A Full Scale Test for Acoustic Fatigue in Pipework

Abstract

Gas flow through a corrugated pipe can produce unacceptable levels of noise. The occurrence of such noise gave rise to concerns about vibration induced fatigue of small-bore subsea pipework in the Schiehallion oil field. In order to check that the subsea pipework was free from noise-induced vibration a full scale replica of the subsea equipment containing the small-bore pipework was built and tested. The test required the generation of acoustic pressures with a 1 bar amplitude and a frequency range of 80 to 800Hz. It was also necessary to arrange for resonant conditions within the pipework and for acoustic nodes and anti-nodes to be swept though a range of possible locations. The test was conducted with full-scale conditions of methane at a static pressure of 170bar and with a range of gas flow rates. Particular attention was given to achieving the correct acoustic and structural natural frequencies together with the correct acoustic and structural damping ratios. The subsea equipment was found to be vulnerable for one operating condition. This vulnerability was removed by retro-fitting a brace to the existing subsea pipework.