Review of Subsea Pipeline for Minimizing Thermal and Pressure Expansion

Abstract

As the offshore oil and gas fields have been exploited in deeper water, subsea pipelines are required to operate at high temperatures and pressures. It causes subsea pipelines to be more subject to movements both in lateral and axial directions due to the loads produced by high temperatures and pressures. Some high temperature pipelines have experienced the cumulative axial displacement of an overall pipeline length over a number of start-up/shut-in cycles, which is commonly known as “Pipeline walking”. The objective of this paper is to review the phenomenon of pipeline walking, expansion bend (Z Piece) and optimize thermal expansion in pipeline by specially focusing on a short and high temperature pipeline and identify key parameters of it in terms of the pipeline design. During designing the pipeline to control or mitigate the accumulated walking over the life of the pipeline system, one can see changing in field layouts and high installation costs related to mitigation
measures. It is therefore important to assess if the walking is a potential issue in the early design phase. This paper highlights the general pipeline technology in terms of the pipeline expansion design, pipeline thickness calculation, analyze the temperature and pressure profiles for the given pipeline and thermal transients along the pipeline during shutdown and restart operations. Understanding an axial movement of short pipelines due to the resultant of the thermal transient is the key selflessness in the pipeline walking assessment. Thus, a numerical model of pipeline based on the thermal transient load is developed by the finite element method. It shows the effect of the transient temperature profile on pipeline walking. Also it focuses on the effect of axial friction factors related to pipe-soil interaction as the sensitivity study. Lastly, we briefly discuss potential mitigation options to prevent pipeline walking. The global axial movement phenomenon can lead to various pipeline integrity consequential effects of accumulated axial walking. Hence, the pros and cons of possible mitigation measures are also discussed in connection with the sensitivity study results.

Keywords: Pipeline walking, Subsea stress analysis, Subsea pipeline, Thickness calculation, Fem analysis