API RBI Tank Case Study 1

API RBI Tank Case Study

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

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Introduction • RBI provisions added to API 653 in Second Edition late 1990s Edition, • Significant changes to the Tank Module in version 8 release,, 2007 • Future improvements planned to the module

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General RBI Information • In general, risk is calculated as a function of time as follows

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 R (t ) = POF (t ) ⋅ FC

for Area − Based Risk for Financial − Based Risk

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Probability of Failure • The probability of failure used in API RBI is:

POF ( t ) = gff ⋅ D f ( t ) ⋅ FMS where : POF ( t ) gff

− the probability of failure as a function of time

− generic failure frequency

D f ( t ) − damage d factor f t as a function f ti off time ti FMS

− 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 • Consequences from component damage, product loss and environmental costs are considered • Tank T kM Modeling d li • 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

Tank

6 Surface Water

Offsite

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2 Onsite Subsurface Soil

4 Ground Water

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Atmospheric Storage Tank RBI • 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

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 56.187

9 600E 4 9.600E-4

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Atmospheric Storage Tank 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-6

3 94E 7 3.94E-7

0 41 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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Atmospheric Storage Tank RBI • 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 height) – Tank rupture assumes all product in the tank is lost – 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 a Financial Risk Target

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Atmospheric Storage Tank RBI • Financial environmental cost from shell course leakage leak FCenviron

leak ⎛ Bblindike ⎞ ⋅ Cindike + Bblssleak − onsite ⋅ Css − onite + =⎜ ⎟ leak ⎜ Bbl leak ⋅ C ⎟ + Bbl ⋅ C ss − offsite ss − offite water water ⎝ ⎠

• Financial environmental cost for a shell course rupture rupture p FCenviron

rupture ⎛ Bblindike ⎞ ⋅ Cindike + Bblssrupture − onsite ⋅ Css − onite + =⎜ ⎟ rupture ⎜ Bbl rupture ⋅ C ⎟ ss − offsite ss − offite + Bblwater ⋅ Cwater ⎝ ⎠

• Total financial environmental cost for shell courses leak rupture FCenviron = FCenviron + FCenviron

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Atmospheric Storage Tank RBI • Component damage cost for shell courses

FCcmd

⎛ 4 ⎜ ∑ gff n ⋅ holecostn = ⎜ n =1 gfftotal ⎜ ⎜ ⎝

⎞ ⎟ ⎟ ⋅ matcost ⎟ ⎟ ⎠

• Outage Days and the cost of business interruption

FC prod = ( Outagecmd + Outageaffa ) ( prodcost ) • Financial Consequence for shell courses

FCtotal + FCcmdd + FC prodd t t l = FCenviron i • The above consequence calculation is for the tank shell courses, a similar consequence calculation is used for th tank the t k floor fl 12

Case Study Background • Refinery is located near, IA • The refinery wanted to use RBI to defer the inspections on two AST. • Local regulators are pushing for internal inspections on these 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 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 Installed in 1956, floor replaced in 1992 30’ diameter, 40’ tall 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 diameter, 48’ tall ll 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 •

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When a risk target is exceeded in API RBI, an inspection is generated to reduce uncertainty Fixed equipment primarily uses an Area Risk Target g – Many case studies – 27-40 ft2/yr target from experience

•

Tank RBI uses a Financial risk target – No well defined case studies for Tank RBI Risk Targets – 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? 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 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-Course 3

COURSE-2

0

-

T-143-Course 4

COURSE-3

0

-

T 143 C T-143-Course 4

COURSE 4 COURSE-4

0

-

T-143-Pressure Vessel

DRUM

0

-

T-173-BTM

TANKBOTTOM

-

11.0

T-173-Course 1

COURSE-1

0

-

T-173-Course 2

COURSE-2

0

-

T-173-Course 3

COURSE-3

0

-

T-173-Course 4

COURSE-4

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 T-143-Course

COURSE 1 COURSE-1

Mineral Wool

Marine

84 8.4

T-143-Course 2

COURSE-2

Mineral Wool

Marine

8.4

T-143-Course 3

COURSE-3

Mineral Wool

Marine

8.4

T-143-Course 4

COURSE-4

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-Course 2

COURSE-2

Fiberglass

Marine

10.9

T-173-Course 3

COURSE-3

Fiberglass

Marine

10.9

T-173-Course 4

COURSE-4

Fiberglass

Marine

10.9

T-173-Course 5

COURSE-5

Fiberglass

Marine

10.9

T-173-Presusre Vessel

DRUM

Fiberglass

Marine

8.4

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RBI Results • Inspection Planning Component Description

Component Type

Thinning Inspection Category

T-143-BTM

T-143-Bottom

TANKBOTTOM

C

T-143-Pressure Vessel

T-143-Shell

DRUM

T-173-BTM

T-173-Bottom

TANKBOTTOM

Component

Cracking Inspection Category

External Damage Inspection Category

2015-02-01

C

C

RBI Inspection Date

2015-10-24

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

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T-17 Bottom – C-level bottom thinning by March of 2017. – S Scanning i off 5 tto 10+% off the th floor fl plates l t while hil supplementing l ti scanning i near the shell and the floor – 100% visual inspection of the floor – Scanning should progressively increase if damage is found.

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T-1 T 1 Pressure P Vessel V l – Modeled M d l d as a pressure vessel, l C C-level l l external t l 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.

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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 g 11.0 mpy py corrosion rate – The calculated bottom thickness at this date using is 0.056” which is above the minimum thickness of 0.05” for tanks with leak detection as prescribed in API 653.

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T-1 Pressure Vessel – Estimated external corrosion rate of 8.4 mpy py – 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 deferral • Found a few bugs in the software – Volume display – Course height changes

• Suggestions for future improvements – Change location of some inputs • Operating height • Specific Gravity • Release and foundation settings

– Make course height component specific – Fluids • Adding more fluids • Using g Level 2 modeler

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