What is Acoustic Induced Vibration?
Acoustic induced vibration (AIV) is the high frequency acoustic excitation of a piping system as a result of gas flowing through a pressure reducing device such as a relief valve, control valve or orifice plate resulting in high noise levels being generated. These high noise levels are a function of the pressure drop across the pressure reducing device and the gas mass flow rate. These high frequencies can result in acoustic fatigue at circumferential discontinuities on the pipe wall, such as small bore connections and fabricated Tees. Acoustic Fatigue is of particular concern as it primarily effects safety related systems, such as relief and blowdown lines.
At WKC we have developed a tool that enables engineers and consultants to screen valves for AIV against the Energy Institute Guidelines (2008).
Energy Institute Guidelines
In January 2008 the Energy Institute (EI) published the ‘Guidelines for the Avoidance of Vibration Induced Fatigue in Process Pipework’.
The EI Guidelines were published to help minimise the risk of vibration induced fatigue of process piping, intended to be used by engineers with no prerequisite vibration knowledge.
The EI method generates a Likelihood of Failure (LOF) score. The LOF is a form of scoring to be used for screening purposes. It should be noted the LOF is not an absolute probability of failure nor an absolute measure of failure.
Acoustic Induced Vibration dB Screening Calculator
This tool can be used to undertake AIV screening assessments of pressure reducing devices. A pressure reducing device with a noise level below 155dB is considered safe in terms of AIV risk of failure and passes the screening assessment. However, if the calculated sound power level is above 155dB limit, a detailed analysis of this device and the downstream piping needs to be conducted