Oil and gas pipework located on the sea floor may sometimes suffer from vibration and possible failure due to fatigue. The vulnerable pipework is usually the small diameter (typically 2 in) pipes in manifold systems. In order to assess this pipework for vibration it is necessary to know the natural frequencies and damping which are significantly influenced by the surrounding fluid. Measurements have been made on an L-shaped pipe to determine how it is affected by the fluid. Interestingly the effect on damping is small. Consequently experiments have also been performed to see the effect of adding vanes to the pipe. This provides a non-linear form of damping. Special signal processing methods have been developed to investigate this damping effect. The paper presents values for damping for pipes with and without vanes. The effect of the vanes is to significantly increase the damping.

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