Non-destructive testing and assessment of dynamic incompatibility between third-party piping and drain valve systems: an industrial case study

This paper presents the outcome of an industrial case study that involved condition monitoring of piping system that showed signs of excess fatigue due to flow-induced vibration. Due to operational requirements, a novel non-destructive assessment stratagem was adopted using different vibration analysis techniques - such as experimental modal analysis and operating deflection shapes - and complemented by visual inspection. Modal analysis carried out near a drain valve showed a dynamic weakness problem (several high-frequency flow-induced vibration frequency peaks), hence condition-based monitoring was used. This could easily be linked to design problem associated with the dynamic incompatibility due to dissimilar stiffness between two third-party supplied pipe and valve systems. It was concluded that this is the main cause for these problem types especially when systems are supplied by third parties, but assembled locally, a major cause of dynamic incompatibility. It is the local assembler's responsibility to develop skills and expertise needed to sustain the operation of these plants. This paper shows the technique used as result of one such initiative. Since high amplitude, low-frequency displacement can cause low cycle fatigue, attention must be paid to ensure flow remains as steady state as possible. The ability to assess the level of design incompatibility and the level of modification required using non-destructive testing is vital if these systems are to work continuously.