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Feel the quality of Plastic Pipe
Verifying the quality of pipe joints is critical, and an increasing number of methods are now fi eld-ready.
Testing joints in plastic pipes lags some way behind that for steel pipes – but this is mainly because plastic pipes are much newer to the market. However, a growing number of techniques allow accurate assessment of the quality of pipe joints.
TWI of the UK has developed a new inspection system that can detect fl aws in electrofusion and butt fusion joints in polyethylene (PE) pipes.
PolyTest enables volumetric testing of PE pipe joints, and now extends TWI’s expertise in ultrasonic testing to a new application. The system enables onsite inspection of both electrofusion and butt fusion joints in HDPE pipes, verified on sizes of 90-710mm outer diameter, with wall thicknesses of 8-65mm.
PolyTest is a portable system that uses phased array ultrasonic testing techniques to identify fl aws in welded joints caused by factors  such as cold fusion, contaminants and pipe under-penetration. The fl exible, modular system consists 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 and enables the attached transducer to complete a full volumetric examination.
TWI has developed bespoke membrane water wedges that house the transducer for PolyTest, for both types of joint. The wedges are optimised to minimise electronic steering by the transducer elements, and the membranes are made of a fl exible material that contains the water and adapts to the shape of the surface they are in contact with. The system provides full coverage of the weld zone while requiring no water supply.
Thorough tests, carried out on more than 200 welded pipe joints with inserted artifi cial fl aws, have validated the system’s inspection  capabilities in joints with wall thickness up to 65mm. With adaptation, even thicker pipes can be inspected. Extensive testing has also helped TWI to determine acceptance criteria and critical fl aw sizes for a wide range of welding processes and material combinations.
PolyTest produces immediate results and provides a permanent record. It conforms to the requirements of EN 13100-3 and relevant forthcoming ASME code, and gives operators increased confi dence in the integrity of their PE welded joints. The system is available for PE pipes in all industry sectors, including gas, water and nuclear, and satisfi es regulatory requirements specifying that welded joints must be volumetrically inspected.
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