Water and metals are thermodynamically
unstable when in contact with each other…
April 2020 SPRAY 27
Storage testing can be used to screen potential corrosion inhibitors;
however, a storage test requires at least one year to complete.
Electrochemical corrosion testing is more precise and the quickest
way to screen a large number of potential corrosion inhibitors—
assuming the appropriate measurement parameters and data
analysis protocols are used.
Changing package materials also can, in some situations,
control and prevent corrosion. However, the options to change
package materials are more limited than the options for corrosion
inhibitors.
In a nutshell…
In summary, water contributes to or causes spray package corrosion
because it is:
• Thermodynamically unstable when in contact with metals
and water that is electrochemically active
• Moves freely in solutions towards metal surfaces
• Attracted to charged surfaces—indeed the electrical field on
charged surfaces often pull water towards the surface, even
when the surface is covered with a polymer coating or a
polymer film
• A carrier of corrosive ions and molecules
• Diffuses easily through polymer coatings and films
• Degrades polymers so they are not barriers between your
formula and metals under polymer coatings and films
Anhydrous formulas are not immune to corrosion. However,
in some instances, there is a non-corrosive concentration range
for contaminant water.
Corrosion inhibitors are an effective way to control or prevent
spray package corrosion by formula water and anhydrous formulas.
However, finding an inhibitor that works for individual
formula-package systems takes time and the effective concentration
for the inhibitor must also be determined.
Corrosion testing is needed to:
• Determine if corrosion will occur
• Determine where in the package corrosion will occur
• Estimate the spray package service life with a specific formula
• Find the non-corrosive concentration range for contaminant
water—if one exists; and
• Find an effective corrosion inhibitor and its effective
concentration range.
Please visit www.pairodocspro.com for more information. Thanks for
reading and I’ll see you in May. Spray