Corrosion Assessment of Aging Drinking Water Pipes by Impact Elastic-Wave Method

The majority of the water distribution pipes which take the greater part of Japanese drinking water utilities' assets are made of iron such as gray/ductile cast iron or steel. It will be necessary to replace most of these pipes due to corrosion in the near future. In general, pipeline assessment which is done before replacement is carried out through digging to take visual observation; however, digging costs and environmental burden due to digging will become a problem.

This study therefore undertakes a research into methods of pipeline assessment which reduce the digging necessity. In the study of the Impact Elastic-Wave Method, elastic-waves were applied to cast iron pipes whose external surfaces were in various states of corrosion (pitting, partial, uniform, etc.); the frequency component of the received waves showed that there was a tendency for the frequency component of the waves for corroded iron pipes to be distributed in a lower range than sound pipes. In addition, it also showed that it is possible to discriminate the thickness reduction of approximately one mm. These results demonstrate the possibility of applying this method to pipeline assessment without or with minimum digging.