Improvement of butt-fusion welding procedure and performance evaluation method for thick-walled bimodal polyethylene pipes

High-density polyethylene (HDPE) pipes have been continuously improved by the progress made by the resin industry and pipe manufacturers. Together with the advanced technology of welding equipment in terms of structure reliability and automations, HDPE pipes have been gradually applied to higher pressure level, bigger diameter, and thicker walls in operations which have become the preferred piping system for nuclear safety application in transporting cooling seawater. There are substantial differences in parameter settings when applying heat and force during different welding procedures, as well as the complicated evaluation methods for mechanical properties, which causes communication barriers between engineers and researchers. Thus, it is necessary to comprehensively study the welding procedures and evaluation methods to standardize the evaluation protocols in the industry. In this paper, based on the assumptions of temperature effect and molecular chain diffusion dynamics at the welding interface, the optimization of the welding procedure is proposed. Some well-established evaluation methods have been used for performance assessment and their feasibilities are discussed. The idea of creating crack along the weld interface is adopted as new method to evaluate the material ability of fracture resistance. Specimens with unilateral notch and weld interface crack are proposed and subjected for quasi-static axial tensile test. The fracture stress and fracture energy at the welding interface are used to differentiate the quality of the joint from different welding procedures. The fracture morphologies of the weld interface are analyzed. A complete picture is drawn for the mechanical fracture resistance of the weld interface. The method used in this paper can be corelated to the pipeline design conditions, therefore could be applied to the real-time engineering applications. Moreover, the evaluation method proposed in this paper is simple, reliable, and easy to implement.