When water leaks into a gas main, it runs downhill until it reaches the point where the pipe inclines upward again, where it accumulates. Eventually, the pipe will fill up, cutting off the gas supply. Simple techniques exist to find these accumulations, but to date, the gas industry has no method for identifying the precise location of the water ingress, which in most cases, is very small indeed.

AOS were contracted by Transco (the UK gas pipeline operator) to come up with a reliable technique for water ingress location, and to engineer a very robust demonstrator for field trials. The AOS research team developed a dual wavelength spectroscopic technique in which one optical wavelength is attenuated by the presence of water whilst the second is not. Surfaces interrogated by a combination of both wavelength will thus show a differential response in the presence of water.

The AOS water ingress detector system is capable of locating water volumes as low as 5 microlitres and can be inserted into live gas mains on a 70m rodding system. The head incorporate a gravity detection and rotatable optics, so that the orientation of the interrogation system can be maintained.

The effectiveness of the system has been confirmed in a number of field trials .

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