Coating Health Monitor (CHM)
ElectraWatch CHM:
Paint coatings are the primary means of corrosion protection for most structures and they can be very effective. However, paint coatings are only temporary; they weather, absorb moisture, blister, become scratched or undergo other mechanical damage. Even fresh paint coatings can exhibit pinholes, holidays, or other coating defects that can adversely affect corrosion protection. Thus, there is a need for corrosion sensors to assess the health and effectiveness of paint coatings, especially on critical structures and equipment.
Although many corrosion sensors have been proposed and developed, many are not suitable for monitoring coating health. A major disadvantage of many of these, such as galvanic couple sensors and some fiber optic sensors, is that they are more properly considered corrosivity sensors; that is, they detect degradation of a sensor element and not degradation of the structure of interest. As such, they measure only how corrosive the environment is and provide no direct information on the condition of the paint coating or the structure. Furthermore, they are consumed and have a limited lifetime and can provide no information concerning any environmental degradation prior to installation. A second disadvantage of many sensors is that they need to be embedded into the structure. This limits them to new construction and poses important issues on the effect of the sensor on structure properties and data acquisition/transfer. These sensors can-not inspect existing structures and cannot be replaced if damaged or past their useful lifetime. ElectraWatch’s electrochemical impedance sensor approach has neither of these critical disadvantages. The technology is suitable for determining coating health and detection of damage under paint coatings.
ElectraWatch’s innovative coating health monitoring system (CHM) is based on electrochemical impedance spectroscopy (EIS). The system consists of a series of mini-potentiostat modules coupled to two or more tape electrodes mounted on top of the paint coating of the structure or equipment being monitored. The electrodes and modules can be coated with a topcoat if desired. They periodically report to a laptop or handheld device so that an inspector can assess the condition at each sensing point. The inspector can then determine if more detailed inspection or maintenance needs to be scheduled. Communications is implemented using the Zigbee wireless protocol. The units are battery powered an estimated battery lifetime of up to ten years, depending on the frequency of measurement and interrogation. This CHM system tracks corrosion damage from its early stages, indicates an assessment of current condition, and provides a prediction of future condition based on accelerated laboratory testing. Aside from the initial installation and eventual battery replacement for the wireless units, it requires no personnel access to the monitored locations.
The CHM offers several advantages over other systems:
It directly inspects and assesses the condition of the coating of interest. It does not involve corrosivity sensors that simply detect degradation of a sensor element.
It is applicable for both new fabrication and retrofitting existing structures. It requires no embedded sensors that must be incorporated into a structure during manufacture or refurbishment and cannot be replaced.
It can detect the intrusion of moisture well before any irreversible corrosion damage occurs while it is also sensitive to the growth of corrosion products during the more severe stages of damage.
The modules monitor coating health on a programmed schedule and store the results in nonvolatile memory so that the results can be retrieved later.
The tape sensor is flexible so that it can conform to edges, corners, and curved surfaces. It is corrosion resistant and has survived >2000 hours of alternate immersion in salt water, but can be easily replaced, if needed, or protected by paint for indefinite life.
The area monitored by the tape sensor depends on the surface wetness so a measurement taken when the surface is wet probes a relatively large area while a measurement taken when the surface is dry is more localized around the tape. That is, the sensor monitors an area around the tape electrode and not just the protected area beneath the tape.
Electrochemical impedance spectroscopy is a well established laboratory technique known to predict materials performance, but hitherto limited to immersion studies. The CHM extends the use of EIS to field applications and allows identical measurements to be taken under service conditions and in the laboratory. As a coating degrades, its EIS spectrum changes. The low-frequency impedance decreases by several orders of magnitude. This decrease in low-frequency impedance takes place as moisture penetrates the coating and is well before any corrosion of the substrate occurs. Thus it can give early warning of decreasing coating protectiveness so that depainting/painting or other maintenance activities can be scheduled.
Potential applications of the CHM include highways, and bridges, military and civilian land vehicles, aircraft, storage tanks, pipelines, and ships. The benefits of the assessment system will become increasingly important as these systems and structures age and are not replaced. CHM devices are strategically placed on a structure in areas that are difficult to access, monitor, and maintain. These wireless remote sensors can be read from up to 500 feet away with a laptop or PDA that displays the current condition of the coating in the area of each sensor. The CHM system can be integrated into existing Condition Based Maintenance (CBM) software or used as a stand-alone system. Benefits of a CHM system include reducing inspection costs and avoiding repainting unnecessary areas. There is also an added safety benefit associated with performing fewer inspections and painting only when necessary in areas that are difficult and dangerous to access.
Download Instruction Manual for the CHM
