Pickling and passivating treatment process for stainless steel pipes

Abstract

The invention discloses a pickling and passivating treatment process for stainless steel pipes, which comprises the steps of pretreatment, liquid preparation and pickling and passivating treatment, wherein the pickling and passivating liquid consists of 20 to 22 percent of nitric acid (with specific gravity of 1.42), 30 to 50 grams per liter of potassium dichromate, 30 to 50 grams per liter of additive and the balance of water. In the pickling and passivating treatment process, pickling and passivating are accomplished in one step to form silvery white bright beautiful surfaces of the stainless steel pipes and form high-quality passivated films, so that the surface quality of the treated metal pipes is improved and the treated metal pipes have high corrosion resistance; the descaling speed and the descaling efficiency are high; the corrosion of the metal substrates is small and the corrosion inhibition rate is high; and acid mist in a cleaning operation process is avoided, and the long-existing NOx and HF serious pollution problem of stainless steel continuous pickling and passivating is solved.

Description

technical field [0001] The invention relates to a stainless steel material surface treatment process, in particular to a stainless steel pipe fitting pickling passivation treatment process. Background technique [0002] The corrosion resistance of stainless steel is mainly due to the fact that the surface is covered with a very thin (about 1nm) dense passivation film, which is isolated from the corrosive medium and is the basic barrier for stainless steel protection. Stainless steel workpieces will form an oxide film when placed in the air, but the protection of this film is not perfect. Usually, it needs to be thoroughly cleaned first, including alkali cleaning and pickling, and then passivated with an oxidant to ensure the integrity and stability of the passivation film. One of the purposes of pickling is to create favorable conditions for passivation treatment and ensure the formation of high-quality passivation film. [0003] During the manufacturing process of stainle...

AI Technical Summary

Problems solved by technology

In the prior art, when stainless steel pipe fittings are pickled and passivated, the process is complicated and there are many steps. The ratio of pickling and passivation solution is often determined by each manufacturer according to its own materials and production experience. The determined ratio is different. Stable, the use effect is not ideal, there are shortcomings such as incomplete removal of oxides on the surface of the pipe fittings after pickling, insufficient passivation film formation, poor finish, etc.

In addition, there are also problems such as slow descaling speed, low efficiency, high corrosion to metal substrates, low corrosion inhibition rate, acid mist generated during cleaning and passivation operations, which affects the health of operators, etc.