Study On Welding Quality Control And Safety Assessment Of Duplex Stainless Steel Pipe

Duplex stainless steel pipes, SAF2205, are widely used in the vital department ofthe national economy, such as chemical industries and offshore applications. Thewelded joints should meet the requirements of mechanical properties and corrosionresistance to ensure pipe security after welding. Thus it in necessary to investigate thewelding technology of SAF2205 pipe to ensure welded joints excellent mechanicaland corrosion resistance properties by designing and evaluating optimum weldingparameters. In addition, welding often makes the microstructure deterioration andgives rise to appearance of welding flaw. So under the guide of "fitness for purpose"principle, safety assessment of pipe structure by SINTAP were carried out to providesecurity assurance. It is very important to investigate the welding quality control andsafety assessment in both academic research and practice.In this paper, on the basis of the optimum phase ratio, two optimum weldingprocedures were chosen from a variety of welding parameters. Reproducibility Testswere conducted to verify the results. Through the mechanical properties and corrosion tests of the welded jointsmade by optimum welding procedure, the results show that the welded joints haveexcellent comprehensive properties to meet the requirements of engineering. Theinvestigation found phase ratio is not unique standard of evaluating comprehensiveproperties of the welded joints. More attention should be paid to microstructure.A three-dimensional finite element numerical simulation is firstly performed onthe girth welded residual stresses of the duplex stainless steel pipes with ANSYS non-liner finite element program. Three-dimensional FEM using mobile heat source foranalysis transient temperature field and welding stress filed in circumferential joint ofpipes is founded. Distributions of axial and hoop residual stresses of the joint areinvestigated. The axial and the hoop residual stresses at the weld and weld vicinity oninner surface of pipes are tensile, and they are gradually transferred into compressivewith the increase of distance away from the weld. The axial residual stresses at theweld and weld vicinity on outer surface of pipes is compressive while the hoop one istensile. The distributions of residual stresses from hoop position compared positive-circle with negative-circle show distinct symmetry. The experimental results showmostly conformity compared with the FEA results. Structure Integrity Assessment Procedure (SINTAP) Failure Assessment Diagram(FAD) method was applied to the SAF2205 pipe mismatch welded joints with surfaceflaw at the weld toe. The result showed that assessment point was located within thedefined range of assessment curve. So the pipeline welded structure with surface flawcan be safely used under the specific conditions.