Disclosed is a method that provides for the calculation and prediction of hoop strength of an expanded pipe, preferably a PVC pipe or conduit. The method includes the steps of: (a) determining hoop strength as a function of relative wall thickness; (b) determining Wall Thickness Ratio (WTR) by dividing a nominal wall thickness of the original conduit by the minimum wall thickness of the expanded conduit; (c) determining long-term hydrostatic strength by at least one of hoop testing and burst testing; and (d) applying an accelerated regression analysis to the results in step (c), yielding a Hydrostatic Design Basis (HDB). The resulting HDB may be plotted against WTR to provide the user with graphical data for use in making design decisions and choosing specific conduit for specific applications.