After air drawing, the surface area of the outer surface of the seamless steel pipe increases, and the surface area of the inner surface decreases, and a neutral layer is required between the inner and outer layers. After the layer between the outer surface and the neutral layer is deformed, the surface area is all increased, while the outer surface layer has a relatively large increase. After each layer between the neutral layer and the inner surface is deformed, the surface area decreases, while the inner surface decreases more.

The above-mentioned change characteristics of the surface area of each layer of seamless steel pipe during the air drawing process will affect the unevenness of metal deformation. One of its characteristics is that the natural extension of each layer along the pipe wall is inconsistent. The natural extension takes the outer surface layer of the seamless steel pipe as the smaller one, and the inner surface layer of the seamless steel pipe as the larger one. The surface layer to the inner surface layer gradually increase.
Another feature is that due to the relationship of integrity, each layer of seamless steel pipe cannot have different extensions during the deformation process. Therefore, each layer needs to contain each other. In fact, seamless steel pipes are mainly used for high-precision structural light pipes, such as cracking pipes selected in petrochemicals, drilling pipes selected in petroleum geology, or seamless pipes used in automobiles and tractors. They all have certain high precision requirements.

Since the natural extension of the metal (called the outer layer) between the outer surface and the neutral layer of the seamless pipe is smaller than the natural extension of the metal (called the inner layer) between the neutral layer and the inner layer, the outer layer needs to be Layer drag. In the process of deformation, the actual extension of the seamless tube is greater than the natural extension, and due to the increase in extension, its thickness decreases. On the contrary, the extension of the inner layer of the seamless pipe is hindered by the outer layer, the actual extension is smaller than the natural extension, and the thickness increases.