Advanced ultrasound assessment of polyethylene butt fusion joint for gas pipelines

Polyethylene (PE) pipes are becoming increasingly prevalent in the gas distribution industry due to their many desirable properties. Polymer materials are inexpensive, lightweight, relatively easy to transport, and resistant to corrosive components of the natural gas they distribute. PE pipe joints in pipelines can be fused using several different methods, but the most preferred welding technique is butt fusion (BF), with good results in field testing. However, joints are considered the weakest spots in a pipeline, and issues with joining processes can exacerbate joint weakness. Thus, the infrastructure industry requires efficient, simple, and effective means for nondestructively inspecting BF joints. A portable device with an integrated automated inspection process will decrease the cost and post processing time of the quality check. Currently, a few methods are commercially available to evaluate the integrity of welding for PE pipes. Some inspection methods for the volumetric inspection of plastic pipe joints, such as X-ray technique, infrared thermal imaging technique, a capacitive sensor, and passive acoustic fail to provide all the desirable parameters such as real-time processing, cost benefits, and accuracy in one. Ultrasonic inspection technique is currently one of the most used NDE methods for PE pipes to investigate the integrity and safety of joints as the technique has been proven effective for inspecting typical defects in PE weld joints. In this work, we make use of this technique and introduce advanced improvements to increase the efficiency of the technique and automize a man job to eliminate any possible “human error” that might lead to a failure and accident. To begin with, seven classes of pipe joints were welded to simulate “defective” and “flawless” BF samples. The defects’ classes were carefully selected, considering any possible miscalculation, and malfunctioning in the welding process that leads to a defect. Contamination, air void, and cold fusion were separately simulated into the joint area and multiple replicas were created for each class. We developed a set of flawless and defective BF joints, using pipes with outer diameters of 2, 4, and 6 inches. The ultrasound system was manufactured, used a 1.8 MHz transducer which was embedded into a customized wedge such that it could be placed on the pipe in contact with the weld bead to propagate the ultrasound beam on the right angle to cover the welded area. Subsequently, using the ultrasonic system, a dataset of thousands of A-scans that we labelled as ‘flawless’ or according to defect type, using the marked joints and current industry standards were developed. The dataset was post-processed and labelled to be further analyzed in MATLAB. All the defective signals were plotted separately and compared to the flawless” group, in each size. The acquired signals in each class were imported into MATLAB classifier and several classifiers were tested. The binary classification showed 90% \u3e accuracy where flawless signals are detected from defective ones. However, the models were not capable of accurately classifying the defect types and the highest detectability was from50% to 70%. Finally, all the PE joint samples were destructively tested with a high-speed tensile test and back bending test according to ASTM F2634 and ASTM F2620. This research shows the applicability of advanced ultrasound for pipe joint characterization. We believe that our approach can extend to a variety of other joining methods and materials for pipe infrastructure assessment