Study On Safe Assessment For Undermatched Weld Joint Of Pipeline

As a kind of engineering structure, the offshore pipeline has the abroad and important applications, which always is used to deliver the oil and the gas. In the same time , as a kind of welded structure ,the welded joint of the pipeline always has the inevitable welding defects, inhomogeneous microstructures, poor mechanical properties,moreover, been objected to residual stresses. All these make the welded joint become the weakest part of the pipeline.Owing to the toughness and hardness of the base metal being different from the weld metal the mismatch effect comes into being. This not only affects whole deformation of the joint, distribution of stress and strain field in the crack tip, but also makes the constraint of crack tip complexity. So the mismatch effective of weld joint is the important factor for fracture action of weld structure in safety assessment. This mismatch in tensile properties can affect the plastic deformation pattern of the defective component, and thus the crack driving force such as the J integral or crack tip opening displacement. Although significant progress has been made on assessing defects in structural components in the last three decades, resulting in several defect assessment methods, these methods are restricted to the homogeneous structure. In principle, the methods for homogeneous structures can be applied to welded structures, if the tensile properties of the weakest material are used; for instance, for overmatched welds, those of the base material. However, such a simplified approach can lead to an unduly conservative result, and thus a defect assessment method specific to strength mismatched structures is needed to reduce excessive conservatism. Recently, defect assessment methods specific to strength mismatched structures have been developed by incorporating the strength mismatch effect into the methods for homogeneous structures.In this study, Structure Integrity Assessment Procedure (SINTAP) which is internationally and the most influential safety assessment standard was applied to safety assessment for welded joints of pipeline of the API 5L X56. Owing to dealing with a great deal data and formulas, we edited program of SINTAP using Visual Basic 6.0, which make the safety assessment quickly, accurately.During the assessment, we understand the regulations and the theories of the SINTAP obtain the tensile property of the base metal and the weld metal, the graph of the engineering and true stress–strain of base metal and weld metal and obtain the fracture toughness of the HAZ and the weld metal by determining the CTOD-R cure...