I advise removing and inspecting valve springs during storage stability corrosion tests, just to be on the safe side. Inspection of valve springs should not add a significant amount of time to a normal corrosion examination. Electrochemical corrosion tests can also be used to confirm that the stainless steel valve springs are not corroded by a given formula. Want to learn more about spray package corrosion? We would be happy to teach our Elements of Spray Package (Aerosol Container) Corrosion short course at your R&D facility. Please contact email@example.com or visit www.pairodocspro.com. Please send your questions/comments/suggestions to firstname.lastname@example.org. Back issues of Corrosion Corner are available from ST&M. Thanks for your interest and I’ll see you in May. Spray April 2014 Spray 31 form chromium halogen/nickel halogen complexes. These metal ion halogen complexes are water soluble and thus removed from the barrier film by dissolution in the formula water or contaminant water. Removal of portions of the film causes localized damage to it. However, the film is able to repair itself as long as the rate of repair is greater than the rate of damage and other chemicals in the environment, such as low pH (i.e., a large number of hydrogen ions) does not prevent the film from repairing itself. Stainless steel pitting corrosion initiates and propagates when the damage by halogen ions exceeds the rate at which the film is repaired, causing holes in the film that develop into pitting corrosion. The mechanism for stainless steel corrosion by halogen ions has somehow been erroneously applied to the steel and aluminum alloys used for spray packages. However, the halogen mechanism is not applicable to these two alloys because they do not form chromium-oxide/nickel-oxide surface barrier films. In addition, the steel alloys used for spray packaging contain amounts of chromium and nickel to control grain size and prevent the surface of the steel from looking like an orange peel. However, the amount of chromium and nickel in these steels is significantly below the 12% minimum needed to form the protective barrier oxide found on stainless steels. I have observed a few instances in which valve springs corroded and broke when exposed to low pH formulas. However, the instances of valve spring corrosion and failure with other consumer products have been rare, making stainless steel the material of choice for valve springs.
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