Taking the stress and strain of buried thermoplastic pipe design


Applications & Jointing # 1995 Edinburgh

This paper summarises current design practices for buried thermoplastic pipelines subjected to combined gravity and internal pressure loadings. It suggests that accurate predictions of stabilised deformations are neither possible nor necessary, but that appropriate structural design methodologies should instead be limit slate based. The latter concept is first considered with reference lo observed behaviour under gravity loads only, and then the likely effect of internal pressurisation is addressed. Existing reservations about current European design approaches are reinforced, in particular with respect to stress and strain value derivations - moreover in the case of thermoplastic pressure pipes it is noted that the beneficial effects of stress redistribution and creep relaxation are generally not taken into consideration. It is concluded that now is an ideal time to review the weaknesses and conservatisms in current design practices and then to develop user friendly analytical techniques that are more appropriate to modem thermoplastic pipe materials.

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