Steel pipe is graded based on the ASTM (American Society for Testing Materials) standards and ASME standards. ASTM International is the company that issues the standards for most of the steel pipe manufactured and ASME generally issues standards for pressure bearing pipes.
ASTM is a large organization that develops standards for different materials which are manufactured and generally used in construction or industry. The organization is what is called a voluntary standards development company and they are independent of the manufacturers. Standards for each type of pipe can be downloaded or purchased in print from ASTM and several other website which host their documentation.
Steel pipe is manufactured in many different ways including seamless pipe, welded pipe, cast pipe. In addition, there are subcategories for each type of pipe. For instance there is single welded pipe, or diagonally (continuously welded pipes) made by welding the edges pf a single strip of metal wound like a curly-q into a cylinder shape. So, each standard is based in part on the type of manufacturing process that creates it.
Grading the Pipe
Pipe is graded is strength in terms of pressure. Each type of pipe is designated with a code like API5L PSL2. There are then many grades for each standard ASTM Code which determine a minimum yield strength and minimum tensile strength. The grades include grade 1, grade 2, grade 3, then grade A, grade B, grade C and continue on to grade X and there is minimum and maximum pressure rating each grade. For instance with API5L PSL2 grade 1 ASTM 252 pipe the minimum yield strength is 30,000 PSI and minimum tensile strength is 50,000 PSI.
Carbon Steel Pipes
Carbon steel pipes like regular steel pipes are graded using the same methods. The ratings include temperature and pressure levels for A106 Grade B carbon steel pipes, for instance. These pipes are generally classified under the ANSI/ASME standards codes.
Each pipe has this separate code based on the ANSI/ASME standards, for instance B 31.1. That is the ANSI code for a particular type of pipe. The grade then specifies how much pressure and the temperature the pipe is made to withstand.