T-95-103-B (02.01.95) Long-Term Specific Ring Stiffness – Flowtite Pipe


Although there are no standardized test methods for determining the long term stiffness of a GRP pipe today, the Committee for European Normalization (CEN) is currently developing one. Using their draft standard, prEN 1225, wet creep tests were conducted on stiffness class SN5000, PN6 and PN16, and on stiffness class SN10000, PN1 pipes. A constant load is placed on the submerged pipe sufficient to cause 3% vertical deflection, and deflections are monitored for up to 10,000 hours. Using a log-log least squares regression, a second order polynomial extrapolation of the pipes 50 year stiffness is determined. This test report can be used to demonstrate that Flowtite pipe’s long term stiffness is atleast 60% of initial (SN10000, PN1). As pressure ratings increase, due to increased glass content, the long term stiffness also increases. The AWWA M45 design method uses initial stiffness for deflection and buckling calculations. ATV 127 uses long term stiffness for static calculations so a value of not less than 60% of initial could be safely used here. This test report can be used to demonstrate the superiority of a filament wound Flowtite pipeUs long term stiffness to that of a centrifugally cast GRP pipe which has high filler content and only chop glass.