-
OFFSHORE STANDARD
The electronic pdf version of this document found through
http://www.dnv.com is the officially binding version
DNV-OS-C201
Structural Design of Offshore Units (WSD Method)
APRIL 2012DET NORSKE VERITAS AS
-
FOREWORDDET NORSKE VERITAS (DNV) is an autonomous and
independent foundation with the objectives of safeguarding
life,property and the environment, at sea and onshore. DNV
undertakes classification, certification, and other verification
andconsultancy services relating to quality of ships, offshore
units and installations, and onshore industries worldwide,
andcarries out research in relation to these functions.
DNV service documents consist of among others the following
types of documents: Service Specifications. Procedural
requirements. Standards. Technical requirements.
Recommended Practices. Guidance.
The Standards and Recommended Practices are offered within the
following areas:A) Qualification, Quality and Safety MethodologyB)
Materials TechnologyC) StructuresD) SystemsE) Special FacilitiesF)
Pipelines and RisersG) Asset OperationH) Marine OperationsJ)
Cleaner EnergyO) Subsea Systems Det Norske Veritas AS April
2012
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
this document, and is believed to reflect the best ofcontemporary
technology. The use of this document by others than DNV is at the
user's sole risk. DNV does not accept any liability or
responsibility for loss or damages resulting fromany use of this
document.
-
Offshore Standard DNV-OS-C201, April 2012Changes Page
3CHANGES
GeneralThis document supersedes DNV-OS-C201, April 2011.
Text affected by the main changes in this edition is highlighted
in red colour. However, if the changes involvea whole chapter,
section or sub-section, normally only the title will be in red
colour.
Main ChangesGeneralUpdated references to latest DNV-RP-C104
instead of DNV-CN 31.5.Minor updates and some clarification in
text.
Section 1 C: Definitions: C231: added Heave Damping Structure:
Structure to increase added mass in heave and reduce the
vertical
motions of the Deep Draught Semi units (DDS). Table D1: added
DDS - Deep draught semi-submersible unit.
Section 3 D400: Lifeboat platforms in previous edition of
document deleted.
Section 11, C700: Guidance note with reference to DNV-RP-C205
included. D104: Guidance note included.
Section 12 B302: Material Grade NV690 E is sufficient for thick
rack plates. C403: Guidance note for dynamic amplification factors
DAF 1.10. D202: Wind (profile and unrestricted service). F1100:
Vertical position of heavy equipment during transit (Guidance
note). F1200: New section on Simplified P effect (including
Guidance note). G304: Spudcan design loads updated.
Section 14 A103: included examples specific to Deep Draught Semi
(DDS) units for Structural categorization, A205: added Special
connections, for example, grouted connections shall be fully
qualified. The process
as presented in DNV-RP-A203 Qualification of New Technology can
be used. C102: included guidance specific to Deep Draught Semi
(DDS) units and Spars for Structural categorization.
C500: Guidance to Minimum Requirements: updated Figure 1 and
included Figures 2 and 3 to captureexamples specific to DDS
units.
D202: added mating, ballasting sequences to include DDS units.
D203: changed to be specific to Spars. D204: added requirements
specific to DDS units. D506: added Air gap and green water
(Wave-on-Deck) are to be considered. Air gap is measured to the
bottom of the deck structure. I103: deleted list of DDF units
eigenmodes. J102: added Relevant model testing should be considered
for novel installation procedures. J103: added Stability check and
ballast capacity design shall include assessment of relevant
load
conditions during transport and installation. J301: changed text
to be specific to Spars. K204: changed text to be specific to
Spars, K205: added For DDS units, the finite element analysis shall
cover all critical transient phases during
installation. L101: in previous edition of document is deleted.
L204: included DDS specific connections. L207: added For mooring
fairlead/riser porch analysis, the effect of disturbed wave field
due to the
presence of columns etc. should also be taken into account.
L209: added The fatigue analysis to riser/keel guide frames shall
account for the interaction between risers
and guide frames where relevant.DET NORSKE VERITAS AS
L210: added text and Table L1 - to be in line with API
requirements. M605: added The structure should be designed to
withstand one compartment flooding under reduced
environment (e.g. 10-yr return probability).
-
Offshore Standard DNV-OS-C201, April 2012Changes Page
4CHANGES
M700: Riser Damage added. Subsection N: Dynamic Riser Design and
Global Performance added.DET NORSKE VERITAS AS
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Offshore Standard DNV-OS-C201, April 2012 Contents Page
5CONTENTS
Sec. 1 Introduction
......................................................................................................................................
13
A. General
..........................................................................................................................................................................
13A 100
Introduction.........................................................................................................................................................
13A 200 Objectives
...........................................................................................................................................................
13A 300 Scope and application
.........................................................................................................................................
13A 400 Other than DNV
codes........................................................................................................................................
13A 500 Classification
......................................................................................................................................................
14
B. References
.....................................................................................................................................................................
14B 100
General................................................................................................................................................................
14
C.
Definitions.....................................................................................................................................................................
15C 100 Verbal forms
.......................................................................................................................................................
15C 200 Terms
..................................................................................................................................................................
15
D. Abbreviations and Symbols
..........................................................................................................................................
18D 100
Abbreviations......................................................................................................................................................
18D 200 Symbols
..............................................................................................................................................................
19
Sec. 2 Design Principles
..............................................................................................................................
22
A.
Introduction...................................................................................................................................................................
22A 100
General................................................................................................................................................................
22A 200 Aim of the
design................................................................................................................................................
22
B. General Design
Considerations.....................................................................................................................................
22B 100
General................................................................................................................................................................
22B 200 Overall design
.....................................................................................................................................................
22B 300 Details
design......................................................................................................................................................
22
C. Design
Conditions.........................................................................................................................................................
23C 100 Basic conditions
..................................................................................................................................................
23
D. Loading
Conditions.......................................................................................................................................................
23D 100
General................................................................................................................................................................
23D 200 Load
....................................................................................................................................................................
24
E. Design by the WSD Method
.........................................................................................................................................
24E 100 Permissible stress and usage factors
...................................................................................................................
24E 200 Basic usage
factors..............................................................................................................................................
24
F. Design Assisted by
Testing...........................................................................................................................................
24F 100
General................................................................................................................................................................
24F 200 Full-scale testing and observation of performance of
existing
structures...........................................................
24
Sec. 3 Loads and Load Effects
...................................................................................................................
25
A.
Introduction...................................................................................................................................................................
25A 100
General................................................................................................................................................................
25
B. Basis for Selection of Loads
.........................................................................................................................................
25B 100
General................................................................................................................................................................
25
C. Permanent Functional
Loads.........................................................................................................................................
26C 100
General................................................................................................................................................................
26
D. Variable Functional Loads
............................................................................................................................................
26D 100
General................................................................................................................................................................
26D 200 Variable functional loads on deck areas
.............................................................................................................
27D 300 Tank pressures
....................................................................................................................................................
27
E. Environmental Loads
....................................................................................................................................................
28E 100
General................................................................................................................................................................
28E 200 Environmental conditions for mobile units
........................................................................................................
28E 300 Environmental conditions for site specific
units.................................................................................................
28E 400 Determination of hydrodynamic
loads................................................................................................................
29E 500 Wave
loads..........................................................................................................................................................
29E 600 Wave induced inertia
forces................................................................................................................................
29E 700 Current
................................................................................................................................................................
30E 800 Wind loads
..........................................................................................................................................................
30DET NORSKE VERITAS AS
E 900 Vortex induced oscillations
................................................................................................................................
30
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Offshore Standard DNV-OS-C201, April 2012 Contents Page 6E 1000
Water level and tidal effects
...............................................................................................................................
30E 1100 Marine
growth.....................................................................................................................................................
30E 1200 Snow and ice accumulation
................................................................................................................................
30E 1300 Direct ice load
.....................................................................................................................................................
31E 1400 Earthquake
..........................................................................................................................................................
31
F. Combination of Environmental Loads
..........................................................................................................................
31F 100
General................................................................................................................................................................
31
G. Accidental
Loads...........................................................................................................................................................
32G 100
General................................................................................................................................................................
32
H. Deformation Loads
.......................................................................................................................................................
32H 100
General................................................................................................................................................................
32H 200 Temperature
loads...............................................................................................................................................
32H 300 Settlements and subsidence of sea bed
...............................................................................................................
32
I. Fatigue loads
.................................................................................................................................................................
32I 100
General................................................................................................................................................................
32
J. Load Effect
Analysis.....................................................................................................................................................
33J 100
General................................................................................................................................................................
33J 200 Global motion analysis
.......................................................................................................................................
33J 300 Load effects in structures and soil or
foundation................................................................................................
33
Sec. 4 Structural Categorisation, Material Selection and
Inspection Principles .................................. 34
A. General
..........................................................................................................................................................................
34A 100
............................................................................................................................................................................
34
B. Temperatures for Selection of Material
........................................................................................................................
34B 100
General................................................................................................................................................................
34B 200 Floating units
......................................................................................................................................................
34B 300 Bottom fixed units
..............................................................................................................................................
34
C. Structural Category
.......................................................................................................................................................
34C 100
General................................................................................................................................................................
34C 200 Selection of structural category
..........................................................................................................................
35C 300 Inspection of welds
.............................................................................................................................................
35
D. Structural Steel
.............................................................................................................................................................
36D 100
General................................................................................................................................................................
36D 200 Material designations
..........................................................................................................................................
36D 300 Selection of structural
steel.................................................................................................................................
37D 400 Fracture mechanics (FM) testing
........................................................................................................................
38D 500 Post weld heat treatment (PWHT)
......................................................................................................................
38
Sec. 5 Structural Strength
..........................................................................................................................
39
A. General
..........................................................................................................................................................................
39A 100
General................................................................................................................................................................
39A 200 Structural
analysis...............................................................................................................................................
39A 300 Ductility
..............................................................................................................................................................
39A 400 Yield check
.........................................................................................................................................................
40A 500 Buckling check
...................................................................................................................................................
40
B. Flat Plated Structures and Stiffened Panels
..................................................................................................................
40B 100 Yield check
.........................................................................................................................................................
40B 200 Buckling check
...................................................................................................................................................
41B 300 Capacity checks according to other codes
..........................................................................................................
41
C. Shell Structures
.............................................................................................................................................................
41C 100
General................................................................................................................................................................
41
D. Tubular Members, Tubular Joints and Conical
Transitions..........................................................................................
41D 100
General................................................................................................................................................................
41
E. Non-Tubular Beams, Columns and
Frames..................................................................................................................
42E 100
General................................................................................................................................................................
42
Sec. 6 Section Scantlings
.............................................................................................................................
43
A. General
..........................................................................................................................................................................
43DET NORSKE VERITAS AS
A 100
Scope...................................................................................................................................................................
43
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Offshore Standard DNV-OS-C201, April 2012 Contents Page 7B.
Strength of Plating and Stiffeners
.................................................................................................................................
43B 100
Scope...................................................................................................................................................................
43B 200 Minimum
thickness.............................................................................................................................................
43B 300 Bending of plating
..............................................................................................................................................
43B 400 Stiffeners
.............................................................................................................................................................
44
C. Bending and Shear in Girders
.......................................................................................................................................
45C 100
General................................................................................................................................................................
45C 200 Minimum
thickness.............................................................................................................................................
45C 300 Bending and
shear...............................................................................................................................................
45C 400 Effective
flange...................................................................................................................................................
45C 500 Effective web
......................................................................................................................................................
45C 600 Strength requirements for simple
girders............................................................................................................
46C 700 Complex girder
systems......................................................................................................................................
47
Sec. 7 Fatigue
...............................................................................................................................................
48
A. General
..........................................................................................................................................................................
48A 100
General................................................................................................................................................................
48A 200 Design fatigue factors
.........................................................................................................................................
48A 300 Methods for fatigue
analysis...............................................................................................................................
49A 400 Simplified fatigue
analysis..................................................................................................................................
49A 500 Stochastic fatigue analysis
..................................................................................................................................
50
Sec. 8 Accidental Conditions
......................................................................................................................
51
A. General
..........................................................................................................................................................................
51A 100
General................................................................................................................................................................
51
B. Design Criteria
..............................................................................................................................................................
51B 100
General................................................................................................................................................................
51B 200
Collision..............................................................................................................................................................
51B 300 Dropped objects
..................................................................................................................................................
52B 400 Fires
....................................................................................................................................................................
52B 500
Explosions...........................................................................................................................................................
52B 600 Unintended flooding
...........................................................................................................................................
52
Sec. 9 Weld
Connections.............................................................................................................................
53
A. General
..........................................................................................................................................................................
53A 100
Scope...................................................................................................................................................................
53
B. Types of Welded Steel
Joints........................................................................................................................................
53B 100 Butt
joints............................................................................................................................................................
53B 200 Tee or cross joints
...............................................................................................................................................
53B 300 Slot
welds............................................................................................................................................................
55B 400 Lap joint
..............................................................................................................................................................
55
C. Weld Size
......................................................................................................................................................................
55C 100
General................................................................................................................................................................
55C 200 Fillet
welds..........................................................................................................................................................
56C 300 Partly penetration welds and fillet welds in cross
connections subject to high
stresses..................................... 56C 400 Connections
of stiffeners to girders and bulkheads, etc.
....................................................................................
57C 500 End connections of
girders..................................................................................................................................
58C 600 Direct calculation of weld
connections...............................................................................................................
58
Sec. 10 Corrosion Control
............................................................................................................................
60
A. General
..........................................................................................................................................................................
60A 100
Scope...................................................................................................................................................................
60
B. Techniques for Corrosion Control Related to Environmental
Zones
...........................................................................
60B 100 Atmospheric zone
...............................................................................................................................................
60B 200 Splash zone
.........................................................................................................................................................
60B 300 Submerged
zone..................................................................................................................................................
61B 400 Internal
zone........................................................................................................................................................
61
C. Cathodic
Protection.......................................................................................................................................................
62C 100
General................................................................................................................................................................
62C 200 Galvanic anode
systems......................................................................................................................................
62C 300 Impressed current systems
..................................................................................................................................
63
D. Coating
Systems............................................................................................................................................................
64DET NORSKE VERITAS AS
D 100 Specification of coating
......................................................................................................................................
64
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Offshore Standard DNV-OS-C201, April 2012 Contents Page 8Sec. 11
Special Considerations for Column Stabilised Units
....................................................................
65
A. General
..........................................................................................................................................................................
65A 100 Assumptions and application
..............................................................................................................................
65
B. Structural Categorisation, Material Selection and Inspection
Principles......................................................................
65B 100
General................................................................................................................................................................
65B 200 Structural categorisation
.....................................................................................................................................
65B 300 Material
selection................................................................................................................................................
66B 400 Inspection
categories...........................................................................................................................................
66
C. Design and Loading
Conditions....................................................................................................................................
69C 100
General................................................................................................................................................................
69C 200 Permanent loads
..................................................................................................................................................
69C 300 Variable functional loads
....................................................................................................................................
69C 400 Tank
loads...........................................................................................................................................................
70C 500 Environmental loads,
general..............................................................................................................................
70C 600 Sea
pressures.......................................................................................................................................................
70C 700 Wind loads
..........................................................................................................................................................
71C 800 Heavy
components..............................................................................................................................................
71C 900 Combination of
loads..........................................................................................................................................
71
D. Structural Strength
........................................................................................................................................................
71D 100
General................................................................................................................................................................
71D 200 Global capacity
...................................................................................................................................................
71D 300 Transit condition
.................................................................................................................................................
72D 400 Method of
analysis..............................................................................................................................................
72D 500 Air gap
................................................................................................................................................................
73
E.
Fatigue...........................................................................................................................................................................
73E 100
General................................................................................................................................................................
73E 200 Fatigue
analysis...................................................................................................................................................
73
F. Accidental
Conditions...................................................................................................................................................
74F 100
General................................................................................................................................................................
74F 200
Collision..............................................................................................................................................................
74F 300 Dropped objects
..................................................................................................................................................
74F 400 Fire
......................................................................................................................................................................
74F 500 Explosion
............................................................................................................................................................
74F 600 Heeled condition
.................................................................................................................................................
74
G.
Redundancy...................................................................................................................................................................
75G 100
General................................................................................................................................................................
75G 200 Brace
arrangements.............................................................................................................................................
75
H. Structure in Way of a Fixed Mooring System
..............................................................................................................
75H 100 Structural
strength...............................................................................................................................................
75
I. Structural
Details...........................................................................................................................................................
75I 100
General................................................................................................................................................................
75
Sec. 12 Special Considerations for Self-Elevating
Units............................................................................
76
A.
Introduction...................................................................................................................................................................
76A 100 Scope and application
.........................................................................................................................................
76
B. Structural Categorisation, Material Selection and Inspection
Principles......................................................................
76B 100
General................................................................................................................................................................
76B 200 Structural categorisation
.....................................................................................................................................
76B 300 Material
selection................................................................................................................................................
76B 400 Inspection
categories...........................................................................................................................................
77
C. Design and Loading
Conditions....................................................................................................................................
77C 100
General................................................................................................................................................................
77C 200 Transit
.................................................................................................................................................................
77C 300 Installation and retrieval
.....................................................................................................................................
78C 400 Operation and
survival........................................................................................................................................
79
D. Environmental Conditions
............................................................................................................................................
79D 100
General................................................................................................................................................................
79D 200
Wind....................................................................................................................................................................
79D 300
Waves..................................................................................................................................................................
80D 400 Current
................................................................................................................................................................
80DET NORSKE VERITAS AS
D 500 Snow and ice
.......................................................................................................................................................
80
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Offshore Standard DNV-OS-C201, April 2012 Contents Page 9E.
Method of Analysis
.......................................................................................................................................................
80E 100
General................................................................................................................................................................
80E 200 Global structural models
.....................................................................................................................................
82E 300 Local structural
models.......................................................................................................................................
82E 400 Fatigue
analysis...................................................................................................................................................
82
F. Design
Loads.................................................................................................................................................................
82F 100
General................................................................................................................................................................
82F 200 Permanent loads
..................................................................................................................................................
83F 300 Variable functional loads
....................................................................................................................................
83F 400 Tank
loads...........................................................................................................................................................
83F 500 Environmental loads,
general..............................................................................................................................
83F 600 Wind loads
..........................................................................................................................................................
83F 700
Waves..................................................................................................................................................................
84F 800 Current
................................................................................................................................................................
84F 900 Wave and current
................................................................................................................................................
84F 1000 Sea pressures during transit
................................................................................................................................
85F 1100 Heavy components during transit
.......................................................................................................................
86F 1200 Displacement dependent
loads............................................................................................................................
86F 1300 Combination of
loads..........................................................................................................................................
86
G. Structural Strength
........................................................................................................................................................
87G 100
General................................................................................................................................................................
87G 200 Global capacity
...................................................................................................................................................
87G 300 Footing strength
..................................................................................................................................................
87G 400 Leg strength
........................................................................................................................................................
88G 500 Jackhouse support strength
.................................................................................................................................
88G 600 Hull strength
.......................................................................................................................................................
88
H. Fatigue Strength
............................................................................................................................................................
88H 100
General................................................................................................................................................................
88H 200 Fatigue
analysis...................................................................................................................................................
88
I. Accidental
Conditions...................................................................................................................................................
89I 100
General................................................................................................................................................................
89I 200 Collisions
............................................................................................................................................................
89I 300 Dropped objects
..................................................................................................................................................
89I 400 Fires
....................................................................................................................................................................
89I 500
Explosions...........................................................................................................................................................
89I 600 Unintended flooding
...........................................................................................................................................
89
J. Miscellaneous
requirements..........................................................................................................................................
89J 100
General................................................................................................................................................................
89J 200 Pre-load
capacity.................................................................................................................................................
89J 300 Overturning stability
...........................................................................................................................................
90J 400 Air gap
................................................................................................................................................................
91
Sec. 13 Special Considerations for Tension Leg Platforms (TLP)
........................................................... 92
A. General
..........................................................................................................................................................................
92A 100 Scope and application
.........................................................................................................................................
92A 200 Description of tendon system
.............................................................................................................................
92
B. Structural Categorisation, Material Selection and Inspection
Principles......................................................................
94B 100
General................................................................................................................................................................
94B 200 Structural categorisation
.....................................................................................................................................
94B 300 Material
selection................................................................................................................................................
95B 400 Design
temperatures............................................................................................................................................
95B 500 Inspection
categories...........................................................................................................................................
95
C. Design Principles
..........................................................................................................................................................
96C 100
General................................................................................................................................................................
96C 200 Design conditions
...............................................................................................................................................
96C 300 Fabrication
..........................................................................................................................................................
97C 400 Hull and Deck
Mating.........................................................................................................................................
97C 500 Sea transportation
...............................................................................................................................................
97C 600 Installation
..........................................................................................................................................................
97C 700 Decommissioning
...............................................................................................................................................
97C 800 Design principles, tendons
..................................................................................................................................
97
D. Design
Loads.................................................................................................................................................................
98D 100
General................................................................................................................................................................
98DET NORSKE VERITAS AS
D 200 Load categories
...................................................................................................................................................
98
-
Offshore Standard DNV-OS-C201, April 2012 Contents Page 10E.
Global Performance
......................................................................................................................................................
99E 100
General................................................................................................................................................................
99E 200 Frequency domain
analysis...............................................................................................................................
100E 300 High frequency analyses
...................................................................................................................................
100E 400 Wave frequency
analyses..................................................................................................................................
100E 500 Low frequency
analyses....................................................................................................................................
100E 600 Time domain analyses
......................................................................................................................................
101E 700 Model testing
....................................................................................................................................................
101E 800 Load effects in the tendons
...............................................................................................................................
102
F. Structural Strength
......................................................................................................................................................
102F 100
General..............................................................................................................................................................
102F 200 Hull
...................................................................................................................................................................
103F 300 Structural
analysis.............................................................................................................................................
103F 400 Structural design
...............................................................................................................................................
103F 500 Deck
..................................................................................................................................................................
104F 600 Extreme tendon tensions
...................................................................................................................................
104F 700 Structural design of tendons
.............................................................................................................................
105F 800
Foundations.......................................................................................................................................................
105
G.
Fatigue.........................................................................................................................................................................
105G 100
General..............................................................................................................................................................
105G 200 Hull and deck
....................................................................................................................................................
105G 300
Tendons.............................................................................................................................................................
105G 400 Foundation
........................................................................................................................................................
106
H. Accidental Condition
..................................................................................................................................................
106H 100 Hull
...................................................................................................................................................................
106H 200 Hull and deck
....................................................................................................................................................
107H 300
Tendons.............................................................................................................................................................
107H 400
Foundations.......................................................................................................................................................
107
Sec. 14 Special Considerations for Deep Draught Floaters
(DDF).........................................................
108
A. General
........................................................................................................................................................................
108A 100
Introduction.......................................................................................................................................................
108A 200 Scope and application
.......................................................................................................................................
108
B. Non-Operational
Phases..............................................................................................................................................
108B 100
General..............................................................................................................................................................
108B 200 Fabrication
........................................................................................................................................................
109B 300 Mating
...............................................................................................................................................................
109B 400 Sea transportation
.............................................................................................................................................
109B 500 Installation
........................................................................................................................................................
109B 600 Decommissioning
.............................................................................................................................................
109
C. Structural Categorisation, Selection of Material and Extent
of
Inspection.................................................................
109C 100
General..............................................................................................................................................................
109C 200 Material
selection..............................................................................................................................................
110C 300 Design
temperatures..........................................................................................................................................
110C 400 Inspection
categories.........................................................................................................................................
110C 500 Guidance to minimum
requirements.................................................................................................................
111
D. Design
Loads...............................................................................................................................................................
112D 100 Permanent loads
................................................................................................................................................
112D 200 Variable functional loads
..................................................................................................................................
112D 300 Environmental loads
.........................................................................................................................................
113D 400 Determination of
loads......................................................................................................................................
113D 500 Hydrodynamic loads
.........................................................................................................................................
113
E. Deformation Loads
....................................................................................................................................................
114E 100
General..............................................................................................................................................................
114
F. Accidental Loads
........................................................................................................................................................
114F 100
General..............................................................................................................................................................
114
G. Fatigue Loads
..............................................................................................................................................................
114G 100
General..............................................................................................................................................................
114
H. Combination of
Loads.................................................................................................................................................
114H 100
General..............................................................................................................................................................
114
I. Load Effect Analysis in Operational Phase
................................................................................................................
114I 100
General..............................................................................................................................................................
114DET NORSKE VERITAS AS
I 200 Global bending effects
......................................................................................................................................
115
-
Offshore Standard DNV-OS-C201, April 2012 Contents Page 11J.
Load Effect Analysis in Non-Operational
Phases.......................................................................................................
115J 100
General..............................................................................................................................................................
115J 200 Transportation
...................................................................................................................................................
115J 300 Launching
.........................................................................................................................................................
115J 400
Upending...........................................................................................................................................................
116J 500 Deck mating
......................................................................................................................................................
116J 600 Riser
installations..............................................................................................................................................
116
K. Structural Strength
......................................................................................................................................................
116K 100 Operation phase for
hull....................................................................................................................................
116K 200 Non-operational phases for
hull........................................................................................................................
116K 300 Operation phase for deck or topside
.................................................................................................................
117K 400 Non-operational phases for deck or
topside......................................................................................................
117
L.
Fatigue.........................................................................................................................................................................
117L 100
General..............................................................................................................................................................
117L 200 Operation phase for
hull....................................................................................................................................
117L 300 Non-operational phases for
hull........................................................................................................................
118L 400 Splash zone
.......................................................................................................................................................
118L 500 Operation phase for deck or topside
.................................................................................................................
119L 600 Non-operational phases for deck or
topside......................................................................................................
119
M. Accidental Condition
..................................................................................................................................................
119M 100
General..............................................................................................................................................................
119M 200 Fire
....................................................................................................................................................................
119M 300 Explosion
..........................................................................................................................................................
119M 400
Collision............................................................................................................................................................
119M 500 Dropped objects
................................................................................................................................................
120M 600 Unintended flooding
.........................................................................................................................................
120M 700 Riser
Damage....................................................................................................................................................
120M 800 Abnormal wave
events......................................................................................................................................
120
N. Dynamic Riser Design and Global Performance
........................................................................................................
120N 100 Dynamic Riser Design
......................................................................................................................................
120N 200 Global Performance
..........................................................................................................................................
121
App. A Cross Sectional Types
....................................................................................................................
122
A. Cross Sectional Types
.................................................................................................................................................
122A 100
General..............................................................................................................................................................
122A 200 Cross section requirements for plastic analysis
................................................................................................
122A 300 Cross section requirements when elastic global analysis is
used
.....................................................................
123
App. B Methods and Models for Design of Column-Stabilised Units
.................................................... 125
A. Methods and Models
...................................................................................................................................................
125A 100
General..............................................................................................................................................................
125A 200 World wide operation
.......................................................................................................................................
125A 300 Benign waters or restricted areas
......................................................................................................................
125
App. C Permanently Installed Units
..........................................................................................................
127
A.
Introduction.................................................................................................................................................................
127A 100
Application........................................................................................................................................................
127
B. Inspection and
Maintenance........................................................................................................................................
127B 100 Facilities for inspection on
location..................................................................................................................
127
C.
Fatigue.........................................................................................................................................................................
127C 100 Design fatigue factors
.......................................................................................................................................
127C 200 Splash zone for floating units
...........................................................................................................................
128
App. D Certification of Tendon System
....................................................................................................
129
A. General
........................................................................................................................................................................
129A 100
Introduction.......................................................................................................................................................
129
B. Equipment categorization
...........................................................................................................................................
129B 100
General..............................................................................................................................................................
129
C. Fabrication
Record......................................................................................................................................................
130C 100
General..............................................................................................................................................................
130
D. Documentation Deliverables for Certification of Equipment
.....................................................................................
130DET NORSKE VERITAS AS
D 100
General..............................................................................................................................................................
130
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Offshore Standard DNV-OS-C201, April 2012 Contents Page 12E.
Tendon Systems and Components
..............................................................................................................................
131E 100
General..............................................................................................................................................................
131E 200 Tendon pipe
......................................................................................................................................................
132E 300 Bottom tendon interface
(BTI)..........................................................................................................................
132E 400 Flex bearings
....................................................................................................................................................
132E 500 Foundations
......................................................................................................................................................
133E 600 Top tendon interface (TTI)
...............................................................................................................................
133E 700 Intermediate tendon connectors (ITC)
..............................................................................................................
133E 800 Tendon tension monitoring system (TTMS)
....................................................................................................
133E 900 Tendon porch
....................................................................................................................................................
134E 1000 Tendon corrosion protection
system.................................................................................................................
134E 1100 Load management program (LMP)
..................................................................................................................
134
F. Categorisation of Tendon
Components.......................................................................................................................
134F 100
General..............................................................................................................................................................
134
G. Tendon Fabrication
.....................................................................................................................................................
135G 100
General..............................................................................................................................................................
135DET NORSKE VERITAS AS
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Offshore Standard DNV-OS-C201, April 2012 Sec.1 Page 13SECTION
1INTRODUCTION
A. General
A 100 Introduction101 This offshore standard provides
principles, technical requirements and guidance for the structural
designof offshore structures, based on the Working Stress Design
(WSD) method.102 This standard has been written for general
world-wide application. Statutory regulations may
includerequirements in excess of the provisions by this standard
depending on size, type, location and intended serviceof the
offshore unit or installation.103 The standard is organised with
general sections containing common requirements and
sectionscontaining specific requirement for different type of
offshore units. In case of deviating requirements betweengeneral
sections and the object specific sections, requirements of the
object specific sections shall apply.
A 200 Objectives201 The objectives of this standard are to:
provide an internationally acceptable level of safety by
defining minimum requirements for structures andstructural
components (in combination with referred standards, recommended
practices, guidelines, etc.)
serve as a contractual reference document between suppliers and
purchasers serve as a guideline for designers, suppliers,
purchasers and regulators specify procedures and requirements for
offshore structures subject to DNV certification and
classification.
A 300 Scope and application301 This standard is applicable to
the following types of offshore structures:
column-stabilised units self-elevating units tension leg
platforms deep draught floaters.
302 For utilisation of other materials, the general design
principles given in this standard may be usedtogether with relevant
standards, codes or specifications covering the requirements to
materials design andfabrication.303 The standard is applicable to
structural design of complete units including substructures,
topsidestructures and vessel hulls. 304 This standard gives
requirements for the following:
design principles structural categorisation material selection
and inspection principles loads and load effect analyses design of
steel structures and connections special considerations for
different types of units.
Requirements for foundation design are given in DNV-OS-C101.
A 400 Other than DNV codes401 Other recognised codes or
standards may be applied provided it is shown that the codes and
standards,and their application, meet or exceed the level of safety
of the actual DNV standard.402 In case of conflict between
requirements of this standard and a reference document other than
DNVdocuments, the requirements of this standard shall prevail.403
Where reference is made to codes other than DNV documents, the
latest revision of the documents shallbe applied, unless otherwise
specified.404 When code checks are performed according to other
than DNV codes, the usage factors as given in theDET NORSKE VERITAS
AS
respective code shall be used.
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Offshore Standard DNV-OS-C201, April 2012 Sec.1 Page 14A 500
Classification501 Classification principles, procedures and
applicable class notations related to classification services
ofoffshore units are specified in the DNV Offshore Service
Specifications given in Table A1.
502 Documentation for classification shall be in accordance with
the NPS DocReq (DNV NauticusProduction System for documentation
requirements) and DNV-RP-A201.
B. ReferencesB 100 General101 The DNV documents in Table B1 are
referred to in the present standards and contain acceptable
methodsfor fulfilling the requirements in this standard. 102 The
latest valid revision of the DNV reference documents in Table B2
applies. See also current DNVList of Publications.103 The documents
listed in Table B2 are referred in the present standard. The
documents include acceptablemethods for fulfilling the requirements
in the present standard and may be used as a source of
supplementaryinformation. Only the referenced parts of the
documents apply for fulfilment of the present standard.
Table A1 DNV Offshore Service SpecificationsReference
TitleDNV-OSS-101 Rules for Classification of Offshore Drilling and
Support Units DNV-OSS-102 Rules for Classification of Floating
Production, Storage and Loading UnitsDNV-OSS-103 Rules for
Classification of LNG/LPG Floating Production and Storage Units or
InstallationsDNV-OSS-121 Classification Based on Performance
Criteria Determined by Risk Assessment Methodology
Rules for Planning and Execution of Marine Operations
Table B1 DNV Reference DocumentsReference TitleDNV-OS-A101
Safety Principles and ArrangementDNV-OS-B101 Metallic
MaterialsDNV-OS-C101 Design of Offshore Steel Structures, General
(LRFD method)DNV-OS-C301 Stability and Watertight
IntegrityDNV-OS-C401 Fabrication and Testing of Offshore
StructuresDNV-OS-D101 Marine Machinery Systems and
EquipmentDNV-OS-E301 Position MooringDNV-OS-F201 Dynamic
RisersDNV-RP-A201 Plan Approval Documentation Types -
DefinitionsDNV-RP-B401 Cathodic Protection DesignDNV-RP-C103 Column
Stabilised UnitsDNV-RP-C104 Self-Elevating UnitsDNV-RP-C201
Buckling Strength of Plated StructuresDNV-RP-C202 Buckling Strength
of ShellsDNV-RP-C204 Design against Accidental LoadsDNV-RP-C203
Fatigue Strength Analysis of Offshore Steel StructuresDNV-RP-C205
Environmental Conditions and Environmental LoadsClassification Note
30.1 Buckling Strength Analysis of Bars and Frames, and Spherical
ShellsClassification Note 30.4 Foundations
Table B2 Other references Reference TitleAISC-ASD Manual of
Steel Construction ASDAPI RP 2A WSD with supplement 1
Planning, Designing and Constructing Fixed Offshore Platforms
Working Stress Design
API RP 2T Planning, Designing and Constructing Tension Leg
PlatformsBS 7910 Guide on methods for assessing the acceptability
of flaws in fusion welded structuresNACE TPC Publication No. 3. The
role of bacteria in corrosion of oil field equipmentDET NORSKE
VERITAS AS
SNAME 5-5A Site Specific Assessment of Mobile Jack-Up Units
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Offshore Standard DNV-OS-C201, April 2012 Sec.1 Page 15C.
DefinitionsC 100 Verbal forms101 Shall: Indicates a mandatory
requirement to be followed for fulfilment or compliance with the
presentstandard. Deviations are not permitted unless formally and
rigorously justified, and accepted by all relevantcontracting
parties.102 Should: Indicates a recommendation that a certain
course of action is preferred or particularly suitable.Alternative
courses of action are allowable under the standard where agreed
between contracting parties butshall be justified and
documented.103 May: Indicates a permission, or an option, which is
permitted as part of conformance with the standard.
C 200 Terms201 Accidental condition: When the unit is subjected
to accidental loads such as collision, dropped objects,fire
explosion, etc.202 Accidental loads: Loads which may occur as a
result of accident or exceptional events, e.g.
collisions,explosions, dropped objects.203 Atmospheric zone: The
external surfaces of the unit above the splash zone.204 Cathodic
protection: A technique to prevent corrosion of a steel surface by
making the surface to be thecathode of an electrochemical cell.205
Characteristic load: The reference value of a load to be used in
the determination of load effects. Thecharacteristic load is
normally based upon a defined fractile in the upper end of the
distribution function forload.206 Characteristic strength: The
reference value of structural strength to be used in the
determination of thedesign strength. The characteristic strength is
normally based upon a 5% fractile in the lower end of
thedistribution function for resistance.207 Characteristic value:
The representative value associated with a prescribed probability
of not beingunfavourably exceeded during the applicable reference
period.208 Classic spar: Shell type hull structure.209
Classification Note: The Classification Notes cover proven
technology and solutions which is found torepresent good practice
by DNV, and which represent one alternative for satisfying the
requirements given inthe DNV Rules or other codes and standards
cited by DNV. The Classification Notes will in the same mannerbe
applicable for fulfilling the requirements in the DNV Offshore
Standards.210 Coating: Metallic, inorganic or organic material
applied to steel surfaces for prevention of corrosion.211
Column-stabilised unit: A floating unit that can be relocated. A
column-stabilised unit normally consistsof a deck structure with a
number of widely spaced, large diameter, supporting columns that
are attached tosubmerged pontoons.212 Corrosion allowance: Extra
wall thickness added during design to compensate for any
anticipatedreduction in thickness during the operation.213 Damaged
condition: The unit condition after accidental damage. 214 Deep
draught floater (DDF): A floating unit categorised with a relative
large draught. The large draughtis mainly introduced to obtain
reduced wave excitation in heave and sufficiently high eigenperiod
in heave suchthat resonant responses in heave can be omitted or
minimised.215 Design brief: An agreed document presenting owner's
technical basis, requirements and references forthe unit design and
fabrication.216 Design temperature: The design temperature for a
unit is the reference temperature for assessing areaswhere the unit
can be transported, installed and operated. The design temperature
shall be lower or equal to thelowest mean daily temperature in air
for the relevant areas. For seasonal restricted operations the
lowest meandaily temperature in air for the season may be
applied.217 Driving voltage: The difference between closed circuit
anode potential and the protection potential.218 Dry transit: A
transit where the unit is transported on a heavy lift unit from one
geographical location toanother.219 Dynamic upending: A process
where seawater is filled or flooded into the bottom section of
ahorizontally floating DDF hull and creating a trim condition and
subsequent water filling of hull or moonpooland dynamic upending to
bring the hull in vertical position.220 Environmental loads: Loads
directly and