Evaluation of a Novel Microwave Based NDT Inspection Method for Polyethylene Joints

Exova is continuing in the long tradition of Pipeline Developments Limited (PDL) in the UK with research, development, testing, quality assurance (QA) and failure analysis of modern plastic pipe materials and joints. Along with this ongoing work Exova has assessed various non destructive testing (NDT) techniques in an attempt to further improve the reliability of Polyethylene (PE) joints in the field. In the past, reliable inspection of PE pipe joints using NDT has proven to be difficult, but this has generally been based upon the use of existing metallic inspection methods, including radiography and ultrasound. However neither radiography nor ultrasound can reliably detect key issues that are known to affect PE joint quality such as fine particulate contamination and cold fusion in butt welds and misalignment and contamination in electrofusion joints. Advances in technology have seen the development of a new non destructive testing (NDT) technique using low voltage microwave imaging. Microwave imaging has been developed in North America by Evisive Inc to inspect modern dielectric materials such as PE. Comprehensive laboratory testing indicated that this technique could be used reliably and repeatedly to detect issues related to poor PE joint fabrication in butt welds and electrofusion joints. Issues which have been identified include fine particle contamination, lack of fusion and misalignment. More recently field trials have been carried out on various PE joints, to establish a correlation between the microwave NDT results obtained and mechanical testing results.