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14 MAY 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 5 The patent-pending CPM method aims to measure corrosion protection throughout buried pipelines without having to drill into the concrete at each test point. Image courtesy of Pond & Co. New Pipe Surveying Method Aims to Limit Concrete Drilling A novel correlation potential mapping (CPM) surveying technique to measure corro- sion protection without exten- sive concrete drilling was recently con- ducted at a nuclear power plant, operated by Duke Energ y in the southeastern United States. The CPM survey, which involves the measurement of pipeline potential with- out the need for drilling concrete, repre- sents an innovation from the mechanical integrity and corrosion management (ICM) team at engineering consulting services provider Pond & Co. (Peachtree Corners, Georgia). According to the com- pany, the CPM technique is capable of measuring and modeling the effect of concrete on potential readings—the IR effect—without having to drill into the surface for a test location. The method enables users to identif y areas with inad- equate cathodic protection (CP) and direct current (DC) interference. "That pipe-to-soil potential, when you have concrete pavement, is very diff icult to measure," explains Sasan Hosein, tech- nical director of corrosion control at the company. "They usually drill holes through concrete and do the measure- ments through those access points." "I was thinking, there should be a bet- ter way to do the survey without drilling through concrete or any conductive pave- ment," he adds. "My background is in math, so I did a little bit of research and started thinking about a new process, a new technique. Because if you want to do a survey someplace like an airport or a nuclear plant, you can't drill through the tarmac or concrete pavement. There has to be a better way." Historically, CP and an external coat- ing have been recognized as the most reli- able and cost-effective means to control corrosion in such settings. To determine the CP system's effectiveness, pipe-to-soil (P/S) potential measurements are used to determine the potential of a pipeline under test with respect to a reference electrode. Additionally, potential mea- surements are used as a qualitative method to identif y corrosion activity. According to NACE SP0308-2008, 1 the measurement test is performed by con- necting the positive terminal of a high- impedance voltmeter to the pipeline through a test point, and the negative terminal to the reference cell. The calculated potentials can give an indication of the severity of both galvanic and electroly tic corrosion cells, Hosein explains, as well as the level of CP perfor- mance. However, the challenges of pipe access prompted Hosein to evaluate a new method. The new method uses a calculated IR drop to provide a def ined integral model to convert pipe-to-concrete measure- ments to P/S measurements. These mea- surements are obtained at 5 to 10 ft (1.5 to 3.0 m) intervals along the length of the pipeline utilizing data logger(s), test lead wire, and copper/copper sulfate (Cu/CuSO 4 ) reference electrodes with ceramic plugs. The potential measure- ments are recorded as a function of dis- tance, rather than time. The CPM route requires one test sta- tion, preferably at a transition point where the pipe emerges from the con- crete. By using that transition area, Hosein says it is possible to calculate the concrete effect in potential readings in mV vs. actual potential—without having to drill. After forming a proprietary equa- tion for the "factoring effect," Hosein began extensively testing the method in 2013 and 2014 using buried pipelines with one test station at a transition point. "I was very surprised with the results," Hosein says. "Every time, it accurately identif ied the potential of the concrete cover, and at the same transition. At that point, we had proof of concept." "Really, all we need is a reading. Then, you can apply that factor on down the line." In 2015 and 2016, the new surveying method moved from experiments to actual industry application. In the case of the nuclear plant, which had more than 20 mi (32 km) of high-priority, critical pipelines running through the facility, the operator was particularly receptive due to the ways in which the CPM method could reduce logistical burdens. "In the presentation, I show them how MATERIAL MATTERS