Yuji Higuchi, Tomohiro Tanishita, Kazushi Yamada, Hiroyuki Nishimura
Papers # 2014 Chicago
Recently, PE resin-back composite pipes have been developed in order to satisfy the higher requirements for gas and water distribution. Although the stress rupture test is now the major test method used to evaluate the long-term performance of these pipes, developing a new, convenient test method making it possible to safely and easily evaluate the properties of composite pipes is needed. Therefore, a simpler method such as the tensile creep test with ring shape specimens was studied as a method for evaluating longterm performance. Although it depends on layer components in some pipes, it is suggested that compared to the stress rupture test, the ring tensile creep test is better able to speedily evaluate long-term performance. This method also has the advantage of being applicable to a pipe with a harder layer such as aluminum; the notched creep test method cannot be applied because of the impossibility of inserting a razor-notch. It is suggested that the new test method could possibly replace the conventional creep testing method.
Metal pipes used for gas and water distribution are buried underground. Long-term durability was a requirement for these pipes because they were not easily repaired or replaced. In recent years, plastic pipes have been more widely used for gas and water distribution. Metal pipes were replaced with PE pipes because of their excellent performance under external forces, such as ground and movement subsidence during Japanese earthquakes. Composite pipes were also developed to satisfy higher long-term durability issues; evaluating their reliability and durability when used for water and gas distribution in more severe environments was needed. It is possible that composite pipe failure was caused by crack propagation and interface delamination between composite layers Bulleri (1). Therefore, investigating the durability of plastic pipes in order to estimate use duration is very important. However, few results of long-term tests such as the creep test or the fatigue test on composite pipes exist Liu and Nairn (2), Shokrieh and Lessard (3). The stress rupture test shown in Figure I has several problems at elevated temperatures in applying internal high pressure and in jointing parts. Because of this, a new, simple test method evaluating long-term performance of composite pipes is required.
In this study, the tensile creep test with a ring shape specimen was studied as a method of evaluating long-term performance. This test specimen was standardized by ASTM as a method of evaluating the tensile strength of pipes’ hoop direction RozentalEvesque et al (4), Hayes (5); we applied it to the creep test. In order to study cracks propagation and interface delamination, the cross-section of the composite pipes was observed.
