API RBI Tank Case Study 1

API RBI Tank Case Study

Presentation Overview

• Introduction• General RBI InformationGeneral RBI Information• Atmospheric Storage Tank RBI Overview• Tank Case Study• RBI Results• Lessons Learned

2

Introduction

• RBI provisions added to API 653 in Second Edition late 1990sEdition, late 1990s

• Significant changes to the Tank Module in version 8 release, 2007,

• Future improvements planned to the module

3

General RBI Information

• In general, risk is calculated as a function of time as followsfollows

( ) ( )R t POF t COF= ⋅

• The probability of failure is a function of time, since damage due to cracking, thinning or other damage mechanisms increases with time

• In API RBI, the consequence of failure is assumed to be independent of time, therefore

( ) ( )( ) ( )

R t POF t CA for Area Based RiskR t POF t FC for Financial Based Risk

= ⋅ −= ⋅ −

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Probability of Failure

• The probability of failure used in API RBI is:

( ) ( ):

f MSPOF t gff D t F

where

= ⋅ ⋅

( )

( )

POF t the probability of failure as a function of timegff generic failure frequencyD t d f t f ti f ti

−

−

( )

f

MS

D t damage factor as a function of time

F management systems factor

−

−

• The time dependency of probability of failure is the basis of using RBI for inspection planning

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Atmospheric Storage Tank RBI

• Level 1 consequence determination only• Result is in financial terms• Result is in financial terms• Consequences from component damage, product loss

and environmental costs are consideredT k M d li• Tank Modeling• Tank Bottom• Separate Shell Courses• As a pressure vessel.

This allows for using the Level 2 consequence modeler

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What is a Tank Failure??

1 Dike Area

Tank6

Surface Water

OnsiteOffsite

Tank6

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Subsurface Soil

Ground Water

4

5Ground Water 5

7


• Fluid properties determined by fluid selection• Hydraulic conductivity and fluid seepage velocity

determined from density and viscosity

Table 7.1 – Fluids and Fluid Properties for Atmospheric storage Tank Consequence Analysis

Level 1 Consequence Liquid Dynamic

determined from density and viscosity

FluidConsequence

AnalysisRepresentative

Fluid

Molecular Weight Liquid Density(lb/ft3)

Liquid Dynamic Viscosity(lbf-s/ft2)

Gasoline C6-C8 100 42.702 8.383E-5

Light Diesel Oil C9-C12 149 45.823 2.169E-5

Heavy Diesel Oil C13-C16 205 47.728 5.129E-5

Fuel Oil C17-C25 280 48.383 7.706E-4

Crude Oil C17-C25 280 48.383 7.706E-4

Heavy Fuel Oil C25+ 422 56.187 9.600E-4

Heavy Crude Oil C25+ 422 56 187 9 600E 4

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Heavy Crude Oil C25+ 422 56.187 9.600E-4


Table 7.2 – Soil Types and Properties for Atmospheric storage Tank Consequence Analysis

Hydraulic Conductivity Hydraulic Conductivity

Soil Type for Water LowerBound(in/sec)

for Water Upper Bound(in/sec)

Soil Porosity

Coarse Sand 3.94E-2 3.94E-3 0.33

Fine Sand 3.94E-3 3.94E-4 0.33

Very Fine Sand 3.94E-4 3.94E-6 0.33

Silt 3 94E 6 3 94E 7 0 41Silt 3.94E-6 3.94E-7 0.41

Sandy Clay 3.94E-7 3.94E-8 0.45

Clay 3.94E-8 3.94E-9 0.50

Concrete-Asphalt 3.94E-11 3.94E-12 0.99

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• Release Rate Calculation– Liquid head is assumed to be constant with time– Leak into ground is as a continuous porous media, by the

soil porosity for tank foundations – Product leakage flow rate through a small hole is a function

of the soil and fluid properties as well as liquid head (fill of the soil and fluid properties as well as liquid head (fill height)

– Tank rupture assumes all product in the tank is lost– Bernoulli or Girard equation used depending on hydraulic Bernoulli or Girard equation used depending on hydraulic

conductivity• API RBI for atmospheric storage tanks is currently based

on financial consequences only which requires the use of on financial consequences only which requires the use of a Financial Risk Target

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• Financial environmental cost from shell course leakage

leak leakBbl C Bbl C⎛ ⎞+ +indike indike ss onsite ss oniteleakenviron leak leak

ss offsite ss offite water water

Bbl C Bbl CFC

Bbl C Bbl C− −

− −

⎛ ⎞⋅ + ⋅ += ⎜ ⎟⎜ ⎟⋅ + ⋅⎝ ⎠

• Financial environmental cost for a shell course rupture

rupture ruptureindike indike ss onsite ss oniterupture Bbl C Bbl C

FC − −⎛ ⎞⋅ + ⋅ += ⎜ ⎟

• Total financial environmental cost for shell courses

penviron rupture rupture

ss offsite ss offite water water

FCBbl C Bbl C− −

= ⎜ ⎟⎜ ⎟⋅ + ⋅⎝ ⎠

leak ruptureenviron environ environFC FC FC= +

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Atmospheric Storage Tank RBI• Component damage cost for shell courses

4

n ngff holecost⎛ ⎞⋅⎜ ⎟∑

1ncmd

total

FC matcostgff

=⎜ ⎟⎜ ⎟= ⋅⎜ ⎟⎜ ⎟⎝ ⎠

∑

• Outage Days and the cost of business interruption

( )( )prod cmd affaFC Outage Outage prodcost= +

• Financial Consequence for shell courses

t t l i d dFC FC FC FC= + +

( )

• The above consequence calculation is for the tank shell courses, a similar consequence calculation is used for th t k fl

total environ cmd prodFC FC FC FC+ +

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the tank floor

Case Study Background

• Refinery is located near, IA• The refinery wanted to use RBI to defer the inspections • The refinery wanted to use RBI to defer the inspections

on two AST. • Local regulators are pushing for internal inspections on

these tanksthese tanks• A similar service argument for other tanks very close to

these tanks was used. Similar Service is a provision added to API 653 in late – Similar Service is a provision added to API 653 in late 2008, but it was not valid at the time of the analysis.

– This argument was not accepted by the regulators.

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Tank Description

• T-1– Diesel Product Tank– Diesel Product Tank– Installed in 1956, floor replaced in 1992– 30’ diameter, 40’ tall– Sits on a ring wall with no release prevention– Sits on a ring wall with no release prevention– No internal inspection since floor replacement

T 17• T-17– Heavy Gas Oil Tank– Installed in 1993

120’ di 48’ ll– 120’ diameter, 48’ tall– Sits on a graded concrete slab– No internal inspection since installation

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T-143

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T-1

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API RBI Risk Targets

• When a risk target is exceeded in API RBI, an inspection is generated to reduce uncertainty

• Fixed equipment primarily uses an Area Risk Targetg– Many case studies– 27-40 ft2/yr target from

experience• Tank RBI uses a Financial risk Tank RBI uses a Financial risk

target– No well defined case studies

for Tank RBI Risk Targets– Trial and error method with Trial and error method with

client input- Inspection costs and production interruption are considered

• Used $15,000/yr risk target consistent with targets used in PRV RBI

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Key Inputs

• Operating conditions – Height, Temperature• Foundation Release Prevention?• Foundation – Release Prevention?• Containment Information• Production Impact• Environmental Impact• Previous inspections

– Corrosion rates– Damage to insulation– Overall condition

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Damage Mechanisms

• Tank Bottom Corrosion• Thinning Damage• Thinning Damage• External Damage (CUI)• No environmental cracking mechanisms active

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Tank Bottom Corrosion

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Thinning Damage

Component Component Type Base Metal Measured Rate (mpy)*

Base Metal Calculated Rate (mpy)

T-143-BTM TANKBOTTOM - 9.5

T-143-Course 2 COURSE-1 0 -



T 143 C 4 COURSE 4 0T-143-Course 4 COURSE-4 0 -

T-143-Pressure Vessel DRUM 0 -

T-173-BTM TANKBOTTOM - 11.0





T-173-Course 5 COURSE-5 5.0 -

T-173-Presusre Vessel DRUM 5.0 -

* Measured rates came from provided UT data

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External Damage

Component Component Type Insulation Type External Environment

Base Material Calculated Rate (mpy)

T 143 Course 1 COURSE 1 Mineral Wool Marine 8 4T-143-Course 1 COURSE-1 Mineral Wool Marine 8.4

T-143-Course 2 COURSE-2 Mineral Wool Marine 8.4



T-143-Pressure Vessel DRUM Mineral Wool Marine 8.4

T-173-Course 1 COURSE-1 Fiberglass Marine 10.9





T-173-Presusre Vessel DRUM Fiberglass Marine 8.4

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RBI Results

Thinning Cracking External RBI

• Inspection Planning

Component Component Description

Component Type

Thinning Inspection Category

Cracking Inspection Category

Damage Inspection Category

RBI Inspection

Date

T-143-BTM T-143-Bottom TANKBOTTOM C 2015-02-01

T-143-Pressure Vessel T-143-Shell DRUM C 2015-10-24

T-173-BTM T-173-Bottom TANKBOTTOM C 2017-03-15

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RBI Results - Inspection Plans

• T-1 Bottom – C-level bottom thinning by February of 2015. – Scanning of 5 to 10+% of the floor plates while supplementing scanning near

the shell and the floorthe shell and the floor– 100% visual inspection of the floor– Scanning should progressively increase if damage is found.

• T-17 Bottom – C-level bottom thinning by March of 2017.S i f 5 t 10+% f th fl l t hil l ti i – Scanning of 5 to 10+% of the floor plates while supplementing scanning near the shell and the floor

– 100% visual inspection of the floor– Scanning should progressively increase if damage is found.

T 1 P V l M d l d l C l l t l • T-1 Pressure Vessel – Modeled as a pressure vessel, C-level external shell inspection recommendation to be completed by October of 2015. – 95 to 100% external visual inspection of the insulation– Follow-up with profile or real time radiography of 33 to 65% of suspect areas – Follow-up of corroded areas with 95 to 100% visual inspection of the exposed

surface with UT, RT or pit gauge. – This inspection does NOT require an entry.

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RBI Results – Risk Drivers

• T-1 Bottom– 15+ years of service with no corrosion data for the bottom– Conservative estimate for tank bottom corrosion rate of 9.5 mpy– The calculated bottom thickness at this date using 9.5 mpy corrosion rate

is 0.101” which is at the minimum thickness of 0.10” for tanks without leak detection as prescribed in API 653.

• T-17 Bottom– 15+ years of service with no corrosion data for the bottom– Conservative estimate for tank bottom corrosion rate of 11.0 mpy– The calculated bottom thickness at this date using 11.0 mpy corrosion rate g py

is 0.056” which is above the minimum thickness of 0.05” for tanks with leak detection as prescribed in API 653.

• T-1 Pressure Vessel– Estimated external corrosion rate of 8.4 mpypy– The insulation has failed on the tank creating a potential CUI concern.

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Lessons Learned

• Received regulatory approval for the Internal Inspection deferralInspection deferral

• Found a few bugs in the software– Volume display

Course height changes– Course height changes• Suggestions for future improvements

– Change location of some inputs• Operating height• Operating height• Specific Gravity• Release and foundation settings

– Make course height component specificMake course height component specific– Fluids

• Adding more fluids• Using Level 2 modeler

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API RBI Tank Case Study 1

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