In 2014 TWI launched PolyTest: a new invention capable of reliably and non-destructively detecting flaws in welds in plastic pipelines.
Several Member companies have already benefited from the new technology, which uses phased array ultrasonic testing techniques to identify flaws in welded joints in polyethylene (PE) pipes caused by factors such as cold fusion, contaminants and under-penetration.
Towards the end of 2014 TWI inspected 40 plastic pipe joints for a client. The joints were in pipeline of two different sizes: 36mm wall thickness and 400mm outer diameter, and 51mm wall thickness and 560mm outer diameter.
PolyTest is a modular system consisting of wheeled chain links that are mounted on the outside of the pipe adjacent to the weld to be inspected. The chain link system is rotated around the circumference of the weld, enabling the attached transducer to complete a full volumetric examination.
Using the system and applying an industry-approved procedure, TWI collected data from each of the joints before analysis and reporting were performed the following day. The acquired data formed a three-dimensional matrix, where combining A-, B- and S-scans helped to accurately locate and size any flaws.
Of the 40 joints that were inspected, seven showed ‘indications’: tell-tale signs of a fault. The client did not accept any of the flaws and the joints were rejected based on the inspection results. A second site visit three weeks later allowed the data to be validated and verified through repeat inspections.
Backing up findings with testing
Having established that the inspections were producing accurate, repeatable results, destructive tests of one of the welds were carried out to determine the cause of the indication. This revealed the presence of a foreign material, which had presumably entered the pipeline in the manufacturing process.
Plastic pipelines carry a number of benefits over their metal equivalents, but the lack of a reliable non-destructive examination technique has traditionally prohibited their use in safety-critical applications such as nuclear power stations. With the introduction of PolyTest, the first commercially available ultrasonic testing device for PE pipelines, that could be about to change.
For more information on PolyTest and TWI’s plastics inspection capability, please contact us.
TWI Ltd (The Welding Institute)