Economic damage related to corrosion has been calculated to be between 3%-5% of the gross domestic product of a country.^1,2,3 This includes secondary damage, like shutdowns of machinery and equipment. The damage to national economies makes the development of effective and environmentally friendly rust preventive products essential. 

Corrosion has always been a topic of concern with greater significance over recent decades as transportation of parts has increased by road haulage or overseas shipment. Temporary protection of ferrous components from corrosion during indoor and outdoor storage remains vitally important. 

Many rust preventives are still based on fast evaporating hydrocarbon solvents. When rust preventives are applied to metal surfaces, the solvents are emitted to the atmosphere as volatile organic compounds (VOCs), causing environmental pollution and risking adverse health effects to operators. Different countries have already implemented guidelines and regulations to reduce or prevent these VOC releases. The regulations are anticipated to become stricter in the future, particularly for California and other U.S. states. Switzerland already has a tax incentive system that encourages the use of VOC-free metalworking fluids, rust preventives and varnishes. The European Union (EU) also has a VOC guideline that is amended by further national restrictions. 

The use of rust preventives based on water as the solvent has clear advantages for human health and the environment. However, obstacles remain when attempting to replace VOCs with water in regard to application and performance. Process adjustments are required (e.g., prolonged drying time or reduced anticorrosion performance) for water-based preventives when compared to more standard solvent-based products. 

Dr. Marvin Redetzky, head of application management for Master Fluid Solutions WDG GmbH in Düsseldorf, Germany, notes that the largest market share in the rust preventives industry goes to solvent-based products. “Many companies offer a broad product portfolio of solvent-based rust preventives for all different requirements (e.g., dewatering or overseas transport).” Currently, he notes that water-miscible products have the lowest market share and “are more often found in special applications (e.g., as a cleaner with corrosion protection in the tube industry).”

STLE member Bridget Dubbert, technical director with Engineered Lubricants Co. (EL) in St. Louis, Miss., agrees that the largest market share “by far is the oil- and solvent-based rust preventives.” Isabell Lange, manager of application technology at LANXESS Deutschland GmbH in Mannheim, Germany, concurs, noting: “Water-based products are still a niche market.” 

Dr. Joseph P V, senior consultant and advisor, Gulf Oil Lubricants India, and former senior manager (R&D), Indian Oil Corp., Faridabad, India, expects the water-based rust preventive business “to grow in the coming years primarily due to the overall increase in the industrial activities related to production based on metal processing, especially in the developing world.” Dr. Joseph P V expects that “environmental awareness and restrictions along with the push for sustainability will carry forward the water-based rust preventive oil market since water-based products have the advantages of lower VOC and superior human and material safety.” He notes: “The growing automotive and infrastructure sectors also will become catalysts for the growth of the water-based rust preventive oil market.”

Legislation 
STLE member Davis Albright, director of technology with AMSOIL Inc. in Milwaukee, Wisc., sees no defined restriction on VOCs for rust preventives in Wisconsin currently; however, she does see restrictions for other industries. She notes that she works “in some of those spaces, such as architectural coatings, and there’s business in states that have defined limits for rust preventives.” As well as possible regulatory limits, some AMSOIL customers set their own limits, and Albright finds: “Awareness of government legislation is self-motivating.” 

Albright also notes: “The South Coast Air Quality Management District (SCAQMD) set forth limits several years ago, and these limits have been adopted by other regions and states.” The SCAQMD is the air pollution control agency for the South Coast Air Basin in California, which includes parts of Riverside, San Bernardino and Los Angeles Counties, and all of Orange County. She expects the trend of setting limits to spread throughout the U.S. 

Redetzky finds: “Requests for VOC-free products usually come from the customers (i.e., occupational safety); however, some countries like Switzerland have an incentive tax on VOCs, making it more a governmental-driven request.” Lange notes that interest in restricting VOC emissions from rust preventives began as much as 20 years ago. 

Kerstin Zübert, technical application manager for Hermann Bantleon GmbH in Ulm, Baden-Württemberg, Germany, notes that restrictions for VOC emissions are already in place in her region. The EU has a VOC Directive⁴ aimed at reducing industrial emissions of VOCs. The Directive covers a wide range of solvent-using activities (e.g., printing, surface cleaning, vehicle coating, dry cleaning, etc.). Facilities using these solvents must comply with emission limit values in the Directive, or with the requirements of the Directive’s reduction scheme. 

Zübert notes that the Directive is implemented differently in the individual EU countries. As an example, she says, “In Germany, the use of VOCs is related to the individual application (e.g., in coatings, which also include corrosion protection, the regulation only comes into effect when annual VOC consumption is >5 - <15 tons).”

Water-based rust preventives
Redetzky states that when considering which parameters are most important for water-based rust preventives, “The corrosion protection performance is the most important factor.” However, he notes, “Water-miscible products usually need heated baths (approximately 60 °C) to form a sufficient film on the metal surface.” While noting that “it would be ideal if a product could be used at room temperature,” he notes that the required application temperature is important as “the lower the application temperature, the lower the energy consumption.” 

Dubbert lists the most important parameters for water-based rust preventives as corrosion protection, ease of use and shelf life. The last two are especially important “since current processes are built around non-water-based rust preventive systems.” She notes that it needs to be “understood that there will be changes in performance and handling, so customer education will be important as the use of water-based rust preventives expands.” Dubbert notes, “We have found the water-based rust preventives are limited in the length and type of protection they can provide.”

Zübert says that performance expectations for water-based rust preventives versus solvent-based rust preventives hinge on time period. For example, water-based rust preventives can be feasible when a short to medium time period of protection is needed (i.e., less than 18 months.) For periods longer than 18 months, water-based rust preventives are less effective. In addition, “If corrosion protection under outdoor exposure is required, water-based alternatives also are not possible or only with restrictions in terms of product stability (e.g., waxes are difficult to incorporate into water).” The mixtures “are usually suspensions, which separate/settle again during storage, and homogenization is then often no longer possible.” She has found customers reject products with a maximum shelf life of only six months. 

Zübert notes that aqueous corrosion protection sounds a bit like a contradiction in terms. “This question always arises because humidity and condensation or water and the salts dissolved in it are the main triggers for corrosion damage; however, the topic of corrosion protection in connection with water also is one of the most important fields of application (e.g., in cooling circuits or in aqueous processing media).” 

Disadvantages of water-based rust preventives
Redetzky identifies four disadvantages of water-based rust preventives:
• High energy costs can be incurred if heated baths are required.
• However, when application temperatures are lower, the risk of microbial growth increases. More chemicals (e.g., biocides) are then needed to control microbial growth in water-miscible rust preventives compared to solvent- or oil-based products.
• The quality of the water (e.g., water hardness, chlorine content, etc.) available at the facility where treatment is occurring needs to be assessed when water-miscible products are used.
• Finally, he notes: “The protective film on the metal surface consists of the additives used in the water-miscible product.” The emulsifiers, which are necessary for this type of product, remain on the metal surface, which might result in a higher affinity to water. This means that high humidity could remove the protective film from the metal surface, leading to reduced performance in countries or environments with high humidity.

Dr. Joseph P V notes that there can be a lack of confidence in the product by the users. He sees “resistance in the users for using water-based products as rust preventives since water is one of the elements of corrosion promotion.” In other words, “the customers have a mental resistance for using anything with water on their valuable article for its corrosion protection.” 

Albright sees efficacy as a potential obstacle to water-based rust preventives. She notes, “It is difficult to achieve the same rust protection using a water-based formula versus a solvent-based formula, especially if the goal is long-term protection in a space that is not climate controlled.” This means water-based rust preventives may not be feasible in severe applications.

A similar efficacy concern Dr. Joseph P V lists is the longer drying time for water-based rust preventives in comparison to the highly volatile solvent-based products. He notes that the longer drying time “may affect the film formation and result in film depletion and inferior performance.” Also, Dr. Joseph P V sees: “Emulsions are very much prone to deterioration by bacterial attack, lowering pH and lowering concentration.” This translates into a need to continuously monitor these parameters. 

Albright believes “water-based formulas can compete with solvent-based formulas for many moderate applications, but infrastructure in the facility using the product is a challenge.” She notes: “Water-based rust preventives need to dry before parts are packaged, just like solvent-based formulas; however, water-based formulations may need longer drying intervals.” The manufacturing process may need to be changed to allow for longer drying periods, or the plant footprint may need adjustment to allow for larger areas where parts are allowed to dry. It could be that dryers or fans would be useful, but they would need to be installed into the process, and then draw energy to operate. 

Anytime a change is needed in a manufacturing process, the end-user must buy in to the change, which Albright notes can sometimes be a challenge. She also expects that “water-based products will carry a higher price tag,” but feels that the benefits of these products can be effectively messaged to clients. She observes: “When it comes to lowering VOCs in the workplace, more and more people are likely to give an audience and recognize the value.”

Dubbert agrees with the potential price increase, noting: “The industry has developed oil- and solvent-based corrosion inhibitors that are not only effective in the field, but they also are very cost effective, which will be a hurdle for the water-based chemistries to compete with.”

Zübert agrees with Redetzky’s water quality point, noting that a major obstacle in using water-based rust preventives can be the water quality available at the customer site. In most cases demineralized water is recommended for mixing the concentrated water-based rust preventives. Additionally, workers may need protective gear when handling treated components. Dr. Joseph P V notes that aside from ensuring that the water quality is acceptable, the user also needs space at the facility to prepare the dilution (e.g., containers, stirrers, etc.).

Dr. Joseph P V also sees a concern with the disposal of water-based rust preventives. Prior to disposal, the emulsion needs to be treated to separate oil from water. 

The future of water-based rust preventives
Lange says, “Mineral oil and water-based rust preventives are both VOC-free, but due to the fact that limited resources of mineral oil are available, it is vital to start saving such petroleum-derived products.” She observes, “It makes sense to find a greener solution, like using water as the ‘solvent.’”

Redetzky observes: “Mineral oil free products should be the future of the rust preventives market; however, a high energy consumption (e.g., heated baths) or microorganisms could be a limiting factor for a widespread use of water-miscible rust preventives.” 

Albright notes: “Necessity is the mother of invention,” and “legislation can create a big ‘necessity!’” The relevant rules and regulations do vary widely throughout the world, but “if a jurisdiction demands limiting VOCs, manufacturers will formulate, and end-users will purchase.” She thinks the message is getting out that eliminating VOC releases is a good goal that is part of “sustainable” thinking. Currently, “Many parts of the world are not on board with ‘sustainability.’” However, she feels that legislation will encourage conversion to VOC-free rust preventives in the next five years. However, Albright says, “Like many chemicals in our industry, people won’t completely stop using certain chemicals or technologies until their hand is forced.”

Albright says, “Like a few other materials in our industry, there are some things that can’t easily be replaced across the board.” In other words, there are “some applications that will remain dependent on solvent-based rust preventives.” However, she does believe that “many applications can be replaced with water-based products,” and that end-users will become more receptive. “Awareness is growing.” She sees the industry as responsible for explaining the risks of VOCs to the end-users and to be sustainability champions. This means offering alternatives and more sustainable choices.

Dubbert agrees, stating, “In 2009-2010 we became aware of the VOC restrictions in the Southern California district (SCAQMD) that have now moved across the country in many capacities, including rust preventives.” That legislation made it clear that the industry would have to respond by learning how to formulate these products without traditional solvents.

When asked if future restrictions of VOC-emitting rust preventives would mean a significant risk for their business, Dubbert responded, “No, I don’t see it as a significant risk, but I do think there could be significant risk to the businesses that use rust preventives from the standpoint of increased cost and decreased metal protection.” While manufacturers of rust preventives will be able to provide customers with satisfactory products, there will be trade-offs in cost, efficacy, film types and ease of use.

Zübert agrees, stating, “We can replace VOC-emitting rust preventives worldwide up to 20% (if the customer is prepared to make appropriate investments in plant technology).” 

Conclusions
Dr. Joseph P V notes that water-based rust preventives are a growth area as ecofriendly and sustainable solutions are needed in almost all areas of human activities. He finds, “This positive trend is slowly driving the demand for water-based rust preventives over solvent-based products.” Research and technological advancements in corrosion protection methods will continue. Dr. Joseph P V finds, “The ever-increasing growth in the automotive sector, the major rust preventive consumer, the globally growing construction industry and stringent government environmental regulations on hazardous chemicals also are further boosting the water-based rust preventive market.”

REFERENCES
1. NBS Special Publication 511-1 and 511-2 (1978), “Economic effects of metallic corrosion in the United States.”
2. Hoar, T.P. (1971), “Report of the committee on corrosion and protection: A survey of corrosion and protection in the United Kingdom, Dept. of Trade and Industry, H.M.S.O., London.
3. Behrens D. and Gräfen H. (2001), “Volkswirtschaftliche Bedeutung der Korrosion” in Kunze E., Korrosion und Korrosionsschutz Bd. 1, Wiley – VCH, Weinheim, pp. 1-17. 
4. Reducing the emissions of volatile organic compounds (VOCs), available here.

Andrea R. Aikin is a freelance science writer and editor based in the Denver area. You can contact her at pivoaiki@sprynet.com.