Acoustic Fatigue of a Steam Dump Pipe System Excited by Valve Noise

Abstract

The steam dump system in Gentilly Nuclear Power Plant consists of four parallel steam pipes, each of which comprises a steam control valve. Two pipes of this system experienced high-cycle fatigue damage. In-situ vibration and dynamic strain measurements were therefore conducted to identify the cause of the damage and formulate suitable counter-measures. The test results pointed to the high-frequency noise of the valve as the primary source causing the fatigue failure. By means of small-scale model tests, using a compressed air network, a new valve stem was developed, which produces a substantially lower noise level than that generated by the original valve stem. Implementing this new stem in the plant, without any other modifications in the valve body or the piping system, significantly reduced the dynamic stresses of the piping, but increased the vibration level of the valve itself. An alternative valve stem, which is a simpler version of the new design, was therefore tested and found to reduce the pipe stresses sufficiently while not increasing the level of valve vibration.