Do you remember or did you know?

Written on: May 1, 2026 by W. Stephen Tait

Hello Everyone. Corrosion is an omnipresent, very complex process. Whether or not it occurs, how fast it proceeds through a spray package and the corresponding package service lifetime are all functions of:

• The chemical composition of a product;
• Its physical form inside the package; and
• The type of packaging material/materials, such as metals, coated metals, laminated metals and plastics.

Believing that corrosion is not going to happen with a particular package-product system often results in surprise corrosion! Corrosion surprises are very disruptive and expensive, with costs ranging from around $16–$183 million, depending on a variety of scenarios. These may include disrupted research and development (R&D) timetables; costly disrupted production with corresponding loss of sales and brand loyalty; or litigation resulting from personal injuries associated with package failures.

Hence—as with all products—an extensive body of knowledge is needed for the successful development, qualification and marketing of products in spray packages.

Therefore… did you know or do you remember that:

• Temperature is often believed to accelerate corrosion. However, the Arrhenius Equation—the basis for this belief—is not valid for materials corrosion. In other words, don’t use higher storage test temperatures as a shortcut for corrosion testing. Storage tests should be conducted for at least one year to minimize surprise corrosion.
• Chloride ions; chlorides do not cause spray package metal corrosion. Chloride ion-induced corrosion only occurs with metals that form passive oxide films, such as stainless steels and nickel-chromium alloys. The aluminum and steel used to fabricate spray packages do not form passive oxide films.
• Galvanic corrosion between aluminum and steel might occur when steel valves are used on aluminum containers, and vice versa. However, the two metals must have electrical continuity between them in order for galvanic corrosion to occur.
• All internal spray package polymer coatings have microscopic holes in them. However, the area surrounding a hole needs to fail and be large enough to cause and support pitting corrosion inside a coating hole. In other words, coating holes do not concentrate metal corrosion at the bottom of the hole.
• Internal coatings for corrosion protection include thin polymers layers, tin metal and chromium metal coatings (both are also thin).
  •  Polymers typically protect the inside of metal containers against atmospheric corrosion while being stored before filling. The coatings inside filled containers become wetted by the product, product water and contaminant water.
  • Wetting typically degrades the barrier properties of the coatings and leads to metal corrosion under the coating. The rate of degradation is determined by the degree of coating cure, coating morphology interactions with the chemical composition of the product and head space gas inside the package.
  •  Tin metal (often called tinplate) is also typically a corrosion protection coating for the inside of metal containers stored in warehouses. However, whether or not the tinplate continues to protect the steel in filled containers is predominantly determined by the product’s chemical composition.
  •  Chromium coatings are very thin layers of combined chromium metal and chromium oxide. This coating is often referred to as tin free steel (TFS). TFS has the same corrosion protection properties and restrictions as those for tin.
• Surfactants modify plastic, metal and coated metal surfaces. Modifications that allow formula and contaminant water to wet surfaces often lead to metal corrosion, plastic corrosion and metal corrosion under polymer coatings.
• Fragrances typically provide some degree of corrosion inhibition. However, a few fragrances, such as those formulated with vanillin, can be corrosive and products containing them require a corrosion inhibitor to achieve the target container service lifetime.
• There are corrosion inhibitors that inhibit metal corrosion for a wide range of corrosive environments. However, there is no one-size-fits-all corrosion inhibitor for every spray product and all package materials. In addition, there is typically an effective concentration range for most corrosion inhibitors; corrosion increases when the inhibitor concentration is outside both ends of the effective range.
• Package service lifetime is the time between when packages are filled and the time when empty packages are recycled. Package service lifetime is estimated (predicted) from corrosion rates.
• Predicting corrosion rates from first chemistry principles is not possible with today’s state of corrosion science. Unfortunately, there are too many factors that affect if corrosion will occur and how fast it will degrade/penetrate the package material. In addition, how and how much each factor affects both corrosion occurrence and rates are unknown at this time.
• Corrosion testing—either a long-term storage test or the shorter electrochemical test—are the best way to predict corrosion and estimate package service lifetime. However, the appropriate test parameters; analysis and interpretation protocols; and metrics are needed for both to be successful. For example, incorporating higher temperatures to accelerate corrosion during both types of tests is inappropriate and often leads to surprise corrosion.
• An extensive corrosion knowledge database can also be used to predict package corrosion and estimate service lifetime. Experience is not knowledge, but experience can become knowledge when it is integrated with extensive corrosion data.

Thanks for your interest and I’ll see you in August. Contact me at 608-831-2076; rustdr@pairodocspro.com or from our two websites: pairodocspro.com and aristartec.com. SPRAY