Long-term buckling performance of HDPE liners

This research examines the long-term performance of high-density polyethyle ne liners frequently used in rehabilitating pipeline networks. Buckling of two groups of samples-each consisting of 20 steel pipes lined with HDPE lin ers-was examined in the laboratory. Group A was subjected to a uniform exte rnal pressure equal to about one-half of the buckling pressure, determined experimentally in a similar short-term test. Group B was subjected to one-t hird to one-fourth of this short-term pressure. Most liners in Group A fail ed (buckled) prematurely before the required ASTM period of 10,000-h. Howev er, all 20 samples in Group B sustained the applied pressure for over 10,00 0 h. It was concluded that a design safety factor of 3 to 4 should be appli ed to short-term pressure to establish the long-term resistance of a flexib le liner. Changes in the liner pipe volume with time, under the uniform pre ssure, were also monitored to estimate long-term creep in the HDPE material .