Materials Performance

DEC 2018

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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33 MATERIALS PERFORMANCE: VOL. 57, NO. 12 DECEMBER 2018 COATINGS & LININGS ESSENTIALS Continued f rom page 31 Continued on page 35 panels that perform electrochemical mea- surements during corrosion testing. Unlike conventional coating tests that rely on an expert's visual evaluation of a test panel at the end of a test cycle, CorRES records corrosion rate data throughout a test and transmits the data over a wired RS-485 interface cable to a base station for evaluation. •is enables researchers to know not only if a coating fails, but exactly when this occurs during a test. Each system includes continuous environmental measurements of temperature and humidity, and a module for evaluating the ability of coatings to pro- tect alloys from stress corrosion fatigue is also part of the system. Data collection and storage are fully automated so that environ- mental measurements, along with corro- sion rate and crack velocity, are continu- ously measured throughout a test. "Legacy systems do not produce time- based, quantitative measurements inside of the test chamber, but rather, these are taken after a panel is removed," Hunter explains. "•ere's a lot of variability in corrosion tests, and CorRES allows us to monitor this variability and provides quantitative data that help us better understand a coating's performance in the lab so we can project how it will perform in the operational environment." •e system is designed for both acceler- ated chamber use in the laboratory and at outdoor sites in the †eld, and it can be operated autonomously or by using a con- nected laptop computer. Interdigitated Electrodes Each multi-sensor panel includes a gold interdigitated electrode, an AA7075-T6 (UNS A97075) aluminum alloy electrode, and an electrode comprised of the AA7075- T6 aluminum alloy and Type 316L (UNS S31603) stainless steel (SS) in a single package. •e specialized test panels included with the system package—prepared, painted, and tested like traditional panels— are used to measure the ability of a coating to protect a given substrate from the envi- ronment as well as inhibit corrosion at a defect. Barrier properties of the intact coat- ing are measured, as well as the corrosion rate of the engineered alloy or dissimilar metal coupling of interest at a defect (galvanic corrosion). "[Conventional] tests focus on aesthetic performance and do not provide data of localized corrosion processes that repre- sent the greatest risk to aircraft structures," Luna says in explaining its technology. More Comprehensive Data According to the Air Force, this system provides a more comprehensive set of data because the sensing elements can measure free corrosion potential via the voltage dif- ference between the immersed metal and Left, a model of the complete CorRES test rack and docking platform assembly with panel array, standard test panels, and mass loss coupons. Right, a closeup of the multi-sensor panel. Photos courtesy of Luna Innovations.

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