Influence of Welding Seam Heat Treatment on Residual Stress of Pipeline Welding

In order to improve power generation efficiency, save energy and reduce greenhouse gas emissions, ultra-supercritical power generation units are currently being built on a large scale in China, some of which have already been put into operation for power generation, and the scale of construction will rank first in the world. Due to the increase in service temperature and operating pressure of ultra-ultra-I critical power plants, creep damage analysis and life prediction of high-temperature pipelines have become research hotspots. In the manufacturing process and operation process of welded components, residual stress may be generated. Due to post-weld heat treatment and creep during service, the residual stress in the weld can be reduced to a negligible level. However, the research results of Thomas et al. showed that when estimating the effective applied stress in the creep process, the influence of residual stress must be considered, and the residual stress has an important influence on the development of creep damage.

In addition, Lee et al. proposed that the residual stress may affect the size of the initial transient stage and the incubation period of crack initiation. So far, the tolerance of residual stress in welded components at high temperature has not been proposed at home and abroad. In most cases, the distribution of residual stress is unknown, and the residual stress distribution recommended by R5, R6 and BS7910 tends to be conservative, and the residual stress is overestimated, leading to too conservative defect assessment results. Therefore, how to accurately estimate the residual stress field of welded components at high temperature is very important for studying the influence of residual stress on creep crack initiation and propagation life, as well as the assessment and prediction of component defects at high temperature. In recent years, some valuable researches have been done on the finite element method to calculate the welding residual stress distribution in China, but there are no reports on the analysis and research of the welding residual stress of the ultra-supercritical new-generation heat-resistant steel P92 steel thick-walled pipeline. .

This article mainly studies the effect of post-weld heat treatment on the residual stress of P92 steel welded joints. First, the infrared thermal imager is used to measure the temperature field distribution of the P92 steel pipeline during welding; then the finite element method is used to conduct the welding process of the pipeline under this guidance. The welding temperature field was simulated and calculated; finally, the welding residual stress distribution was calculated according to the temperature field before and after the heat treatment, and the stress relief effect of the heat treatment was studied.

The infrared thermal imager was used to measure the temperature field distribution of the steel pipeline during the welding process, and the temperature cycle curve of the P92 steel welding process was obtained; the finite element method was used to simulate the entire welding process of the P92 steel pipeline multi-layer multi-pass welding, and the The welding temperature field distribution is in good agreement with the measured results of the P92 steel welding temperature field, which verifies the accuracy of the simulation calculation; the indirect method is used to calculate the residual stress field formed by the circumferential weld of the steel pipe by using the temperature field results, and the analysis is focused on Changes in welding residual stress before and after post-weld heat treatment. The results show that the post-weld heat treatment can obviously eliminate the welding residual stress of the P92 steel pipeline, but it cannot be completely eliminated, and there is still a large tensile residual stress in the weld.