In gas piping systems exposed to pressure drops, the high frequency generated by the flow could provoke acoustic induced vibration.

Acoustic induced fatigue is a particular concern as it could lead to catastrophic failure of piping components in a significant short period of time in some cases in a matter of days, hours or minutes. The reason being that this type of excitation can generate high frequency vibration of the pipe wall which takes the form of pipe wall flexural modes, resulting in high dynamic stresses with the potential of generate fatigue at circumferential discontinuities on pipe wall.

The typical approach of the designers is to conduct the acoustic induced vibration (AIV) screening by calculating the acoustic power level at the source (PWL) as per the Energy Institute’s screening method.

Alternatively, there is a different methodology proposed by Eisinger, which is based on an acoustic induced vibration fatigue chart corresponding to the relationship between the acoustic energy parameter in terms of the downstream Mach number, pressure drop, diameter and wall thickness.

While the aforementioned screening methods can be deemed sufficient during the detailed engineering phase of the facility, practitioners are advised to bear in mind, that any anomaly detected during commissioning and start-up after construction of the piping system should be thoroughly assessed by a dedicated study, including the verification that the “as-built” matches the issued for construction documentation and the thorough analysis of vibration data, etc. collected at field.

This paper describes a case study of a piping system that during the start-up of the facility was observed with abnormal levels of noise and it was perceived with a relatively high frequency piping vibration.

The system in question was a particular concern as the AIV screening methods were circa the border line of the acceptability criteria for both the Energy Institute and Eisinger Method, this finding plus the abnormal vibration and noise at field raised the doubt of the owner of whether or not the system was at risk of having an acoustic induced fatigue failure.

Consequently, the system was thoroughly studied by collecting and analyzing vibration and strain gauges data from the field to primordially corroborate the original detailed design, and to conduct fatigue life predictions that allowed to determine that the system was not at risk of fatigue.

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