System Pressure Rating & Residual Life # 2004 Milan
ISO MRS and ASTM HDB rating systems have been successfully used for more than four decades in Europe and North America. MRS differentiates well the three generations of HDPE materials by classifying them as PE63, PE80 and PE100. However, HDB classifies all three generations of HDPE as only one PE 3408. When calculating MOP, MRS uses a minimum design coefficient of C=1.25. HDB uses a maximum design factor of F=0.5. C (1 F ) = 0.63 . In order to compare these two rating systems on the same page, design reference strength (DRS) is introduced. MRS is connected with DRS through the parameter coefficient, Cp, and HDB with DRS through the parameter factor, Fp. For a given HDPE that minimally meets ISO 9080 and ASTM D 2837, Cp and Fp are 1 and 1.53 respectively. C p (1 F p ) = 1.53 . The ultimate design coefficient, C ultimate = C × C p = 1.25 , and ultimate design factor, Fultimate = F × F p = 0.77 . C ultimate (1 Fultimate ) = 1.03 . This means the current MRS and HDB rating systems are equivalent and have the same design baseline. Nevertheless, since the minimum requirements in D 2837 are too low, HDB fails to differentiate HDPE materials. A detailed step-by-step analysis reveals the similarities and differences of the two rating methods. A possible revision to D 2837 to harmonize the two rating systems is given. This paper also discusses the important end-use parameters of application temperatures and design times.