Development of a lifetime assessment method for PVC gas and water pipes using micro-indentation.
Start / End:
Feb 2010 to Jan 2014
Consultant Licensing and Safety at NRG
Emiel Drenth (2015). Towards condition based asset management of uPVC pipes. PhD Thesis, University of Twente, The Netherlands, ISBN 978-90-365-3992-0.
Summary of PhD Thesis
The Dutch gas and water distribution networks consist of considerable amounts of unplasticised poly(vinyl chloride) (uPVC) pipes. Most of the failures in uPVC gas pipes are caused by impact loading events from digging activities. The risk of (fatal) incidents after impact damage is higher for brittle pipes than for ductile pipes. The occurrence of brittle failure is considered the main limit for the service life of uPVC gas pipes. Brittle pipes should therefore be located and replaced.
Physical ageing leads to an increase in the yield stress of the PVC pipe material. The increase in the yield stress due to physical ageing can induce brittle failure behaviour of the uPVC pipe when it is impacted. If this is case the yield stress reached a critical value at which the transition from ductile to brittle failure behaviour occurs. The residual lifetime of the uPVC pipe follows from the time it takes for the material to reach the critical yield stress from its current yield stress. The yield stress at which a ductile-to-brittle transition is occurs is influenced by the level of gelation (the initial production quality of the pipe). This implies that (i) physical ageing should be monitored non-destructively in time and (ii) the level of gelation should be known for accurate residual lifetime predictions.
In previous a PhD project Roy Visser developed a framework for residual lifetime assessment of uPVC gas pipes. In this second PhD project the emphasis is on improving the existing residual lifetime assessment method towards a level that in-situ application in uPVC pipes becomes realistic. A new method to non-destructively determine the yield stress has been developed and a systematic investigation on the variation in physical aging kinetics, as observed in the previous PhD project, has been carried out. A new method to determine the critical yield stress has been developed using a validated criterion for the critical yield stress (Figure 1). The in-situ determination of the level of gelation of uPVC pipes has been investigated as well (Figure 2). Finally, a proposal for the practical implementation of the residual lifetime assessment method is described.
Emiel Drenth is currently working at NRG in Arnhem, a company which provides consultancy and services for nuclear reactors in the Netherland and abroad.
Figure 1: Embrittlement by physical ageing is demonstrated in a pipe saw test. The pipe saw test, can be employed to determine the critical yield stress for prediction of the residual lifetime of uPVC pipes.
Figure 2: A demonstration of the microMethylene Chloride (microMC) test. Photographs of concavities milled on the inner surface of a uPVC pipe wall. Left: no attack induced by MC at 5 °C, Right: initiation of attack by MC at 10 °C. This test can be used to determine the level of gelation of uPVC pipes.
This project is a collaborative research project between Liander, Cogas Infra & Beheer, Enexis, Stedin, Bureauleiding, Vitens, Rendo Netwerken and Delta Netwerkbedrijf