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Surface treatment: 1. After all weld repairs on stainless steel pressure vessels are completed, surface treatment shall be carried out in accordance with the requirements of the design drawings. 2. All impurities on the surface of pressure vessels, such as welding spatter, slag, scale, weld scars, pits, and oil stains, must be removed thoroughly. Carbon steel brushes must not be used to clean the surface of stainless steel pressure vessels during this process. 3. When mechanical polishing is used, alumina or chromium oxide should be chosen as the polishing abrasive; materials such as iron sand must not be used as abrasives. Abrasives should be stored separately according to their different particle sizes; they must not be mixed together. 4. Each polishing wheel can only be bonded with abrasives of one grain size. After bonding the abrasive to the polishing wheel, the drying temperature and drying time must be strictly controlled depending on the type of abrasive used. 5. The polishing grade should be increased step by step, from coarse to fine. After the rough polishing, a 10x magnifying glass should be used to inspect the surface; if small spots are found in certain areas, those spots must be polished clean, and no noticeable depressions are allowed before proceeding with the fine polishing. 6. Throughout the polishing process, the surface temperature of the polished layer should always be controlled to prevent deformation and overheating, and the consistency of the polishing pattern should be maintained. 7. When using electrochemical polishing or other methods for polishing, process tests should be conducted in advance, and the polishing of workpieces must be carried out strictly in accordance with the specified process requirements. 8. Pressure vessels or pressure components made of austenitic stainless steel and composite steel plates that require resistance to intergranular corrosion shall be subjected to pickling and passivation treatment. When such steel components are required to undergo heat treatment according to the drawing specifications, they must also be pickled and passivated after heat treatment. Pickling and passivation treatment: Pickling and passivation procedure: Degreasing → Pickling → Passivation → Water washing → Drying, etc. a) Process tests must be conducted on the workpiece before acid cleaning and passivation, in order to determine appropriate formulations and operating procedures (including safety protocols). Samples of the pickling and passivation solutions should be taken regularly for testing, so as to adjust their concentrations in a timely manner ； b) Where there are carbon steel components on stainless steel pressure vessels, effective measures must be taken during the pickling process to prevent the carbon steel parts from being corroded ； c) Acid cleaning and passivation should primarily be carried out by immersion; wet wiping or the use of acid cleaning and passivation pastes is also acceptable. (1) Removal of oil stains: Stainless steel parts should have all oil stains and other foreign substances removed thoroughly before acid washing or passivation (Inspection method and requirements: Sprinkle water on the surface of the part; a uniform and continuous water film should form, remaining intact for at least 30 seconds, with no other foreign substances or residues that could affect the quality of the part present on the surface). The cleaning method can involve using gasoline, alkaline solutions, or cleaning agents to remove oil stains, followed by rinsing with water; it is not allowed to scrub the surface of the workpiece with carbon steel brushes. (2) Acid washing: Typically, the treatment involves several steps such as loosening the oxide scale, etching, and removing the residues from the etching process. Operators must wear acid-resistant clothing, gloves, masks, and protective goggles while carrying out these operations. When carrying out pickling inside a container, a properly inspected gas mask must be worn, and the operation must be conducted under the supervision of a qualified person. The requirements for the pickling process are as follows: a) Remove the oxide scale: The solution contains 80 g/L to 120 g/L of nitric acid at a concentration of 66%; the solution temperature is room temperature, and the treatment time is less than 60 minutes ； b) Etching: The solution contains 200 g/L to 250 g/L of sulfuric acid at a concentration of 98%, and 80 g/L to 120 g/L of hydrochloric acid at a concentration of 36%; the temperature of the solution is 40°C to 60°C, and the process continues until the oxide scale is completely removed ； c) Removal of erosion residues: The solution contains 30 g/L to 50 g/L of nitric acid at a concentration of 66%, and 5 g/L to 15 g/L of hydrogen peroxide at a concentration of 30%; the solution temperature is room temperature, and the treatment time is 10 s to 60 s. Pickling can also be carried out using a pickling paste; the formula for this paste (for reference) is: 20 mL of hydrochloric acid (specific gravity 1.19), 100 mL of water, 30 mL of nitric acid (specific gravity 1.42), and 150 g of bentonite. Pickling paste pickling is mainly suitable for large containers or local treatment. At room temperature, apply the pickling paste evenly to the clean equipment (to a thickness of about 2 mm–3 mm), let it sit for one hour, and then gently brush it away with clean water or a stainless steel brush until a uniform white etched finish is achieved. The surface of the stainless steel after pickling must not show any visible traces of the cleaning solution, nor any uneven color patterns. Welds and surfaces that have been heat-treated must not exhibit any oxidized colors. After pickling, it must be rinsed thoroughly with clean water to ensure that no residual cleaning solution remains. (3) Passivation: During the corrosion process, corrosion products are formed on the metal surface (the corrosion products of stainless steel mainly consist of Cr2O3). These products are very dense and adhere firmly to the metal surface, thereby hindering the corrosion process and resulting in a reduction in the corrosion rate; this phenomenon is known as passivation. When treating parts, components, or finished products with a passivation solution, the items to be treated must be completely submerged in the passivation solution to prevent severe corrosion in the areas above the liquid surface. Stainless steel passivation can also be achieved using a passivation paste. The formula for this paste (for reference): 30 mL of nitric acid (67% concentration), 4 g of potassium dichromate, along with bentonite (100–200 mesh), which is added and mixed until a paste-like consistency is obtained. Passivation paste is mainly suitable for large containers or local treatment. Apply the passivation paste evenly to the surface of the pickled container at room temperature (about 2 mm to 3 mm thick), and check after 1 hour until a uniform passivation film has formed on the surface. (4) Washing and drying: The passivated stainless steel should be thoroughly cleaned immediately after being removed from the passivation solution; once it is at a neutral pH, any water residues should be wiped off or dried with hot air. If necessary, an additional step of dilute alkali neutralization can be added after the first wash to remove residual acid in complex cavities. The chloride content in water must not exceed 25 mg/L. (5) Recording: The operator shall record the main process parameters for pickling and passivation, and keep these records intact; they must be retained for at least 7 years. (6) Inspection after pickling and passivation a. Inspection of the passivation film: For stainless steel pressure vessels that require resistance to intergranular corrosion, inspection of the passivation film should be avoided on the surfaces in contact with the medium after surface treatment. The inspection of the passivation film shall be carried out in accordance with the specifications provided in the design drawings; if no such specifications are given, the blue-spot method shall be used (a solution is prepared by mixing 1 g of hematite salt with 3 mL of 65%–85% nitric acid and 100 mL of water. The filter paper is soaked in this solution and then applied to the surface to be tested, or the solution can be applied directly to that surface. If the passivation film on the surface is incomplete or contaminated with iron ions, a blue color will appear). The presence of blue spots within 30 seconds indicates that the sample fails the inspection. b. Color requirements: 1) The mechanically processed parts should retain the original color of stainless steel after pickling ； 2) After pickling, the surface of heat-treated parts should be a dull light gray to dark gray due to differences in material composition ； 3) The surface of the parts after acid pickling and chemical passivation is a grayish color with a slight yellow tint. c. Unacceptable defects: 1) Residual oxides, mechanical impurities, dirt, etc. on the surface of the parts after pickling or passivation ； 2) The areas that require passivation have not been passivated ； 3) The parts have been corroded ； 4) The parts are not thoroughly dried, with residual moisture ； 5) There are severe color differences on the main surfaces of the same part. d. The inspection records of the passivation film must be retained for at least 7 years. e. Discharge of pickling and passivation solutions: The pickling solutions that need to be discharged must undergo neutralization; they can be released only after meeting the **wastewater discharge standards. Pressure testing and packaging transportation: 1. After the manufacture of stainless steel pressure vessels, pressure resistance tests shall be carried out in accordance with the specifications provided in the design drawings. 2. After the hydrostatic test of stainless steel pressure vessels, the water should be drained immediately, and any water residues should be dried off. In cases involving non-corrosive media, when it is not possible to dry water traces due to structural reasons, the chloride content in the test water must not exceed 25 mg/L. 3. During pressure tests, airtightness tests, and other related procedures for stainless steel pressure vessels, if the passivation layer on the surfaces in contact with the medium is damaged, measures should be taken promptly to re-passivate those surfaces. 4. After the manufacture of the stainless steel pressure vessel, all sealing surfaces and pipe ends should be given appropriate protective measures in a timely manner. The carbon steel parts of the container should be painted with protective paint, while the stainless steel parts generally do not require painting for protection, unless otherwise specified in the design drawings. 5. Effective measures must be taken during the transportation of stainless steel pressure vessels to prevent iron ion contamination and damage to the equipment’s surface.