Stainless steel pickling and passivation process regulations program documents

1, subject content and scope of application
1.1 Subject content
This specification specifies the requirements, methods and precautions for cleaning, pickling and passivation of stainless steel pipe fittings with oil and rust stains on the surface.
1.2 Scope of application
This procedure applies to the pickling and passivation treatment of chromium and nickel austenitic stainless steel fittings manufactured by the company.
2, cited documents
The following cited standards, documents should be the latest version. When this procedure and the new standards, documents, conflict with the content, the conflict part of the latest standards, documents, according to the corresponding provisions of the content of the implementation.
General Inspection Procedures
3, pickling, passivation process
Degreasing cleaning dirt clean water washing passivation clean water rinsing blow-dry
4, pickling, passivation pretreatment
4.1 Manufacturing of stainless steel fittings according to the requirements of the drawings and process documents after completion of the required items to check the pass, before pickling, passivation pre-treatment.
4.2 If the product is welded, clean the weld seam and both sides of the weld slag and spatter, and the surface of the machined parts of the pipe fittings should be gasoline or cleaning agent to remove oil and other dirt.
4.3 Removal of foreign matter on both sides of the weld seam, stainless steel wire brush, stainless steel spatula or grinding wheel removal, removal is completed with clean water (chlorine ion content in the water does not exceed 25mg / l) flushed clean.
4.4 When the oil is serious then use 3-5% alkali solution to remove the oil, and rinse with clean water.
4.5 For stainless steel hot working parts of the oxide skin can be used mechanical sand blasting method to remove, sand must be pure silicon or aluminum oxide.
4.6 The development of pickling, passivation safety measures to determine the necessary appliances and labor protective equipment.

5, pickling, passivation solution and paste formula
5.1 Pickling solution formula: nitric acid (specific gravity 1.42) 20%, hydrofluoric acid is 5%, the rest is water. The above is the volume percentage.
5.2 Pickling paste formula: hydrochloric acid (specific gravity 1.19) 20 ml, 100 ml of water, nitric acid (specific gravity 1.42) 30 ml, bentonite 150 grams.
5.3 Passivation solution formula: nitric acid (specific gravity 1.42) 5%, potassium dichromate 4 grams, the rest is water. Above the Hugh product percentage, passivation temperature is room temperature.
5.4 passivation paste formula: nitric acid (concentration of 67%) 30 ml, 4 grams of potassium dichromate, plus bentonite (100-200 grams) stir until the paste.
6, pickling passivation operation
6.1 Only pre-treated fittings can be pickling passivation treatment.
6.2 Pickling solution pickling is mainly used for small diameter fittings overall treatment, you can use the method of spray brushing. The solution is checked every 10 minutes or so at a temperature of 21-60°C until a uniform white acid etched finish is presented.
6.3 Pickling Paste Pickling is mainly suitable for large diameter fittings or localized treatment. At room temperature will pickling paste outside the uniform clean equipment (about 2-3mm thick), stay an hour with clean water or stainless steel wire brush gently brush, until it presents a uniform white acid-etched finish.
6.4 Passivation solution is mainly applicable to small diameter pipe fittings overall treatment, can be used to dip or spray brush method, when the solution temperature at 48-60 ℃, every 20 minutes to check, when the solution at 21-47 ℃, every hour to check until the surface to generate a uniform passivation film.
6.5 Passivation paste is mainly suitable for large-diameter fittings or fittings local treatment, at room temperature will be uniformly coated with passivation paste on the surface of the pickled container (about 2-3mm), 1 hour after the check until the surface to generate a uniform passivation film.
6.6 Pickling passivated fittings must be rinsed off the surface with clean water, and finally test the rinsed surface with acidic litmus paper at any place to make the PH value between 6.5-7.5, and then wipe dry or blow dry with compressed air.
6.7 Pipe fittings after pickling and passivation handling lifting and storage is prohibited when bumping and scratching the passivation membrane

7、Precautions
7.1 When dispensing liquid, water should be put into the acid-resistant container in proportion, and then add acid slowly in proportion to prevent the acid from being poured too fast causing splash injury.
7.2 Pickling passivation treatment, the first operation should be first in the pipe fittings on the local surface or similar materials for the test.
7.3 Pickling process, the operator must be careful, timely observation, to prevent excessive surface corrosion of fittings. Carbon steel fittings should take effective measures to prevent corrosion.
7.4 After pickling the stainless steel surface shall not have obvious traces of corrosion, there shall be no uneven color mottling, welds and hot work surface shall not have oxidation color.
7.5 Operators in the operation, must wear good acid-resistant clothing, gloves, masks and eye protection. Acid washing in the container, must bring a qualified inspection of the gas mask, and under the supervision of a person.
7.6 There are corrosion requirements of austenitic stainless steel pipe fittings according to the drawing requirements for heat treatment, do pickling passivation treatment.
7.7 The above pickling passivation formula and operation, concentration, volume ratio, liquid temperature and operating time can be allowed to do a small amount of appropriate adjustments according to the situation. Pickling passivation liquid can be reused, but must ensure that the appropriate concentration and volume ratio