Non Destructive Evaluation of Improper Fusion for Polyethylene Heat Fusion Socket Joint
Seonghee Kil, Jeongrock Kwon, Keebong Yoon
Papers # 2014 Chicago
Non destructive evaluation(NDE) of polyethylene electrofusion socket joint could be a kind of methods to support the elelctro fusion processes and procedures. Defects example of lack of fusion, porosity, foreign material, inserting defect and dislocation of heating wires could be detected by using phase array ultrasonic imaging methods. However, in some cases, joint had been failed for other reasons except above mentioned defects, and this defect does not seem to be a certain shape. This paper studies about detecting results by using phase array ultrasonic imaging methods of improper fusion for polyethylene electrofusion joint and comparing those results with crush test results of same test specimens. Density of test material for detecting of improper fusion was 0.939g/cm3, and outside diameter of pipe was 225mm, SDR 11. 17 test specimens had been prepared by changing proper heating time from 0% to 130%. In addition to 17 test specimens, one specimen had been prepared by attaching the soil in the fusion zone of the pipe, another specimen had been prepared with two defects which were artificially made with paper, and other specimen had not been scrapped on the surface of the pipe and had been inserted into the socket and electrofused. Therefore, total 20 test specimens had been made. By using phase array ultrasonic imaging methods, heat affected zone was detected. Also, the distance between heating wires and heat affected zone was measured. The distance between heating wires and heat affected zone was varied by heating times. To compare this NDE result with destructive test, crush test was conducted according to ISO 13955(crush decohesion test) 7.2(electrofusion sockets). The distance from the 1st heating wire to the last one was 50mm, and tests were carried out three times. Brittle failure length was measured in the fusion plane at the outer edge of the fitting parallel of the pipe axis. From this study, improper fusion could be detected by using phase array ultrasonic imaging methods and measuring the distance from heating wires to indication of heat affected zone. The distance between heat affected zone and heating wires was varied by heating times. No scraping, defect inclusion and soil inclusion specimen were completely separated. Specimens applied heating times from 10 to 30% of proper heating time were separated also.
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