Study On Post Weld Local Heat Treatment Of P92Steel Pipeline

With the rapid development of national electricity utility, there is increasingrequirement in thermal power technology. The new type T/P92martensitic steels withexcellent resistance of creep, steam oxidation and high-temperature corrosion arebeing wildly used for SC/USC main steam pipes and reheating pipes.After the welding assemble of P92pipes, there often exist residual stressesthroughout the welded joints, which will be a serious threat to the in-service safetyand consequently affect its operation life. Post weld heat treatment is an essentialapproach to improve the organization and eliminate welding residual stress. However,in the assemble site of power plants, due to the limitation of the heat treatment furnace,there is no condition to carry out overall heat treatment and local heat treatment canonly be conducted as an alternative method. In field conditions, for the purpose ofguaranteeing the effect of stress elimination during the local heat treatment, selectionof reasonable local heat treatment specifications is very significant. Therefore, withregard to newly martensitic steels P92pipes, especially those large-diameter andthick-wall ones, for the purpose of guaranteeing the performance of welding jointsand its service reliability, it’s of crucial reference value to study the heating areastandards of local heat treatment.In this article, according to the on-site conditions, local heat treatmentexperiment was conducted on thick-wall P92pipelines with the use of resistanceheating method of flexible porcelain and temperature fields of welded joints indifferent stages of heat treatment were obtained. Numerical analysis method wasemployed and finite element simulation technology of P92pipeline local heattreatment was developed. The technology was able to obtain the temperature fielddistribution of welded joints during the whole process of local heat treatment, andexperimental data were compared with simulative results. With the use of thistechnology, heated area specifications of local heat treatment for P92thick-wall pipesin on-site conditions were studied and established.Faced with complicated construction conditions such as on-site weldingassembly or repair welding, finite element analysis system for local heat treatment ofASME P92steel pipe was studied and developed on the basis of secondary development of ANSYS, and the problem of low efficiency and poor adaptabilityamong finite element software was solved. The system provides friendly and intuitiveinterface which is easy to operate and use. Imputing dimensions of actual pipeline,environment variable parameters and relative parameters of local heat treatmentmerely, engineers can obtain the temperature field of welded joints relativelyaccurately, and heated area parameters for local heat treatment are analyzed andevaluated. Based on through-thickness temperature criterion, the system is able tohelp people quickly find out appropriate heated band width and gradient control bandwidth corresponding to any specification of P92pipe, and reference was provided forpractical engineering applications.