Failure Analysis on Premature Fracture of Polyethylene Pipe for Floor Heating System

Polyethylene (PE) pipes are widely used in floor heating system due to their corrosion resistance, low cost and other advantages. This paper investigated the premature fracture of PE pipe for floor heating system in a residential building in the northern part of China for only serving less than 3 years, while the design service life was 50 years. In order to ascertain the root causes of this failure, a series of macro- and micro-scope characterization methods were conducted. The comprehensive analysis results showed that failure mechanism of the failed pipe was slow crack cracking with defects. Low molecular weight and substandard molecular weight distribution are the root causes of that premature fracture. Excessive bending, fibrous inclusions and shrinkage holes in the matrix are also important causes of the failure. Subsequently, the influence of polymer molecular weight on the mechanical properties of materials and the micro-configuration response of polymer pipes under tensile stress was analyzed in depth. It is theoretically demonstrated that polymer microstructures such as molecular weight distribution fundamentally affect the properties of polymer materials, which should be paid enough attention in the process of production and use. At last, several countermeasures are thus put forward in order to enhance safety operation and reliability of the PE pipes for floor heating system.