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# 1992 Eindhoven
Eight excavated HDPE pipes of the 1st generation along with 3 modern PE types have been investigated. Comonomer content as a function of molecular weight of the old HDPE pipes appeared to be nonoptimal with respect to the modern PE types. Further unwanted effects in the old pipes were : particles, oxydation, inhomogeneity. Premature failures were due to previously unexpected effects of external point loadings.
Author(s) : Ernst van der Stok, Frans Scholten
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...
Author(s) : Frans Scholten, Ernst van der Stok
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....
Author(s) : Frans Scholten, Ernst van der Stok, Britta Gerets, Mirko Wenzel, Mike Boege
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...
Author(s) : Ernst van der Stok, Jeroen Weller, Frans Scholten
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...
Author(s) : Frans Scholten, Ernst van der Stok, Jan Breen
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...
Author(s) : Frans Scholten
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...
Author(s) : Ernst van der Stok, Frans Scholten
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...
Author(s) : Hella J.M.Rijpkema, Hendrik J.Roebers, Marco C.A.Mekes
The application of plastic pipework for gas inside buildings is still restricted by national laws or local regulations in many countries, while other countries allow this application. The exclusion of plastics is in the main based on the supposed fear of the impact of a fire on the pipework and the escape of unburned...
Author(s) : Van der Stok, Scholten
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...
Author(s) : E.J.W. van der Stok, F.L. Scholten, L.G.P. Dalmolen
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...
Author(s) : Frans Scholten and Mannes Wolters
PA11, PA12 and plasticized PA6.12 pipes are interesting candidates for gas transport and distribution pipelines at 16 bars pressure, which is beyond the maximum pressure for PE100 pipeline systems (10 bars). However, PA pipelines are not meant as an alternative to PE pipelines, but to steel pipelines. Therefore,...
Author(s) : F.Scholten
Segments from 32 mm gas service pipes installed in 1975-1976 and from 40 mm water service pipes installed in 1967-1968 in Germany have been excavated and tested for residual quality. Two different HDPE resin populations discovered among the German gas pipes were also found among excavated Dutch gas pipes. Internal...
Author(s) : Scholten, Shin
Ultrasonic detection equipment was used to investigate defective pipes and fusion joints. The following examples of its application are presented. Electro-fused joints were tested in four different 110mm PE100 and PEX pipes. The PEX pipes showed a less complete fusion between pipe and fitting in comparison to PE100...
Author(s) : Scholten, Gueugnaut, Berthier
Detergents of the type nonylphenol ethoxylate (NPE) are often used in PE pipe tests at 80°C like the Full Notch Creep Test, Cone test and Constant Load test. However, evidence is presented that this class of detergents is very vulnerable to oxidation by oxygen from the air surrounding the tests baths. This leads to a...
Author(s) : Oesterholt, Scholten, Roebers
Worldwide more and more buildings are connected to natural gas. Until recently the gas within the building was exclusively distributed through metal pipe systems, such as straight copper pipes, soldered together and straight steel pipes, screwed together. About six years ago some pilot projects with PEX (crosslinked...
Author(s) : Scholten, Wolters
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...
Author(s) : Rijpkema, Wolters
In the Netherlands about 20,000 km of uPVC (unplasticized PolyVinylChloride) gas pipes are in use. The oldest uPVC pipes have been in operation for over 30 years now. These systems were usually designed for a period of between 30 and 50 years. Probably, however, the actual service life will turn out to be much...
Author(s) : Zefrin, Scholten
The gas industry in the Netherlands uses not only PE and metal but also unplasticized and impact modified PVC as pipe material for the distribution of natural gas.For a number of years the phenomenon of crazing in PVC and impact modified Pvc gas pipes caused by the combined action of mechanical stresses and certain...
Author(s) : Scholten, Rijpkema
Author(s) : Scholten, Wolters
