Steven Folkman, Ron Bishop
Papers # 2016 Berlin
One of conditions design engineers face is selecting an appropriate pipe wall thickness (or DR) that will accommodate both maximum operating pressure and repeated surge pressure events. Methods for assessing the number of cycles to failure is quite well developed for PVC pipe. Fracture mechanics approaches can be very accurate and address the actual failure mechanisms that occur. Unfortunately, a typical design engineer is not trained in facture mechanics analysis and the numerous parameters needed. The current AWWA C900 standard has a suggested design procedure in Appendix B. This approach requires input of a mean stress and a stress amplitude and typically requires a root finding approach to calculate a number of cycles to failure. Experience has shown that this method is cumbersome and time-consuming for most design engineers to use. This paper suggests modifications to AWWA guidelines for PVC pipe in the North America when accounting for fatigue failure considerations. Another concern is that the design process needs to consider a variety of stress amplitudes and cycle counts when calculating the expected life of the pipe. This paper outlines a simple and conservative procedure that can be easy to apply and can accommodate multiple stress amplitudes. The paper includes examples for designers to follow in selecting an adequate DR rating for PVC pipe.