Effects Of Large Diameter Sawl Pipe Forming Process On The Mechanical Properties Of Blank Sheet

Oil and gas pipeline is the main carrier of today’s energy output. At present, thepipeline industry has an increasingly high demand on pipeline steel while the low-endproducts have been excess.Large diameter longitudinal submerged arc welded pipes arehigh quality pipe with good properties of pipeline steel and more in line with the needs ofeconomic and social development. The plastic deformation of the pipeline causes thechanges in materials strength performance index. It can produce Bauschinger effect andhardening phenomenon in forming process and during the performance test of the pipe.The Bauschinger effect makes the yield strength of the materials decrease, and thehardening phenomenon makes the yield strength of the materials increase. Researching thepipeline strength index variation with plastic deformation, establishing the pipelinehardening model and determining the approximate relationship between the blank and theproducts have very important significance on the pipeline steel production and theapplication of the basic theory of pipeline steel forming.Aiming at the UOE forming and JCOE forming methods, which are the two mainforming methods in large diameter SAWL pipe manufacturing field, the deformationprocess, deformation characteristics and the distribution of stress and strain of plates intwo different forming processes and the following mechanical expanding processes wereanalysed by numerical simulation on UO、JCO and the following mechanical expandingforming technological process. Deformation feature points in UOE and JCOE formingprocesses were determined. The tangential strains deformation history graph of the featurepoints was drawed. The extent of deformation and deformation history of each part of thesheets were revealled by analyzing the tangential strains deformation history of the featurepoints. The basis for the establishment of line pipe material performance prediction modelwas provided.By the pipeline steel uniaxial positive loading test and uniaxial reverse loading test,the variation rule of the X80pipeline steel yield strength with the variation of thepre-strains under different loading paths were achieved. The features of X80pipeline steelharding model is analysed to be in line with the mixed hardening model by uniaxial reverse loading test for pipeline steel. The variation rule was obtained, which the mixedhardening model coefficient increases with the increasing of the pre-strain. The coefficientand parameters of the mixed hardening model were determined according to the results ofthe test data.X60pipeline steel bending specimen was produced which has the same equivalentstrain with UOE forming. According to API SPEC5L standard tensile tests on specimensflattened rectangle method, the materials performance variation rule of X60pipeline steelunder different degrees of bending was analyzed. Mathematical model which is forachieving the mechanical properties of X60pipeline steel blank was established.Based on the above studies, according to the completed industrial test in some pipeplant, test datas of X60, X70and X90pipeline steel were studied respectively. Variationrule of X60pipeline steel blank material properties before and after forming was obtained.It was in line with the variation rule of the mathematical model of the mechanicalproperties of X60pipeline steel established previously. The variation trend of X90highgrade pipeline steel blank was achieved, whose yield strength is lower than the blank afterthe JCO forming process while higher than the blank after the mechanical expandingprocess.