Before the stainless steel pipe enters the pickling and passivation process, corresponding pretreatment work must be done so as to obtain a stainless steel pipe surface that meets expectations after the pickling and passivation process.
Pretreatment work mainly includes the following aspects.
The first is based on pre-written drawings and the requirements of the process documents, after the completion of the production of stainless steel pipe inspection of the specified project to ensure that the relevant standards are qualified.
Followed by clean welding seams and spatter and spatter on both sides. When removing foreign materials on both sides of the weld, use a stainless steel wire brush or grinding wheel to remove; the surface of the machined parts of the stainless steel pipe should be cleaned with gasoline or detergent. If you remove grease, dirt, etc., if the oil is severe enough to be removed with a suitable alkaline solution, it is important to note that after both removals are completed, rinse with clean water with a chloride ion content of less than 0.5%.
Mechanical sandblasting can be used to remove oxide scale from stainless steel hot work parts, where the sand must be pure silicon or alumina.
Finally, it is necessary to formulate a good pickling and passivation safety measure and determine suitable labor and protective equipment.
Pickling and passivation can be used for the overall treatment of smaller, unprocessed parts. When the temperature of the solution is in the range of 21-60°C, it should be checked every 10 minutes until a uniform white acid etching finish is exhibited.
Pickling using pickling pastes is mainly suitable for the local treatment of large pipes or components. The treatment method is to evenly apply the pickling paste to the clean equipment at room temperature, apply a thickness of about 2-3mm or so, and then use a clean water or stainless steel wire to gently brush until it shows an even white acid etch. The finish is only finished.
The passivation solution is mainly suitable for use in the overall treatment of small tubes or components. It can be immersed or sprayed. When the solution temperature is 48-60°C, it should be checked every 20 minutes when the solution is at 21-47°C. At that time, it needs to be checked once every hour until the surface forms a uniform passivation film.
The passivation paste is also mainly applied to large-scale pipe fittings or localized treatment. The passivation paste is evenly coated on the surface of the acid-washed stainless steel tube at room temperature. After 1 hour, it needs to be inspected until a uniform passivation film is formed on the surface. .
Pickling passivated tubes or components must be cleaned with clean water, and then use acidic litmus paper to detect all areas of the flushing surface. The requirement is to maintain the pH in the range of 6.5-7.5, then wipe clean or use compression The air is blown dry. Pickling and passivating stainless steel pipes cannot be bumped and scratched during handling and lifting to prevent damage to the passivation film.
Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)