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The remaining quality of the PVC gas grid - Results of 10 years of on-going research

 

Papers # 2016 Berlin

To prevent an enormous surge in the replacement costs of the Dutch PVC gas distribution grid a so-called Exit Assessment programme was started in 2004. This programme determines the actual quality of old excavated PVC-U and PVC-Hi pipes using a tensile-impact test at temperatures varying from -25°C to +47,5°C, whereby the brittle-ductile-transition-temperature is determined. With this research the average remaining quality of the Dutch PVC grid is determined. Also prioritizing pipe replacement becomes possible by distinguishing between pipe populations based on PVC-U types, diameter or installation year. 

This decade most of the PVC-U pipes used for the distribution of natural gas in the Netherlands will reach their initially specified lifespan of 50 years. To prevent an enormous surge in the replacement costs of these pipes, it is of increasing importance to determine the remaining material quality. Therefore a so-called Exit Assessment programme was started in 2004.

Field failure studies have shown that the lack of ductile behaviour during excavation damage is the most important reason for incidents involving PVC in the Netherlands. Therefore in this programme the quality of old excavated PVC-U and PVC-Hi pipes is determined using a tensile-impact test at temperatures varying from - 25°C to +47,5°C, whereby the brittle-ductile-transition-temperature (TBD) is determined. 

With this research programme the average remaining quality of the Dutch PVC grid is determined. In this paper the relation between the diameter and the material properties are shown. Also the difference in the production quality of two PVC-U types in the early sixties of the last century is made visible. This knowledge gives the Dutch grid operators an opportunity to prioritize the replacement of old PVC-U pipes based on material quality instead of service time only.

Finally it is shown that through the years there has been a major improvement in the impact resistance of PVC. Well known of course are the improvements from PVC-U to PVC-Hi and latest PVC-O. However this research also shows that within PVC-U itself the material quality has made a large improvement over the years, due to improvements in the production process of PVC-U.

Related keywords : Polyvinyl Chloride (PVC), Brittle-ductile-transition-temperature (T BD ), Remaining Quality Gas Grid, Prioritizing Replacement, Tensile-impact Test, gas pipe, gas supply.
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