It is important to carefully consider safety, reliability, maintainability, environmental impact and financial losses that can result from unplanned equipment outages due to faulty instrumentation (spurious trips) of Centrifugal Gas Compressors during its operation. It is all the more significant to consider the above aspects specifically during the design phase of compressor systems. Spurious tripping of equipment contribute to the production loss, risk to operations and also impacts the carbon footprint due to unwanted flaring. Optimizing the trip voting logic can reduce such spurious trips and increases the availability/integrity of equipment.

This paper provides guidance to rotating equipment/instrumentation engineers to review the existing trip voting logic for radial bearings vibrations of Centrifugal Gas Compressors and explores the possibility of implementing the 2004 voting logic considering both ends of the shaft.

The study highlights the benefit of adopting 2004 voting logic over other voting logics such as 1002 and 2002 for Centrifugal Compressor radial bearing vibrations to minimize the unwanted trips.

2004 voting logic is defined as follows:

If either end of the machine experiences high radial vibration and one of the X or Y probe reaches the trip level, and at the same time, if any other end also recognizes this increase in vibration level and crosses alarm limit of the machine, then it is a vote to trip. If only one of the four probes on the machine shows a high level or high-high level, it can be attributed typically to probe malfunction, and should not actuate a machine trip.

A study to optimize the voting logic was conducted to improve the machine reliability and availability by reducing unwanted trips due to malfunctioning of instruments. The study methodology includes:

  1. Evaluation of various industry options and generally proposed Centrifugal Compressor OEMs recommendations and guidelines in API-670.

  2. Historical data analysis of operating equipment.

  3. Comparison of advantages and disadvantages of the proposed logic (2oo4) over other voting logics i.e. 1oo2, 2oo2.

  4. Risk assessement and risk reduction performed by SIL evaluation for these Safety Integrity Functions (SIFs).

Keywords:
centrifugal compressor radial vibration trip, shutdown, machinery protection rack, compressors engines and turbines, instrument, Probe, availability, vibration, radial bearing vibration, orbit
Subjects:
Processing Systems and Design, Safety, Compressors, engines and turbines
Copyright 2018, Society of Petroleum Engineers
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