Chemical Engineering May 2016 - 68

PHA/HAZOP/QRA
(quantitative risk assessment)
RBI
Extreme
High
RCM
Med high
Med
Med low
Low
Negligible
Likelihood of failure (failure rate)
Figure 1. This graphical " consequence-of-failure " risk matrix shows the areas covered by process hazard
analysis (PHA), risk-based inspection (RBI) and reliability centered maintenance (RCM)
risk in a facility so that appropriate
and targeted mitigation actions can
be taken at the right time. that being
said, there are three common risk
identification and mitigation frameworks
that are currently being used
in process facilities today. these include
process hazard analysis (pha),
risk-based inspection (Rbi), and reliability-centered
maintenance (Rcm).
let's briefly characterize each.
PHA. the pha came out of osha's
psm standard and is one of the 14
elements listed above. every five
years, subject matter experts come
together for a couple of weeks and
identify the major events that could
happen at different " nodes " in a unit.
the general idea is to use guidewords
to systematically focus the
team on the identification of process
deviations that can lead to undesirable
consequences, the risk ranking
of those deviations, and the assignment
of actions to either lower the
probability of those failures or the
consequence if the failures do occur.
while a pha would not identify maintenance
strategies or detailed corrosion
mitigation or identification strategies,
it focuses on safety and not unit
reliability. in the end, the major deliverable
is a set of actions that have to
be closed out to ensure compliance
with the psm standard. typically, this
process is owned and facilitated by
the psm manager or department.
RBI. Rbi arose from an industry
study in the 1990s that produced
api (american petroleum institute)
580 and 581, which describe a systematic
risk identification and mitigation
framework that focuses only on
loss of containment. For this reason,
when an equipment item or piping
segment (typically called " piping
circuit " ) is evaluated, the only failure
that is of concern to the facility is the
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67
Consequence of failure

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Chemical Engineering May 2016

Table of Contents for the Digital Edition of Chemical Engineering May 2016