ABSTRACT:

Various industry efforts are underway to improve or develop new methods to address the design of pipelines in harsh arctic or seismically active regions. Reliable characterization of tensile strain capacity of welded pipelines is key to the development of strain-based design methodologies. The tensile strain capacity of a welded pipeline is best characterized by pressurized full-scale tests with tension or bending loading. Full-scale tests of welded pipelines are also essential to validate predictive tensile strain capacity methodologies. Pressurized full-scale tests can also be used to prove the capacity of materials for pipelines with strain-based designs. Currently, no standardized fullscale testing procedure is available in codes and standards. This paper discusses the design, testing, and analysis of full-scale tests for strain-based pipelines. A comprehensive numerical and experimental program has been undertaken to optimize the specimen design. Finite element analysis (FEA) has been used to determine the effects of such factors as specimen length, the number of girth welds (thus pipe pups) and weld spacing, and the impact of pipe tensile property variability. Considerations for companion small-scale tests are discussed relative to full-scale tests to understand the effect of material variability and prediction of strain capacity.

INTRODUCTION

In order to meet the increasing energy needs of the world, the oil and gas industry has increasingly moved to developing resources in remote arctic and seismically active regions. Pipelines installed in these harsh regions may be subjected to large ground displacements. For example, large soil displacements associated with seismic activity (fault crossing, soil liquefaction, and lateral spreading) can subject a buried pipeline to longitudinal strains well in excess of 0.5%. Soil displacements in areas of discontinuous permafrost in arctic regions can also result in longitudinal strains in excess of 0.5% in the pipeline due to thaw settlement or frost heave.

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