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NDT.net Issue - 2015-11 - NEWS

PolyTest examines polyethylene pipe welds for Italian public utility

TWI Ltd (The Welding Institute)176, Great Abington, Cambridge [United Kingdom]
NDT.net Journal
Issue: 2015-11
Case Study

TWI has used its unique non-destructive plastics testing system to carry out inspections of a large number of joints in polyethylene pipes for an Italian gas infrastructure company.

One of the most recent inventions to be created at TWI is PolyTest, a phased array ultrasonic inspection device capable of reliably detecting flaws in butt fusion and electrofusion joints in plastic piping.

At the end of 2013, some of PolyTest’s developers took the system to Italy for a one-day seminar demonstrating its capabilities. Following the seminar, the infrastructure arm of Italian utility A2A, A2A Reti Gas [A2A Gas Networks], expressed an interest in having some of their pipelines inspected.

Phased array inspection

TWI subsequently travelled to Milan to carry out inspections of more than 30 electrofusion and butt fusion joints in polyethylene pipes used to transport natural gas. The work was carried out over four days, with preliminary results provided to the client immediately and a more comprehensive report supplied following detailed examination of the results back in the UK.

The PolyTest scanner system uses phased array ultrasonic technology to detect flaws in welds caused by factors such as under-penetration, contaminants and cold fusion. Comprising a set of wheeled chain links, transducers with two types of custom-designed membrane water wedges and interpretative software, PolyTest provides detailed data on the presence and size of detected flaws, describing results across four different images simultaneously to enable precise and thorough analysis.

Results verified through testing

TWI conducted inspections of 33 joints in total: 25 electrofusion and eight butt fusion. Although no fault indications were detected in the majority of the pipes, a number were found to contain anomalies. PolyTest was able to determine the likely cause of each indication, identifying factors including a lack of fusion, voids around the locations of heating wire, under-penetration and contamination. A selection of destructive tests were carried out on some of the inspected joints, which confirmed flaws that correlated with the ultrasonic data.

For more information on PolyTest and TWI’s plastics inspection capability, please contact us.

TWI Ltd (The Welding Institute)

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