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Several Treatment Methods for Pickling and Passivation of Seamless Steel Pipes

Date:2020-01-09    keywords:pickling and passivation,seamless steel pipe
a. Pickling passivated seamless steel tube dipping method. Stainless steel pipelines, elbows, small parts, etc. are most suitable for this method, and the processing effect is the best. Because the treatment part can be fully immersed in the pickling passivation solution, the surface of the pickled passivation seamless tube is completely reacted, and the passivation film is dense and uniform. This method is suitable for continuous batch operation, but needs to be replenished with new solution as the reaction concentration of the solution decreases. The disadvantage is that due to the limitation of the shape and capacity of the acid tank, it is not suitable for large-capacity equipment and pipelines that are too long and wide in shape; long-term use will reduce the effect due to solution volatilization and other reasons. Special sites, acid pools and heating equipment are required.

b. Pickling passivated seamless steel tube plaster method. Stainless steel pickling passivation paste has been widely used in China and has a series of product supplies. It is manually operated and suitable for on-site construction. Welding treatment of stainless steel chemical containers, welding discoloration, corner dead ends, escalator back and large-area passivation are all used. 

The advantages of the paste method are that no special equipment and site are needed, no heating equipment is required, and the site is flexible in operation. The pickling and passivation are completed at once, and the independence is strong; the passivation paste has a long shelf life, and a new passivation paste is used for each application. In general, the reaction stops after the passivation of the surface layer is finished, it is not easy to be over-corroded, and it is not limited by the subsequent flushing time. Weakness such as welds can also strengthen passivation. Disadvantages are poor operating environment for workers, high labor intensity, high cost, and poor treatment of the inner wall of stainless steel pipelines, which need to be combined with other methods.

c. Seamless steel tube pickling and spraying method. It is suitable for a single product with a fixed site and a closed environment or equipment with a simple internal structure for pickling and passivation, such as the spray pickling process on a board production line. For stainless steel chemical containers, it can be used for pickling the inner wall of containers.

Its advantages are fast continuous operation, simple operation, low impact on workers' corrosion, and high solution utilization. This method has many restrictions, such as: 1. There must be no residues or impurities in the container. 2. The pickling solution stays in the container for too long, and the reaction will cause over corrosion of the stainless steel. Therefore, it is necessary to continue the operation and prepare a large amount of cleaning water at any time. It will cause serious consequences in the event of power outage, water outage, shutdown, etc. 3. A large container should be used for waste acid and waste water discharge. 4. As the reaction time increases and the solution impurities increase, the effective components of the pickling solution gradually decrease. The solution concentration must be detected at any time and new solutions must be added in time.

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