Flow Induced Vibration Generated at a Tee Junction of a Large Diameter Pipe

Abstract Under certain circumstances Flow Induced Vibration (FIV) caused by turbulence around a tee junction can excite high frequency shell modes of vibration within a piping system. This can occur with acoustic excitation levels below those that may be identified with current high frequency acoustic excitation screening methods. This type of flow induced vibration has caused damage to piping systems in some operating facilities. As a practical screening method, a vibration index composed of basic process information and piping data has been proposed to evaluate the shell mode FIV. This is supported by small-scale experimental testing with a 4 inch pipe and numerical simulations previously. It was also experimentally confirmed that the pressure fluctuation, i.e. sound pressure level in a 20 inch pipe near the branch injection point can be evaluated in a wide frequency range by combining both effects of Acoustically Induced Vibration (AIV) from the noise source and FIV caused by the hydrodynamic loading related to turbulence at the tee junction. This method will be included in the upcoming 3rd edition of the Energy Institute Guidelines for the Avoidance of Vibration Induced Fatigue Failure in Process Pipework (AVIFF). This paper presents an example with supporting data of this type of flow induced vibration exciting shell modes of a large diameter pipe in an operating facility. The calculated vibration stresses at the pipe in both the original and the modified cases by the proposed evaluation methods show good agreement with those by the field measurements. Hence, the applicability of the proposed evaluation method for AIV and FIV to large-scale systems has been verified.