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

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-109
pnfnt
n
=
psafe
n
5.10.6 Determination of Final Nonflammable, Nontoxic Consequence Areas
For each hole size, the component damage and personnel injury consequence area for each of the
nonflammable, nontoxic events can be added up and probability weighted using Equation (3.198) and Equation
(3.199).
( )
CA = pnfnt ⋅ max CA , CA
(3.198)
nfnt pexp bleve
f , cmd , n f , cmd,n f , cmd , n
( )
CA = pnfnt ⋅ max CA , CA , CA
(3.199)
nfnt pexp bleve leak
f , inj, n f , inj,n f , inj, n f , inj,
n
The final nonflammable, nontoxic consequence areas are determined as a probability weighted average of the
individual consequence areas calculated for each release hole size. The probability weighting uses the generic
frequencies of the release hole sizes as provided in Part 2, Table 3.1. Equation (3.200) and Equation (3.201)
are used to calculate the final probability weighted nonflammable, nontoxic consequence areas.
CA
nfnt
f , cmd
⎛
4
nfnt
⎜∑
gffn
⋅CAf , cmd , n ⎟
n=
1
= ⎜
⎟
⎜ gfftotal
⎟
⎜
⎝
⎞
⎟
⎠
(3.200)
CA
nfnt
f , inj
⎛
4
nfnt
⎜∑
gffn
⋅CAf , inj,
n ⎟
n=
1
= ⎜
⎟
⎜ gfftotal
⎟
⎜
⎝
⎞
⎟
⎠
(3.201)
5.10.7 Calculation of Nonflammable, Nontoxic Consequence Areas
leak
a) STEP 10.1—For each hole size, calculate the personnel injury areas for steam and acid leaks, CA ,
f , inj,
n
as is detailed in STEPs 10.1 through 10.3 of Section 4.10.6.
b) STEP 10.2—For the rupture case, calculate the component damage consequence area, CA
,
the personnel injury consequence area, CA
,
pexp
f inj
, of a physical explosion.
pexp
f cmd
, and
1) Calculate the stored vapor volume, V
s
, of the equipment component being evaluated.
2) Determine the amount of potential energy in the stored vapor expressed as an equivalent amount of
TNT, W , using Equation (3.204).
TNT
3) An overpressure limit of 34.5 kPa (5.0 psi) is used for component damage consequence area. This
pexp
overpressure limit is used to determine the safe distance, xs , from the explosion using the
cmd
following four-step iterative procedure.
i) Guess at an acceptable component damage distance from the physical explosion,
pexp
xs .
cmd