(40r) Putting Compressor Failures into Perspective for the PHA

A Process Hazard Analysis (PHA) is required to address OSHA Process Safety Management (PSM) and EPA Risk Management Program (RMP) regulations. Understanding the potential process hazard is widely recognized as a foundational element of PSM and RMP, and in addition to simply meeting regulatory requirements, can be a critical mechanism for flushing out potential vulnerabilities early in the design process for capital projects.

The consequences of many of the hazards evaluated by the PHA Team are relatively easy to characterize. However, rotating equipment consequences can be a bit more difficult to pin down. The failure mechanisms and release pathways associated with compressors can be complex, and determining the consequences (and severities) has been very reliant on “expert judgement” and operational experience. Determining the impact on a compressor associated with:

• Blocked inlet
• Blocked outlet
• Backspin

is not only dependent on compressor design characteristics, but also on process conditions:

• Temperature
• Pressure
• Process chemistry – Impacting not only the potential for and magnitude of damage, but also release quantity and phenomenology

Changes in temperature, pressure, and process composition can also result in a direct potential hazard.

When confronted with these challenges, a PHA Team will often overpredict severity, which can skew not only the PHA results, but also impact priorities for capital project investments in safety systems, mechanical integrity programs, and alarm rationalization.

This paper will review some common compressor and seal designs, correlate failure mechanisms to important elements to be reviewed in the PHA and associated consequences, correlate these consequences to industry-observed failures and frequencies, and identify safety measures that should be considered by the PHA Team for specific configurations. The objective of the paper will be to provide a better foundation for the evaluation of compressor failures in the PHA, as well as an improved basis for severity estimations (often overpredicted).

Although the focus of the paper will be on consequences (and severities), a brief overview of contemporary surge protection strategies will be provided, with a focus on their treatment as safeguards and within the mechanical integrity program.