Ultrasonic
Testing NDT - Risk Based Inspections
By John Taylor
Recently I had the opportunity to attend a three day
class given by Equity Engineering Group on the American Petroleum Institute's
Recommended Practice for Risk Based Inspections (API 580 & 581).
It was a great class held in a little Louisiana town
known for great music and great food. While the petro-chemical industry is a
major user of this inspection approach, it can be utilized in the pulp and
paper, power generation and terminal storage industries as well as many others.
Since API 580/581 is based on risk based inspections the
question is: how do you define risk? Quite simply it is the probability of
failure multiplied by the consequences of failure. This analysis of risk is not
only a common definition which relates to all of us and at any age but one that
we use when making daily decisions. Do we sky-dive or play pool? It all depends
on how well prepared we are to jump out of an airplane or what the environment is
like at the bar where we shoot pool. The more you think about those choices the
more information is needed to decide on the proper course of action. So the key
to any good risk based program is information.
That was the great thing about the Equity Engineering's
course. It led you through the initial steps to develop a program that would be
appropriate for the facility and the types of equipment that was being utilized
there.
There are two references that RBI uses. The first is API
580 which gives the minimum requirements and the basic elements for
implementing an RBI program. It also details what makes up a good RBI team and
many of the problems that the team can encounter while assembling information.
API 581 is the procedure that gives the details and formulas for assessing the
condition and inspection frequencies. It assigns the probability of failure and
consequence in a logical mathematical sequence.
Top ten lessons learned about RBI:
1. The mechanism for corrosion and deterioration must be
known before an adequate RBI
program can be started. It is important that a capable corrosion specialist be
a member of the team.
2. Inspections must be designed to reduce
uncertainty. Without certainty probability becomes too elusive to measure.
Inspections alone do not reduce risk.
3. Everyone involved must understand and appreciate the
measuring systems that are designed to reflect both the area risk and the
financial risk associated with equipment failure.
4. In any RBI study, consistency is more important than
accuracy.
5. The RBI program must follow a defined working process
that will assure both consistency and reproducibility.
6. Always match the inspection technique with the damage
mechanisms that are associated with the equipment type and process. Otherwise
you may not find any defects.
7. While the probability of failure changes over time,
the consequences of failure are not controlled by time.
8. Since risk is dynamic it is vital that the RBI process
chosen can be updated easily when new information is discovered.
9. The consequence and risk results for atmospheric
storage tanks are in financial terms alone. The consequences considered are
from component damage, product loss or environmental penalties.
10. RBI can only define an acceptable
level of risk to the owner-user. A Risk Based Inspection program is a blend of
solid communication, quality information and good judgment. And good judgment
comes from experience and experience as we all know comes from bad judgment.
Just as in any of life’s adventures, mitigating risk is
all about understanding how to assess and manage the probability of
failure.
John Taylor is President of Nova Data Testing a leading
Ultrasonic Testing NDT specialist. For
all your testing needs, go to http://ultrasonictestingndt.com/
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