Lateral Buckling of Deepwater Pipelines in Operation

Abstract

Deepwater pipeline systems are regularly designed to operate under high pressure and high temperature (HPHT) conditions. These operating environments typically mean that the systems are susceptible to Euler buckling, more commonly referred to as lateral buckling. An effective design solution, promoted by the SAFEBUCK JIP [1],[2] and now regularly adopted within the industry, is to accommodate the thermal expansion with planned buckle sites, thereby controlling the loads within the system. Traditionally, operators have spent a great deal of resources in designing, manufacturing and installing pipeline systems. However, it is equally important to demonstrate that the system is fit for service and that operational loads do not exceed the extreme design cases. In some instances, there have been a number of instances where lateral buckling has caused full bore rupture in offshore pipelines. In order to verify the long-term integrity of a pipeline system, it is essential to confirm the location, mode shape and amplitude of both the planned and rogue (unplanned) lateral buckles. This can be accomplished via pipeline surveys. Recent pipeline survey work was conducted on a pipeline system in the Gulf of Mexico. The data exhibited some areas of unexpected performance, which highlights the fact that operating uncertainty exists and that lateral buckling is an unstable phenomenon. The design Finite Element (FE) models were calibrated using the measured buckle shapes, and the fatigue life was estimated using recorded operational pressure and temperature data. The survey work performed has proven invaluable when assessing the long-term integrity of the pipeline system. This paper presents a review of the methods used for surveying a pipeline system in the Gulf of Mexico, a summary of the results obtained from the subsequent analysis and pipeline FE model calibration, as well as ‘lessons learned’ for future projects with similar design challenges.