Greig
Assessment for Performance # 1988 Bath
The catastrophic phenomenon of rapid crack propagation in 250 mm diameter polyethylene pipes has been investigated at a full scale test facility. Tests at +3°C were conducted with pipes, either completely fully of water or containing a small percentage of air. The safe, maximum pressures were measured.
Rapid crack propagation (RCP) occurs when a crack, once initiated, runs down the plastic pipeline at high speed. If the pressure in the pipeline is reduced sufficiently then the crack will arrest after only a few metres. The crack may be initiated in any manner which produces a high speed crack but for polyethylene (PE) pipes this is most likely by high speed impact from an excavator or by the failure of a defective butt weld.
British gas have already investigated the critical conditions for buried PE pipes (125 mm to 315 mm) pressurised with nitrogen (1, 2). It was found that the pipeline behaviour would change from the crack arrest condition to fracture of the total test length (25 m) above a critical pressure. The critical propagation pressure was very sensitive to pipe temperature; increasing rapidly as the temperature was raised.
Tne Water Industry was concerned whether the same phenomenon could occur in PE pipes full of water or containing a small percentage of air for it is very difficult to remove all the air in the pipeline during high pressure commissioning tests.
Consequently, as part of the sponsored research programme “EVALUATION OF THE LONG-TERM SERVICE PERFORMANCE OF PLASTIC PIPES FOR WATER SUPPLY", the behaviour of hydrostaically pressurised blue 250 mm x 24 mm (SDR11) and yellow 250 mm x 15 mn (SDR17) at +3°C was investigated at the British Gas Engineering Reserch Station's Test Site at Spadeadam.
Related papers
Author(s) : Ian Aldridge, Declan Robinson, Dave Smart, Chris Reed, Martyn, Greig, Trevor Stafford, David Christie-Lowe, Alec Erskine
For the UK polyethylene (PE) gas pipe network, the first installations now exceed 40 years in the ground, with an original design life of 50 years. It was thus timely to review the current condition and performance history of these first generation PE materials. A major 4 year project was started in 2010 to examine...
Author(s) : Ewing, Greig, Stafford
Funded by a UK government “Smart” Award, the authors have researched, and partially developed, a novel concept for temporarily reducing the external diameter of a PE pipe and then allowing recovery to full diameter as a close fit within a host main. The novelty lies in the four-lobed collapsed pipe geometry, which...
Author(s) : Greig
One of the main design criteria for limiting the operational pressures of polyethylene (PE) gas pipes is its resistance to rapid crack propagation (RCP). Below a critical pressure the crack arrests but above the whole pipeline may be fractured. The paper discusses the critical pressures measured during European and...
Author(s) : Ewing, Greig
Operation of high density polyethylene (HDPE) pipes at 7 bar has been very successful in British Gas over the last few years. Using HDPE pipes at higher pressures requires a high level and correct balance of pipe properties of strength, stress crack and rapid crack propagation resistance. Raised levels of jointing...
Author(s) : Ward, Atkinson, Greig, Hansard
A novel die-drawing process has been developed at Leeds University. By incorporating a mandrel, pipes may be expanded hoopwise whilst being drawn axially. Such biaxially-oriented pipes have properties better suited to the transmission of gases and liquids than either isotropic or longitudinally-drawn pipes. In this...
Author(s) : Greig, Lawrence
Hydrostatic s~ress rupture testing at 80°C of polyethylene gas pipe currently takes sver 1000 ho7.1rs to determine its good stress cracking performance. This is excessively long for quailty control purposes so a rapid rest is being developed using fatigue pressurlsac. :on, 2gajn on notched...
Author(s) : Greig
As polyethylene pipes increase in size above 250 mm, the avoidance of high-speed brittle fracture propagation becomes of overriding importance. More stringent operating and test pressures have had to be introduced. A full scale test programme on a variety of pipe sizes is being conducted by British Gas. In this paper,...
Author(s) : Greig, Ewing
Fracture propagation is a phenomenon in which a long brittle crack runs along the pipeline at high speeds of...
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