The present paper describes a creep rupture investigation on aramid fibre yarns (Twaron 1000 and Kevlar 29) supplied by Teijin and Du Pont respectively. The ISO 9080 extrapolation procedure, which was developed for thermoplastic pipe materials, was used to model and interpret the results. The 4 parameter version of this procedure fitted the results well and gave useful predictions of the long term stress rupture behaviour, lending confidence to existing qualification procedures for the use of aramid fibre in reinforced thermoplastic pipe (RTP), and other applications involving continuous high tensile loads. Creep strain measurements on yarns showed a near constant degree of creep deformation per decade. Although they may involve some of the same mechanisms the creep and stress rupture processes appear to operate independently and on different time scales. It was found that creep deformation in aramid yarns is unlikely to be a significant problem at stress levels corresponding to a 20 year lifetime.
This paper describes a glass fibre based composite repair system for steel tubular pipes that can cope with internal and external corrosion, as well as mechanical damage. The original objective, to develop a rehabilitation technique for pressures up to 40 bar, has been achieved and significantly higher pressures seem viable. The most critical parameter for tubes subject to internal corrosion, was identified as the ability of a bonded repair system to resist the formation of pressurised blisters. It is shown that, for bonded repairs, the key parameter determining blistering resistance is the fracture toughness of the metal/composite interface in the presence of pressurised fluid. The effective value of this parameter was found to be lower than might be expected on the basis of published fracture toughness values of laminates. This was attributed to the presence of pressurised water at the metal/composite interface. A fracture mechanics based criterion is proposed to enable the performance of repair systems to be assessed and compared.To address different repair scenarios, especially for higher pressures and when surface preparation may be difficult, a novel version of the rehabilitation system has been developed, which does not depend on achieving a bond at the metal/composite interface.
The present study discusses the possibilities offered by ramp pressure loading tests to generate data for determining the long term load-bearing characteristics of plastic pipe systems. In addition to ramp pressure loading, procedures are also considered where the pressure is held at a constant value for a period of time, after which the product is subjected to a ramped pressure burst test. The method discussed relies on the material in question obeying Miner's Law in its static fatigue behaviour. The pipe system to which the procedure has been applied is Reinforced Thermoplastic Pipe (RTP), in which the reinforcement is aramid fibre. However, the results are expected to apply to any polymeric system where there is evidence of conformity to Miner's Law. A set of ramp loading tests, and constant pressure plus burst tests are reported and compared with the results of conventional 'constant pressure' stress rupture tests and a method is proposed for converting these results into 'equivalent' constant pressure values. The results obtained on RTP using this new approach lie close to those generated using constant pressure.
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