Bridging the gap

Summary

In the process industry, it is still common that users strictly separate machine protection equipment from condition monitoring. Machine operators frequently face a time-consuming troubleshooting based on minimum diagnostic data e.g. from the DCS system. For many years, flight data recorders have been a common standard in the aviation industry to perform post-incident analyses of aircraft accidents. Such transient data recorders are also available for machinery protection systems. Captured data can be used to improve the traditional snapshot monitoring program and support cost-efficient condition monitoring purposes without waiting for an analyst to come.

Maintenance strategies and condition monitoring of machines

When operating rotating equipment, different maintenance strategies are applied. The simplest method is to run a machine until it stops due to a failure – taking the risk that a comparably small damage can cause expensive consequential damages. When wear processes in the machine are well understood and the timely progress of wear is known, wear-parts should be replaced shortly before their lifetime is reached to maximize use of the wear potential and prevent component failures (Preventive Maintenance). However, the lifetimes of components of reciprocating compressors, such as valves and bearings, are not subject to linear wear what makes it difficult to decide on the best time to replace a component mainly on operating hours. Maintenance decisions on components that are experiencing non-linear wear-out are challenging and can not be made time-based. They require monitoring of certain parameters that allow judgment on the component’s condition and an estimation of the best time to replacement. This is named Predictive Maintenance.

Which maintenance strategy is applied depends mainly on two parameters:
a) the criticality of the machine
b) the availability of a spare compressor

The total population of machines can be grouped into four main categories.
Category I Critical, unspared
Category II Critical, spared
Category III Uncritical, spared
Category IV Uncritical, unspared

Generally: the more critical a machine – the less acceptable it is to run it to failure or to rely on preventive maintenance. An unexpected failure with a machine shutdown has a negative effect on the production or safety. The availability of a standby compressor will reduce the requirement for predictive maintenance, but has no effect on the level of safety that is required.

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