<title>In-situ ultrasonic thickness measurement of underground water mains</title>

Abstract

In North America, most of the water mains pipes have been fabricated with either cast or ductile iron. It is well known that unprotected iron water mains are prone to corrosion resulting sometimes in serious metal loss and even major water leaks. At present time, water utilities have thus to replace parts of their water distribution pipes ont he basis of their average age, the number of breaks per kilometer per year, the hydraulic efficiency and water quality. In this paper, an ultrasonic technique which will enable the in-situ measurement of the pipe wall thickness is presented as an alternative to these inaccurate criteria. Such a technique can be used to map the defects along a water main and to evaluate their severity even if a mortar lining has been used to avoid the formation of tubercles. This technique uses water as the ultrasonic couplant and will not notably disturb the flow. The novelty of the approach relies on the use of a specialized model for ultrasonic propagation in multilayers coupled with a variable gain amplifier which increases significantly the dynamic range of the ultrasonic measurement systems. This system has been successfully used to produce images of corroded or graphitized areas in cast iron pipes of 6 inches nd 8 inches in diameter. The ultrasonic images agree well with the corresponding optical images. Thickness measurements have been also performed on water mains specimens around the defects found. The results indicate that the remaining iron thickness in the corroded regions can be estimated, in most cases, after proper signal processing.