Fracture Mechanisms
Plastic Pipes Conference Association # 2001 Munich
Vanspeybroeck
Although total safety in the gas industry may be an impossible dream, each engineer must definitely use every possible means to come near to this perfection. In view of this objective some gas companies join their efforts for combined research and development in order to improve standards or specifications and research was undertaken to avoid Rapid Crack Propagation. Three countries involved in this research, have developed 4 test methods (Figure 1):
• In Belgium, where research was undertaken by Electrabel in co-operation with the university of Gent, the modified Robertson test was developed and presented to ISO TC 138 in May 1979.
• In France, research was undertaken by Gaz de France, where the classic Charpy test has been adapted.
• In the United Kingdom research was done on one side by British Gas leading to the Full Scale test and at the Imperial College of London where Doctor Leevers proposed his Small Scale test.
The study on the risk of RCP in polyethylene dates from 1973 when British Gas extrapolated its experiences acquired on steel to PE proposing a model based on “fracture mechanics”. At that time, Professor Vancrombrugge of the University of Gent/Belgium, was studying the phenomenon by performing tests on pipes by extrapolation of the Robertson test (established in times of war to measure the phenomenon RCP on the ships).
All this research is discussed within a subgroup of ISO TC 138 with Becetel as convenor. Due to controversial economical aspects, some lobbying groups try to postpone the introduction of such test methods.
RCP has been debated in the ISO standardization during more than 25 years. Finally two test methods were developed and accepted at the international level ISO 13477 {in the United States (ASTM/F 1589)} under the name S4 (Small Scale Steady State Test).
Parallel to the development of the Small Scale laboratory test, research was undertaken by British Gas, leading to the Full Scale test (ISO 13478). This test was based on considerable experience with steel pipe and Full Scale field trials with thermoplastic pipes.
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