Use of an Irregular Cone to Reduce Ice-Induced Vibration of a Vertical Riser Pipe

Abstract

A vertical riser pipe is often mounted on the leg of an offshore platform to transport oil and gas. However, severe ice-induced vibrations and low-cycle fatigue damage of welded joints have been observed on the outside vertical riser of a platform when ice sheets interact with the riser in the Bohai Sea. In this study, an irregular cone is first proposed and mounted on the platform to decrease ice-induced vibrations. The vibration responses and the numerical analysis of the riser are then measured and simulated, respectively. The observed data and security analysis indicate that the stress amplitude of the welded joints on the riser structure compromises the endurance limit on fatigue damage. The security of the riser structure is found to be substantially stronger after mounting the irregular cone, thus providing a reference design for outside riser structures to reduce ice-induced vibrations.