Manufacturing requirements for austenitic stainless steel pressure vessels

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Manufacturing environment and process equipment: 1. The manufacturing of stainless steel pressure vessels and their pressure-bearing components requires dedicated manufacturing workshops, as well as specialized tools and facilities; such manufacturing must not be carried out alongside the production of ferrous metal products or other goods. 2. To prevent contamination by iron ions and other harmful impurities, the production area for stainless steel pressure vessels must be kept clean and dry, with rubber or wooden mats laid on the floor. Wooden stacking racks must be used for storing component semi-finished products and finished products. 3. The processing and welding equipment for stainless steel pressure vessels shall be capable of meeting the requirements for manufacturing such vessels. Special roller frames (such as those with rubber lining), lifting fixtures, and other processing equipment should be used during the manufacturing of stainless steel pressure vessels. The lifting cables used to lift containers or components should be made of nylon ropes or metal cables wrapped in flexible materials such as rubber hoses, in order to prevent damage to the surface of the materials. Persons entering the production area should wear soft-soled shoes, and be sure to avoid shoes with any sharp hard objects in their soles (such as nails), to prevent scratching the stainless steel surface. 4. During handling and transportation, stainless steel materials or components should be equipped with appropriate transport tools to prevent contamination by iron ions as well as scratches and dents. 5. The surface treatment of stainless steel pressure vessels should take place in a separate facility equipped with necessary environmental protection measures. 6. When lifting stainless steel plates, prevent the plates from deforming. Machining, forming and welding: 1. Stainless steel pressure vessels produced in bulk must be marked according to templates, which should preferably be made of stainless steel. 2. Marking should be done on a clean wooden board or a smooth surface; it is strictly prohibited to use a steel needle to make marks or punches on the surface of stainless steel material that cannot be removed during processing. 3. When cutting the material, the stainless steel raw material should be moved to a dedicated area; it is strictly prohibited to cut and remove the material directly on top of piles of stainless steel sheets. Material cutting methods can include plasma cutting, wire cutting, mechanical cutting, and other such techniques. For sheets that have been cut or perforated using methods such as plasma cutting or wire cutting, if welding is required afterward, the oxides at the cut edges must be removed until the metallic luster is visible. When cutting materials with a sheet shear, the worktable of the shear should be cleaned thoroughly before cutting. To prevent scratches on the surface of the sheets, soft materials such as rubber should be used to cover the pressure plate, which serves to prevent the sheets from flipping or moving during cutting. 4. The cut edges and perimeters of the sheets shall be free from cracks, dents, tears, and similar defects. 5. The cut materials should be neatly stacked on the pallet so that they can be lifted together with the pallet; soft materials such as rubber, wooden planks, or blankets should be placed between the sheets to prevent damage to their surfaces. 6. Round bars and pipes can be cut to size using methods such as lathes, saws, manual steel saws, or grinding machines. If welding is still required, the grinding residue and burrs at the cut edge must be removed. 7. The marking of stainless steel compression component materials, as well as the verification of such markings, shall be applied in the appropriate locations on the materials of each component as required, and written records of the material cutting process shall also be kept. 8. When rolling stainless steel sheets into circles, an iron-ion-free material should be placed on the surface of the rolling mill’s rollers or on the surface of the stainless steel itself. 9. When performing mechanical processing such as turning, drilling, boring, milling, and planing, water-based emulsions are generally used as coolants. 10. For stainless steel components, chlorine-free liquid degreasers should be used to remove grease and other impurities before heat processing or heat treatment can be carried out. The combustion gas in the furnace chamber used in hot working or heat treatment processes should be neutral or slightly oxidizing ； For components that do not require removal from the metal surface after hot working or heat treatment, the sulfur content of the fuel oil used for heating should be below 0.3%. Heating with coal or coke is strictly prohibited. 11. When hot-forming stainless steel end caps, it is necessary to strictly control the temperature inside the furnace, as well as the starting and ending temperatures of the pressing process, in accordance with the heat treatment specifications and stamping procedures (the final temperature after hot processing should be above 850°C; rapid cooling is required after processing, such as through forced air or water spraying), and proper records must be kept. Heating in the same furnace as carbon steel heads is not allowed. The tools and forming dies used for thermoforming must be clean, with no contaminants such as carbon steel shavings or scale allowed. 12. For stainless steel end caps, elbows, metals, and other components that have been formed through hot working, if the material is to undergo tests for intergranular corrosion susceptibility, intergranular corrosion resistance tests shall be carried out as required after hot working ； If, after hot working, the material of the component does not meet the requirements of the intergranular corrosion resistance test, solution treatment or stabilization treatment should be carried out (stabilization treatment is only applicable to stainless steels containing stabilizing elements). There should be a heat treatment process and heat treatment time – temperature curve records (curves recorded using an automatic recorder). An intergranular corrosion test should be conducted after heat treatment. 13. During the shell assembly process, tools such as wedges and shims that are temporarily needed and come into contact with the shell surface should be made of stainless steel suitable for the shell. 14. Forced assembly of stainless steel pressure vessels is strictly prohibited, and tools that may cause iron ion contamination must not be used during the assembly process. The openings in the container should be created using plasma or mechanical cutting methods. 15. Before welding, the oil and other contaminants at the weld joint must be cleaned away using a chlorine-free liquid degreaser or other methods. Grooves cut by plasma cutting should be polished to a metallic shine. 16. During welding, carbon steel shall not be used as the ground clamp; the ground clamp must be secured to the workpiece, and spot welding for fixation is prohibited. 17. The welding of stainless steel pressure vessels must strictly follow the welding procedure specifications, with strict control over the interpass temperature. When using carbon arc gas gouging to clean the root of a weld bead, care must be taken to prevent carburization; the carburized layer must be removed by grinding ； When welding stainless steel pressure vessels that require resistance to intergranular corrosion, the weld seams in contact with the working medium should be welded last (when welding duplex stainless steel, the weld seams in contact with the working medium should be welded first). 18. During welding, an arc must not be initiated directly on the un-welded surface of the stainless steel. When using shielded metal arc welding, a spatter-proof coating over a range of 100 mm on both sides of the weld should be applied to facilitate the removal of spatter. 19. Unqualified welds may be reworked, but the number of rework attempts on the same area should not exceed two. For welds that remain non-compliant after two repair attempts, any further repairs must be approved by the technical supervisor of the manufacturing unit before each attempt, and the number of repairs, the locations involved, and the details of the repairs must be recorded in the product’s quality certificate. For components requiring resistance to intergranular corrosion, the original requirements are still maintained after weld repair. 20. For welding test plates of stainless steel pressure vessel products that require resistance to intergranular corrosion, intergranular corrosion tests shall be conducted in accordance with the provisions of the design drawings. 21. During the manufacturing process, sharp or hard objects should be avoided to prevent scratching of the stainless steel surface. If working inside a container, protective measures such as installing padding should be taken. 22. Any defects on the surface of stainless steel pressure vessels, such as local dents or scratches that affect their corrosion resistance, must be repaired.