API-618 Standard requires pulsation and vibration analysis of reciprocating compressors systems to prevent the system from damages. This analysis is carried out on major piping but often small bore connections are missed out in analysis and mistakes in site fabrication add up to this problem. These small bore connections on reciprocating compressor causes serious problems due to vibrations around reciprocating compressor.
This paper describes the issues of small-bore connection on Refinery CCR Platformer Net Gas Compressors where series of failures observed on small bore connection and associated tubing. Vibration/pulsation was the major contributing factor to various failures. Contributory Reasons for failure were analysed and reasons was found due to inadequate design of piping & tubing supports, Transmittal of vibration to platforms. It was found that small bore connections for PT, volume bottle drains, TI/TW were vibrating with high vibration velocity and amplitude. Max Vibration readings were found 705 micron. The dominant peak of vibration frequency is located at 15/17 X RPM. All vibrations were low frequency vibrations (< 300 Hz).
The problem was overcome by reducing SBC length and provision of better supports, reduced span for tube and pipe supports, replacement of tubes with higher schedule carbon steel pipes, shifting of instruments to less vibration areas such as basement of compressor house etc. Various modifications explained for reduction of vibration levels. Study compares condition prior to modification and new modification proposals. Modification improved vibration levels and no further failure reported.
Study indicates that more attention is warranted for small-bore attachments both in design stage and during operation. It is recommended to remove SBCs wherever possible, redesigning them so they are less susceptible to vibrations and relocating them to areas of less base motion.