Modern standards require frame sensors and more for compressor vibration monitoring
This paper reviews and discusses the machinery protection philosophy for reciprocating compressors that once was state of the art. It examines how technology, as well as applicable standards, have evolved since the 1970s. At that time many refineries were built with a large fleet of reciprocating compressors installed. This should have been the beginning of compressor vibration monitoring. For decades, reciprocating compressors did not enjoy the high-priority monitoring given to centrifugal machines. The reasons why are partially based on the higher number of centrifugal machines in comparison to reciprocating compressors. Operators just did not fear severe damages due to the lower kinetic energy of these comparably slow-running machines.
However, they show the highest number of damages while being process-critical at the same time. Although this is a crucial combination, insufficient protection and condition monitoring principles are still being applied on some reciprocating machinery.
At all times, operators, engineering procurement and construction companies (EPCs) and original equipment manufacturers (OEMs) have followed the existing, applicable guidelines and standards during the final engineering stage. Those standards were valid at the time of construction, and to a large extent are still valid today. However, upon reviewing the age of the reciprocating compressor population, one will recognize that, in many cases: These large, critical machines have never been replaced. They have been in operation since their initial startup date many decades ago, many without compressor vibration monitoring.
To understand why, even after numerous catastrophic failures, we still find inadequate machinery protection on many of these machines, a view into the history of applicable standards can help to lift the fog.
API sets standards for compressor vibration monitoring
The American Petroleum Institute (API) has always been one of the leading organizations in compiling information about available and proven monitoring technologies for critical machinery. Transforming them into standards that have become widely used as guiding standards is one of the institute’s jobs. It is remarkable that the first revision of the widely known API Standard 670 was released in 1976. It was named “Non-contacting Vibration and Axial Position Monitoring System,” a standard focused on the application of proximity sensor-based machinery monitoring. The second revision of the same standard was released in 1986.
As a consequence of evolving compressor vibration monitoring technology, API has followed up with a parallel standard covering vibration technology within the 1981-released API 678 “Accelerometer-Based Vibration Monitoring System — 1st Edition.” This was the beginning of effective reciprocating compressor vibration monitoring.
The third revision of API 670, released in 1993, was not only an extension and update of the previous API 670, but also incorporated and thereby replaced the API 678 standard focused on accelerometer-based monitoring. To better reflect its safety-relevant character, API 670 was renamed “Machine Protection Systems” in its fourth edition released in 200 and still valid today.
From its very beginning in 1976 until the current fourth edition, the API standards covering monitoring of critical machinery focused very much on the technical requirements of centrifugal equipment (e.g., gas and steam turbines, centrifugal compressors). These require monitoring axial and radial shaft positions, speed an surge along with bearing and frame vibration.
Until 200/2008, when the API 670 fifth edition task force was formed, reciprocating compressors had never been in focus within API 670. The API 670 fifth edition, released in November 2014, offers valuable information and guidance on how to effectively protect reciprocating compressors.
Users and machinery protection system vendors have agreed upon the inclusion of applying crosshead acceleration as a safety shutdown parameter, which is a pivotal decision.
While the machine-specific standards (such as API 610, API 611, API 612, API 613, API 6161, API 617 and API 618) mainly deal with the aspects of machinery design, installation, performance and support systems, limited guidance for monitoring and safeguarding is offered. API 670 increasingly developed to become the central document of all aspects for machinery protection in one concise standard along with useful appendices, covering machinery with special needs like reciprocating compressors.
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