Basic requirements and precautions for welding of urea high-pressure equipment

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Precautions: (1) The welding rod should be baked as required before use, and stored in a drying box or insulated container for easy access when needed. (2) Tungsten inert gas welding should be used as much as possible during repairs to improve the corrosion resistance of the welds. (3) On the premise of ensuring good weld fusion, the amount of welding heat input should be minimized; the welding speed should be relatively high to reduce repeated heating and prevent local overheating. (4) The moisture in the base material should be removed before welding to prevent the formation of pores. (5) When welding, an arc starting plate should be used as much as possible, and the start and end points of the arc should be directed outside the weld. (6) When performing arc welding, protective measures must be taken for the area surrounding the weld to prevent spatter from damaging the base material, especially the pipe ends. The crater at the end of the weld should be ground off, and re-melting or filler welding should be carried out ； The covering layer weld should cover the entire weld surface as much as possible. (7) The overlap width between adjacent weld passes on the same layer should be 1/3 to 1/2 of the width of a single weld pass. (8) The corrosion-resistant layer weld shall consist of at least two layers, with the thickness of the corrosion-resistant layer guaranteed to be greater than 4 mm. (9) When performing multi-pass welding, the root pass must be fully penetrated; after welding, perform penetrant testing and ferrite content determination ； Weld the second layer only after confirming there are no defects ； Each weld layer should be cleaned with a stainless steel brush and then rinsed thoroughly with acetone ； The starting points of each weld shall be staggered ； The surface layer is subjected to visual inspection, penetrant testing, and ferrite content determination. (10) Welds must be free from defects such as undercut, porosity, lack of fusion, and incomplete penetration. The weld surface should not be polished to avoid affecting its corrosion resistance.