Lifetime of Pipes
Plastic Pipes Conference Association # 1992 Eindhoven
Marhsall, Harry, Ward, Pearson
Existing test methods used for the characterisation of long term strength properties of plastic materials for use in pressure pipe duties have been reviewed. A notched "C" ring type test has been developed to define the long term crack resistance and strength properties of a CPE modified PVC. Since materials of this type are inmnsically ductile and are highly resistant to cracking, data have been analysed in terms of net section stress as the control on failure. Direct agreement with data from pressurised pipe tests has been obtained. The pressurised pipe test for PE has been re-evaluated in terms of elastic, viscoelastic and plastic phases of deformation. It has been shown that predictions made from elastic strain measurements in the short term may be used in the prediction of the long tenn pressure regression performance. In addition, it has been shown that relaxation of pressure in the history of a pipe results in an enhancement of its overall lifetime.
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