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The effects of pipe strain and flange misalignment on vibration in reciprocating compressor systems
By Ramin Rahnama, Kelly Eberle and Steven Crocker
Presented at the GMRC Gas Machinery Conference, 1 October 2018, Kansas City, MO
1. Abstract
Pipe strain and flange misalignment have been shown to lead to higher than normal vibrations in piping systems. The problem of high vibration due to pipe strain is more common on reciprocating compressor packages due to several factors such as high dynamic forces that are part of normal operation, compact design for equipment packages and improper piping assembly and installation processes.
This paper presents insights into the effects of pipe strain, measures to reduce pipe strain and case studies that show the effect of pipe strain and flange misalignment on piping vibration.
2. Introduction
Many vibration problems are the result of, or amplified by, pipe strain or flange misalignment. In some cases, the measured vibration amplitudes are double, triple or even higher when under pipe strain, compared to after relieving pipe strain. Pipe strain on the main line can intensify vibrations on small-bore attachments, which can lead to failures.
Although the effect of pipe strain on piping vibration is observed on many packages, particularly with units that are assembled on tight schedules or minimum quality control checks, this topic is rarely discussed at industry events. Howes and Maxwell (1) discussed pipe strain effects on vibrations and presented some examples in 2013. Some industry standards such as API 686 (2) and ASME B31.3 (3) include limits for pipe strain and flange misalignment. However, these limits are mainly set for increasing the reliability of the machinery, rather than reducing vibrations on the piping and attached components.
This paper summarizes the authors’ experience as well as work completed for a GMRC-funded research project (4) on this topic. This paper reviews several case studies. A theory on the reasons for higher vibrations due to excessive pipe strain is discussed. In addition, suggestions are made to reduce pipe strain in reciprocating compressor packages, and future studies are proposed.
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