Plastic Pipes Conference Association # 1998 Gothenburg
Hillmansen, Davis, Leevers
Rapid Crack Propagation in PE-100 gas pipes is governed primarily by a brittle-tough transition temperature TBT,above which ductile deformation will absorb energy and promptly arrest a fast-running brittle crack. Even at low temperatures, a layer of plastically deformed material is formed at the pipe bore during fracture, but only becomes effective when the pipe transition temperature is exceeded. To relate this post-yield deformation behaviour to the microscopic propenies at the bore of a PE-I00 pipe, it is important to isolate the 'true' or local macroscopic behaviour of the material under high-rate tension. A simple tensile test at constant displacement rate will certainly characterise yielding of PE-100, but post-yield deformation is generally inhomogeneous, and local changes in sample geometry and strain rare can lead to erroneous impressions of material response. To overcome this, true stressltrue strain data for pipe grade PE has been captured at a constant local strain rate using a video controlled tensile machine. Localised post-yield deformation in PE-I00 is characterised ar low strain rates over a range of temperatures, giving a family of isothermal true stressltrue strain curves. However, at the extremely high strain rates produced in rapid crack propagation, adiabatic heat generation increases material temperature and deformation becomes thermally coupled. A Finite Element model incorporating the isothermal true stressltrue strain data is therefore used to explore the strain rate and associated temperature dependence of rapid deformation in this material.
Related papers
Author(s) : Patrick Leevers, Christos Argyrakis
There is renewed interest in the correlation between critical pressures from lab-scale (S4) and full-scale RCP tests. The standard, supposedly material-independent correlation factor does provide a lower bound for data from many PE grades, but for some grades it is overconservative and for PA12 its applicability has...
Author(s) : P.Leevers
This paper outlines a PE100 design methodology which gives central importance to the separate modelling and measurement of plane-strain and plane-stress dynamic fracture resistance. The former is difficult to measure but can be estimated from weight-average molecular weight; the latter is related to high-rate adiabatic...
Author(s) : Krishnaswamy, Leevers, Lamborn, Sukhadia, Register, Maeger
The influence of molecular architecture on the rapid crack propagation (RCP) resistance of a wide variety of high-density polyethylene (HDPE) pipes was investigated. It was concluded that high molecular weight, high crystallinity and a relatively narrow molecular weight distribution are important architectural...
Author(s) : Leevers, Henderson, Pereira
Laboratory-scale S4 tests have been used to determine whether it would be possible, at any realistic working pressure, for a loosely-fitted PE liner within a rigid host pipe to fail by Rapid Crack Propagation (RCP). The standard ISO 13477 S4 method was modified by replacement of the containment ring cage by a rigid,...
Author(s) : Maeger, Vanspeybroeck, Lamborn, Mamoun, Leevers, Oliphant
As polyethylene pressure pipes enter the global marketplace under an ever-wider range of operating conditions, there is increasing emphasis on their rapid crack propagation performance. It is important that both producers and end-users are able to rely on the robustness of the rapid crack propagation test results and...
Author(s) : Patrick Leevers
International Standard ISO 13477 defines the ‘S4’ RCP test itself, and specifies two procedures which use it. The first procedure, already well embedded in referring standards, evaluates a critical pressure at constant temperature (usually 0°C) below which RCP arrests. The second procedure evaluates, at constant...
Author(s) : Ivankovic, Tropsa, Jasak, Leevers
This work presents a 3D coupled solid-fluid model for predicting fast failures in pressurised plastic pipes. It is developed within a unified computational procedure where both solid pipe and pressurising media are discretised using the Finite Volume method. The coupling is achieved across the pipe-fluid interface...
Author(s) : Davis, Burn, Whittle
The C-ring test method is widely used by the water industry to determine the fracture toughness of poly(vinyl chloride) (PVC) pipes. The test currently forms a draft ISO standard (ISO/DIS 11673.2) and an interim Australian/New Zealand Standard (AS/NZS 1462.19(Int)) for fracture toughness assessment. Whilst results...
Author(s) : Leevers, Moreno, Paizis
The resistance of PE pipes to rapid crack propagation depends strongly on temperature. The critical pressure measured using ISO 13477 ‘S4’ tests increases abruptly above a transition temperature Tc. For PE100 grades Tc has become a primary index of quality : it must remain below 0°C despite a tendency to increase...
Author(s) : Burn, Davis, DeSilva, Marksjo, Tucker, Geehman
To allow long-term strategies to be implemented for the replacement or refurbishment of water pipelines, a planning model called the Pipeline Asset and Risk Management System (PARMS) has been developed. This model, although based upon life cycle costing methodologies has been designed to incorporate whole of life...
Author(s) : Douglas, Leevers
A model for dynamic and impact fracture has been recently proposed whereby the fracture event is controlled by adiabatic heating and subsequent melting of the cohesive crack tip craze. The crack initiation resistance is shown to be an inherent function of specimen geometry and impact speed. This theoretical framework...
Author(s) : Davis, Greenshields, Dabas, Leevers
The study of Rapid Crack Propagation (RCP) in pressurised pipelines is of particular importancr to th? g a industry, where the possibility of such a failure must he minimised. Polyethylene (PE) currently dominates the market for plastic gas pipelines, and as the demands for larger diameters .and higher operating...
Author(s) : Leevers
The international standardisation of tests for Rapid Crack Propagation (RCP) is approaching completion, and requirements for product and systems standards x e well established. Yet some basic issues about RCP remain contentious. In contrast to slow crack growth, there is a near-absence of service failure data, and in...
Author(s) : Hazra, Leevers
In previous work on the impact behaviour of pipe grade polyethylene (PE), the 'thermal decohesion model' was proposed by Leevers [ l ] to explain the embrittlement of PE under impact and at low temperatures. One of the initial assumptions of the model was that the crack tip craze could be represented by a Dugdale...
Author(s) : Venizelov, Greenshields, Leevers
An analytical I-D model of the gas discharge process in the small scale steady State ( ~ 4 ) test for rapid g a c k propagation (RCP) in thermoplastic pipe has been developed. Because the gas can exert a powerful crack driving force, such a model is essential to an understanding of the test. This model yields a...
Author(s) : Greenshields, Leevers
Previous research has concluded that rapid crack propagation (RCP) cannot be sustained in 100% water pressurised pipe. However, this paper shows that by reducing the decompression wave speed in water to below the crack speed, it is possible t o sustain fast cracks in thermoplastic pressure pipe. T h e prediction of R...
Author(s) : Leevers, Greenshields, Venizelos, Ivankovic
The development of pipe-grade materials to resist slow crack growth and ductile rupture has been spectacularly successful. It is a measure of this success that concern with Rapid Crack Propagation (RCP) has increased to the level evident at this conference. Stronger materials encourage the use of higher...
Author(s) : Greenshiels, Leevers
The failure of a pipe by rapid crack propagation (RCP) can, by its nature, be highly desmctive and must be avoided. Research over the past ten years has concentrated on gas pressurised pipelines and has resulted in a greater awareness and understanding of the problem. Recent attention has focused on RCP in...
Author(s) : Leevers, Venizelos, Ivankovic
The small-scale 'S4' test for rapid crack propagation seems set to acquire the status of a specifying standard for polyethylene gas distribution pipe. This paper describes parallel research projects on pressureinstrumented S 4 t e s t s a n d on Finite-Volume numerical analysis of S4 and full-scale tests....
Members of the Association
