Welding heat treatment effect experiment

1.1 Test process

Infrared thermal imaging camera was used to measure the temperature distribution of P92 steel pipe welding process. First, the emissivity of P92 steel is calibrated, and the value is 0.9. The P92 steel pipe specification is 90 mm×45 mil1. In order to be used for subsequent test work, a single-sided V-shaped groove is specially designed, and the weld bead is designed to be 18 layers. The P92 pipe is standing on the work frame and is welded by flat welding. The infrared thermal imager is used to align the center of the weld bead groove for real-time welding. The relationship between the peak temperature and the distance from the fusion line. Finite element simulation of the P92 steel pipe welding The heat cycle curve calculates the welding stress field before and after heat treatment of the P92 steel pipe girth weld joint, and analyzes the effect of heat treatment on the elimination of welding residual stress.

The distribution of residual welding stress on the outer surface of the pipe perpendicular to the welding direction, including circumferential stress, axial stress and radial stress, and the zero point of the abscissa is the position of the straight groove. After the post-weld heat treatment, the circumferential residual stress on the outer surface of the welded joint of the P92 steel pipe is redistributed, the stress gradient is reduced, the stress in the weld area is significantly reduced, and the peak tensile stress drops by 146.3MPa, which is 42% of the original. The overall stress value in the joint area is more uniform than before heat treatment, and the peak compressive stress is also significantly reduced. After heat treatment, the peak and amplitude of the axial residual stress are reduced, and the peak of compressive stress is reduced more obviously, and the peaks appear in the weld area. The weld area has both compressive stress and tensile stress, and the situation is more complicated. The peak value of radial compressive stress decreases significantly after heat treatment, and the peak value of tensile stress does not decrease significantly, but the stress peak value before heat treatment itself is very small. The distribution curve of the residual welding stress on the inner surface of the pipe welding joint perpendicular to the welding direction, and the zero point of the abscissa is the straight groove position. The residual stress distribution along the wall thickness at the straight groove of the pipe welding joint. The zero point of the abscissa in Fig. 7 is the outer surface of the pipe. Before heat treatment, the circumferential and axial tensile stress peaks in the weld zone of the inner wall of the pipeline were as high as 200 MPa, and the tensile stress peak decreased significantly after heat treatment; both the circumferential tensile stress peak and the axial stress peak decreased significantly after the heat treatment, and the radial stress peak also appeared. The reduction. Therefore, the stress relief effect of heat treatment is more obvious, but there are still some residual tensile stresses, which may affect the life of welded joints. In summary, in the evaluation of the creep behavior of welded joints at high temperatures, it is necessary to further study the redistribution of residual stress in the creep process and the influence mechanism on creep damage, so as to realize the high temperature creep life of welded joints. Accurate assessment.

in conclusion

(1) In the steel pipe welding process, the temperature field distribution of the welded joint was measured by an infrared thermal imager, and the welding thermal cycle curve of the steel was obtained.

(2) Combined with the measured welding thermal cycle curve, the finite element method, the use of life and death element technology and Gaussian mobile heat source were used to simulate the metal deposition during the welding process, and the numerical simulation of the entire process of multi-layer and multi-pass welding of steel thick-walled pipes was realized. .

(3) The indirect method is used to solve the residual stress field of the steel welded joint before and after heat treatment at 760℃. The results show that the post-weld heat treatment has a more obvious stress relief effect on the joint, but there is still a large tensile residual stress in the weld. Therefore, the influence of residual stress should be considered in the defect assessment and life prediction of pipelines under high temperature.