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These were published internally as an on-line database. This database also had all the other reliability data relating to e.g., PRVs, ESD valves, fire and gas detectors, deluge valves, etc. These were used for RCM studies, Quantitative Risk Analysis, etc.


Maintainers are generally very good at collecting data. We use sophisticated CMMS to record the history, using failure and repair codes to speed up analysis. We also collect calibration data from tests on protective instrument loops, relief valve bench tests, trip tests, etc. Do we use this vast pile of data effectively?

We can compute important site-specific failure data that we can use to adjust our maintenance strategies to improve safety levels and cost performance. There are hurdles to cross, but these are within our reach.

Using our own data is better than using published data from others. Knowing the MTBFs, we can reset the test frequencies logically (see pages 163 to 172 in Reference i).


Degradation depends on the original design and build-quality as well as the way we operate and maintain the equipment. Hence the operational reliability of seemingly identical equipment varies from plant to plant. Maintenance strategies should be based on the physical degradation mechanism, the rate at which it occurs, and the consequence of failure. This policy will help minimize operational risks—to safety, environment, and profitability.

The rate of degradation can be defined accurately with reliability parameters. In order to be meaningful, one should as far as possible compute these parameters using one's own operating context. The use of generic databases is sometimes necessary, but we must be conscious of the possible sources of error.


i. Narayan, V. 2004. Effective Maintenance Management: Risk and Reliability, Strategies for Optimizing Performance. New York:

Industrial Press. ISBN 0-8311-3178-0

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