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17 MATERIALS PERFORMANCE: VOL. 57, NO. 4 APRIL 2018 Information on corrosion control and prevention Continued on page 18 The noncontact CP inspection tool takes measurements of electric currents in seawater. Photo courtesy of FORCE Technology. Field-Gradient Sensor Measures Electric Currents in Seawater WINNER 2017 A recently developed f ield-gradient sensor (FiGS) tool from technological service provider FORCE Technolog y Norway AS (Hvalstad, Norway) can detect electric currents in seawater, and has shown promise in identif ying corrosion problems as well as characterizing the cathodic protection (CP) system status on pipelines and subsea structures, even when buried. The noncontact inspection tool, which takes accurate measurements of electric currents in seawater with a high degree of sensitivity, is a recipient of an MP 2017 Corrosion Innovation of the Year Award. The patent-pending technolog y has a wide area of application, including the measurement of current output from galvanic anodes—important data for evaluating the remaining lifetime of anodes. The technolog y can also measure current density on pipelines and struc- tures such as bare steel, coated steel, and concrete. The tool's developers say it can easily be incorporated into existing CP inspection programs. The f ield-gradient sensor's accuracy and resolution also allow it to detect very small coating holidays or defects and cal- culate their size on critical pipelines and other subsea structures that are exposed, partially buried, completely buried, or surrounded by rocks. A lthough the signal strength of the sensor gets weaker at lon- ger distances from the pipe, measure- ments can be made for structures buried at depths of 2 m (6.6 ft) or more. Inspections of pipelines—often buried or covered—are often conducted by inter- nal pigging, excavation, or diving opera- tions, the developers explain. But while internal pigs can provide information on internal pitting and wall thickness, often they do not provide information about the status of external CP. Inspection surveys with the f ield-gradient tool can be carried out by attaching the product to remotely operated vehicles (ROVs) or autonomous underwater vehicles (UAVs). "The benef it of using the f ield-gradi- ent sensor is that it will give you all the information because it gathers data con- tinuously as it passes over the given struc- ture," says Jens Christofer Werenskiold, principal engineer with FORCE Technol- og y. He notes that it is an alternative to excavations or diving operations, which can be more expensive and/or pose a safety risk to workers involved. The sensor was initially developed earlier this decade and partially funded by oil and gas operators Statoil (Stavan- ger, Norway), Shell (The Hague, The Neth- erlands), and Gassco (Kopervik, Norway), with the expectation of making a tool small enough to detect minute coating damage on a direct electrically heated (DEH) pipeline. Pipelines with DEH have a signif icant amount of current f lowing through the pipe wall. If coating damage occurs, this acts as a discharge point, resulting in severe metal loss. "Current density is the most impor- tant design factor in CP designs and, in certain cases, the actual values may devi- ate considerably from the design values," says Leiv Erling Gry tten, FORCE Technol- og y's sales manager. Other uses of the tool can include col- lecting potential measurements within 5 mV of contact-measured potentials and measuring current drain to buried struc- tures, such as piles and wells. By mapping the seabed around the buried structures, the f ield-gradient data can be used to cal- culate the amount of current delivered into the seabed, which can then be com- bined with FORCE Technolog y's computer software to model the potentials of a CP system conf iguration. "The high-quality mapping of f ield- gradient data has opened possibilities, not only to predict the future perfor- mance and degradation of a CP system— thereby reducing the frequency of