Fore ship. AP

H080 - Strengthanalysis Strength analysis of fore ship area. FI

H050 - Structuraldrawing Engine room area. AP

H050 - Structuraldrawing Aft ship. AP


H080 - Structuralanalysis Strength analysis of aft ship area. FI

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H050 - Structuraldrawing Wave breaker. AP

H052 - Midshipsection AP

H060 - Shellexpansion drwg. AP

H061 - Framingplan May be part of shell expansion plan, H060. AP

H062 - Longitudinalsection drawings AP

H070 - Standarddetails FI

H080 - Strengthanalysis

Part ship analysis as requested for the unit types.For details, see Ch.2 Sec.7.

FI

H082 - Longitudinalstrength analysis Scantlings of longitudinal plate and stiffeners. FI

H085 - Fatigueanalysis For details, see Ch.2 Sec.4. FI

H110 - Preliminaryloading manual AP

H111 - Finalloading manual AP

H120 - Dockingarrangement plan May be excluded for units not intended for dry-docking. FI111 Ship hull

structure

H134 - Hole andpenetration plan AP


Module support and interface to hull structure relatedto process handling of hydrocarbons. Positions, weight/loads, interface/footprint to hull structure. For drill/wellintervention units the drill floor support/footprint to hullstructure to be included as applicable.

FI

H050 - Structuraldrawing

Drawing of support structure including surroundingstructure. AP

111Supportfor topsidemodules

H080 - Structuralanalysis

Structural documentation report according to Ch.2 Sec.2[3.11]. FI

111.62 Stern frame H050 - Structuraldrawing

Normally not applicable for OI units (no propulsion), or forunits with thrusters propulsion. AP

111.7 Bottom Z030 -Arrangement plan

Retractable or fixed bottom equipment like DP thrusters,including resulting loads acting on the supporting structure,and details of sealings.

FI

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111.8 Moonpool H050 - Structuraldrawing

Moonpool side plates, including stiffeners and girders, asapplicable. AP

112 Super-structure


Deck load to be specified on drawing if not given in thedesign load plan H020. AP

113 Deck houses H050 - Structuraldrawing

Deck load to be specified on drawing if not given in thedesign load plan H020. AP

221.322

Anchorwindlasssupportingstructure


Including foundation and fixation (bolts, chocks and shearstopper), and information of chain breaking load and footprint loads.Normally not applicable for OI units and for units withredundant DP system.


AP

225.1 Servicehatches


Applicable for hatches that are not certified, typically largehatches. AP

233 Manholes Z030 -Arrangement plan An overview of positions and types. FI

Z030 -arrangement plan FI

H050 - Structuraldrawing AP300

Supportstructureof hullequipment

H080 - Structuralanalysis

Equipments above 50 KN or when bending moment exceed100 KNm. Equipment weight, loads, foot print to beincluded.For details, see Ch.2 Sec.5 [4].

FI

311 Internalaccess

H200 - Shipstructure accessmanual

Plan or drawings showing access arrangement and accessopenings with requirement to safe access to tanks,cofferdams and other spaces within the whole unit.For details, see Ch.2 Sec.1 [4.2].

AP

321.332

Anchorchainstoppersupportingstructure


Including foundation and fixation (bolts, chocks and shearstopper), and information of chain breaking load and footprint loads.Normally not applicable for OI units and for units withredundant DP system.


AP

Z030 -Arrangement plan FI

Z090 - Equipmentlist AP321 Anchoring

arrangement

H100 - Equipmentnumber calculation

Covering windlasses, anchors, grade of anchor chain, typeand braking load of chain, wire and fibre ropes.Normally not applicable for OI units and for units withredundant DP system.

For details, see Ch.2 Sec.5 [1.1]. AP

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Z030 -Arrangement plan FI

H050 - Structuraldrawing AP321.67

Turretsupportingstructure,or spreadmooring H080 - Structural

analysis

Applicable for OI units or 1A units without propulsionFor details, see Ch.2 Sec.5 [3].

FI

324 Z030 -Arrangement plan

Location on the unit, fitting types, dimensions, SWL, maxbreaking load, limit angles, and the purpose (mooring and/or harbour towing, emergency towing, or tow to location,as applicable.For details, see Ch.2 Sec.5 [2].

FI

324.6

Passivetowing andquay sidemooringarrangement H050 - Structural

drawingHull supporting structure incl. information of design loadand angles, as applicable. AP


Position/locations, if not present on the generalarrangement plan. FI

331.12331.15

Pedestaland supportfor Inboard/shipboardcranes


Crane pedestal and connection to hull support structure,incl. material type/grade, scantling and weld type. AP


Position/locations, crane reaction forces at sleewing ringand top of boom rest. FI


Crane pedestal and connection to hull support structure,incl. material type/grade, scantling and weld type. AP331.22331.25

Pedestaland supportfor offshorecranes

H080 - Structuralanalysis For details, see Ch.2 Sec.5 [7]. FI

412.73Propellershaftbrackets


Conventional propeller shaft brackets.Normally not applicable for OI units (no propulsion), or forunits with thrusters only.

AP

413.4 Propellernozzles


Conventional propeller nozzle.Normally not applicable for OI units (no propulsion), or forunits with thrusters only.

AP

406 Enginerooms

C030 -Arrangement plan

Unmanned machinery, filling time calculation.Applicable for units with E0 notation.

FI

801 Vesselarrangement

Z010 - generalarrangement plan FI

1.5 Certification requirements

1.5.1 Certification requirements for anchors, anchor windlass, chain stoppers and anchor equipments arespecified in DNVGL-RU-SHIP Pt.3 Ch.1 Sec.3 [3.1.2].

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Guidance note:

Anchor equipments for temporary mooring may be excluded for units without propulsion intended for permanent mooring at sitespecific location, or for units with redundant propulsion system, see see DNV GL rules for classification of offshore units as listed in[1.1.4] for details.


1.5.2 Certification requirements to watertight and weathertight doors and hatches are given in DNVGL-OS-C301 Ch.3 Sec.1 [3].

1.5.3 Certification of materials and welding are given in DNVGL-RU-SHIP Pt.2.

1.5.4 Descriptions and definitions of the certification requirements are given in DNVGL-RU-SHIP Pt.1 Ch.3.

2 Additional class notations - structural strength

2.1 Fatigue methodology specification

2.1.1 GeneralThe technical requirements given in this subsection represent extended fatigue specification applicable for theadditional class notation FMS(year).The FMS notation is primarily intended for the hull structure including topside and turret interface to hull,but the principles may also be applied for the topside and the turret structures on request. The FMS notationis generally mostly relevant for units permanently moored at one specific location, where inspection andpossible repairs at location are more cumbersome compared to units intended for docking.The calculated fatigue damages form the basis for the qualitative risk based inspection (RBI) evaluationas part of the class in-service inspection program (IIP) for the unit. For details related to DNV GL classrequirements for RBI periodical survey requirements, see DNVGL-RU-OU-0300 Ch.3 Sec.1 [1.2].

2.1.2 Documentation requirementsThe following documents shall be submitted for the FMS notation.

Table 3 Documentation requirements - FMS

Functionalcode Object Documentation type Description/comments Info

H084 - Wave loadanalysis For details, see Ch.2 Sec.2 [3.9]. FI

H085 - Fatigue analysis See [2.1.3], [2.1.4] and [2.1.5] below. FI

H080 - Design analysis111 Ship hull

structure


Documentation report or drawing summing up calculatedfatigue damage results. FI

2.1.3 Scope for fatigue methodology specification notationThe details listed in Table 4, in addition to the details listed in Ch.2 Sec.4 Table 3 shall be analysed. Aftmost,midship and foremost areas shall be analysed, see Ch.2 Sec.7.

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Guidance note:

In aftmost and forward area, additionally positions may need to be included for fatigue calculations depending of structuralarrangement and turret support system.


Table 4 Additional details to be analysed for FMS notation

No Hot spot detail Description

9

Longitudinal stiffener-transverse frameconnections located in thedeck, bottom, inner bottom,side and inner side includingconnected web stiffener, cutout and collar plate

As a minimum the following number of stiffener-frame/BHD connections should beanalysed within each area:

— 1 detail connection at the main deck— 2 detail connection at the bottom— 2-3 details connections at the side close to full load and ballast drafts— 2 details connections at each longitudinal bulkheads.

The SCFs defined in DNVGL-CG-0152 App.A may be applied.

10 Bilge keel

Longitudinal end connections shall be analysed. In addition, in case support bracketsare required see Ch.2 Sec.5 [8.2.1], these shall also be analysed.

SCFs defined in DNVGL-CG-0129 App.A may be applied.Hull girder loads, local loads from sea pressure, and drag loads from roll and heavemotion shall be considered.

2.1.4 Calculation methods and principlesSpectral fatigue analysis methodology shall in general be applied for the FMS notation. Either a full stochasticmethod, a component stochastic method, or a combination of full and component stochastic methods, seemethod 3a) and 3b) given in Ch.2 Sec.4 Table 1.The dynamic loads shall be based on direct loads from a linear wave load analysis as described in Ch.2 Sec.2[3.9.4]. Correction for splash zone according to DNVGL-CG-0129 Sec.5 [3.4] shall be considered.

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Combination of high cyclic wave loads, and slowly varying cyclic loads like tank filling loading conditions, riserloads, mooring loads, may be performed according to DNVGL-CG-0129 App.H [7]. For turret interface to hullstructure, see Ch.2 Sec.5 [3.4].The local dynamic stress range shall be calculated using a fine mesh analysis as described in Ch.2 Sec.3[4.4]. Selection of positions and number of local stress analysis needed, should be based on a screeningprocess as described in [2.1.5] below.Fraction of time in loaded and ballast condition, time in transit and operation, are given in Ch.2 Sec.7.

2.1.5 Initial screening processInitial screening process by using defined stress concentration factors (SCF) should be performed in order toget an overview and localize fatigue critical areas for further investigation. Screening analysis may be basedon prescriptive analysis method as given in Ch.2 Sec.4 Table 1, together with tabulated stress concentrationfactors given in DNVGL-CG-0129 App.A.The DFF’s given in Table 5 below shall be considered in the fatigue screening, unless otherwise specificagreed.

Guidance note:

A SCF of 2.25 together with S-N curve D for the screening process, will cover most details.


2.1.6 Design fatigue factorsDesign fatigue factors for the FMS notation are stricter than the generic DFFs as defined in Ch.2 Sec.4 [1.3] .Other DFFs than given in Table 5 may be accepted on a case by case evaluation, but need to be accepted byall involved parties (owner, operator, DNV GL).

Table 5 DFF’s for structure areas wrt inspection interval, accessibility for inspection and repairs

Structure Example5-year inspectioninterval carried

out in dry docking

5-year inspectioninterval, carried

out afloat.

External structure, accessible forregular inspection and repair in dryand clean conditions is possible.

Main deck plate, topside and equipmentsconnections to main deck plate. 2 2

External structure where accessfor inspection is limited, and whererepair in dry and clean conditionsnot is possible.

Side shell and bottom plate, includingbilge keel, fairlead structure, riser tubes. 2 3

Internal structure, accessible andnot welded directly to submergedpart.

Transverse frames, transverse BHD,longitudinal BHD, stringers, cross ties. 2 2

Internal structure, accessible andwelded directly to the submergedpart.

Longitudinals, transverse frames,transverse BHD’s welded to the bottomplate or side shell plate below thescantling draft.

2 3

Non-accessible structure, notplanned to be accessible forinspection and repairs duringoperation.

Void spaces, sea chests, smallcofferdams, and topside supports withpassive fire protection.

5 5

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Figure 1 Example of DFF in bottom area for units not intended for dry docking intervals for FMSnotation

2.2 R - Restriction in use

2.2.1 For units with propulsion, having the main class notion 1A, and have limitations due to:

— restricted transit, see Ch.2 Sec.1 [2.2.2]— restricted survival condition, Ch.2 Sec.1 [2.4]

shall hold the additional class notation R. The limitation of the restriction, e.g. geographical areas, significantwave height (Hs), etc, shall be clearly defined in the design basis and the restriction will be stated in theclass appendix.

2.2.2 For units without propulsion having the main class notion OI, restricted class notation is not applicable.Limitations in case of restricted tow to location see Ch.2 Sec.1 [2.6], or inspection see Ch.2 Sec.1 [2.5] willbe stated in the appendix to classification certificate.

2.2.3 The information of restrictions shall be clearly explained in the following document:

Table 6 Documentation requirements - R



H010 - Structuraldesign basis

Description of limitation related to transit or operation asapplicable for the unit. FI

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2.3 FIELD - Field specific design

2.3.1 Units designed for one specific location holding the main class notion OI, will be given the classnotation FIELD(qualifier), where the qualifier gives the specific location (field). The field location is basis forthe dynamic loads as specified in Ch.2 Sec.2 [3.2]. The field location will additionally be specified in the classappendix.

2.3.2 The information of field location shall be clearly explained in the following document:

Table 7 Documentation requirements - FIELD


H010 - Structuraldesign basis FI

111 Ship hullstructure H084 - Wave load

analysis

Description of scatter diagram or 100 years significantwave height with corresponding periods as foundapplicable. FI

2.4 FAB - Fabrication specification

2.4.1 For storage and production units permanently moored at harsh locations, the FAB notation ismandatory. The FAB notation may also voluntary be assigned for storage and production units permanentlymoored at benign water, and other ship shaped unit types.The objective of FAB is to reduce the risk of disruption in the unit's production due to repair of possible welddefects from fabrication, by increasing the non-destructive testing (NDT) scope during fabrication of the hullstructure. The requirements to NDT given in Table 8 shall then be complied with for the FAB notation.

2.4.2 The NDT scope may be further increased by the qualifier +, i.e. FAB(+). The requirement in Table 8for FAB(+), and the fabrication tolerances given in DNVGL-OS-C401, shall then be complied with.

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Table 8 NDT scope for hull and offshore interface structure - FAB and FAB(+)

Testing method 1)

FAB FAB(+)Inspectioncategory Inspection member Weld connection

MT/PT RT/UT MT/PT RT/UT

III

— General hull structuraldetails not specific listedbelow

— Laydown platforms— Mezzanine decks, platforms— Outfitting steel— Pipe support structure— Stair towers— Foundation attached to

main deck where weight ofequipment < 50 ton

— Foundation attached toother deck where weight ofequipment > 50 ton

— Butt and T-joints, full pen— T-joints, partly pen— Fillet welds

5%

5%

-

5%

-

-

5%

5%

5%

5%

-

-

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II

— Sheer strake at strengthdeck within 0.4L amidship

— Stringer plate in strengthdeck within 0.4L amidship

— Deck strake at longitudinalbulkhead within 0.4Lamidship

— Bilge strake— All watertight bulkheads

independent of location— Side longitudinal

connections to transverseframes and bulkheadsindependent of location

— Shipboard crane pedestal— Foundation attached to

main deck where weight ofequipment > 50 ton

— Main structures in drillfloor— Main supporting structures

(substructure) for helideckpancake

— Mating ring for STL/STPstructure

— Riser balcony and pull instructure

— Shipboard crane pedestalsupports

— Offshore crane boomrest and main supportingstructures

— Support structures ofheavy machinery andequipment typically;thrusters, gantry and rails,winches, davits, towingbrackets, hawser winch,etc.

— Davits and support ofappliances for lifesavingequipments

— Topside support stools andmain supporting structures

— Moonpool bulkheads


10%

10%

-

10%

-

-

20%

20%

20%

20%

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-

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— Areas where thelikelihood of occurrenceof detrimental defects areconsidered to be extra high2)

— Hopper knuckle weldconnections of transverseframes

— Offshore crane pedestal— Deck and bottom plates

in way of 500mm frommoonpool corners

— Foundations and mainsupporting structures foroffshore crane pedestals

— Foundations and mainsupporting structuresfor flare tower, anchorline fairleads and chainstoppers, riser fairleads

— Main supporting structuresfor turret

— Supporting structures forderrick and drillfloor


40%

40%

40%

40%

-

-

100%

100%

100%

100%

-

-

1) See DNVGL-RU-SHIP Pt.2 Ch.4 Sec.7 [4] for specifications.- MT testing shall be applied for ferro-magnetic materials.

- RT shall be applied for T-joints.2) Welds produced by yards with limit experience of required welding method, or welds produced by high heat input (>50 KJ/cm).

2.4.3 The extended NDT requirements to the FAB notation shall be reflected in the following documents.

Table 9 Documentation requirements - FAB


103 Structuralfabrication

H0131 - Non destructive testing plan(NDT) Extended NDT plan AP

111 Ship hullstructure H010 - Structural design basis Description of the NDT extent FI

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CHANGES – HISTORIC

July 2015 edition

Main changes July 2015

• GeneralThe revision of this document is part of the DNV GL merger, updating the previous DNV standard into a DNVGL format including updated nomenclature and document reference numbering, e.g.:

— Main class identification 1A1 becomes 1A.— DNV replaced by DNV GL.— DNV-RP-A201 to DNVGL-CG-0168. A complete listing with updated reference numbers can be found on

DNV GL's internet.

To complete your understanding, observe that the entire DNV GL update process will be implementedsequentially. Hence, for some of the references, still the legacy DNV documents apply and are explicitlyindicated as such, e.g.: Rules for Ships has become DNV Rules for Ships.

• Ch.2 Sec.1 Material selection and fabrication principles— Sec.1 [3.2.6] Included specification of length for topside module.

• Ch.2 Sec.2 Design principles— Sec.2 [1.1.3]: A reference to arrangement of water tight bulkheads given in DNV Rules for ships Pt.3 Ch.1

Sec.3 A is included— Sec.2 [2.6] New guidance note clarifying benign waters criteria wrt use of characteristic wave bending

moment.

• Ch.2 Sec.3 Design loads— Sec.3 [3.8] Including definitions of sagging and hogging in guidance note.

• Ch.2 Sec.4 Strength of hull structure— Sec.4 [2.2.8] Rewritten clause in line with original intention.— Sec.4 [5.5.5] Rewritten clause in line with original intention.— Sec.4 Table 7: Permissible peak stress for the LRFD method limited to the material tensile stress.

• Ch.2 Sec.5 Strength of topside structures— Sec.5 Table 3 Removed previous column c) as ALS is not a required design condition for topside structure.

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