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

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RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-97CAflamf , cmd⎛4flam⎜∑gffn⋅CAf , cmd , n ⎟n=1= ⎜⎟⎜ gfftotal⎟⎜⎝⎞⎟⎠(3.178)The equation for probability weighting of the personnel injury consequence areas is given by Equation (3.179).CAflamf , inj⎛4flam⎜∑gffn⋅CAf , inj,n ⎟n=1= ⎜⎟⎜ gfftotal⎟⎜⎝⎞⎟⎠(3.179)In Equation (3.178) and Equation (3.179), the total GFF is as calculated in STEP 2.2.5.8.9 Calculation of Flammable Consequence Areasa) STEP 8.1—Determine the mass fraction of the release rate that contains a flammable component,flammfrac . This can be determined by adding the mass fractions of all flammable components in themixture.b) STEP 8.2—For each hole size, calculate the flammable release rate, rateflamn, using Equation (3.106). Alsoflamflamcalculate the liquid portion, rate , and the vapor portion,ln ,rate , of the flammable release rate usingvn ,Equation (3.107) and/or Equation (3.108), as applicable. Note that for two-phase releases both valuesshould be calculated.c) STEP 8.3—For each hole size, select the appropriate event tree using Figure 5.2 and Figure 5.3 and thephase of the fluid after flashing to atmosphere in STEP 1.3. For the leak cases (small, medium, and largehole sizes), use Figure 5.2. For the rupture case, use Figure 5.3.d) STEP 8.4—For each hole size, including the rupture case, calculate the probability of ignition of therelease.1) Determine the probability of ignition at ambient temperature for the liquid portion of the release,ambflampoiln,, using Equation (3.109) and the value of rate obtained in STEP 8.2. Note that for theln ,rupture case or some of the larger hole sizes a maximum value of 25.2 kg/s (55.6 lb/s) should be used.2) Determine the probability of ignition at ambient temperature for the vapor portion of the release,ambflampoivn,, using Equation (3.110) and the value of rate obtained in STEP 8.2. Note that for thevn ,rupture case and some of the larger hole sizes, a maximum value of 25.2 kg/s (55.6 lb/s) should beused.3) Determine the maximum probability of ignition for the liquid,using Equation (3.111) and Equation (3.112).aitpoi , and the vapor,laitpoi , at the AITv4) Calculate the probability of ignition for the liquid, poi , and the vapor,ln ,poi,temperatures using Equation (3.113) and Equation (3.114), respectively.vn, at normal storage5) For two-phase releases, calculate the probability of ignition, poi , at normal storage temperatures2,nusing Equation (3.115).

3-98 API RECOMMENDED PRACTICE 581e) STEP 8.5—For each hole size, determine the probability of immediate ignition given ignition.1) Obtain the probabilities of immediate ignition at ambient conditions for the liquid portion and the vaporambambpoii,portions of the release, lnpoii,and vn, from Table 5.3, based on whether the release is aninstantaneous or continuous liquid or vapor release.2) Calculate the probability of immediate ignition given ignition at storage conditions for the liquid portionpoii,of the release, lnpoii,, and the vapor portion of the release, vn, using Equation (3.128) andaitEquation (3.129). Use a value for the probability of immediate ignition at the AIT,poii=1.0.poii2,n3) For two-phase releases, calculate the probability of immediate ignition given ignition,normal storage temperatures using Equation (3.118) and the flash fraction,STEP 1.3.f) STEP 8.6—Determine the probability of VCE given a delayed ignition., atfracfsh, calculated in1) Determine the probability of VCE given delayed ignition, pvcedi , from Table 5.3 as a function of therelease type and phase of release. The probability of a VCE given delayed ignition for a liquid releaseis pvcedi ; for a vapor it isln ,pvcedi .vn ,2) For two-phase releases, calculate the probability of VCE, given delayed ignition, pvcedi2,nEquation (3.119) and the flash fraction,frac calculated in STEP 1.3.fshg) STEP 8.7—Determine the probability of flash fire given delayed ignition., using1) Determine the probability of flash fire given delayed ignition, pffdi , from Table 5.3 as a function ofthe release type and phase of release. Alternatively, Equation (3.120) and Equation (3.121) can beused to obtain these values.2) For two-phase releases, calculate the probability of flash fire given delayed ignition, pffdi2,nEquation (3.122) and the flash fraction,frac calculated in STEP 1.3.fsh, usingh) STEP 8.8—Determine the probability of a fireball given an immediate release, pfbii , using Equation(3.123) or Equation (3.124).i) STEP 8.9—Select the appropriate event tree. For small, medium, and large hole sizes, select the eventtree from Figure 5.3 based on whether the release is a liquid, vapor, or two-phase release. For the rupturecase, select the event tree from Figure 5.4 based on whether the release is a liquid, vapor, or two-phaserelease.j) STEP 8.10—For each hole size, determine the probability of each of the possible event outcomes on theevent tree selected in STEP 8.9. As an example, the probability of each of the event outcomes for leakageof a vapor from a small, medium, or large hole size is shown below. All other event tree outcomes can becalculated in a similar manner.1) Probability of a pool fire given a release:ppoolvn ,= 0.0(3.180)

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-97

CA

flam

f , cmd

4

flam

⎜∑

gffn

⋅CAf , cmd , n ⎟

n=

1

= ⎜

⎜ gfftotal

(3.178)

The equation for probability weighting of the personnel injury consequence areas is given by Equation (3.179).

CA

flam

f , inj

4

flam

⎜∑

gffn

⋅CAf , inj,

n ⎟

n=

1

= ⎜

⎜ gfftotal

(3.179)

In Equation (3.178) and Equation (3.179), the total GFF is as calculated in STEP 2.2.

5.8.9 Calculation of Flammable Consequence Areas

a) STEP 8.1—Determine the mass fraction of the release rate that contains a flammable component,

flam

mfrac . This can be determined by adding the mass fractions of all flammable components in the

mixture.

b) STEP 8.2—For each hole size, calculate the flammable release rate, rate

flam

n

, using Equation (3.106). Also

flam

flam

calculate the liquid portion, rate , and the vapor portion,

ln ,

rate , of the flammable release rate using

vn ,

Equation (3.107) and/or Equation (3.108), as applicable. Note that for two-phase releases both values

should be calculated.

c) STEP 8.3—For each hole size, select the appropriate event tree using Figure 5.2 and Figure 5.3 and the

phase of the fluid after flashing to atmosphere in STEP 1.3. For the leak cases (small, medium, and large

hole sizes), use Figure 5.2. For the rupture case, use Figure 5.3.

d) STEP 8.4—For each hole size, including the rupture case, calculate the probability of ignition of the

release.

1) Determine the probability of ignition at ambient temperature for the liquid portion of the release,

amb

flam

poiln

,

, using Equation (3.109) and the value of rate obtained in STEP 8.2. Note that for the

ln ,

rupture case or some of the larger hole sizes a maximum value of 25.2 kg/s (55.6 lb/s) should be used.

2) Determine the probability of ignition at ambient temperature for the vapor portion of the release,

amb

flam

poivn

,

, using Equation (3.110) and the value of rate obtained in STEP 8.2. Note that for the

vn ,

rupture case and some of the larger hole sizes, a maximum value of 25.2 kg/s (55.6 lb/s) should be

used.

3) Determine the maximum probability of ignition for the liquid,

using Equation (3.111) and Equation (3.112).

ait

poi , and the vapor,

l

ait

poi , at the AIT

v

4) Calculate the probability of ignition for the liquid, poi , and the vapor,

ln ,

poi

,

temperatures using Equation (3.113) and Equation (3.114), respectively.

vn

, at normal storage

5) For two-phase releases, calculate the probability of ignition, poi , at normal storage temperatures

2,n

using Equation (3.115).

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