Experimental Research On Testing And Evaluation Of Welding Residual Stress Based On Metal Magnetic Memory Method

It will produce a lot of welds in the process of manufacture of the Pressure equipment.Due to the inhomogeneity of weld microstructure and the welding residual stress generated in the weld,the weld is called the weakest position.So as to ensure the safe operation of the equipment,it is necessary to test and evaluate the welding residual stress.Currently,the hole method and X-ray method.are widely used in the welding residual stress testing.The blind-hole method will cause damage to the pressure equipment,for the X-ray method,the detection efficiency is low and it cost a lot.Metal magnetic memory technology is a new nondestructive testing technology which is quickly and accurately locate the local stress concentration which is caused by the defects.But the use of thetesting evaluation research and application of the welding residual stress is not enough.In view of the problem of magnetic memory technology,the main research contents and conclusions of this paper include:(1)Magnetic memory method is used to detect the leakage magnetic signals of Q345 R flat butt welded specimen which size is 600 × 360 × 36mm(length × width ×height).The relationship between magnetic signal(Hp)and gradient value(K)and the residual stress of welding is analyzed based on the residual stress value of the X-ray method detecting.The rapid assessment methods of welding residual stress distribution law based on the "magnetic-gradient" curves is proposed.(2)Semicircular arched specimens with the diameter of 600 mm and thickness of36 mm are loaded and unloaded then.The relationship between stress and the magnetic signal changes under loading conditions was analyzed.The results showed that in the loading phase: as the load increases,the magnetic signal curve along the direction of the stress increase is gradually gentle,and the curve peak to peak(Hpp)and gradient mean(Kave)decreases.But there is no clear relationship between the magnetic signal strength values and stress change of the single point.After removal of the applied load,specimen stress recovery to the state before loading.But the magnetic signal strength values and the magnetic signal curve change in loadingphase specimen did not disappear with the removal of the load.For the the same specimen on the same measuring point,the same stress values corresponding to different magnetic signal strength,which shows that magnetic signal intensity of a single point can’t alone determine the stress level of the specimen,and specimen magnetic signal strength have suffered the impact by once load.(3)The heat treatment of the plate butt welded specimen was carried out at the temperature of 600 for incubation of 2 hours.The change of the residual stress and the relevant parameters of the magnetic signal were analyzed after heat treatment.The results showed that,the variation trend of residual stress level of the specimen before and after heat treatment is consistent with the change trend of the magnetic signal curve peak to peak and the average gradient.It showed that it is feasible to evaluate the effect of heat treatment on the elimination of stress according to the change of the magnetic signal curve peak to peak and the average value of the gradient before and after heat treatment.(4)The "magnetic-gradient" curve method was proposed in this paper was used to rapidly evaluate the welding residual stress of pipeline with the diameter of600 mm and wall thickness of 10 mm.And the evaluation results were tested by X-ray method.The results showed that the "magnetic-gradient" curve is more accurately to evaluate the distribution of the welding residual stress.