Stainless steel pickling passivation process specification_FAQ

1 Subject content and scope of application 1.1 Subject content This regulation specifies the requirements, methods and precautions for the cleaning, pickling and passivation of oil stains and rust stains on the surface of stainless steel containers (including parts and components). 1.2 Scope of application This regulation is applicable to the pickling passivation treatment of chromium and nickel austenitic stainless steel vessels manufactured by our company. 2 Reference documents The following reference standards and documents should be the **** version. When this regulation conflicts with the new standard or document content, the conflicting part shall be implemented in accordance with the corresponding provisions of the **** standard and document. 'General Regulations for the Manufacturing of Stainless Steel Pressure Vessels' 'General Inspection Procedures' 3 Pickling, passivation process, degreasing, cleaning dirt, clean water, passivation, clean water, rinse and dry 4 pickling, pretreatment before passivation 4.1 Pair manufacturing The stainless steel container or parts after completion can be pickled and passivated pretreatment only after the specified items are inspected according to the requirements of the drawings and process documents. 4.2 Clean up the welding seam and the welding slag and spatter on both sides, and the surface of the machined parts of the container should be cleaned with gasoline or cleaning agent to remove oil stains and other dirt. 4.3 When removing foreign objects on both sides of the weld, use a stainless steel wire brush, stainless steel spatula or grinding wheel to remove it. After removing it, use clean water (chloride ion content in the water not to exceed 25mg/l) to wash it clean. 4.4 When the oil pollution is serious, use 3-5% alkali solution to remove the oil pollution and rinse it with clean water. 4.5 The oxide scale of stainless steel hot-worked parts can be removed by mechanical sandblasting, and the sand must be pure silicon or alumina. 4.6 Develop safety measures for pickling and passivation, and determine necessary utensils and labor protection articles. 5 Formulation of pickling, passivation solution and paste 5.1 Formulation of pickling solution: 20% nitric acid (specific gravity 1.42), 5% hydrofluoric acid, and the rest is water. The above is the volume percentage. 5.2 The formula of pickling cream: 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. 5.3 The passivation solution formula: nitric acid (specific gravity 1.42) 5%, potassium dichromate 4 grams, and the rest is water. For the above percentage of the product, the passivation temperature is room temperature. 5.4 Formulation of passivation paste: 30 ml of nitric acid (concentration 67%), 4 g of potassium dichromate, add bentonite (100-200 mesh) and stir until it is a paste. 6 Pickling passivation operation 6.1 Only the containers or parts that have been pretreated can be pickled and passivated. 6.2 Pickling liquid pickling is mainly used for the overall treatment of smaller unprocessed parts and can be sprayed. When the temperature of the solution is 21-60℃, check it every 10 minutes or so until it shows a uniform white acid etching finish. 6.3 Pickling cream pickling is mainly suitable for large containers or local treatment. Clean the pickling paste evenly on the equipment (approximately 2-3mm thick) at room temperature, leave it for one hour and then gently brush with clean water or a stainless steel wire brush until it presents a uniform white acid-etched finish. 6.4 The passivation solution is mainly suitable for the overall treatment of small containers or parts. It can be immersed or sprayed. When the solution temperature is 48-60℃, check every 20 minutes. When the solution is 21-47℃, every hour Check once until a uniform passivation film is formed on the surface. 6.5 Passivation paste is mainly suitable for large containers or partial treatments. Spread the passivation paste evenly on the surface of the pickled container (about 2-3mm) at room temperature, and check after 1 hour until a uniform passivation film is formed on the surface . 6.6 The surface of the pickling passivation container or parts must be rinsed with clean water. Finally, use acid litmus paper to test any part of the rinsed surface to make the pH between 6.5-7.5, and then wipe dry or blow dry with compressed air . 6.7 After the containers and parts are pickled and passivated, it is forbidden to bump and scratch the passivation film during transportation, hoisting and storage. 7 Precautions 7.1 When preparing the liquid, put the water in the acid-resistant container according to the proportion, and then slowly add the acid according to the proportion, so as to prevent the acid from being poured too fast to cause splashing and injury. 7.2 Pickling passivation treatment, the first operation should be tested on the partial surface of small parts or similar materials. 7.3 During the pickling process, the operator must carefully observe in time to prevent excessive corrosion on the surface of the container. Effective measures should be taken for carbon steel parts to prevent corrosion. 7.4 After pickling, the surface of stainless steel shall not have obvious corrosion marks, shall not have uneven color markings, and the welding seam and hot processed surface shall not have oxidation color. 7.5 When operating, the operator must wear acid-resistant clothing, gloves, respirators and protective goggles. For pickling in the container, a qualified gas mask must be worn and carried out under the supervision of a special person. 7.6 After the austenitic stainless steel parts with anti-corrosion requirements are heat treated according to the drawing requirements, they are pickled and passivated. 7.7 The above-mentioned pickling passivation formula and operation, concentration, volume ratio, liquid temperature and operation time can be adjusted appropriately according to the situation. The pickling passivation solution can be reused, but the proper concentration and volume ratio must be ensured. brush