Local post weld heat treatment method by primary and secondary distributed heat source

Local heat treatment is an important means to ensure the safety of pressure-bearing equipment over its entire life cycle. This study takes a xylene tower segmented barrel as the research subject and proposes a novel heat treatment method by adding a secondary heating band at a certain distance from the primary heat source. The primary heating band improves the microstructure of the weld. The secondary heating band eliminates residual stresses on the internal surface of the weld and neutralizes waist-closing deformation. This research established a local heat treatment model for primary and secondary heating. Factors influencing stress relief were investigated, including the effects of temperature, band-width of the secondary heating band, spacing between the primary and secondary heating, and so on. Results show that traditional local heat treatment produces new secondary stresses on the inner surface due to the constraint effect. Primary and secondary heating distributed heat source local heat treatment can produce compressive stress on the inner surface of the weld due to reversible deformation. The width and spacing of the primary and secondary heating bands are crucial to stress relief. Engineering design methodology is proposed, shedding light on the heat treatment of extremely large pressure equipment.