Precautions for repairing stainless steel containers

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The following precautions should be taken when repairing stainless steel containers; they are provided here for your reference. 01 When repairing stainless steel pressure vessels, care should be taken to prevent sharp or hard objects from scratching the stainless steel surface. If work is to be performed inside the vessel, protective measures such as laying down liners should be taken. 02 Stainless steel plates shall be cut by plasma cutting or mechanical processing. When mechanical processing is used for cutting, the machine tool must be cleaned thoroughly. The use of carbon arc air gouging for cutting is not permitted. When rolling stainless steel, the rolling machine should have its roll surfaces covered with iron-ion-free materials. 03 During repairs involving replacement or patching of the shell, tools that come into contact with the shell surface—such as wedges and shims—required temporarily should be made of stainless steel material compatible with the shell. 04 When repairing stainless steel pressure vessels requiring resistance to intergranular corrosion, the welding procedure specifications must be strictly followed during welding. The interpass temperature must be carefully controlled; when removing the root pass, the carburized layer should be thoroughly ground off. The reworked areas must still meet the original requirements. Before repairing stainless steel pressure vessels, oil, dirt, and other impurities at the joints should be cleaned off using acetone or alcohol. When using plasma cutting to create grooves, the surfaces must be polished until they exhibit a metallic luster. During welding, it is prohibited to strike an arc directly on any non-welding surfaces of the stainless steel. When performing manual arc welding, a spatter-resistant layer should be applied over a 100-mm area on both sides of the joint to facilitate the removal of weld spatter. 06 After repair, stainless steel pressure vessels must be pickled and passivated. Generally, immersion is the primary method for pickling and passivation; however, wet wiping or application of a paste can also be used. 07 The surface of stainless steel after pickling shall show no obvious signs of corrosion, no unevenly colored spots; the surfaces subjected to welding or hot working shall be free from any oxide coloration. After pickling, it must be thoroughly rinsed with water; no pickling solution may remain. After passivation, the stainless steel surface should be rinsed with water; once neutralized, the water residues should be dried off. 08 After surface treatment of stainless steel pressure vessels requiring resistance to intergranular corrosion, it is necessary to inspect the passivation film. Generally, the inspection is carried out in accordance with the specifications outlined in the drawings; if no such specifications are provided in the design drawings, the blue spot method should be used for the passivation film inspection.