Which factors will affect the effect of acid pickling and passivation of 310S stainless steel seamle

The following are some factors that can affect the acid pickling and passivation effect of 310S stainless steel seamless pipes: 

The composition and concentration of the pickling and passivation solution

Different combinations and concentrations of acids have different effects on the surface of stainless steel. For example, the commonly used mixture of nitric acid and hydrofluoric acid. Nitric acid plays the role of oxidation and removing impurities, while hydrofluoric acid can effectively dissolve the oxide scale on the surface of stainless steel. If the concentration of nitric acid is too high, it may cause excessive corrosion on the surface of the stainless steel; if the concentration of hydrofluoric acid is too high, it may erode the stainless steel substrate, affecting the performance of the pipe material. 

Controlling temperature and time

An increase in temperature usually accelerates the reaction rate of acid pickling and passivation. However, excessively high temperatures may cause the reaction to become too intense, resulting in excessive corrosion on the surface of stainless steel. At the same time, it will also increase the evaporation and consumption of the acid solution, causing environmental pollution and rising costs. If the processing time is too short, it may not be able to fully remove impurities and form a complete passivation film; if the time is too long, it may damage the formed passivation film. 

The cleanliness of the pipe surface

If there are oil stains, dust, iron filings and other impurities on the pipe surface before the acid pickling and passivation process, it will hinder the full contact between the acid solution and the stainless steel surface, affecting the effect of acid pickling and passivation. These impurities may form a barrier layer on the pipe surface, preventing the acid solution from effectively removing the oxide scale and other contaminants, resulting in an uneven or incomplete passivation film. 

The material and surface condition of the pipe

The composition fluctuations, microstructure, and surface roughness of 310S stainless steel all affect the effect of acid pickling and passivation. For instance, if the pipe contains a large amount of impurity elements or has segregation phenomena, it may cause uneven local reactions during the acid pickling and passivation process. Pipes with a rougher surface have a larger contact area between the acid solution and the metal during acid pickling and passivation, and the reaction may be more intense. However, they may also have residual acid after incomplete cleaning, which can affect the quality of the passivation film. 

Cleaning and drying after acid pickling and passivation

If the cleaning is not thorough after acid pickling and passivation, the remaining acid will continue to react with the stainless steel surface, destroying the passivation film and reducing the corrosion resistance. At the same time, the quality of the cleaning water is also very important. If the water contains a lot of impurities or metal ions, it may contaminate the surface of the pipe and affect the passivation effect. The drying process cannot be ignored either. A humid environment is likely to cause rust on the surface of the pipe, and timely drying treatment should be carried out. The drying temperature and method should also be appropriately controlled to avoid damaging the passivation film.