Industrial # 2006 Washington DC
The CRS (Categorized Required Strength) concept was developed within the ISO pressure rating system to provide more flexibility to the design engineer. One of the major uses of CRS is to provide a design basis of 100 years for plastic piping applications. With the CRS concept plastic pipe can now have a design basis or design life of 100 years and be considered equivalent to other piping materials, such as steel or iron pipe, which claim a 100year design life. Another major application for the CRS concept is to pressure rate plastic pipe at the actual use temperature. This can be useful for high temperature applications or in areas that have a low ground temperature. The design engineer can determine the appropriate conditions for the plastic pipe application, and design accordingly. In this paper, we will review the CRS concept, how it is validated within ISO 9080, how it is determined within ISO 12162, what its limitations are, and finally, how it is used in typical plastic piping applications to make plastic pipe more cost competitive with metal pipe. The Plastics Pipes Institute (PPI) publishes CRS values in its public listing of TR-4, which is available on the PPI website – www.plasticpipe.org. We will also describe an actual field installation where a gas company had planned to use steel pipe for operation at 160 psig. Because of the CRS concept and use of the PE 100 material’s CRS value of 11.2 MPa at 14°C, the gas company was able to use 4” SDR 11 pipe operating at 160 psig. The gas company saved money by using PE pipe instead of steel pipe due to lower installation costs. In addition, the gas company will continue to have cost savings because there is no need for cathodic protection, no maintenance, and no concerns about corrosion.