Depending on the operating method, there are six main methods for acid pickling and passivation of stainless steel: immersion method, paste method, brushing method, spraying method, circulation method, and electrochemical method. Among these, the immersion method, paste method, and spraying method are more suitable for acid pickling and passivation of stainless steel tanks and equipment.
Immersion Method: This method is most suitable for stainless steel pipelines, elbows, small parts, and provides the best treatment effect. As the treated parts can be fully immersed in the acid pickling and passivation solution, the surface reaction is complete, and the passivation film is dense and uniform. This method is suitable for continuous batch operations but requires the continuous replenishment of fresh solution as the concentration of the reacting solution decreases. Its drawback is that it is limited by the shape and capacity of the acid tank and is not suitable for large-capacity equipment or pipelines with excessively long or wide shapes. If not used for a long time, the effectiveness may decrease due to solution evaporation, requiring a dedicated site, acid tank, and heating equipment.
Paste Method: The acid pickling paste for stainless steel is widely used domestically and is available in a series of products. Its main components include nitric acid, hydrofluoric acid, corrosion inhibitors, and thickening agents, in specific proportions. It is manually applied and suitable for on-site construction. It is applicable to the pickling and passivation of stainless steel tank welds, discoloration after welding, deck tops, corners, dead angles, ladder backs, and large areas inside liquid compartments.
The advantages of the paste method are that it does not require specialized equipment or space, heating equipment is not needed, on-site operation is flexible, acid pickling and passivation are completed in one step, and it is independent. The passivation paste has a long shelf life, and each application uses a new passivation paste for one-time use. The reaction stops after the surface layer of passivation, making it less prone to over-corrosion. It is not restricted by subsequent rinsing time, and passivation in weak areas such as welds can be strengthened. The disadvantage is that the work environment for the operator may be poor, labor intensity is high, costs are relatively high, and the effect on the inner wall treatment of stainless steel pipelines is slightly inferior, requiring a combination with other methods.
Spraying Method: Suitable for fixed sites, closed environments, single products, or equipment with simple internal structures for acid pickling and passivation, such as the spraying pickling process on a sheet metal production line. Its advantages are fast continuous operation, simple operation, minimal corrosive impact on workers, and the transfer process can spray the pipeline again with acid. It has a relatively high utilization rate of the solution.
Post time: Nov-29-2023