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Determination of the slow crack growth resistance of PA12 pipe grades

 

Mario Messiha, Andreas Frank, Isabelle J. Berger, Jan Heimink, Hermann van Laak, Florian Arbeiter, Gerald Pinter

Papers # 2018 Las-Vegas

Since the last decade polyamide 12 (PA12) has been successfully introduced as material for SDR 11 gas piping systems up to 18 bar, representing itself as an attractive alternative to steel pipes for high-pressure applications. Practical experience has confirmed that beside the higher strength, PA12 pipe grades also show an excellent resistance against relevant pipe failure mechanisms such as slow crack growth (SCG) as well as any third-party attack or external surface damages. Within the current paper, four different PA12 materials with varying macromolecular structure were investigated. On the one hand, a major focus was put on the general applicability of the Cyclic Cracked Round Bar (CRB) Test as fracture mechanical test method. On the other hand, the influence of the molecular weight, expressed by the relative viscosity number VNrel, on the fracture mechanical failure behavior was examined. The results demonstrate that the Cyclic CRB Test is a suitable method to provoke real SCG, and that the viscosity number has a considerable influence on the SCG resistance of PA12.

Related keywords : polyamide 12, gas piping systems, slow crack growth, cyclic cracked round bar test.
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