TestPEP project success provides a method of inspecting welded joints in plastic pipes
TWI has completed a three-year EU funded project on the development and validation of a non-destructive evaluation (NDE) system for testing welded joints in plastics pipes in response to the lack of commercially available equipment for inspecting these welds. The research will lead to a longer average service life of plastics pipe systems and lower leakage rates, resulting in reduced risk of serious accidents and pollution, which in turn will bring significant economic benefits, as more widespread use of these materials occurs. It will also make it easier for plastic pipes to replace metals in safety critical applications, such as nuclear power stations.
The team designed and manufactured a phased array ultrasonic inspection system specifically for examining both butt fusion (BF) and electrofusion (EF) joints in polyethylene (PE) pipe with outside diameters between 110 and 1000mm. New phased array ultrasonic probes, water wedges, scanning system and flaw detector were designed and manufactured specifically for inspecting welded joints in PE pipes. The same scanning system is used for inspecting both BF and EF joints over a wide range of pipe sizes; four different probe/wedge assemblies were manufactured, which cover the complete range of pipe sizes and the two joint types. The flaw detector was designed to be fixed directly on to the scanner in the trench, which meant that it had to be compact, waterproof, lightweight, robust, battery operated and with a large internal memory. The capability of the system was evaluated using over 100 welded test pipe samples containing defects of known size, including planar flaws, particulate contamination and cold welds.
TestPEP system for inspecting welds in PE pipe
As part of the project, algorithms and software have been developed for analysing the inspection data collected from EF joints. The software generates a map of the weld, estimates the size of any flaws in the weld and sentences the joint based on a comparison between the measured flaw size and critical values, which were determined by carrying out long-term mechanical testing of the flawed joints.
The complete prototype phased array ultrasonic inspection system was assessed both in the laboratory/factory and in the field. Trials carried out on samples containing both real and artificial defects proved that all of the key flaw types highlighted by the European plastics pipes industry (embedded planar flaws, fine and coarse particulate contamination, pipe misalignment, voids, cold welds and pipe under-penetration in EF joints) can be detected with the developed system.
The procedures developed in the TestPEP project are currently being incorporated into ISO and ASME standards.
For further information please see the TestPEP website
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