The API RBI Tank Module & Examples of Tank RBI

Assessments

The Equity Engineering Group, Inc. March, 2010

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2

Presentation Overview

• Introduction & General RBI Background • Storage Tank RBI Overview • API RBI Tank Module • Two Case Studies

– Tank Inspection Variance – Tank Inspection Prioritization

• Summary & Conclusions

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3

Introduction

• RBI provisions added to API 653 in late 1990s

• Current API 653 includes inspection intervals that account for RBI assessment (and similar service; use of RPB’s, CP, etc.)

• Significant enhancements were made to the API RBI Tank Module in Version 8 released in 2007 Cop

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General RBI Background

• API 580 Risk Based Inspection – provides guidance on developing an RBI program – What is RBI – What are the key elements of an RBI program – How to implement an RBI program

• API 581 Risk Based Inspection Technology –

provides details of an RBI program that complies with API 580 – API RBI software based on API 581 methodology – A quantitative approach – Detailed procedures and calculations

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General RBI Background

• In general, Risk is the product of probability of failure and consequence of failure

• POF is a function of time since many damage

mechanisms (fatigue, thinning, cracking, creep, etc.) can be functions of time – so, Risk is time-dependent

• In API RBI, the COF is assumed to be independent of time, so:

( ) ( )R t POF t COF= ⋅

( ) ( )( ) ( )

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

• The probability of failure used in API RBI is a function of three terms:

( ) ( )

( )

( )

:

f MS

f

MS

POF t gff D t Fwhere

POF t the probability of failure as a function of timegff generic failure frequencyD t damage factor as a function of timeF management systems factor

= ⋅ ⋅

−

−

−

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7

API RBI Generic Failure Frequency

• From API 581 – Part 2 Table 4.1:

• GFF are based on statistical analysis of best available data and experience of the API RBI Sponsor Group

Table 4.1 – Suggested Component Generic Failure Frequencies ( )[1 thru 8]

Equipment Type Component Type as a Function of Hole Size (failures/yr)

(failures/yr) Small Medium Large Rupture

Compressor COMPC 8.00E-06 2.00E-05 2.00E-06 0 3.00E-05 Compressor COMPR 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Heat Exchanger HEXSS 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Heat Exchanger HEXTS 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Heat Exchanger HEXTUBE 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Pipe PIPE-1 2.80E-05 0 0 2.60E-06 3.06E-05 Pipe PIPE-2 2.80E-05 0 0 2.60E-06 3.06E-05 Pipe PIPE-4 8.00E-06 2.00E-05 0 2.60E-06 3.06E-05 Pipe PIPE-6 8.00E-06 2.00E-05 0 2.60E-06 3.06E-05 Pipe PIPE-8 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Pipe PIPE-10 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Pipe PIPE-12 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Pipe PIPE-16 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Pipe PIPEGT16 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Pump PUMP2S 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Pump PUMPR 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Pump PUMP1S 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Tank650 TANKBOTTOM 7.20E-04 0 0 2.00E-06 7.20E-04 Tank650 COURSE-1 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Tank650 COURSE-2 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Tank650 COURSE-3 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Tank650 COURSE-4 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Tank650 COURSE-5 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Tank650 COURSE-6 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Tank650 COURSE-7 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Tank650 COURSE-8 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Tank650 COURSE-9 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Tank650 COURSE-10 7.00E-05 2.50E-05 5.00E-06 1.00E-07 1.00E-04 Vessel/FinFan KODRUM 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Vessel/FinFan COLBTM 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Vessel/FinFan FINFAN 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Vessel/FinFan FILTER 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Vessel/FinFan DRUM 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Vessel/FinFan REACTOR 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Vessel/FinFan COLTOP 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Vessel/FinFan COLMID 8.00E-06 2.00E-05 2.00E-06 6.00E-07 3.06E-05 Note: See references [1] through [8] for discussion of failure frequencies for equipment

gffgfftotalgff

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8

Tank Failure – What is Impacted

Subsurface Soil

Surface Water

OnsiteOffsite

1

Ground Water

Tank

Dike Area

6

32

4

5

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Tank RBI – API RBI • Consequences from component damage, product loss

and environmental costs are considered - Level 1 consequence determination only in API RBI Tank Module

• Result is in financial risk terms

• Tank Modeled as several components - Tank Bottom; Shell Courses

• When safety consequences need to be considered in addition to financial model a tank shell a pressure vessel shell, as well Cop

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Tank RBI – API RBI

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

Fluid

Level 1 Consequence

Analysis Representative

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

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

determined from density and viscosity

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Tank RBI – API RBI

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

Soil Type

Hydraulic Conductivity for Water Lower

Bound (in/sec)

Hydraulic Conductivity 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 0.41

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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Tank RBI – API RBI

• Release Rate Calculation – Liquid head is assumed to be constant (maximum) with

time – Leak into ground is treated as a continuous porous media;

based on the soil porosity given for the tank subgrade – Product leakage flow rate through a small hole is a function

of the soil and fluid properties as well as liquid head – Bernoulli or Girard equation used depending on hydraulic

conductivity

• API Tank RBI modules uses a Financial Risk Target

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Tank RBI – API RBI

• Financial environmental cost from shell course leakage

• Financial environmental cost for a shell course rupture

• Total financial environmental cost for shell courses

leak leakindike indike ss onsite ss oniteleak

environ leak leakss offsite ss offite water water

Bbl C Bbl CFC

Bbl C Bbl C− −

− −

⋅ + ⋅ += ⋅ + ⋅

rupture ruptureindike indike ss onsite ss oniterupture

environ rupture rupturess offsite ss offite water water

Bbl C Bbl CFC

Bbl C Bbl C− −

− −

⋅ + ⋅ += ⋅ + ⋅

leak ruptureenviron environ environFC FC FC= +

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Tank RBI – API RBI • Component damage cost for shell courses

• Outage Days and the cost of business interruption

• Financial Consequence for shell courses

• A similar consequence calculation is done for the tank

floor

total environ cmd prodFC FC FC FC= + +

4

1n n

ncmd

total

gff holecostFC matcost

gff=

⋅ = ⋅

∑

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

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15

API RBI - Risk Targets

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

• Fixed equipment primarily uses an Area Risk Target: 27-40 ft2/yr target is typical (from experience, case studies)

• Tank RBI uses a Financial risk target. No well defined case studies for Tank RBI Risk Targets: - Typically determined with client input to be in the $15,000 to

$50,000/yr range; inspection costs and production interruption are considered Cop

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API RBI - Key Inputs

• Operating conditions – Height, Temperature, SG • Foundation – Design, Release Prevention, Soil Type • Containment Information (dike, possibility of off-site

contamination) • Production Impact • Environmental Impact • Previous inspections

– Corrosion rates – Damage to insulation – Overall condition

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17

API RBI Inspection Effectiveness

• Grade Inspections – (A through E)

• API 581 – Part 2 Tables in Section 5 – Based on type of damage that is of concern

• Typically, an intrusive and non-intrusive method of inspection is listed

Table 5.10 – Guidelines for Assigning Inspection Effectiveness – Tank Bottoms

Inspection Category

Inspection Effectiveness

Category Soil Side Product Side

A Highly Effective

a. Floor scan 90+% & UT follow-up b. Include welds if warranted from

the results on the plate scanning c. Hand scan of the critical zone

Commercial blast Effective supplementary light Visual 100% (API 653) Pit depth gauge 100% vacuum box testing of suspect welded joints Coating or Liner: a. Sponge test 100% b. Adhesion test c. Scrape test

B Usually Effective

a. Floor scan 50+% & UT follow-up OR a. EVA or other statistical method

with Floor scan follow-up if warranted by the result

a. Brush blast b. Effective supplementary light c. Visual 100% (API 653) d. Pit depth gauge Coating or Liner: a. Sponge test >75% b. Adhesion test c. Scrape test

C Fairly Effective

a. Floor scan 5-10+% plates; supplement with scanning near Shell & UT follow-up; Scan circle and X pattern

b. Progressively increase if damage found during scanning

c. Helium/Argon test d. Hammer test e. Cut coupons

a. Broom swept b. Effective supplementary light c. Visual 100% d. Pit depth gauge Coating or Liner: a. Sponge test 50 – 75% b. Adhesion test c. Scrape test

D Poorly Effective a. Spot UT b. Flood test

a. Broom swept b. No effective supplementary lighting c. Visual 25-50% Coating or Liner: Sponge test <50

E Ineffective None None Copyri

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API RBI – Tank Damage Mechanisms

• Tank Bottom Corrosion – Product Side – Soil Side

• Shell Thinning Damage

• Shell External Damage (CUI)

• Often, no other mechanisms:

– Fatigue – Creep – Cracking

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API RBI – Typical Input (Bottom)

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API RBI - Typical Input (Shell)

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API RBI – Typical Input (Thinning)

Tank 1 – Tank Bottom

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Case Study 1

• Two refinery AST – RBI used to defer the inspections – variance from jurisdiction

• A similar service argument was used for other tanks

very close to these tanks

• Similar Service argument was not accepted by the regulators for these two tanks

• Both were last inspected in the early 1990’s

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Tank Descriptions

• Tank 1 – Diesel Product Tank – Installed in the late 50’s, floor replaced in early 90’s – 30’ diameter, 40’ tall – Sits on a ring wall with no release prevention – No internal inspection since floor replacement

• Tank 2

– Heavy Gas Oil Tank – Installed in early 90’s – 120’ diameter, 48’ tall – Sits on a graded concrete slab – No internal inspection since installation

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Thinning Damage

Component Component Type Base Metal Measured Rate (mpy)*

Base Metal Calculated Rate (mpy)

TANK 1-BTM TANKBOTTOM - 9.5

TANK 1-Course 2 COURSE-1 0 -

TANK 1-Course 3 COURSE-2 0 -

TANK 1-Course 4 COURSE-3 0 -

TANK 1-Course 4 COURSE-4 0 -

TANK 1-Pressure Vessel DRUM 0 -

TANK 2-BTM TANKBOTTOM - 11.0

TANK 2-Course 1 COURSE-1 0 -

TANK 2-Course 2 COURSE-2 0 -

TANK 2-Course 3 COURSE-3 0 -

TANK 2-Course 4 COURSE-4 0 -

TANK 2-Course 5 COURSE-5 5.0 -

TANK 2-Presusre Vessel DRUM 5.0 -

* Measured rates came from provided UT data Cop

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External Damage

Component Component Type Insulation Type External Environment

Base Material Calculated Rate (mpy)

TANK 1-Course 1 COURSE-1 Mineral Wool Marine 8.4

TANK 1-Course 2 COURSE-2 Mineral Wool Marine 8.4

TANK 1-Course 3 COURSE-3 Mineral Wool Marine 8.4

TANK 1-Course 4 COURSE-4 Mineral Wool Marine 8.4

TANK 1-Pressure Vessel DRUM Mineral Wool Marine 8.4

TANK 2-Course 1 COURSE-1 Fiberglass Marine 10.9

TANK 2-Course 2 COURSE-2 Fiberglass Marine 10.9

TANK 2-Course 3 COURSE-3 Fiberglass Marine 10.9

TANK 2-Course 4 COURSE-4 Fiberglass Marine 10.9

TANK 2-Course 5 COURSE-5 Fiberglass Marine 10.9

TANK 2-Presusre Vessel DRUM Fiberglass Marine 8.4

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RBI Results

Component Component Description

Component Type

Thinning Inspection Category

Cracking Inspection Category

External Damage

Inspection Category

RBI Inspection

Date

TANK 1-BTM TANK 1-Bottom TANKBOTTOM C 2015-02-01

TANK 1-Shell TANK 1-Shell DRUM C 2015-10-24

TANK 2-BTM TANK 2-Bottom TANKBOTTOM C 2017-03-15

• Inspection Planning

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RBI Results - Inspection Plans

• TANK 1 Bottom – C-level bottom thinning inspection by early 2015. – 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.

• TANK 2 Bottom – C-level bottom thinning by March of 2017.

• TANK 1 Shell – C-level external shell inspection by fall 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 in non-intrusive.

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Results

• A request/report was written to the jurisdiction to request a variance to extend the inspection intervals

• Meeting was held with the jurisdiction to present

the results, answer questions, provide general education on API 580/581 and the API RBI methodology.

• Variance was subsequently approved

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Case Study 2 • RBI used to prioritize tank inspections and determine

level of inspection for each tank

• Tank farm in a refinery with about 25 AST in variety of services: – Slop Tanks – Fuel Oil – Diesel – Gasoline – Jet Fuel – Alkylate – Reformate – Additives

• Range of typical tank sizes and details

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RBI Results – Inspection Plan • Inspection Planning (selected examples)

Component Component Description

Thinning Inspection Category

Cracking Inspection Category

External Damage

Inspection Category

RBI Inspection

Date

TANK 1-BTM Slop Tank-Bottom A 2013-02-21

TANK 1-BTM Slop Tank-Shell C A 2021-06-07

TANK 2-BTM Slop Tank-Bottom A 2009-09-21

TANK 3-BTM Gasoline-Bottom A 2022-03-22

TANK 3-BTM Gasoline-Bottom A 2012-02-17

TANK 4-BTM Jet Fuel-Course 2 C A 2016-07-02

TANK 4-BTM Jet Fuel-Course 3 C A 2023-06-28

TANK 5-BTM Marine Diesel-Bottom A 2009-09-21

TANK 6-BTM Fuel Oil-Course 1 C A 2011-10-30

TANK 6-BTM Fuel Oil-Course 2 B 2011-12-29

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Results

• 20-plus tanks included about 170 “components”

• About 50 components (30%) had recommended inspections in the plan period (before 2025); a couple had recommendations for inspection in the short term

• About half the tanks had recommended bottom inspections (typically considered intrusive) in the plan period

• The timing and required level of inspections were

defined for these tank components – resources allocated in an effective way

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Results

• Frequently, RBI results for larger populations of equipment are presented in a Risk Matrix format – Provides a look at

multiple components relative ranking

• Matrix not done for

either of these two case studies, but as an example:

2 4

3

1 11

3

7

5

2

3

4

12 16 13 7 2

7 0.14

6

6

11

19

8

50

5

16 0.32

17 0.34

10 0.20

Unit X

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Tank RBI - Summary

• Uses of API RBI include: – Evaluating internal inspection interval variances – Prioritizing, determination of critical components – Determining needed level of inspection

• Jurisdiction/regulatory issue:

– Get early project involvement; educate, as needed – Seek examples of preferred reporting format/content

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Tank RBI - Summary • API RBI documents are undergoing revision:

– API 580 and 581 re-writes, some of this is related to tank sections

– API 653 section on inspection intervals and RBI is undergoing a review and further revision

• Continued enhancements to API RBI software: – Addition of fluid modeler used for other fixed equipment

– unlimited fluid capabilities – Level 2 consequence analyses will be available for tanks – Area (Safety) Risk will be available – API 620 allowable stresses/calculations – Settlement as a damage mechanism – Impact of annular ring and additional foundation/design

details

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35

Thank You!

Questions

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