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Research Papers: Materials and Fabrication

Development of Nondestructive Test and Safety Assessment of Electrofusion Joints for Connecting Polyethylene Pipes

[+] Author and Article Information
Jinyang Zheng1

 Institute of Process Equipment, Zhejiang University, Hangzhou 310027, P. R. Chinajyzh@zju.edu.cn

Jianfeng Shi

 Institute of Process Equipment, Zhejiang University, Hangzhou 310027, P. R. China

Weican Guo

Institute of Process Equipment, Zhejiang University, Hangzhou 310027, P. R. China;  Zhejiang Special Equipment Inspection and Research Institute, Hangzhou 310020, P. R. China

1

Corresponding author.

J. Pressure Vessel Technol 134(2), 021406 (Jan 30, 2012) (5 pages) doi:10.1115/1.4004869 History: Received February 20, 2011; Revised August 10, 2011; Published January 30, 2012; Online January 30, 2012

Polyethylene (PE) pipes are widely used in transporting natural gas since 1960s. However, there are few published literatures on method for safety assessment of PE pipes. This paper introduces recent work in developing ultrasonic nondestructive testing (NDT) equipment and research on safety assessment of electrofusion (EF) joints of PE pipes. According to the geometrical characteristics and ultrasonic response, defects in EF joints can be divided into four categories, i.e., poor fusion interface, voids, structural deformity, and over welding. The defect of the poor fusion interface includes three typical forms, i.e., cold welding, unscraped oxide skin, and contamination of the fusion interface. Cold welding, which is the most common and dangerous defect, has been successfully detected by using ultrasonic NDT equipment and assessed with a patented cold welding Eigen-line method.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 2

Poor fusion interface (cold welding). (a) Sectional view and (b) ultrasonic image

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Figure 3

Voids. (a) Sectional view and (b) ultrasonic image.

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Figure 4

Structural deformity (wire dislocation). (a) Sectional view and (b) ultrasonic image.

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Figure 5

Relation between supplied power per unit area and heating time with temperature

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Figure 6

Setup of shearing test

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Figure 7

Setup of peeling test

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Figure 8

Failure mode of peeling tests. (a) Defect in outer welding zone, (b) defect in middle welding zone, (c) defect in inner welding zone, and (d) no defect in welding zone

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Figure 9

Relation of peeling energy to size and position of defect

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Figure 10

Peeling energy of cold welding joints

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Figure 11

Failure mode of cold welding joints. (a) Brittle interface, (b) partly brittle and partly ductile, and (c) ductile interface.

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Figure 12

Cold welding Eigen-line

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Figure 13

Relation of distance between Eigen-line and heating wire and welding time

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Figure 1

Poor fusion interface (2 mm artificial defect). (a) Sectional view and (b) ultrasonic image.

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