2017 Volume 29 Issue 3 Pages 75-85
There are mainly two grades of polyethylene pipes for hot water supply and heating.
The excellent molecular structure polyethylene resins having resistance to stress crack growth are used because hot water is flowed for a long time in both polyethylene pipes.
Furthermore, various additives are mixed to prevent the thermal degradation of polyethylene pipes at the elevated temperature. In this study, the stress rupture test and the continuous hot water circulation test were con-ducted using extruded polyethylene pipes mixed two kind of polysilane and a nucleating agent. As a test results, the time to failure of polyethylene pipes mixed two kind of polysilane was longer than that of a polyethylene pipe without additives. The time to failure of polyethylene pipes mixed a nucleating agent is similar to that of a poly-ethylene pipe without additives. According to precise observation at the failure part, it was found that there was a small degraded colored layer at the inner surface of polyethylene pipes mixed two kind of polysilane compared with polyethylene pipes without additives. In addition, it was found that the generation and the growth of degraded colored layer and small cracks was delayed due to diffusion of polysilane to the inner surface and to protection of adhesion of metal oxides such as copper oxide and iron oxide.
