The pressure of the seamless steel pipe is generally composed of pieces of standard parts, so the pressure pipe design component is the selection of its standard parts. The pressure level of pipelines is determined to the pressure level of its standard parts.

Pipeline pressure level consists of two parts:
One is nominal pressure rating which is expressed in the Nominal pressure of the standard parts. The other is wall thickness rating which is expressed in the wall thickness of the stand parts.

The pressure grade of the pipes:
The parameters of channels characteristics which are determined by the nominal pressure level and wall thickness are called the pressure grade of the seamless steel pipe. To simplify the description, we often call the nominal pressure rating as pipe pressure grades.

The calculation of the pressure grades is not only the basis for pipeline design, but also the core of design. It is the basis of the arrangement of pressure pipe, and pressure pipe stress precondition for checking the design. And it is also an important factor which will affect investment in infrastructure and reliability of pipelines.