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

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-31
4.10.3 Consequences of Acid and Caustic Leaks
For caustics/acids that have splash type consequences, water was chosen as a representative fluid to
determine the personnel consequence area. Acid or caustic leaks do not result in a component damage
consequence. The consequence area was defined at the 180° semi-circular area covered by the liquid spray
or rainout. Modeling was performed at three pressures; 103.4 kPa, 206.8 kPa, and 413.7 kPa (15 psig, 30 psig,
and 60 psig) for four release hole sizes (see Table 4.4). Continuous liquid releases were modeled only since
instantaneous gas releases are assumed not to produce rainout. The results were analyzed to obtain a
correlation between release rate and consequence area and were divided by 5 since it is believed that serious
injuries to personnel are only likely to occur within about 20 % of the total splash area as calculated by the
above method.
The resulting consequence area for nonflammable releases of acids and caustics is calculated using Equation
(3.72) and Equation (3.73).
CA
b
,
= 0.2⋅ ax
(3.72)
CONT
inj n
INST
CA
,
= 0.0
(3.73)
inj n
The constants a and b shown in Equation (3.72), are functions of pressure and are shown in Table 4.9.
Since there are no consequences associated with an instantaneous release of acid or caustic, the
instantaneous/continuous blending factor, fact , is equal to 0.0.
IC
n
4.10.4 Blending of Results Based on Release Type
The consequence area calculations yield significantly different results depending on whether the continuous
area equations are used or the instantaneous area equations are used. The nonflammable, nontoxic personnel
injury consequence area for steam or acid leaks can be calculated for each hole size using Equation (3.74).
( )
CA = CA ⋅ fact + CA − fact
(3.74)
leak INST IC CONT IC
inj, n inj, n n inj, n
1
n
Note that there is no need to calculate a component damage area for nonflammable releases of steam or
acid/caustic.
leak
CA
,
= 0.0
(3.75)
cmd n
4.10.5 Determination of Final Nonflammable, Nontoxic Consequence Areas
The final nonflammable, nontoxic consequence areas are determined as a probability weighted average of the
individual consequence areas calculated for each release hole size. Nonflammable, nontoxic consequences
do not impact equipment so damage areas are not calculated. Probability weighting uses the generic
frequencies of the release hole sizes provided in Part 2, Table 3.1. Equation (3.76) is used to calculate the
probability weighted nonflammable, nontoxic consequence area for steam, caustic, or acid releases.
CA
nfnt
f , inj
⎛
4
leak
⎜∑
gffn
⋅CAinj,
n ⎟
n=
1
= ⎜
⎟
⎜ gfftotal
⎟
⎜
⎝
⎞
⎟
⎠
(3.76)