Additional Information - Posters
Plastic Pipes Conference Association # 1995 Edinburgh
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 closed-form analytical expression for the pressure decay behind the crack tip, as a function of distance, crack velocity and crack opening angle (COA). It is based on the primary assumptions that the discharge process is predominantly radial, and the gas flow velocities inside the rupturing pipe are negligible. The former is due to suppression of axial decompression in the S4 test and the latter due to crack openings considerably smaller than those observed during RCP in ductile steel pipes. Both assumptions are based on experimental and numerical evidence. The only uncertainty in the model is the unknown relationship between crack speed and crack opening angle. Using values of C O A based on evidence from fast photography, and assuming a linearly decreasing dependence of COA on crack speed, very good correlation between model and experiment has been achieved. This model should prove to be a valuable tool for the efficient formulation of a "coupled" RCP numerical model of the s4 test (in which the behaviour of both the structure and the fluid as well as their interaction is considered) since it eliminates the need for numerical solution of the fluid dynamics.
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) : 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) : 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...
Author(s) : Venizelos, Greenshields, Ivankovic
Over 30 years ago, fast brittle fracture was identified as an inherently catastrophic failure mode in pressurised plastic gas pipelines. Although fast cracks seemed difficult to initiate, subsequent rapid crack propagation (RCP) was thought to be possible at pressures lower than the rated pressure, imposed by design...
Author(s) : Greenshields
Brittle failures in service water pipelines sometimes occur at relatively low pressures and for no apparent reason. This paper presents a review o f research into brittle fracture in water pipes and questions some o f the received assumptions which obscure tlie subject. The hydrostatic S4 test is proposed to measure...
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) : 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....
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