June 2016 Spray 33 preventing package metal corrosion. Changing fragrance will result in corrosion when the new fragrance is a less effective inhibitor. The current package/components are identical to the new ones—therefore they will also be corrosion resistant Not all packaging components are the same from a corrosion perspective, even when the chemistry or physical specifications are identical. For example, there are two types of morphologies for the holes in the tin coatings on tinplated steel. Tinplate with both types of morphologies conform to the ASTM specifications for tin mill products; however one of the morphologies has symmetrical round holes that expose more base steel. The new formula ingredients are not corrosive The new formula ingredients by themselves might not be corrosive. However, corrosion is often a synergistic process involving multiple ingredients. Therefore, synergy often produces corrosion by a mixture of ingredients that are each separately not corrosive. The changes are small Very small changes often produce significantly large changes in corrosion behavior. For example, a small amount of an effective corrosion inhibitor transforms a package/ component eater into a non-corrosive formula. Small amounts of contaminant water in anhydrous formulas also cause significant corrosion and reduction in package/ component service life. There’s not enough time for corrosion testing Figure 1 demonstrates that short storage test times increase risk. Electrochemical corrosion testing should be conducted if the development timetable is too short to complete a one-year storage test. However, electrochemical tests with technically incorrect parameters are often as bad as an abbreviated storage test or no testing at all. Next month I’ll discuss storage corrosion tests and electrochemical corrosion tests, along with their associated advantages/pit falls. 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 anticorrosion 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 July. Spray
Spray June 2016
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