Our site uses cookies necessary for its proper functioning. To improve your experience, other cookies may be used: you can choose to disable them. This can be changed at any time via the Cookies link at the bottom of the page.


Fusion Welding of Crosslinked PE [PE]

 

Plastic Pipes Conference Association # 1995 Edinburgh

Ovington, Stafford

This paper summarises a comprehensive study examining the factors which influence the weldability of crosslinked polyethylene W E ) whilst gaining an understanding of the nature ofjoints at a molecular level. Butt welding of XLPE to XLPE was investigated using both chemical @eroxide)and radiation crosslinked PE. The compatibility of both types of XLPE with all of the conventional PE pipeline grade materials was assessed using both bun and electrohion welding. The findings were used to weld a selection of large diameter, thick walled fittings, manufactured using the low production cost rotational moulding technique. Materials used were high flow, low grade polyethylene's which were subsequently crosslinked during production by peroxides or after production by irradiation. The crosslinked fittings produced bad improved stress crack resistance and were welded to conventional MDPE. This work led to the development of the interface layer technique of jointing, which involves the bun welding of two XLPE pipes interposed with a layer of MDPE. Methods of introducing the MDPE interface layer were developed into a single stage butt weld operation using pre-formed MDPE caps. It was concluded that XLPE could best be described as a modified thermoplastic with chemical linkages introduced between the long polymer chains to create a three dimensional network. The resulting material retains many of the characteristics of the parent polymer but some physical properties can be drastically changed. In particular, flow of the material above its melting point can be prevented, effectively changing a thermoplastic material into an elastomer. This limited mobility of the bulk material is the cause of faulted butt welds between XLPE and XLPE. Although having slits in the bead region, centrally, strong bonding was observed, indicating the possibility of material flow on a micro level. This can be aided by more precise weld preparation, reduced dwell times and jointing to a higher flow thermoplastic. Experimentation has proved that although crosslinked materials do not flow in their melt state, they can still be welded. Microshuctural examination has shown that this is only made possible due to an ability for molecular scale movement, albeit limited. The scale of this effect varies with the crosslinking process and more specifically with the actual crosslink sites. It is believed that chemical XLPE will in general, be more difficult to weld than radiation XLPE. This is due to the crosslinks occurring in the amorphous regions only, which become more prevalent at the weld interface during welding. This will funher hinder the already sensitive wetting and diffusion reactions taking place at the weld interface on a molecular level, the ability and existence of which results in bonding.

Please note that the whole article content is available on PPCA website only :

Related papers

2016 Berlin : Asset management of polyethylene gas networks

Author(s) : Ian Aldridge, Declan Robinson, Dave Smart, Chris Reed, Martyn, Greig, Trevor Stafford, David Christie-Lowe, Alec Erskine

For the UK polyethylene (PE) gas pipe network, the first installations now exceed 40 years in the ground, with an original design life of 50 years. It was thus timely to review the current condition and performance history of these first generation PE materials. A major 4 year project was started in 2010 to examine...

2006 Washington DC : A Novel Approach to PE Pipe Insertion Using Four-Lobe Vacuum Collapse

Author(s) : Ewing, Greig, Stafford

Funded by a UK government “Smart” Award, the authors have researched, and partially developed, a novel concept for temporarily reducing the external diameter of a PE pipe and then allowing recovery to full diameter as a close fit within a host main. The novelty lies in the four-lobed collapsed pipe geometry, which...

2006 Washington DC : Development of Large Diameter Multi-Pipe Bundles for Long Distance No-Dig Installations

Author(s) : Bircumshaw, Orchard, Kenworthy, Stafford

Funded by a UK government “SMART” award, the authors have explored the design options and practical solutions for installing large diameter multiple pipe ducts over very long distances. The work has involved consideration of the groundwork problems of microtunnelling or directional drilling at up to 1.5m (60ins)...

2001 Munich : The Challenge and Opportunity of High Voltage Cable Pipes

Author(s) : Stafford, Bircumshaw

The very high costs of underground electrical power transmission preclude its widespread usage even where social and environmental concerns make it highly desirable. This paper examines the technologies of below ground alternatives to overhead power lines and identifies the opportunities for introducing pipeline...

1995 Edinburgh : New Opportunities for New Pipes

Author(s) : Stafford

This paper is conceived as a review of current trends in the market and in the technology for thermoplastic pressure pipes. The application of any technical development depends on that subtle combination of the pull of needs and the push of new ideas. For more than 25 years British Gas has been actively involved in...

1995 Edinburgh : PE for Large Diameter Re-lining

Author(s) : Ovington

Trenchless contractors throughout the world sometimes feel they have an uphill job trying to gain acceptance for non-disruptive technology. A major obstacle is that trenches, however dangerous and however much traflic chaos they cause, are cheaper. However with the implementation of the new Road and Street Works...

1985 York : PE Jointing Techniques

Author(s) : Maine, Stafford

Since 1969, when polyethylene pipe systems were first used to distribute gas in the U.K., the vast majority of joints have been constructed using heated tool fusion techniques. The jointing processes involved require a high level of operator participation. The paper describes the development of fusion jointing...

In Field Quality Control of Fusion Jointing Methods

Author(s) : Stafford, Maine

Members of the Association

BOREALISBOROUGEFormosa Plastics CorporationHanwha TotalEnergiesINEOS O&PIRPCKorea Petrochemical IND. Co., LTD (KPIC)LyondellBasellORLEN UnipetrolPetroChina Dushanzi Petrochemical CompanyPRIME POLYMERSABICSCG Chemicals & Thai PolyethyleneSinopecTASNEE