July 2016 Spray 39 Electrochemical corrosion tests use sensitive electronic instruments to measure the electrical and ionic currents generated by corrosion. Consequently, electrochemical tests provide corrosion results in significantly less time than a corresponding storage stability test as shown in Figure 1. The sensitivity of the corrosion measurement instruments also improves the reliability of the corrosion tests (significantly lower risk in Figure 1). The information obtained from electrochemical tests includes the: • Types of corrosion that will occur • Rates of corrosion for each package component • Estimation of spray package component service lifetimes • Estimation of the component failure magnitudes as a function of time • Product stability with filled container age and higher temperatures The most common mistakes made with electrochemical tests are: • Not testing all spray package components • Insufficient numbers of replicate samples • Inappropriate instrument and test parameters • Insufficient test length • Incorrect modeling of the corrosion parameters obtained from the raw instrument data • Incorrect interpretation of data extracted with models • Not determining how package component and ingredient concentration variability affects spray package corrosion Electrochemical tests have a higher correlation with actual spray package corrosion than a corresponding storage test, as shown in Figure 1, and electrochemical test results are obtained in significantly less time than a corresponding storage test. However, electrochemical tests do not provide information about product efficacy as the age of filled containers increases, nor weight lost from filled containers as age increases. Hence, storage testing is recommended to obtain these types of information. The main points for the May through July Corrosion Corner articles are: No corrosion testing and testing with the wrong parameters both lead to unexpected corrosion with package failures (leaking). Package failures are significantly more expensive than properly designed corrosion tests. We would be happy to teach our Elements of Spray Package (Aerosol Container) Corrosion short course at your R&D facility. We have also introduced the Corrosion Partnership Program, which makes our electrochemical corrosion laboratory, corrosion consulting and anti-corrosion technology conveniently available for your R&D program. Contact: rustdr@pairodocspro.com; 608-831-2076; www.pairodocspro.com. Back articles of Corrosion Corner are available from Spray. Thanks for your interest and I’ll see you in August. Spray
Spray July 2016
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