Engineering Critical Assessment On X56 Pipeline Steel

As a kind of engineering structure, the submarineline has the abroadand important applications, which always is used to deliver the oil and thegas. At the same time, as a kind of welded structure, the welded joint ofthe pipeline always has the inevitable welding defects.With the development of the engineering practice, people graduallyuse the principle of the "fitness for use" to assess the influence of thewelding defects on the structures, and don't required that the structureshould not contain any welding defects. This movement not only take intoaccount of the economic cost of the structure, but also provide the stabletheoretical basis and experimental verification for the safe performanceof the structure.This paper uses the principle of the "fitness for use" and theregulation of the BS7910:1999 to make an engineering critical assessment(ECA) for the submarineline which is developed by the COOEC and islocated between Lvshun and Dalian.To finish the assessment, at first, we understand the regulations andthe theories of the BS7910 and make the assessment software. Then, weobtain the tensile property of the X56 pipe by the analysis of the tensileand yield strength value which is obtained from the mill certificates,obtain the tensile property of the weld by performing the tensile testing ofthe weld metal and obtain the fracture toughness of the HAZ and the weldmetal by determining the CTOD-R cure of them. After that, we performthe relevant assessment to determine the critical/tolerable size of thedifferent kind of flaws and the flaws located in the different zones of thejoint. The assessment results are obtained by the iterated calculation andare calculated for the laying condition and for "as laid" condition prior totrenching and burying, which offer the basis for the check and accept ofthe welding defect when the joint is detected by the NDT.