1.Necessity of pickling of stainless steel seamless pipes
Austenitic stainless steel seamless pipes have good corrosion resistance, high temperature oxidation resistance, good low temperature performance and excellent mechanical and bioenergy. Therefore, they are widely used in chemical, petroleum, power, nuclear engineering, aerospace, ocean, medicine, light industry, textile and other departments. Its main purpose is to prevent corrosion and rust.
The corrosion resistance of stainless steel seamless pipes mainly depends on the surface passivation film. If the film is incomplete or defective, the stainless steel will still be corroded. Pickling and passivation treatment is usually carried out in engineering to maximize the corrosion resistance potential of stainless steel. In the process of forming, assembly, welding, weld inspection (such as flaw detection, pressure resistance test) and construction marking of stainless steel equipment and components, surface oil, rust, non-metallic dirt, low melting point metal pollutants, paint, welding slag and splashes are brought. These substances affect the surface quality of stainless steel equipment and components, destroy the oxide film on its surface, reduce the steel’s resistance to overall corrosion and local corrosion (including pitting and crevice corrosion), and even cause stress corrosion cracking.
2.Tips for pickling and passivation of stainless steel seamless pipes in summer
When pickling and passivation of stainless steel seamless pipes in summer, the following points should be noted:
(1) Safety protection
Pickling and passivation treatment involves the use of acidic solutions, so strict safety measures must be taken. Operators should wear appropriate protective equipment, including chemical protective clothing, acid-proof gloves, protective glasses and acid-proof masks, etc., to prevent acidic liquids from damaging the skin, eyes and respiratory system.
(2) Ventilation and exhaust
The pickling and passivation process will produce acidic gases, so it is necessary to ensure that the treatment area has a good ventilation system and the exhaust system can well discharge the acidic gases to keep the indoor air fresh and avoid harm to operators.
(3) Temperature control
The high temperature in summer will affect the temperature of the pickling and passivation solution. Ensure that the temperature of the pickling solution is controlled within an appropriate range, generally adjusted according to specific process requirements. Too high a temperature may cause corrosion to intensify or uneven film formation, while too low a temperature may reduce the passivation effect.
(4) Pickling time control
The control of pickling time is very important for the effect of passivation treatment. In the high temperature environment in summer, the pickling time may need to be adjusted accordingly to ensure sufficient processing time so that the passivation film is formed evenly and has good performance.
(5) Surface cleaning and neutralization treatment
After the stainless steel seamless pipe is pickled and passivated, the surface of the workpiece should be cleaned and the residual pickling liquid should be removed. At the same time, neutralization treatment is carried out to neutralize the residual acidic liquid to avoid corrosion to subsequent processes and equipment.
(6) Waste liquid treatment
The treated pickling liquid is a hazardous waste and should be properly handled in accordance with relevant regulations. It is prohibited to discharge the waste liquid directly into the drainage system or the environment. A legal waste liquid treatment method should be selected to comply with environmental protection requirements.
