Requirements related to the fabrication of stainless steel pressure vessels

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I. Manufacturing environment: Production should take place in a dedicated facility, and it must be strictly separated from products made of carbon steel. If carbon steel components are used, the facility where such components are manufactured should be separate from the facility used for manufacturing stainless steel products. The production area must be kept clean and dry; rubber or wooden mats should be laid on the floor, and wooden shelving should be used for storing components, semi-finished products, and finished products. During the manufacturing process, special roller frames should be used (e.g., rollers lined with rubber). For lifting containers or components, it is advisable to use rope slings or metal slings encased in flexible materials such as rubber or plastic. Personnel entering the production area must wear work shoes whose soles contain no sharp objects like metal nails. During handling and transportation, stainless steel materials or components should be equipped with appropriate transport tools to prevent contamination by iron ions and scratches. The surface treatment of stainless steel pressure vessels should take place in a separate facility equipped with necessary environmental protection measures. II. Materials: The stainless steel materials and welding materials used in the manufacture of pressure vessels shall comply with the corresponding **standards or industry standards, as well as the relevant provisions of the \"Regulations on Safety Inspection of Fixed Pressure Vessels\". They must also come with a quality certificate issued by the material manufacturer. When materials of foreign brands are used, they shall meet the requirements specified in 2.1.2 of the \"Regulations on Safety Inspection of Fixed Pressure Vessels\". For materials used in main pressure-bearing components, if the authenticity of the quality certificate cannot be verified, or if there are doubts regarding their performance and chemical composition; for foreign materials, hot-rolled austenitic stainless steel plates; or when design documents require re-testing—in any of these cases, it is necessary to conduct a re-test on the raw materials. When the design specifications require retesting of the raw materials for their intergranular corrosion resistance, the shape, dimensions, processing methods, and testing procedures for the specimens used in such retesting shall, unless otherwise specified in the design specifications, comply with the requirements of GB/T4334. The stainless steel materials should have clear incoming inspection marks. This marking should be made using chlorine- and sulfur-free marker pens; polluted materials such as paints should generally not be used, and stamping on the surface of the material is prohibited. Appropriate measures must be taken when lifting steel plates to prevent deformation. The ropes and rigging used for lifting should have protective covers to avoid damaging the surface of the material. III. Machining, Forming, and Welding When using a template for marking, it should be made of a material that will not contaminate or damage the surface of the stainless steel. Marking should be done on a clean wooden board or smooth platform. It is strictly prohibited to use steel needles for marking or punching on the surface of stainless steel materials that come into contact with the medium. During material cutting, laser cutting, plasma cutting, or mechanical cutting methods should be employed in accordance with the requirements of the design drawings and layout plans. Remember: Mark the material for transplantation first before cutting it; materials without markings or with unclear markings must not be processed further. The marking of stainless steel compression component materials should be applied by spraying ink in appropriate locations on the materials of each component (the ink must be free of chlorine and sulfur), and written records of the material cutting should also be kept. When milling grooves, the machine tool should be cleaned thoroughly; to prevent scratches on the surface of the sheet metal, soft materials such as rubber should be used to cover the pressing feet. The materials that have been laid down should be neatly stacked on the frame, so as to be lifted together with the frame; soft materials such as rubber or wooden planks should be placed between the boards to prevent damage to their surfaces. Round steel and steel pipes can be cut using machine tools, saw blades, or grinding machines. Moreover, grinding wheel residues, burrs, etc. at the cut area must be removed. When rolling stainless steel plates, a material free of iron ions should be applied to the surface of the rolls of the plate rolling machine or to the surface of the stainless steel plate. When machining components, water-based emulsions are generally used as coolants. During the shell assembly process, tools such as temporary wedges and shims that come into contact with the shell surface should be made of stainless steel material compatible with the shell. Stainless steel pressure vessels must not be assembled by force; assembly must be carried out strictly in accordance with the requirements of the design drawings and layout plans. Tools that could cause iron ion contamination must not be used during the assembly process. Openings in the container shall be made by plasma or mechanical cutting. Before welding, it is necessary to use a chlorine-free liquid degreaser or other methods to clean off oils and other contaminants from the weld joint. Grooves made by plasma cutting should be polished to a metallic shine. During welding, it is not permitted to use carbon steel materials as ground clamps. The ground clamp must be securely fastened to the workpiece; spot welding for this purpose is prohibited. The welding of stainless steel pressure vessels is carried out in strict accordance with welding procedure specifications, with careful control of the interpass temperature. When using carbon arc gas gouging to clean the root of the weld bead, the carburized layer must be ground off. When welding stainless steel pressure vessels that require resistance to intergranular corrosion, the weld seams in contact with the working medium are welded last. During welding, the arc must not be initiated directly on the non-welded surface of the stainless steel. When using manual arc welding, a spatter prevention coating of 100 mm on each side of the weld should be applied to facilitate the removal of spatter. Unqualified welds may be repaired, but the number of repairs on the same area should not exceed two. For welds that remain unqualified after two repairs, any further repairs must be approved by the chief technical officer, and the number of repairs, the location, and the details of the repairs must be recorded in the product’s quality certification documents. In cases where components are required to resist intergranular corrosion, the original requirements must still be met even after the welds have been repaired. During the manufacturing process, sharp or hard objects should be avoided to prevent scratching of the stainless steel surface. When working inside a container, protective measures such as laying down liners should be taken. IV. Non-destructive testing: The non-destructive testing methods used for each piece of equipment, as well as the testing frequency and timing, are all carried out in accordance with the requirements specified in their respective design documents. For specific requirements, please refer to the respective manufacturing process cards and welding procedure specifications. V. Surface treatment After all weld repair work on stainless steel pressure vessels is completed, surface treatment shall be carried out in accordance with the requirements of the design drawings. Impurities on the surface of pressure vessels such as welding spatter, slag, scale, weld scars, and oil stains must be removed completely. Carbon steel brushes must not be used to clean the surface of stainless steel pressure vessels during this process. Before pickling, oil stains must be removed from the surface of the workpiece, which should then be rinsed thoroughly with water; it is not allowed to use carbon steel wires to scrub the surface of the workpiece. 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. The surface of the stainless steel after pickling must not show any visible traces of the cleaning solution, nor any patches with uneven coloring. Welds and surfaces that have undergone heat treatment must not exhibit any oxidized colors. After pickling, the surface must be rinsed thoroughly with water to ensure that no residual cleaning solution remains. The passivated stainless steel surface should be rinsed with water, and once it is neutral, the water droplets should be dried off. A passivation film inspection should be conducted at the surface in contact with the medium, and once the inspection is successful, the passivation film in that area should be repaired. The inspection of the passivation film is carried out using the blue dot method. The acid washing and passivation solutions that need to be discharged must undergo neutralization; they can only be released after meeting the **wastewater discharge standards**. VI. Pressure testing and transport packaging: 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. After the hydrostatic test of stainless steel pressure vessels, the water should be drained immediately and any traces of water removed; the chloride content in the water used for testing must not exceed 25 mg/L. During pressure testing, airtightness testing, and packaging of stainless steel pressure vessels, if the passivation film on the surfaces in contact with the medium is damaged, measures should be taken promptly to re-passivate those surfaces. After the manufacture of stainless steel pressure vessels, all sealing surfaces and pipe ends shall be given appropriate protective measures in a timely manner, and the carbon steel parts of the vessels shall be treated to prevent corrosion in accordance with the requirements of the design documents. And it is nitrogen-sealed before being stored.