This investigation was undertaken to develop a method for estimating the long-time strength of thermoplastic pipe by means of short-time burst strength tests. A parameter previously developed by integrating Arrhenius' law between limits and incorporating an expression for the kinetic order of the reaction was used. This general parameter was found to be applicable to all types of plastics. Four types of thermoplastic pipe were investigated: high-density polyethylene, acrylonitrile-butadiene-styrene, high-impact polyvinyl chloride, and normal-impact polyvinyl chloride.