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

RISK-BASED INSPECTION METHODOLOGY, PART 5—SPECIAL EQUIPMENT 5-5
Online monitoring adjustment factor, F OM —Some lined components have monitoring to allow early
detection of a leak or other failure of the lining. The monitoring allows orderly shutdown of the
component before failure occurs. If on-line monitoring is used, and it is known to be effective at
detecting lining deterioration, F OM = 0.1; otherwise F OM = 1.0. Examples of monitoring systems
include thermography or heat sensitive paint (refractory linings), weep holes with detection devices
(loose alloy linings), and electrical resistance detection (glass linings).
e) STEP 1.5 – Determine t
min using one of the following methods:
1) For the API STD 620 and API STD 650 tank courses, determine the allowable stress, S , weld joint
efficiency, E , and calculate the minimum required thickness, min , using component type in Part
2, Table 4.2, geometry type in Part 2, Table 4.3 and per the original construction code or API 579-
1/ASME FFS-1 [1] or API STD 620, as applicable.
2) API STD 650 Tank bottoms can be modeled with two components. If the component type is
Tank650 TANKBOTTOM, use t min
= 0.1 in if the storage tank does not have a release prevention
barrier or t min
= 0.05 in if the storage tank has a release prevention barrier, in accordance with API
STD 653 [2]. If the component is a Tank650 TANKBOTEDGE, use the minimum thickness for an
annular ring or the critical zone (for tanks without annular rings), whichever is applicable, in
accordance with API STD 653.
3) API STD 620 Tank bottom t min
is determined by using API STD 620. If the component is a Tank620
TANKBOTEDGE, use the minimum thickness for an annular ring or the critical zone (for tanks
without annular rings), whichever is applicable, in accordance with API STD 653.
4) A specific t min
calculated by another method and documented in the asset management program
may be used at the owner-user's discretion.
f) STEP 1.6 - Determine the tank bottom component A
rt
parameter using Equation (5.2) based on t from
STEP 1, Cr,
bm from STEP 1.2, age
tk and t
rdi from STEP 1.4. Note that the age parameter in these
equations is equal to agetk
from STEP 1.4.
1) For tank courses, go to STEPs 7 through 15 in Part 2, Section 4.5.7 and skip to STEP 1.8.
2) For tank bottom components, calculate the A
rt
parameter using Equation (5.2).
A
rt
=
⎡⎛
t
−
−( C ⋅age
) ⎞
⎣⎝
⎠
rdi r,
bm tk
max ⎢⎜1 ⎟, 0.0
tmin
+ CA
g) STEP 1.7 – For tank bottom components, determine the base damage factor for thinning,
Table 4.3 and based on the
1.3.
h) STEP 1.8 – Determine the DF for thinning,
⎤
⎥
⎦
t
D
thin
fB
(5.2)
, using
A
rt parameter from STEP 1.6 and inspection effectiveness from STEP
Thin
( )
D , using Equation (5.3).
Tank , Thin
f
AST , Thin
Df = max ⎡ DfB ⋅FWD ⋅FAM ⋅FSM
, 0.1⎤
⎣
⎦
(5.3)
The adjustment factors in are determined as described below.
1) Adjustment for Welded Construction, WD
otherwise, F
WD
= 10 .
F – If the component is welded (i.e. not riveted), then F = 1;
WD