The craft of manufacturing of seamless steel pipes

The first step to make the seamless steel pipes is generally started with a hot extrusion to form the tube hollows from billets which has typically a drilled hole and is pushed through a die and over a mandrel with the process of air cooling or water quenching afterwards. The manufacturing processes for seamless pipes mainly include the following methods.

Hot Rolling:

- Round Billet Preparation: First, the round steel billet is heated to an appropriate temperature to ensure good plasticity.

- Piercing: The heated round billet is pierced into a hollow shell using a piercing machine.

- Rolling: The pierced shell is rolled by a continuous rolling mill to achieve the desired size of the seamless steel pipe. Multiple rolling passes may be required to ensure uniform dimensions and wall thickness.

- Sizing and Reducing: The rolled steel pipe is further adjusted by a sizing mill and reducing mill to achieve precise outer diameter and wall thickness.

Cold Drawing:

Preparation: The hot-rolled seamless steel pipe is pickled to remove surface scale and then lubricated.

Cold Drawing Forming: The treated steel pipe is drawn through a cold drawing machine to gradually achieve the desired outer diameter and wall thickness.

Heat Treatment: During the cold drawing process, the metallographic structure of the steel changes, necessitating annealing or normalizing to restore the mechanical properties and toughness of the steel.

Cold Rolling:

- Preparation: Similar to the cold drawing process, the hot-rolled seamless steel pipe is first pickled and lubricated.

- Cold Rolling Forming: The treated steel pipe is passed through a cold rolling mill, undergoing multiple passes to gradually reduce the diameter and wall thickness and achieve a smoother surface.

- Heat Treatment: The cold-rolled steel pipe also requires heat treatment to restore its mechanical properties.

Piercing Method:

- Heating: The solid steel billet is heated to piercing temperature.

- Piercing: The heated billet is pierced into a hollow shell using a piercing machine.

- Rolling and Sizing: The hollow shell undergoes multiple rolling and sizing processes to achieve the desired dimensions and specifications.

Extrusion:

- Preparation: The steel billet is heated to extrusion temperature.

- Extrusion Forming: The heated billet is extruded through a die using an extrusion machine to form a seamless steel pipe. The extrusion process allows control over the outer diameter and wall thickness of the pipe.

Each manufacturing process has its unique advantages and applicable scope. Selecting the appropriate process based on production needs and material characteristics ensures the quality and performance of the seamless pipes.