TWI Industrial Member Report Summary 370/1988
G R Edwards
This report presents experimental results of non-destructive tests carried out on medium and high density polyethylenes and on hot plate butt fusion welds in these materials. The experimental work is introduced with a brief review of a literature survey conducted to assess the current use of non-destructive testing (NDT) methods and procedures on bulk plastics.
Hot plate butt fusion welds in high density polyethylene (PE) bar were examined using conventional ultrasonic test equipment. Some anomalies were revealed in the test results and these were investigated further in studies of acoustic velocity, acoustic attenuation and frequency dispersion, which were also extended to a variety of plastic materials. As a result of these parametric studies, an ultrasonic test procedure was drawn up for testing hot plate butt fusion welds in PE pipe. It includes the use of new probe designs.
Radiography was introduced as a back-up to the ultrasonic testing of pipe welds, but its usefulness in examining weld upset and detecting volumetric flaws became apparent and therefore a low kilovoltage X-ray procedure was developed.
The work formed part of an initial programme of research into NDT methods for use on welds in thermoplastics and thermoplastic composite materials.