Inspection results of damaged polyethylene electrofusion joints using ultrasonic imaging method [PE]

Non destructive testing methods of electrofusion(EF) joints of thermoplastics pipes are required for fusion joint safety and for the long term reliability of a pipe system. Electrofusion joints, which are joined at the proper fusion process and procedures, may encounter defects due to the difference of ovality between pipes and coupling, improper fusion process or porosity result from electrofusion joining. These defects can cause the failure of pipeline and by extension, they can be caused the limit to expand the use of plastics pipes. This paper studies two inspection results using ultrasonic imaging method for damaged polyethylene electrofusion joints. One case, gas was leaking from 250mm diameter polyethylene electrofusion joints which was electrofused at 22, December 1994 and operation pressure was 2.45kPa. First, surface inspection was conducted and then in order to find the types of defects examination using ultrasonic imaging method was performed. Lack of fusion and inappropriate inserting for polyethylene pipes into electrofusion coupling were found and causes of the gas leak were judged that misalignment and insert defect. Destructive inspection was performed and each inspection results were compared to. Results of ultrasonic imaging method and destructive inspection were the same. Second case was for the 400mm diameter electrofusion joints. Study was performed by using ultrasonic imaging method and destructive test. By the result of ultrasonic imaging method, located circumferentially porosities were found at fusion joint and the size of porosities was about 8mm. Note that the width of heating wires was about 80mm so the size of porosity was less than 10% of width of heating wires. At this inspection,3.5MHz phased array sensor was used.