Plastic Pipes Conference Association # 1995 Edinburgh
Schmutz, Kramer, Zweifel
In recent years several specifications arose on determination of oxidation induction time (OIT) for polyethylene pipes. Depending on pipe applications, whether they transport water or gas at what pressure, an OIT of 10 to 20 min at an isothermal temperature of 200 or 210°C is specified. With such a specification it is believed that the pipe will have the necessary long-term thermal stability for up to 50 years and residual antioxidant for welding.
In this paper the OIT, oxidation temperature (T,,), and mechanical properties of a PE-MD pipe resin are measured and compared. The study was carried out on compression molded plaques after hot water storage and on pipe samples submitted to hydrostatic pressure tests.
For the analysis of the OIT a specific technique was used. The samples were tested at an isothermal temperature of 170°C in air.
The data show that the OIT is not a very accurate tool to assess the deterioration status of a polymer. No good correlation could be found between the OIT and the brittle failure of the PE-MD pipe.
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