ASTM A249 welded coil: How does the surface treatment process improve corrosion resistance?

During the manufacturing process of ASTM A249 welded coil, after welding, heat treatment and other steps, impurities such as scale, welding spatter, and oil stains often remain on the surface of the pipe. These impurities not only affect the appearance quality of the pipe, but more importantly, they will reduce the corrosion resistance of the pipe and shorten its service life. Therefore, surface treatment must be carried out to remove these impurities and improve the surface finish and corrosion resistance of the pipe.

Pickling is the first step in the surface treatment of ASTM A249 welded coil. The main purpose is to remove the scale and rust on the surface of the pipe. The scale is a dense oxide layer formed by high temperature or chemical reaction during the processing of the pipe. It not only affects the appearance of the pipe, but also may become the starting point of corrosion and reduce the corrosion resistance of the pipe.

The pickling process usually uses inorganic acids (such as sulfuric acid, hydrochloric acid) or organic acids (such as citric acid) as pickling liquids. The pickling liquid reacts chemically with the oxides on the surface of the pipe to generate soluble salts and water, thereby removing the scale. At the same time, pickling can also remove oil and other impurities on the surface of the pipe, providing a clean surface for subsequent processing.

During the pickling process, the concentration, temperature and time of the pickling solution need to be strictly controlled to avoid damage to the pipe matrix or pickling solution residue due to excessive pickling. Excessive pickling will not only damage the surface structure of the pipe, but may also introduce new corrosion risks. Therefore, sufficient rinsing and neutralization treatment must be carried out after pickling to ensure the cleanliness of the pipe surface and the complete removal of the pickling solution.

Passivation treatment is the second step in the surface treatment of ASTM A249 welded coils, and it is also a key step to improve the corrosion resistance of pipes. The purpose of passivation is to form a dense oxide film on the surface of the pipe, which can prevent the corrosive medium from directly contacting the pipe matrix, thereby improving the corrosion resistance of the pipe.

The passivation process usually uses an oxidant (such as nitric acid, dichromate, etc.) as a passivation solution. The passivation solution reacts chemically with the surface of the pipe to form a dense oxide film. This oxide film not only has excellent corrosion resistance, but also improves the surface finish and aesthetics of the pipe.

During the passivation process, the concentration, temperature and time of the passivation solution also need to be strictly controlled. If the concentration of the passivation solution is too high or the temperature is too low, the oxide film may be too thick or uneven, affecting the corrosion resistance and surface quality of the pipe. If the passivation time is too long, it may cause excessive corrosion of the pipe matrix. Therefore, after passivation, sufficient rinsing and drying are also required to ensure the cleanliness of the pipe surface and the complete removal of the passivation solution.

After pickling and passivation treatment, the surface finish and corrosion resistance of ASTM A249 welded coiled tube are significantly improved. Pickling removes the oxide scale and impurities on the surface of the pipe, making the surface of the pipe smoother and cleaner. The passivation treatment forms a dense oxide film on the surface of the pipe, which can effectively prevent the corrosive medium from directly contacting the pipe matrix, thereby extending the service life of the pipe.

In addition, pickling and passivation treatment can also improve the welding performance and processing performance of the pipe. A clean and smooth surface is conducive to the formation of welded joints and the control of welding quality. A dense oxide film can reduce friction and wear of the pipe during processing, improving processing efficiency and product quality.