Study on the Effect of Material Characteristic on the Limit Pressure of the Pipeline Girth Weld Containing Welding Defect

Abstract

Abstract For long-distance oil and gas pipelines, pipeline construction is actually a vast project which involves longdistance welding process. Because of technology and artificial factors, there are various types of welding defects in pipeline girth welds, such as cracks, porosity, slag inclusions, inadequate penetration, incomplete fusion and so on. Pipeline is often subject to a series of adverse conditions, including cyclic loading, pressure fluctuation, corrosion, high temperature, shock and so on, which seriously impair the performance of pipeline. Girth weld defect is one of the underlying causes, which leads to early damage to welded structure and arouses catastrophic accident. Therefore, the quality control of pipeline welds is very important to ensure the safety of pipelines. It is necessary to carry out stress analysis on the girth weld of pipeline containing welding defects to provide technical basis for the size control of pipeline weld defects. In order to study the influence of material characteristic on the limit pressure of pipeline girth weld containing porosity, based on the real structure of the girth weld, a finite element model of pipeline girth weld containing porosity was established. Stress analysis with different size of porosity was performed. And the effect of the yield strength, hardening exponent and mismatch on the limit pressure of the girth weld were analyzed. The appropriate failure criterion is selected to determine the failure of pipeline girth weld with porosity. It turned out that the local maximum Mises stress of porosity defect increases with the increase of yield strength and the strength matching factor. The local plastic area of porosity defect increases with the increase of hardening exponent. The pipeline limit pressure increases with the increase of yield strength and the strength matching factor, and the pipeline limit pressure decreases with the increase of porosity defect size under the internal pressure. The finite element results provide a reference for the tolerance size of girth weld defects, which is of great significance for making full use of the performance of pipe material and improving the quality and efficiency for pipeline safety management.