A statistical approach for evaluating material property degradation in fibreglass reinforced plastic composite piping

The Pickering Nuclear Generating Station contains Fibreglass Reinforced Plastic composite piping and components in service since 1971. The Fibreglass Reinforced Plastic components are periodically inspected and analysed to ensure that any degradation experienced over time will not compromise structural integrity. A number of samples have been removed from service and subjected to laboratory tests to identify trends in the rate of material property degradation and possibly provide estimates of future performance. In this paper, we propose a statistical approach to evaluate possible trends in material property degradation over time, with a 36-inch Fibreglass Reinforced Plastic pipe used as a demonstrative example. The calculated elastic modulus is highly sensitive to variability in the tested material. The calculated flexural rigidity is less sensitive to variations in sample properties such as thickness and is therefore a better indicator of degradation trends over time. The results highlight the importance of improving the quality of the degradation trend data by carrying out repeat non-destructive tests on identical samples under tightly controlled test conditions and procedures. (author)