The first step to make the seamless 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 seamless pipe wall thickness is defined by the gap between the piercing ram and the extrusion die. It is difficult to control the wall thickness uniformity and it is difficult to achieve good finish quality. The surface of the extrusion billet is initially machined in order to remove any surface defects otherwise it will exert a bad effect on the surface quality of the finished product.
If there is any need to further reduce the tube hollows down to a required size, use the pilgering to finalize the finish and size of the tubes. Cold work improves the mechanical properties and tolerances.
Cold pilger is the preferred production process since this technique provides a high forming rate, narrow tolerances and good productivity yields. In general seamless tubes receive some type of finishing treatment and heat treatment after completion of the manufacturing process and all piping shall be supplied in the heat treated condition.