An Argon Plasma Etching Method for the Investigation of Craze Microstructure in PVC Gas Pipes


Testing and Processing # 1985 York

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 gas components has received attention. In this contribution an argon plasma etching method is presented that is very well suited for the investigation of craze microstructure using Scanning Electron Microscopy. The reason for this is that craze material that has absorbed certain gas components is not or only to a minor extent attacked by the argon plasma, whereas the surrounding material is strongly attacked.

It can be shown by means of this preparation method that many crazes formed in

PvC in natural gas environments do not show fribrillation but merely show signs

of localized absorption, swelling and de-gelation behaviour. This is probably due to the low mechanical stresses that are present during craze formation in many practical situations. In other crazes produced in the laboratory using higher stresses a high extent of fibrillation can be made clearly visible by the argon plasma treatment. Another conclusion this preparation method allows is that crazes caused by different chemicals show different microstructures.

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

Related papers

2016 Berlin : Determining the residual quality of PE pipes using the strain hardening test

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...

2016 Berlin : Predicting the lifetime of PE50 gas pipes under point loading

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....

2016 Berlin : Residual quality of excavated UPVC gas and water distribution pipelines

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...

2016 Berlin : 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

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...

2014 Chicago : Designing Against Rapid Crack Propagation in PVC Water Pipes

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...

2014 Chicago : Energy-to-Failure to Assess the Quality of Electro Fusion Joints in PE Pipes

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...

2014 Chicago : Two Complementary Tests to Determine the Quality of PE 100RC

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...

2012 Barcelona : Strain hardening tests on PE pipe materials

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...

2010 Vancouver : 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

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...

2010 Vancouver : Pa pipes for 16 bars gas pipelines

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,...

2010 Vancouver : Residual quality of first generation PE gas and water pipes

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...

2006 Washington DC : Non-Destructive Ultrasonic Inspection to Detect Flaws in Plastic Pipe Walls and Joints

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...

2001 Munich : A More Reliable Detergent for Cone and Full Notch Creep Testing of PE Pipe Materials

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...

2001 Munich : Opportunities for Plastics in Flexible Indoor Gas Pipe Systems

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...

1998 Gothenburg : Welding of Peroxide, Silane and Electron Beam Crosslinked PE Pipes

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...

1992 Eindhoven : Field failures in PE Gas Pipes - Analysis versus Lifetime Prediction

Author(s) : Scholten, Rijpkema

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,...

Methane Permeation through Advanced High-Pressure Plastics Pipes

Author(s) : Scholten, Rijpkema

The Slow Peel Test as a Tool for Assessing the Integrity of Electro Fused Joints

Author(s) : Scholten, Wolters

Members of the Association

BOREALISBOROUGEFormosa Plastics CorporationINEOS O&PIRPCKazanorgsintez PJSCKorea Petrochemical IND. Co., LTD (KPIC)LyondellBasellPetroChina Dushanzi Petrochemical CompanyPRIME POLYMERSABICSCG Chemicals & Thai PolyethyleneSinopecTASNEE