4.2　The Vertical Extrusion Process

4.2.1　The solid round billet，polygonal ingots or hollow billet may be used as raw material for vertical extrusion process.

4.2.2　Technical specifications of the billets，such as chemical composition，shall comply with those specified in the relevant current national standards related to steel pipe products.

4.2.3　Hollow billets should be used under the following circumstances:

1　extruding metals that are difficult to be deformed；

2　extruding thin-wall pipe products；

3　extruding rare-metal pipes that are very easy to stick the piercing rod；

4　using the extrusion press which has no independent piercing unit.

4.2.4　The surface or inner of the billets shall be free of defects like lap，scab，crack，shrinkage cavity，etc.

4.2.5　The outside diameter of the billet shall match the inside diameter of the piercer container.