T-99-107 (18.03.99) Strain Corrosion Performance – Flowtite Sewer Pipe


One of the most important design parameters for a GRP sewer pipe is it’s long term strain corrosion resistance to sulfuric acid. ASTM D3262-96 Fiberglass Sewer Pipe requires the GRP pipe manufacturer to demonstrate through qualification tests, carried out in accordance with ASTM D3681-96, that the pipe is capable of resisting 5% H2SO4 for 50 years when deflected (strained) to the allowable in-ground limit permitted by the manufacturer. The strain levels presented in ASTM D3262-96 are based on 5% in-ground vertical deflections. This test report presents the strain corrosion test results on Flowtite sewer pipe manufactured with Advantex ECR glass reinforcements. Using log-log least squares regression, the resulting predicted 50 year failure strain for Flowtite sewer pipe is 0.66%. This report can be used with end users and consultants to demonstrate that the necessary qualification tests for a GRP sewer pipe, in accordance to ASTM D3262-96, have been carried out. It is also a proof statement on the longevity of a sewer pipe. A minimum factor of safety of 1.5 is applied to the pipes predicted 50 year strain capability, but that is based on 50 years of exposure to 5% H2SO4 at it’s maximum permitted in-ground deflection level. The highest sulfuric acid concentration we measured in a sewer system was 4%, and this was in the Middle East where ambient temperatures are generally high. It is believed this is a very conservative test requirement which should lead to safe, long term performance of a sewer pipe.