Why do seamless pipes need coating?

The reason why seamless pipes can be used in many places and natural environments is that the structure of the appearance design is varied, and it can take into account the work regulations that ordinary steel pipes cannot complete, which has been recognized and favored by everyone. In the production process of seamless pipe, in order to better improve its performance index, coating will be carried out on its surface. So what are the factors that affect the coating of seamless pipes?

Envirnmental factor

The passive film of the seamless pipe is a thermodynamically inhibited metastable structure, and its maintenance effect is related to the medium in the environment. But no matter what environment the seamless pipe is used in, it needs to be cleaned regularly to remove the harmful substances attached to the surface.

Chloride

Chloride ions are very harmful to the coating of seamless pipes, and the content of chloride ions in the passivation solution should be strictly controlled during the passivation of the surface. Many chemical materials used for passivation have limited requirements for chloride ion content; when configuring passivation solution and cleaning water, there are also strict water quality requirements for chloride ions to ensure that the passivation waste does not contain chloride ions.

Internal factors

The content of nickel in the seamless pipe is low and the passivation performance is low, so the content of martensite and chromium and nickel have a great influence on the passivation performance of the seamless pipe.

Cleanliness

The more lubrication on the surface of the seamless pipe, the lower the roughness, the more difficult it is for foreign matter to adhere, and the corrosion will be reduced to a low point. Additionally, post-passivation cleaning should be stopped carefully so that residual acid can promote anodic response, maintain film integrity, and ensure enhanced corrosion resistance of the seamless pipe.

Tips: the production process of seamless pipes can be divided into two types: cold-drawing and hot-rolling. The production process of cold-rolled seamless pipes is generally more complicated than that of hot-rolled pipes, but the accuracy of cold-rolled steel pipes dimension  is higher than that of hot-rolled steel pipes.

Author
Chase Liu