TWI has developed a pioneering method of reliably detecting flaws in joints in polyethylene (PE) pipes using ultrasonic waves.
PolyTest™ is an inspection system designed and optimised specifically for the volumetric non-destructive testing of electrofusion (EF) and butt fusion (BF) joints in PE pipes. The equipment includes:
- phased array ultrasonic probes, operating at the optimal frequencies for PE pipes of wall thicknesses between 10 and at least 60mm
- membrane water wedges, which have been designed to give full coverage of the weld fusion zone
- a simple and flexible scanner that can accommodate pipes with outside diameters ranging from 100 to at least 800mm.
Thorough tests, carried out on more than 200 welded pipe joints with inserted artificial flaws, have validated the system’s inspection capabilities in joints in pipe diameters up to 800mm and, with adaptation, even larger diameters can be inspected. Extensive testing has also led to TWI determining acceptance criteria and critical flaw sizes for a wide range of welding processes and material combinations.
PolyTest brings numerous benefits to industry:
- One system for inspecting both EF and BF joints in PE pipes
- Fully portable system allowing in-trench inspection
- Can inspect welded joints between pipes and reducers, elbows and tee fittings
- Validated inspection system backed up by structural assessment data developed through long-term performance testing
- Critical flaw sizes and acceptance criteria determined for butt fusion and electrofusion welds in various PE pipe materials
- System complies with the requirements of EN 13100-3 and forthcoming ASME code
- Increased confidence in the integrity of PE welded joints
- Applicable for PE pipes in all industry sectors, including gas, water and nuclear
- Proven consistent detection of:
- particulate contamination
- lack of fusion
- cold fusion
- pipe under-penetration in EF joints
- Ultrasonic inspection system producing immediate results and a permanent record.
An innovative solution to a long-standing problem
The traditional practice for assuring the quality of BF and EF welded joints in PE pipes during installation is by recording the welding parameters used, together with a visual inspection of the welded joint and a short-term hydrostatic pressure test, supplemented by the destructive testing of welds on a sample basis using a short-term test on specimens cut from the welded joint.
Visual inspection can only examine the external surface of the pipe weld; it cannot provide evidence of embedded flaws or a weld with incomplete fusion or cold fusion. In addition, if a defect exists in a welded joint there is only a small chance that it will be included in a specimen that has been cut for mechanical testing and mechanically testing a weld and then replacing it with one of unknown quality does not ensure the integrity of the pipeline.
Volumetric non-destructive examination (NDE) can provide a complete analysis of the whole welded joint and does not destroy perfectly good welds. It is therefore the only method that has the potential to ensure the integrity of the installed welded joints in a PE pipeline.
For more information about PolyTest, please visit the PolyTest system website.
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