Detailed Description of Entry
Industry challenge – optimising the assessment of the integrity of polyethylene welded joints
Current industry practice for assuring the quality of butt fusion and electrofusion welded joints in polyethylene (PE) pipes during
installation is by: i) recording the welding parameters; ii) carrying out a visual inspection of the welded joint; iii) performing a short-term
hydrostatic pressure test; iv) destructive testing of welds on a sample basis using a short-term test on specimens cut from the welded
joint.
This practice has some limitations: i) visual inspection covers the external surface of the pipe weld only; it cannot provide evidence of
embedded flaws or a weld with incomplete or cold fusion; ii) if an embedded defect exists in a welded joint there is only a small chance
it will be included in a specimen cut for mechanical testing; iii) performing a mechanical test on a weld, then replacing it with one of
unknown quality does not ensure the integrity of a pipeline.
Delivering increased confidence using ultrasonic inspection
Volumetric non-destructive evaluation (NDE) offers an answer to these quality assurance challenges as it enables complete analysis of
a whole welded joint without destroying a perfectly good weld.
In this knowledge, a project team at TWI comprising polymer scientists and inspection specialists scoped a programme to design,
TM
optimise and subsequently introduce, a portable field inspection system known as PolyTest for volumetric NDE of electrofusion and
butt fusion welding joints in PE pipes. The system was subsequently evaluated successfully through an extensive series of blind and
field trials carried out in partnership with the water and gas industry sectors.
PolyTest
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equipment
Phased array ultrasonic probes, operating at the optimal frequencies for PE pipes
Membrane water wedges, designed to give full coverage of the weld fusion zone
Simple and flexible scanner to accommodate a wide range of pipe diameters
System capabilities
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Proven consistent detection of particulate contamination, lack of fusion, cold fusion and pipe under-penetration
Determines critical flaw sizes and acceptance criteria for butt fusion and electrofusion welds in various PE pipe grades
Provides immediate results and a permanent record.
Versatile system capable of inspecting pipes with:
o outside diameters between 100 and at least 800mm
o wall thicknesses from 8 to at least 60mm
Can be adapted for pipe diameters outside given ranges
Benefits
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One system for inspecting electrofusion and butt fusion joints in PE pipes
Applicable for PE pipes in all industry sectors, including gas, water and nuclear
Full portability, allowing in-trench inspection
Inspection of 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
Complies with EN 13100-3 and forthcoming ASME Code
The team developed procedures to enable detection of all types of flaw that may occur in PE pipe welds, including planar lack of fusion,
particulate contamination and cold welds. To support this, it conducted extensive performance testing to determine acceptance criteria
and validated the capabilities of the developed inspection techniques using joints containing known flaws in PE pipe diameters up to
710mm.
As a result, TWI’s ultrasonic field inspection service using the PolyTest
industry.
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system is generating worldwide interest in the plastics pipe
On-site inspection using the PolyTest
TM
system
Typical scan results on butt fusion (left) and electrofusion (right) joints