Can Users Benefit from Pipe Standards that Allow Less Conservative Pressure Classifications?

Water and wastewater pipe product standards, e.g., those developed by AWWA or ASTM, are commonly cited in project specifications and largely relied upon in project design. Different pipe materials have different standards, and many materials have more than one pipe standard. These pipe standards outline the minimum requirements, but do not contain all of the engineering and administrative information normally contained in specifications. In addition to standard dimensions and minimum QA/QC testing requirements, most pressure pipe standards include pressure class (PC) or pressure rating (PR) designations that provide for some margin of safety. This paper reviews the standards for several commonly specified water/wastewater pipe products with regard to their methodology for arriving at the recommended pressure class designations. Both similarities and differences in the methodologies employed are explained. Their impact with regard to various pipe applications is also evaluated. This review includes recent proposals that advocate a less conservative approach to assigning pressure class for some water and pressurized wastewater pipe products. The effects that different pressure classification approaches have on in-service performance, reliability, longevity, and sustainability are discussed. Pressure pipe design factors should not be raised, or safety factors reduced, until in-service or simulated service evaluations substantiating equivalent risk and life expectancy have been well documented. In the absence of such test results, allowing a lower safety factor or higher design factor is not in the public's best interest.