Problems with Volatile Corrosion Inhibitors in the Metal Finishing Industry

How VCIs Work

To illustrate the problems with VCIs, it is important first to understand how VCIs work. VCI chemicals are inserted into coatings, adhesives, plastics, powders, foams, and sprays and are part of, or placed into, packaging to inhibit corrosion of a stored item. Once there, VCI crystals slowly vaporize. This vapor moves from the initial packaging from which it was contained and fills the entire volume within the storage system with a continuous chemical cloud. When the vapor concentration reaches a certain level, equilibrium is established (provided the package is air tight) and some crystals condense rapidly onto the surface of the item.

VCI molecules form an invisible, thin protective film on all surfaces, including cracks and crevices. This VCI film adheres to the item, helping it resist the corrosive action of dissolved corrosive gas ions contained within water vapor. Corrosion usually is prevented as long as the chemicals remain active. VCI effectiveness depends on many factors, including package integrity and porosity, temperature, humidity, acidity, and UV exposure. Often, however, VCI packaging is not air tight and VCI vapors leak into personnel workspaces and cargo carriers.

VCI manufacturers rarely list the chemicals used in their formulations. VCIs can contain many organic and inorganic hazardous chemicals, including those categorized as aromatic and aliphatic amines, nitrites, chromates, borates, zinc salts, polyphosphates, azoles, preservatives, toluene derivatives, phosphanates, and special formulas. To increase the naturally low vapor pressure of some VCIs, solvents may be added. These added solvents may include alcohols, ethers, mineral spirits, acetates, naphthenic distillates, glycols, and others. VCIs must vaporize to be beneficial.

VCI Hazards

A review on TOXNET, a database maintained by the National Institutes of Health on chemical safety, shows nearly all VCI and solvent chemicals to be hazardous by OSHA definition. OSHA Standard 1910.1200(c) defines hazards to include irritants, sensitizers, and flammables. The importance of properly identifying which chemicals are hazardous cannot be overstated. When identified, hazardous chemicals must then be listed on the Material Safety Data Sheet (MSDS) and VCI packaging would then be labeled with relevant hazards for downstream users. There are some limited trade secret and concentration exceptions to the MSDS chemical listing.

Beyond the chemicals themselves, some VCIs and many solvents used in these products emit volatile organic compounds (VOCs). VOCs are determined by some governments to be toxic smog components. Efforts are underway in many countries to significantly reduce them. Even the preservatives sodium nitrite, sodium molybdate, BHA, and BHT, which are incorporated into some VCIs, are not safe. While these preservatives may be FDA approved for some food applications, they pose significant skin absorption and inhalation threats in the higher concentrations required for corrosion prevention.

VCIs pose a further threat because, as a recent study by the German Workers Safety Association showed, carcinogenic nitrosamines were formed from the combination of secondary amines and nitrites in 23 of 40 VCI packaging products tested. This was a well-known problem with some metalworking fluids but only just discovered in VCI packaging. The outcome resulted in the German government issuing a regulation (TRGS-615) banning throughout Germany certain VCI formulations and restricting certain other VCI chemical concentrations.

Workers most affected by VCI exposure include VCI extrusion workers, packaging personnel, shippers, and those handling the protected items directly, such as metalworkers and even end users of the previously protected item. Because VCI chemicals emit a vapor cloud, a respiratory and skin contact risk is an obvious threat during packaging and unpackaging.

Although workers installing VCI packaging may be wearing the recommended personal protective gloves and respirator, it is less likely that workers handling or removing the packaging will be so outfitted. This is partly because many VCI manufacturers market their products as safe, thus users will not find many chemicals listed on a VCI MSDS.

To acknowledge the hazard would require disclosure and thus increase market resistance. However, OSHA’s Hazard Communications Guidelines states that “most chemicals used in the workplace have some hazard potential, and thus will be covered by the rule.” At great risk are people who apply an open flame to VCI plastic. VCI chemicals are thermally active—the more heat applied, the more is emitted from the packaging.

Exposure of these VCI chemical vapors to an open flame, which occurs with heat shrinking, can create toxic gases such as aniline and nitrobenzene.

The OSHA Technical Center recently reviewed VCI MSDSs and documentation. In a July 29 internal letter, the study author itemized several important points. First, “VCIs are hazardous chemicals and do fall under the OSHA Hazard Communication Standard—29 CFR 1910.1200.” Second, “VCIs may present a physical hazard, a health hazard or both a physical and health hazard.” Third, “VCIs do not meet the definition of ‘articles,’ but they do meet the definition of ‘hazardous chemicals.’” Fourth, the strict rules for claiming an ingredient as “trade secret” are outlined. And fifth, “claiming ignorance (‘I don’t know what is in this material and I don’t want to know!’) to avoid accountability does not eliminate responsibility. Manu-facturers are still responsible for the correct identification and warnings listed for each VCI.”

The implications of OSHA finally weighing in on VCIs cannot be overstated. It will change the way companies protect their parts.

A less obvious respiratory threat is the heating of VCI-protected metals that retain VCI chemicals. This heating may come about from cutting, brazing, welding, or soldering. During the heating process some VCI chemicals are released from the metal they coated, and some VCI chemicals thermally decompose into such toxic gases as nitrobenzene and aniline.

A physical contact threat exists for workers handling VCI-protected parts. Many VCI manufacturers claim VCI chemicals leave the parts within about three hours after depreservation, while some claim continued protection. One VCI manufacturer claims that opening a VCI package will not adversely affect the protection, stating, “VCIs already adsorbed on the metals will not be disturbed immediately and will continue protecting the metal.” Despite the inconsistency of VCI marketing related to VCI persistence, a layer of VCI chemicals is present to absorb into the skin of workers handling the parts.

An OSHA guidance states that “a major route of workplace exposure to these chemicals is through skin contact with contaminated surfaces. For example, aromatic amines are persistent chemicals and once released into the work environment they may remain on surfaces for months and even years. When contaminated surfaces are contacted by unprotected skin, significant exposures are possible.

“Dermal and ingestive routes of entry are much more significant than inhalation for a large number of chemicals,” the guidance states. “For example, a 15-minute exposure of the hands and forearms to liquid glycol ethers... will result in a dose to the body well in excess of the eight-hour inhalation dose at their recommended air exposure limits. Unfortunately, many industrial hygienists are only familiar with air sampling and fail to evaluate significant exposures caused by surface contamination.” In addition, OSHA reports that “some studies have shown that solvents containing chemicals may act as a vehicle allowing the chemicals to permeate gloves and protective clothing.”

VCI Adherence

Because VCIs persist on the surface or equipment and permeate some materials, VCI adherence onto metal and plastic parts may interfere with the manufacturing coating adhesion process. Adhesion refers to a coating’s bond to an item’s three-dimensional surface.

Poor surface adhesion allows coatings to delaminate and can cause a surface tension differential, thus allowing void spaces to form. Further, a contaminant can attract and hold dust and corrosive gases that incidentally embed additional corrosion elements beneath the coating layer.

Regrettably, a lack of scientific study exists on coating adhesion to VCI-contaminated metallic or plastic parts. Some VCI manufacturers claim the VCI packaged parts are “clean” immediately after packaging removal and can be coated, while others acknowledge a more prolonged coating persistence of hours. For example, one major VCI manufacturer identifies the properties of the molecules-thick VCI film as “oily,” “clear dry,” “light, wax-like,” and “waxy.” But it discounts the effects on any applied coating, stating “it is unnecessary to remove them and they have little effect on adhesion or subsequent coatings.”

A 1999 Quaker Chemical Corp. study compared various coatings’ adhesion withdifferent types of corrosion-inhibiting metalworking fluids (MWF), which are similar to VCIs. It found coating adhesion ranging from 10 to 100%, depending upon several factors. The predominant factor was the oil content in the MWF. The best adhesion came with a very low solvent-based coating, and the worst adhesion was with a water-based coating over an oil-based MWF.

Conclusions

In the metal finishing industry, questions regarding the use of VCIs should be asked, researched, and answered. For example, can the metalworking industry be complacent with the health of its workers and the quality of its product? Inthis era of ISO-certified suppliers and processes, can a contaminant in the process be lightly dismissed? What is the VCI effect on adhesion? Will VCI chemicals and solvents chemically react with the coating? What is the legal liability of VCI users in terms of potential legal action?

Ultimately, the VCI and metal finishing industries need to take several steps regarding VCIs. VCI manufacturers need to market their VCI products responsibly. This includes accurately adhering to the OSHA definition of hazardous, identifying all risks and exposure limits, issuing accurate and complete MSDSs, and promoting the use of hazardous labeling for VCI-contained packaging. They further need to test all chemicals and chemical combinations put into their products prior to release for contact and respiratory risks.

The metal finishing industry should independently validate VCI industry claims while testing VCI contamination potential and coating adhesion. Industry also must demand complete and accurate MSDSs. A better understanding of volatile corrosion inhibitors by the metal finishing industry will result in a healthier workplace and a better product.

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