Behavior and Preventive Measures of Strain Aging of Domestic X80 Linepipe Steel

Aiming at the problems during strain aging of linepipe steel,the tensile properties of domestic X80 plate and longitudinal submerged-arc welded pipe body were tested after aging at different temperatures.The behavior and preventive measures of strain aging of domestic X80 linepipe steel were investigated.The results show that the strain aging effect of both X80 linepipe steel with 1% pre-strain and SAWL pipes after hydrostatic test and cold expansion was significant after aging at 210 ℃.The yield strength and yield-to-tensile ratio of specimens made from X80 linepipe steel were increased by 6% and the ones from the pipe body were increased by 9.5% and 6.9% respectively.In addition,the stress-strain curves exhibited significant yield plat form.To minimize the strain aging effect of high strength linepipe steel,some measures are suggested to be taken,such as reducing the temperature rise of the specimen as much as possible during tensile properties testing,decreasing heating temperature before anticorrosion treatment and shortening heating time delicately during coating,lowering C and N contents in linepipe steel and developing two-phase steel as well as applying on-line heating treatment just after accelerated cooling.