Kiwa Technology (The Netherlands)
More than 20,000 km of rigid PVC (or PVC-U) pipes are currently in use for the distribution of natural gas in the Netherlands. In this decade the majority of these pipes will reach their initially specified lifespan of 50 years. In the light of a possible replacement surge it is increasingly important to establish the actual material quality of these pipes. To gain insight in the remaining quality of the PVC-U pipes in the Dutch gas distribution net, a so-called Exit Assessment program was started in 2004. In this program the quality of existing PVC-U material is determined by measuring the brittle-ductile transition temperature of the excavated pipes with a tensile impact test. The ultimate goal for Dutch Distribution System Operators (DSOs) is to assess the remaining quality in the field without the need for removal of pipe segments.
The color of the material on the inside and outside of a pipe can change because of physical processes, for instance due to stress whitening or uv-radiation. Both the color measurement using an ultraviolet-visible spectroscopy (UV-vis) and the hardness measurement using the Leeb rebound hardness test, can be performed non-destructive and could give more information about the remainder quality of the PVC pipe. Goal of ongoing research is therefore to find a correlation between this tensile impact test and the non-destructive techniques (NDT).
The first experiments with UV-Vis measurements on both the inside and outside of PVC pipes show a relation with the surface roughness of the pipe. Ongoing measurements on the current database with tensile impact test results will give the opportunity to search for correlations between the tensile impact test, the UV-Vis measurements and the Leeb hardness test on the inside or outside of the PVC pipe wall. If this correlation is established new opportunities for NDT measurements in the fields can be developed like measurement of the outside color of PVC pipes in the field or development of a sensor for measurements on the inside while using a robot. This paper therefore gives valuable insight in the color measurement of PVC pipes. Besides the correlation between the UV-Vis, Leeb hardness and the tensile impact measurements is investigated, revealing insight in the usefulness of these non-destructive technique for PVC pipes.