Vibration of a curved subsea pipeline due to internal slug flow

Abstract

Subsea oil and gas pipelines undergo vibration due to "slug" flow within the internal fluid contents of the pipeline. This slug flow is generated by the differences in density of the internal fluid. It acts as a traversing force along the length of the pipeline and causes structural vibration of unsupported pipeline spans. The resulting vibration of the pipeline may cause high cycle fatigue due to these fluctuating forces. Previous modelling of a moving slug within pipelines has been undertaken for straight pipe span sections. As unsupported pipeline spans are often curved, understanding the impact this curvature has on the traversing fluid load is important. This paper presents a Finite Element model to investigate the effect pipeline curvature has on the slug flow induced forces, resulting in vibration and hence possible fatigue damage to the pipeline structure. Furthermore, the paper presents a technique for using commercial finite element packages for analysing the dynamic response of curved beams to time variant moving loads.