Risk Based Inspection
By Stephen J. Gliebe
Is Risk Based Inspection (RBI) for You?
Are you looking to improve reliability and possibly reduce the cost
associated with fixed equipment inspection and maintenance? A risk based
inspection approach may be what you need.
A well designed RBI program can:
- Provide strategies to achieve desired level of mechanical
integrity and reliability
- Reduce downtime - increase availability
- Lower risk
- Optimize inspection and maintenance costs
- Focus resources on areas that make the most sense
- Provide the basis for future inspection and maintenance budgets
There are three primary types of RBI methodologies described in API RP
580, Risk Based Inspection:
- Qualitative RBI uses data based on descriptive information using
engineering judgment and experience as the basis for the analysis of
probability and consequence of failure.
- Quantitative RBI integrates relevant information such as facility
design, operating practices and operating history into a uniform
methodology. It is a much more in depth analysis than a qualitative
assessment. It is also a much more data intensive, time consuming and
- Semi-Quantitative RBI incorporates aspects from both the
qualitative and quantitative approaches.
Getting Started - The Qualitative Approach
While all three methodologies may ultimately be applied in your
facility, a qualitative assessment may be all that is needed. The
following example illustrates the use of a qualitative analysis.
- Facility maintenance cost reductions were desired by management
since they felt their historical costs were significantly higher than
they should have been.
- RBI was identified as a methodology to achieve the cost reduction
objective in the inspection and maintenance areas.
- Based on plant experience, 15% of the vessels in a unit were
selected as having the highest probability of achieving cost savings.
- A qualitative RBI assessment was performed.
- Inspection plans were developed for each piece of equipment.
- Internal inspection intervals were extended for half of the
equipment evaluated. This resulted in an estimated
15% annual reduction in fixed equipment
maintenance costs while still maintaining the required plant
reliability. Put another way, the estimated
savings were approximately 10 times the engineering costs to do the
study, which was completed in approximately six weeks elapsed time.
There is certainly a place for all three approaches to RBI, and there
are various methodologies used for each of them. But many plants can
achieve most, if not all, of their goals using a qualitative approach.