Development and Assessment of Ultrasonic Inspection System for Polyethylene Pipes

The American Society of Mechanical Engineers (ASME) is revising the published Code Case (N-755) for the use of polyethylene (PE) in nuclear power plant buried pipe systems. However, the United States Nuclear Regulatory Commission (NRC) has not approved this Code Case due to a number of concerns; one of which is the lack of validated non-destructive examination (NDE) techniques for inspecting welded joints in PE pipes. This paper describes the development of an ultrasonic phased array system and procedures for the inspection of welded joints in PE pipes of diameters between 125 and 1000mm. The system includes hardware and software which has been designed specifically for inspecting PE pipe joints. The system has been assessed by a number of organizations and the results of these trials will be presented. Alongside the development of the inspection system, a major program of work has been carried out to develop acceptance criteria for flaws in PE pipe welds. The types of flaws investigated included particulate contamination, planar flaws and cold fusions. The critical flaw sizes and contamination levels were determined based on both long-term and short-term testing of welded joints in PE pipes.