Effect of Welding on a High-Density Polyethylene Liner

This paper describes part of an ongoing research project concerning high-density polyethylene (HDPE) liners used for pipeline rehabilitation. Tests were conducted in the laboratory, where a steel sleeve was welded on the outside surface of a steel pipe lined with a HDPE liner. Recommendations were made to establish welded joints using stitch welds of length equal to the minimum length specified by the applicable codes, with a center-to-center spacing of three times the weld length. A waiting period may be required between consecutive stitch welds, especially for small-diameter pipes. A second group of tests was conducted to evaluate the material performance of a liner strengthened by butt-fused HDPE rings. The overall stiffness of the liner increased with the addition of the butt-fused rings. Tension tests were conducted on dog-bone-shaped samples extruded from the stiffened liner. The butt-fusion process used to attach the stiffening rings increased the average tensile strength and average elasticity modulus of the material in the fusion area.