Influence of joining on the fatigue and fracture behavior of high density polyethylene pipe

Polyethylene pipes have been used in a spectrum of corrosion-critical applications, including distribution systems for oil, gas, water, and chemicals. In this paper, the influence of joining on bending fatigue and fracture behavior of high density polyethylene pipe is presented and discussed, and performance is compared with a plain unwelded counterpart. High density polyethylene pipes were joined using electrofusion and butt-fusion techniques. Stiffness and strength of the electro-fusion joined pipe was far inferior to the butt-fusion and the plain unwelded pipe. Tensile failure of the butt-fusion joined specimen occurred at the fusion zone, while tensile failure of the electro-fusion joined pipe specimen occurred at the fusion joint. Bending fatigue resistance, quantified in terms of life to failure, of the pressurized pipe was superior to that of the unpressurized pipe. The fatigue resistance of the butt-fusion joined specimen was superior to that of the electro-fusion joined pipe specimen. The unwelded plain polyethylene pipe had bending fatigue resistance superior to that of the butt-fusion joined counterpart. Rationale for the differences observed in bending fatigue life is presented, and intrinsic differences in failure characteristics are highlighted.