Buckling Analysis of Offshore Pipeline with Various Buckle Arrestor Configurations under Static Axial Load

Abstract

During the last three decades, offshore oil and gas exploration and production has ventured into deeper seas as many shallow water fields are already exhausted. Today the production has reached ocean depth of approximately 7,000 ft., while exploration for oil resources is conducted at depths of 11,000 ft. With the development of oil and gas fields in different parts of the world, such as Gulf of Mexico (U.S.), North Sea, Southeast Asia, Brazil, Mediterranean Sea, Persian Gulf, Middle East, South China Sea, Australia etc., the economic importance of offshore pipelines can be gauged by the fact that around a third of the oil and gas extracted worldwide comes from offshore resources. Offshore pipelines are major components used by oil and gas industry for drilling, production and transmission. As a result of the greater depth of oil exploration, offshore pipelines are subjected to several forces such as pressure (internal and external), temperature, axial force acting on pipelines due to the difference between the temperature of material carried and ambient temperature and interaction of the pipelines with the surrounding material. The external forces acting on the pipelines result in buckling of offshore pipelines. Free spanning of offshore pipelines subjects them to bending forces. Offshore pipelines are subjected to lateral buckling, upheaval buckling which causes disruption of offshore facilities and interrupts the supply of oil. Therefore, buckling of offshore pipelines should be controlled within permissible limits. Several methods are employed to control buckling and ensure uninterrupted functioning of offshore pipelines. Use of buckle arrestors, advanced materials and latest techniques such as use of sensors to monitor offshore pipelines are the methods adopted to control buckling. Current research work focuses on the improvement in structural properties of offshore pipelines stiffened with buckle arrestors of different configurations and placed at different locations along the pipeline. Finite element modeling was performed, and experiments were conducted on pipeline models made of stainless steel of grade SS304 which is suitable for offshore applications. Finite element analysis of offshore pipeline models stiffened with buckle arrestors of different configurations was performed to understand significance of varying length and placement of buckle arrestors. The optimum length of buckle arrestors was identifiedii from finite element analysis, and pipeline models were fabricated for conducting experiments. Comparison of finite element analysis results and experimental outcomes showed that the efficiency of buckle arrestors increased by increasing the dimensions and location of buckle arrestors. Three point bending experiments were conducted on the pipeline models to determine flexural capacity of the pipeline models.