Key points of welding process for 12Cr1MoVG alloy pipes

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　　(1) Before welding, the weld groove and the areas on each side thereof within a range of not less than 3 times the thickness of the workpiece should be preheated to 250–350°C. During welding, it is necessary to ensure that the temperature of the base material (both the inner and outer surfaces) within the preheating area remains above the preheating temperature, with the interpass temperature staying between 250°C and 350°C. 　　(2) Each weld must be completed in one pass. If welding is interrupted, it is necessary to ensure that the temperature in the weld groove and within a range of at least 150 mm on each side remains above the preheating temperature (250–350°C) until welding resumes. It is necessary to ensure that both the inner and outer surfaces of the welded part reach the specified preheating temperature. 　　(3) The welding electrodes used must be dried strictly in accordance with the requirements; they should not be stored in the insulation bucket for more than 4 hours. Any remaining welding materials must be returned to the welding material drying oven at the end of the work shift, and it is not allowed to leave them in the insulation bucket. 　　(4) After each weld is completed, hydrogen elimination heat treatment must be carried out immediately. The dehydrogenation heat treatment temperature is 250–350°C, with a holding time of 30 minutes. After the insulation work is completed, that area is covered with aluminum silicate panels to implement slow cooling measures. 　　(5) Arcing at non-welding areas of the weld is prohibited. Arc pits and scars resulting from arc abrasion, as well as weld scars remaining after removing temporary attachments, must all be polished smooth, and a 100% magnetic particle inspection in accordance with JB/T4730.4 shall be conducted, with acceptance at grade I. 　　(6) Defects such as undercutting, cracks, pores, cratering, and inclusions are not allowed on the surface of the weld and heat-affected zone. The slag on the weld joint and the spatter on both sides must be ground off and removed completely. 　　(7) For the areas that fail the flaw detection and require repair, preheating must be carried out as required before root cleaning and patch welding can be performed. After the patch welding is completed, non-destructive testing is carried out as required.