API RP 581 - 3rd Ed.2016 - Add.2-2020 - Risk-Based Inspection Methodology
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API RP 581 - 3rd Ed.2016 - Add.2-2020 - Risk-Based Inspection Methodology

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5-12 API RECOMMENDED PRACTICE 581g) STEP 6.7 – Calculate the total barrels of fluid within the dike from a rupture,of fluid in the on-site surface soil that,Bbl −rupturess offsiteBbl −rupturess onsite, and the total barrels of fluid that reach water,Equation (5.29), respectively.Bbl⎛ P ⎞= Bblrelease⎜1−⎟⎝ 100 ⎠rupture rupture lvdikeindikeruptureBbl , the total barrelsindike, the total barrels of fluid in the off-site surface soil that,Bblleakwater, using Equation (5.26) through(5.26)rupture Ponsiterupture ruptureBblss− onsite= ( Bblrelease − Bblindike)(5.27)100Prupture offsite rupture rupture ruptureBblss−offsite = ( Bblrelease −Bblindike − Bblss−onsite)(5.28)100( −− )Bbl = Bbl − Bbl + Bbl + Bbl(5.29)rupture rupture rupture rupture rupturewater release indike ss onsite ss offsiteh) STEP 6.8 – Calculate the financial environmental cost for a course rupture,ruptureFC .environFC = Bbl ⋅ C + Bbl ⋅ C + Bbl ⋅ C + Bbl ⋅ C (5.30)rupture rupture rupture rupture ruptureenviron indike indike ss−onsite ss−onite ss−offsite ss−offite water wateri) STEP 6.9 – Calculate the total financial environmental cost from a leak and a rupture, FCenvironleakFC is from STEP 12.5 andenvironleakruptureenviron environ environruptureFC is from STEP 12.8.environ, whereFC = FC + FC(5.31)j) STEP 6.10 – Calculate the total financial COF, FCtotal , using Equation (5.32).FCtotal = FCenviron + FCcmd + FCprod+ FCaffa + FC(5.32)injConsequence of Failure Methodology for Storage Tank BottomsThe COF associated with storage tanks is concerned primarily with the financial losses due to loss ofcontainment and leakage through the storage tank bottoms. Safety/area based consequences are notcalculated for storage tank bottoms Detailed procedures for calculating the financial COF for bottom platesare provided in this section.The procedure for determining the COF for storage tank bottom components consists of calculations forfinancial COF based on environmental consequences, component damage cost and business interruptioncost. storage tank consequence analysis for flammable and/or explosive or toxic are not calculated forstorage tank bottoms.Required Properties at Storage ConditionsThe tank bottom financial COF is calculated using one of the following approaches:⎯ Select the representative fluid from Table 4.5 that most closely matches the stored fluid⎯ Determine the dynamic viscosity and density of the stored fluidHydraulic Conductivity for Storage Tank BottomThe amount of and rate of leakage from storage tank bottoms is dependent on the type of soil and itsproperties as well as whether or not the storage tank bottom has a release prevention barrier (RBP). A list ofsoil types and properties used in the storage tank consequence analysis routine is shown in Table 4.7.

RISK-BASED INSPECTION METHODOLOGY, PART 5—SPECIAL EQUIPMENT 5-13The fundamental soil property required in the analysis is the soil hydraulic conductivity, kh. The hydraulicconductivity as a function of soil type is provided in Table 4.7 based on water. The hydraulic conductivity forother fluids can be estimated based on the hydraulic conductivity, density, and dynamic viscosity of water,denoted as k , ρh,water w, and µw, respectively, and the density and dynamic viscosity of the actual fluidusing Equation (5.33).l wh, prod= kh,water ⎜ ⎟⎜ ⎟ρwµlk⎛ ρ ⎞⎛ µ ⎞⎝ ⎠⎝ ⎠Fluid Seepage Velocity for Storage Tank Bottom(5.33)The seepage velocity of the fluid in the storage tank bottom or product through the soil is given by Equation(5.34) where khis the soil hydraulic conductivity and psis the soil porosity.vels,prodkh,prod= (5.34)psCalculation of Fluid Seepage Velocity for Storage Tank Bottom1) STEP 7.1 – Determine properties including density, ρl, and dynamic viscosity, µl, of the stored fluid. If aLevel 1 analysis is being performed, select the representative fluid properties from Table 4.5.2) STEP 7.2 – Calculate the hydraulic conductivity for water by averaging the upper and lower boundhydraulic conductivities provided in Table 4.7 for the soil type selected using Equation (5.35).kh, water 31( kh, water−lb+ kh,water−ub)= C(5.35)23) STEP 7.3 – Calculate the fluid hydraulic conductivity, k , for the fluid stored in the storage tank usingh,prodEquation (5.33) based on the density,conductivity for water, k , from STEP 7.2.h,waterρl, and dynamic viscosity,µl, from STEP 7.1 and the hydraulic4) STEP 7.4 – Calculate the product seepage velocity, vel , for the fluid stored in the storage tanks,produsing Equation (5.34) based on fluid hydraulic conductivity, k , from STEP 7.3 and the soil porosityh,prodprovided in Table 4.7.Release Hole Size SelectionA discrete set of release events or release hole sizes are used for consequence analysis as outlined in Table4.8.Calculation of Release Hole SizesThe following procedure may be used to determine the release hole size and the associated generic failurefrequencies.a) STEP 8.1 – Determine the release hole size, dn, from Table 4.8 for storage tank bottoms.b) STEP 8.2 – Determine the generic failure frequency, gffn, for the dnrelease hole size and the totalgeneric failure frequency from Part 2, Table 3.1 or from Equation (5.36).gfftot4= ∑ gff(5.36)n=1n

5-12 API RECOMMENDED PRACTICE 581

g) STEP 6.7 – Calculate the total barrels of fluid within the dike from a rupture,

of fluid in the on-site surface soil that,

Bbl −

rupture

ss offsite

Bbl −

rupture

ss onsite

, and the total barrels of fluid that reach water,

Equation (5.29), respectively.

Bbl

⎛ P ⎞

= Bblrelease

⎜1−

⎟

⎝ 100 ⎠

rupture rupture lvdike

indike

rupture

Bbl , the total barrels

indike

, the total barrels of fluid in the off-site surface soil that,

Bbl

leak

water

, using Equation (5.26) through

(5.26)

rupture Ponsite

rupture rupture

Bblss− onsite

= ( Bblrelease − Bblindike

)

(5.27)

100

P

rupture offsite rupture rupture rupture

Bblss−offsite = ( Bblrelease −Bblindike − Bblss−onsite

)

(5.28)

100

( −

− )

Bbl = Bbl − Bbl + Bbl + Bbl

(5.29)

rupture rupture rupture rupture rupture

water release indike ss onsite ss offsite

h) STEP 6.8 – Calculate the financial environmental cost for a course rupture,

rupture

FC .

environ

FC = Bbl ⋅ C + Bbl ⋅ C + Bbl ⋅ C + Bbl ⋅ C (5.30)

rupture rupture rupture rupture rupture

environ indike indike ss−onsite ss−onite ss−offsite ss−offite water water

i) STEP 6.9 – Calculate the total financial environmental cost from a leak and a rupture, FC

environ

leak

FC is from STEP 12.5 and

environ

leak

rupture

environ environ environ

rupture

FC is from STEP 12.8.

environ

, where

FC = FC + FC

(5.31)

j) STEP 6.10 – Calculate the total financial COF, FC

total , using Equation (5.32).

FCtotal = FCenviron + FCcmd + FC

prod

+ FCaffa + FC

(5.32)

inj

Consequence of Failure Methodology for Storage Tank Bottoms

The COF associated with storage tanks is concerned primarily with the financial losses due to loss of

containment and leakage through the storage tank bottoms. Safety/area based consequences are not

calculated for storage tank bottoms Detailed procedures for calculating the financial COF for bottom plates

are provided in this section.

The procedure for determining the COF for storage tank bottom components consists of calculations for

financial COF based on environmental consequences, component damage cost and business interruption

cost. storage tank consequence analysis for flammable and/or explosive or toxic are not calculated for

storage tank bottoms.

Required Properties at Storage Conditions

The tank bottom financial COF is calculated using one of the following approaches:

⎯ Select the representative fluid from Table 4.5 that most closely matches the stored fluid

⎯ Determine the dynamic viscosity and density of the stored fluid

Hydraulic Conductivity for Storage Tank Bottom

The amount of and rate of leakage from storage tank bottoms is dependent on the type of soil and its

properties as well as whether or not the storage tank bottom has a release prevention barrier (RBP). A list of

soil types and properties used in the storage tank consequence analysis routine is shown in Table 4.7.

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