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

5-82 API RECOMMENDED PRACTICE 581
Initiating Event
Frequency
Equipment
Type
PRD DRRF
Qualifier
Overpressure
Potential
Background and
Comments
Piping or
other liquid
filled
equipment
1.0 N/A
Operating pressure or
bubble point pressure
of contained fluid at
140 °F, whichever is
larger
Assumption is made that
the probability of a leak
is 1.0 (flange leaks),
modeled as a 1 /4 in.
hole. The probability of
rupture is assumed to be
0.0. For fluids that will
not boil, since the
pressure is relieved
immediately upon
leakage, the pressure
for the consequence
calculation will be the
normal operating
pressure of the piping.
Not likely to result in
rupture, likely to cause
flange leaks/small leaks,
heated only.
If the fluid can boil due
to solar energy, the
consequence pressure
could be maintained at
the bubble point
pressure of the
contained fluid. Leak
and rupture probabilities
will be calculated as a
function of the bubble
point pressure.
1 per 100 years
(manual valve
w/admin controls)
1 per 10 years
(manual valve w/o
admin controls or
control valve
Multiply initiating
event frequency
times the number of
applicable block
valves located in
process flow path
Cold side of
heat
exchangers
1.0 N/A
Operating pressure or
bubble point pressure
of contained fluid at
the hot side fluid inlet
temperature,
whichever is larger
Added increase in
potential overpressure
with additional heat
transfer from hot side.
For liquids that do not
boil, the assumption is
made that the probability
of leakage is 1.0 (flange
leaks), modeled as a 1 /4
in. hole, and the
probability of rupture is
0.0.
If the cold side fluid can
boil, the consequence
pressure could reach the
bubble point pressure of
the stored fluid at the hot
side fluid inlet
temperature. Leak and
rupture probabilities will
be calculated as a
function of the bubble
point pressure.