Performance Estimation of a Remote Field Eddy Current Method for the Inspection of Water Distribution Pipes Sophie Duchesne 1 ; Nabila Bouzida 2 ; and Jean-Pierre Villeneuve 3 Abstract: Remote Field Eddy Current (RFEC) technology allows the in situ inspection of metallic water distribution pipes. RFEC tools provide the location and magnitude of corrosion defects on the inspected pipes. The capacity of an RFEC tool to detect corrosion defects is evaluated in this paper by comparing its results with those obtained from the analysis of computed tomography (CT) scan images of the inspected pipes. Localization and characteristics of defects identified with the RFEC tool and from the CT scan images were compared for six cast iron pipes. An original method is proposed for the analysis of the CT scan images from which wall thickness losses were estimated by using the basic principle that the attenuation coefficient of X-rays in a homogenous material is a linear function of its density. The results show that the RFEC tool is able to localize most of the defects identified from the analysis of CT scan images. These findings reveal that the tested RFEC probe provided reliable information on the main corrosion defects, and thus on the general structural integrity of the inspected pipes. DOI: 10.1061/(ASCE)WR.1943-5452.0000136. © 2011 American Society of Civil Engineers. CE Database subject headings: Cast iron; Corrosion; Imaging techniques; Inspection; Magnetic fields; Pipe networks; Radiography; Water distribution systems. Author keywords: Cast iron; Corrosion; Imaging techniques; Inspection; Magnetic fields; Pipe networks; Radiography; Water distribution systems. Introduction Each year, replacement and repair of aging water distribution pipes represent important infrastructure expenditures. In 2001, the American Water Works Association (AWWA) predicted expenditures on the order of US$250 billion over the 30 following years for the replacement of drinking water pipes and asso- ciated structures in the United States (AWWA 2001). According to Burn et al. (2007), annual worldwide expenditure for mainte- nance and rehabilitation of water distribution pipes is more than US$33;000 million=year, and should rise significantly in the fu- ture, as existing assets increasingly come to the end of their useful lives. This context has led to the development, during the last few decades, of various prediction models and planning tools for water distribution pipe renewal (see e.g., the pioneers Shamir and Howard 1979; or more recently, Kleiner and Rajani 2010; Dridi et al. 2009; Giustolisi and Berardi 2009; Mailhot et al. 2003; Pelletier 2000). Although these tools and models are quite helpful in prioritizing pipes that should be replaced and/or rehabilitated in a specific network, the actual decision to replace a pipe is often founded on a variety of other factors, including inspection data provided by various methods. Among the existing nondestructive methods for the inspection of water distribution pipes, the sonic and acoustic leak detection methods (Fuchs and Riehle 1991) are the most often used in North America (Makar and Chagnon 1999). However, these techniques can only reveal problems on a pipe after a failure has occurred and cannot predict where future breakdowns are likely to happen. Because corrosion is the main process leading to cast iron pipe failure (Agbenowosi 2000; Rajani et al. 2000), specific inspec- tion techniques have been developed to detect corrosion sites on metallic pipes (Dingus et al. 2002). These techniques can play a significant role in the planning of water distribution pipe renewal. Indeed, in 1992 more than two thirds of all existing water pipes in the United States were metallic (Kirmeyer et al. 1994, cited in Kleiner and Rajani 2001). Even though PVC is currently the most popular material for newly installed water pipes in North America, most of the small diameter pipes that were installed up until the 1990s are made of ductile or gray cast iron. In Quebec City, Canada, for example, 89% of water pipes with known material are made out of ductile or gray cast iron. This means that the vast majority of pipes that will need to be replaced in the following years are metallic. Since the 1990s, Remote Field Eddy Current (RFEC) inspection techniques have become commercially available for the inspection of gray and ductile cast iron pipes (Dingus et al. 2002). These tech- niques can be used in situ to determine the residual thickness of cast iron pipes along their lengths. In some cities, such as Quebec City, results from those inspections are one of the factors that is taken into account in the decision whether aging pipes should be re- placed. In practice, the RFEC inspection results are generally used for the mid- to long-term planning of water pipes renewal. Indeed, the estimation of pipe deterioration state, for pipes of different ages and at different locations, provides information useful to managers to decide which pipes should be replaced or rehabilitated and when these renewal interventions should take place. When the inspected pipes are properly selected, the information provided by the RFEC 1 Professor, Institut National de la Recherche Scientifique, Centre Eau Terre Environnement, 490 de la Couronne, Québec G1K 9A9 Canada (corresponding author). E-mail: sophie.duchesne@ete.inrs.ca 2 Research Assistant, Institut National de la Recherche Scientifique, Centre Eau Terre Environnement, 490 de la Couronne, Québec G1K 9A9 Canada. E-mail: nabila.bouzida@ete.inrs.ca 3 Professor, Institut National de la Recherche Scientifique, Centre Eau Terre Environnement, 490 de la Couronne, Québec G1K 9A9 Canada. E-mail: jpv@ete.inrs.ca Note. This manuscript was submitted on April 19, 2010; approved on October 24, 2010; published online on December 4, 2010. Discussion per- iod open until April 1, 2012; separate discussions must be submitted for individual papers. This paper is part of the Journal of Water Resources Planning and Management, Vol. 137, No. 6, November 1, 2011. ©ASCE, ISSN 0733-9496/2011/6-521–530/$25.00. JOURNAL OF WATER RESOURCES PLANNING AND MANAGEMENT © ASCE / NOVEMBER/DECEMBER 2011 / 521 Downloaded 14 Feb 2012 to 198.73.162.104. Redistribution subject to ASCE license or copyright. Visit http://www.ascelibrary.org