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Sensing Technology Predicts When It’s Time to Recoat

By Gretchen Jacobson

Army corrosion professionals at Torii Station in Okinawa are using a postage stamp-size sensor to remotely detect the onset of corrosion on structures such as this dish antenna for communications. Photo courtesy of the Army Corps of Engineers ERDC-CERL.

Army installations throughout the world have unique corrosion-related challenges that depend on environment, facility age and design, equipment type, and many other factors. Torii Station, home to the 10^th Area Support Group, 1^st Battalion, 1^st Special Forces Group, among other Army units, is located in the warm marine environment of Okinawa, Japan.

Known for its beautiful beaches and intricate coral reefs, the island of Okinawa also presents particular challenges to personnel charged with protecting facilities from atmospheric corrosion in the wet, salty climate.

Severe coating degradation is a prevailing problem on aboveground, protective structures for mission-critical equipment at Torii Station—particularly the Command Control, Communications, Computer and Intelligence, Surveillance and Reconnaissance Facility, and a dish antenna for communications. The dish antenna, for example, required complete recoating only 18 months after its last coatings application. Corrosion professionals from the Army Engineering Research Development Center (ERDC)-Construction Engineering Research Laborabory (CERL) determined that intrusive moisture at undetected holidays, or pinholes, in the coating caused high corrosion rates and ultimately, a premature and costly failure.

"We concluded that we needed a way to remotely detect the onset of corrosion before it becomes a severe problem, especially on structures not easily accessible to visual observation," said Ashok Kumar of ERDC-CERL. "We identified a remote sensing method that will reduce maintenance costs by predicting and scheduling repainting when it is really required, based on pre-selected corrosion rate criteria."

Researchers conducted a 33-year field test in seawater at La Costa Island, Florida, to evaluate a similar linear polarization measurement-based technology now being used at Torii Station. Photo courtesy of the Army Corps of Engineers ERDC-CERL.

The technology involves an advanced postage stamp-size sensor that is based on an electrochemical technique called linear polarization resistance (LPR). Working in an electrolyte—in this case, moisture from the atmosphere that accumulates on a metal surface—LPR is used to analyze electrochemical reactions and measure corrosion rates directly, in real time. Each sensor requires 0.1 megawatt of power from associated node electronics.

"The metal sensor is made of the same metal as the underlying surface where the corrosion rate is being evaluated," explained Kumar. "They are placed at strategic locations and covered with the same coating as the rest of the structure."

LPR signals from the sensors are multiplexed together at the nodes and then transmitted to a main computer via a wireless radio system. Once the data is collected, interpreted, and displayed, the corrosion team can determine where corrosion is imminent and which areas of a structure require immediate attention. In addition, they may find that a mission-critical structure does not need recoating when originally scheduled. This helps take the guesswork out of maintenance, thereby optimizing maintenance labor and funds.

After implementing and analyzing the remote sensor systems, the ERDC-CERL team will issue a final report summarizing the project plan format and lessons learned. In this way, they will allow the technology to be successfully used at multiple regions and installations throughout the Army.