# 2004 Milan
The required performance of polyethylene pipes for gas distribution is firstly described. As an evaluation method for slow crack growth, the relation between crack growth length and time under test was obtained to investigate the stress crack resistance of polyethylene pipes for gas distribution after conducting three-point bending tests at 23 degrees C for fifteen years as the maximum test period. The incubation period leading to crack initiation was much longer and the crack growth was slower for domestic resins. The relation between the stress intensity factor and the crack growth rate of several pipes are also discussed. The full-notch tensile creep test is specified by JIS K6774, which is now under consideration for adoption by ISO as a standard. The data on and the results of the full-notch tensile creep tests have been accumulated for several years to decide whether to introduce new resins or modified resins, and to evaluate the lot-to-lot variation of resin production for the quality control of polyethylene pipes. The fullnotch tensile creep test is also applied to the evaluation of fusion joints, especially electrofusion joints, as well as the substrate of pipes. The test results have also been accumulated to determine suitable fusion conditions and to evaluate fusion integrity between different grades of pipes or joints.