Welding of Peroxide, Silane and Electron Beam Crosslinked PE Pipes [PE]

# 1998 Gothenburg

An investigation has been carried out into butt welding and electrofusion welding of PEX pipes, which had been crosslinked using the peroxide, silane and electron beam processes (PEXa, PEXb and PEXc respectively). A new hypothesis was set-up to explain the good weld quality of PEXa pipes electrowelded with regular commercial couplers produced from MDPE and PE I00 materials. This "mixed crystal hypothesis" combined with the existing "adhesion" and "flow process" theories provides a theoretical basis to explain the welding behaviour of PEXa with MDPE and PE100 materials, both in the form of pipe and thin foils. It is based on modem views about the importance of tie molecules needed for good long-term properties. The mixed crystal hypothesis postulates. that the strength of a weld between MDPE or PElOO and PEXa depends on formation of "mixed crystals" which contain chain parts from both the uncrosslinked and the crosslinked material. In these mixed crystals, thought to be formed on the welding plane during crystallisation of the weld at around 1 1 5 "C, tie chains from both materials are incorporated. This provides the strong physical bond between the two types of material needed to explain the good weld quality. To test the model, measurements on welded thin foils of MDPE and PEXa were carried out. Peel tests showed that for degrees of crosslinking of PEXa between 70 and 90%. this parameter does not affect the good weld qualities obtained. Moreover, the presence of residual uncrosslinked molecular chains in PEXa is not a necessary requirement to obtain a good weld strength. The good weld quality of PEXa pipes electrowelded using MDPE and PE100 couplers is illustrated by Scanning Elrclron Microscopy. However, the quality of electrofusion welds with PEXb and PEXc pipes was unsatisfactory. Butt welding of PEXa pipes to MDPE pipes is still very difficult, due to frozen-in extrusion stresses in the PEXa pipes, which lead to poor weld quality.

Please note that the whole article content is available on PPCA website onlySource : 1998 Gothenburg


Related papers

DETERMINING THE RESIDUAL QUALITY OF PE PIPES USING THE STRAIN HARDENING TEST

Author(s) : Ernst van der Stok, Frans Scholten 2016 Berlin

Samples machined directly from pipe show that orientation has a large influence on the strain hardening modulus. No effects arising as a result of residual stresses were found. Samples machined in the axial direction from a hydrostatic pressurised pipe showed no effect as a result of this mechanical degradation. For...

PREDICTING THE LIFETIME OF PE50 GAS PIPES UNDER POINT LOADING

Author(s) : Frans Scholten, Ernst van der Stok 2016 Berlin

The residual quality of first generation PE50 gas pipes, installed in Netherland between 1961 and 1979, is still remarkably good. The only premature failures of a few PE50 pipes were exclusively caused by point loads. When under point loading, they started failing in practice after 8 to 26 years, in a brittle manner....

RESIDUAL QUALITY OF EXCAVATED UPVC GAS AND WATER DISTRIBUTION PIPELINES

Author(s) : Frans Scholten, Ernst van der Stok, Britta Gerets, Mirko Wenzel, Mike Boege 2016 Berlin

The current condition of 35-50 years old uPVC main (110 mm) and service (32 mm) pipes for gas and water distribution was assessed. From 27 excavation sites in total about 400 segments of 1.2 meters length each were tested using many techniques. The K-value (average molecular weight) of the PVC, the degree of gelation...

THE EFFECT OF RESIDUAL STRESSES AND EXTERNAL EFFECTS ON THE FRACTURE BEHAVIOUR OF PVC PIPES

Author(s) : Ernst van der Stok, Jeroen Weller, Frans Scholten 2016 Berlin

This paper describes falling-weight tests as a first step towards determining the effect of residual stresses on the fracture behaviour of old PVC-U gas pipes at impact. Results showed that the level of surrounding pipe support, the quality of the material and the diameter of the striker had a major effect on the...

Designing Against Rapid Crack Propagation in PVC Water Pipes

Author(s) : Frans Scholten, Ernst van der Stok, Jan Breen 2014 Chicago

Very occasionally PVC-U water pipes suddenly fail due to a long brittle crack with a length of many meters which propagates with the speed of sound along the pipe and causes extensive water loss. This phenomenon has been recognized as Rapid Crack Propagation (RCP). The conditions under which RCP can occur are an...

Energy-to-Failure to Assess the Quality of Electro Fusion Joints in PE Pipes

Author(s) : Frans Scholten 2014 Chicago

When electro fused joints in newly installed PE100 pipelines are tested using the Peel test (ISO 13954 [1]) they too often fail in a brittle manner. Contamination in the interface between the surfaces to be fused is usually the cause. About 77 % of the contaminants in 39 cases of brittle test bars could be identified...

Two Complementary Tests to Determine the Quality of PE 100RC

Author(s) : Ernst van der Stok, Frans Scholten 2014 Chicago

The Strain Hardening (SH) test and the Point Load Test (PLT) are two complementary tests designed to determine the quality of PE 100-RC. The SH test is a resin test, whereas the PLT is a pipe test. The SH test is a tensile test performed at 80 °C. Extensive research on the SH test has been conducted and published in...

NON-DESTRUCTIVE AND IN-SITU DETERMINATION OF THE DEGREE OF GELATION OF PVC PIPES

Author(s) : Emiel Drenth, Ton Bor, Roy Visser and Mannes Wolters 2012 Barcelona

Various non-destructive methods, based on different physical principles, were investigated for their ability to differentiate between uPVC pipes having various levels of gelation. It was found that the micro-hardness method was not able to differentiate between uPVC samples of different levels of gelation. A possible...

STRAIN HARDENING TESTS ON PE PIPE MATERIALS

Author(s) : Van der Stok, Scholten 2012 Barcelona

The Strain Hardening (SH) test developed by Kurelec et al. has been applied to a variety of PE pipe and resin materials. The clear trend in the strain hardening modulus, of first, second and third generation PE pipe resins and PE100 RC pipe resins, illustrates the large progress in resin quality during the past four...

COVER BLOW-OFF RESISTANCE OF REINFORCED THERMOPLASTIC PIPES FOR GAS SERVICE

Author(s) : E.J.W. van der Stok, F.L. Scholten, L.G.P. Dalmolen 2010 Vancouver

A mathematical model was set up to assess the equilibrium gas pressure in the annulus of the reinforcement layer of an RTP pipe. This is done by using the theory of gas permeation, ruled by Fick's Law and the theory for a temperature gradient over the pipe wall, ruled by Fourier's law. The model allows calculating the...

Members of the Association

BOREALISBOROUGEINEOS O&PIRPCKorea Petrochemical IND. Co., LTDLyondellBasellPetroChina Dushanzi Petrochemical CompanyPRIME POLYMERSABICSCG Chemicals & Thai PolyethyleneSinopecTASNEE
TOP