Shin, Jang, Kwon, Lee
# 2004 Milan
Thousands of kilometers of polyethylene (PE) pipes are newly installed every year. However, up to date, there are no reliable nondestructive testing methods to determine the quality of the joint of the PE piping system. In this paper, an innovative nondestructive testing (NDT) method for electrofusion (EF) joints is proposed and the test concepts as well as results are presented. The fundamental concept of the nondestructive testing method is based on the ultrasonic array technology, which can obtain the high-resolution ultrasound image of the cross section of test specimen. For the experiment, a developed ultrasonic array system with three different array transducer is used. A 5MHz transducer can test various diameter ranges of PE pipes with reasonable sensitivity and penetration power. A 3.5MHz and a 7.5MHz transducer can be used for the high-penetration and high-resolution test purposes, respectively. For the nondestructive testing, ultrasonic array transducer is placed at the outer surface of the EF joint and the cross section image of the EF joint is captured in real time. In the ultrasonic image of the EF joint, the arrangement of heating wire wound at fusion interface is individually identified. Geometrical information of the fusion joints such as thickness, wire location, wire gap, fusion length, and cold zone are also identified and measured in the image. The image also shows defects such as void, imperfect fusion interface, inclusions, and wire dislocations. Since ultrasound is non invasive, the test method can be applied for in-service as well as pre-service inspection. The ultrasonic imaging technique is a very promising method for the nondestructive testing of fusion joint in PE pipes.