Slow Crack Growth
Plastic Pipes Conference Association # 2004 Milan
Beech, Clutton
Design of pipe systems for lifetimes in excess of 100 years depends on accelerated testing of pipe at different temperatures, and standard extrapolation methods for assessment of the minimum required strength. However resistance to slow crack growth is an essential parameter to take into account for the development of PE materials for pressure pipe applications. The ISO 13479 Notched Pipe Test (NPT) has become well established as the benchmark test, being referenced in ISO, European, and many national and industry product standards for PE gas and water pipe. For the development of materials accelerated small-scale tests to allow rapid screening of materials and to gain an understanding of the effect of changes to the material structure are required. In recent years the Full Notch Creep Test (FNCT) has gained popularity with European PE suppliers, particularly as a tool in the development of high performance PE 100 materials. In order to accelerate this test on a notched square bar, detergents are used. A test programme using both tests on three different pipe compounds has been carried out to gain a greater understanding and interpretation of the results. The study has allowed conclusions to be reached on the interpretation of test results and the suitability of each test for product specifications.
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