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Jointing PE pipes
By Jonathan Morris is a Senior Asset Management Consultant with Opus International Consultants Limited.
Modern PE pipes are now pretty reliable, so most in-service failures that aren’t caused by stray digger buckets are due to problems with the joints. This means that joint quality is an important factor in pipeline durability, especially for fusion joints.
Fusion jointing
Fusion jointing is much like welding a metal - it involves pressing two melted surfaces together so that when the joint cools the original components form a single piece. Correctly made fusion joints can be as strong and as ductile as the original pipe material.
The main forms of fusion jointing are:
- butt fusion, which involves pressing the melted ends of two pipes together,
- socket fusion in which the outside of a pipe and the inside of a socket are fused together,
- saddle fusion in which a fitting is fused onto the outside of a pipe.
For butt fusion, the jointing surfaces are heated with a hot metal plate, but socket and saddle fusion joints are now usually made using electrofusion fittings which have built-in heating coils.
The influence of site practice
Although the combination of good quality control by the manufacturers and automation of the equipment reduces the risk of joint problems, site practice still has a major influence on joint quality. Examination of joint failures shows that two common causes of joint problems are:
- poor preparation – pipe ends not cut square, insufficient scraping or contamination of the joint after scraping.
- lack of clamping – not using clamps or removing the clamps too early, before the joint has set properly.
The underlying reasons for these can include lack of training, time pressures or lack of proper equipment. As always, it’s easy to see them coming with the benefit of hindsight, but it is still worth trying to cover them when the contract is being let or is underway. It is also worth remembering that on-site quality assurance doesn’t have to be difficult – it can be as simple and practical as marking joints with the welder’s certificate number or initials.
Recipe for success
The best way to produce good joints on site time after time is to:
- Clean the jointing surfaces before fusion and keep them clean and dry. This includes using a mechanical scraper when electrofusion jointing larger pipes (especially DN125 and above).
- Protect the joint (and your welders) from the weather using a welding shelter, and by not welding when conditions are completely unsuitable.
- Use clamps to stop the components from moving during jointing and while they cool. Only join compatible materials together.
A cross section through a butt fused pipe joint showing the profile of the weld beads.
| A PE pipe with electrofusion saddle and electrofusion reducer on the service pipe.
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NZWETA provides training in Reticulation and PE jointing. For more information, contact Jonathan Mackey at the Environmental Training Centre.
Jonathan Morris is a Senior Asset Management Consultant with Opus International Consultants Limited. Jonathan has a background in pipeline materials installation and assessment, and a doctorate in non-destructive testing. Before moving to New Zealand to do risk based asset management he spent 5 years in the UK managing a Water Industry technical support programme for plastic pipelines and helped revise many of the UK Water Industry Specifications and manuals dealing with plastic pipes. Jonathan’s speciality in Opus is pipeline condition management, which involves identifying what information you really want, finding a practical way of getting it and then doing as much as you can with it.
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