SAFEBUCK JIP: Operational Integrity of Deepwater Flowlines

Abstract

Abstract This paper reviews the requirements for monitoring pipelines susceptible to lateral buckling and walking, focusing specifically on the methods available for surveying such pipelines, the accuracy required and the subsequent review and analysis of system integrity, which has also provided important lessons for future projects. Deepwater pipeline systems are customarily designed to operate at high temperatures and pressures. The subsequent large compressive loads that are generated under such conditions lead to a natural susceptibility for the pipeline to buckle. Historically, buckling in pipelines has been remediated by trenching and burying. However as water depths increase, traditional methods become more difficult to implement. A more elegant and cost effective solution for deepwater developments involves controlling the buckle formation rather than avoiding it altogether. With projects embracing this design approach and sustained funding for research and JIPs such as SAFEBUCK, our understanding has significantly advanced in recent years, allowing the lateral buckling strategy to be adopted as a safe and reliable design solution. However, lateral buckling and pipeline walking can, and in some cases, has caused pipeline failures. To demonstrate that the system is fit for service, it is essential to obtain good quality out-of-straightness (OOS) and visual survey data, along the whole pipeline, during operation, to confirm pipeline system integrity. Recent deepwater pipeline survey work conducted in West Africa and the Gulf of Mexico has proven that good quality data can be collected in deepwater and that such data is fundamental to the assessment of long-term integrity. In particular, these surveys identified some areas of unexpected behavior that required subsea intervention. The data from such surveys also advances the industry's understanding of the complex behavior of such pipeline systems and their behavior. Phase III of the SAFEBUCK JIP includes a dedicated task to collect and share data and lessons learned from operating pipelines on recent projects - without sharing potentially sensitive project specific data - as a key to the better understanding the actual pipeline responses, when compared to the original design intent. Introduction Many operating deepwater or high-pressure, high-temperature (HPHT) pipeline systems have adopted the controlled lateral buckling design solution. With further projects implementing this method, and continued high levels of support and funding for research and Joint Industry Projects such as SAFEBUCK, the industry's level of knowledge and understanding has greatly increased. One of the reasons for initiating the JIP was the occurrence of unexpected lateral buckles in a number of pipelines, leading in some cases to pipeline failure. These failures included three catastrophic full-bore pipeline ruptures and one pipeline abandonment. The lateral buckling design process has improved steadily, with a focus on reliable buckle formation, reducing peak loads, and controlling fatigue. Meanwhile inspection methods, which require high positional accuracy, have significantly improved over recent years enabling some high quality surveys to be performed. However, operational experience with such systems is still relatively immature, with little feedback on their performance. The modest level of monitoring carried out has highlighted the importance of operational integrity inspections and identified some new concerns that need to be addressed during the design phase on future projects.