FATIGUE ANALYSIS DUE TO MULTI-SPANNING SUBSEA PIPELINES IN IRANIAN SOUTH PARS GAS FIELD

The subsea Pipelines plays an important role in the offshore industries which is usually installed to transport the production from subsea wells to pipeline end manifold(PLEM) or export production from the offshore facilities to the onshore terminations. There are some methods to decrease the span length such as change route,or adjust wall thickness or grade of material. Lower spans by using man-made supports may reduce VIV fatigue damage but encountering harsh climate is unavoidable forsome cases and free spans may occur [[1] [2] ]. Subsea pipeline free spans are mainly triggered by seabed unevenness/scouring or artificial supports/rock beams, etc. The vortex shedding frequency caused by a flow normal to a free span is governed by the pipeline outer diameter, the current velocity and the Strouhal’s number. Once the shedding frequency reaches the natural frequency of a span then it starts to vibrate and VIV occur. So free span analysis has an ineligible effect on the design of subsea pipeline[3] . In this paper, the main objective is to present a procedure for the multi-spans fatigue assessment of existing submarine pipeline in Iran South Pars Gas Fieldby using the DNV-RP-F105 and ABAQUS software.