Over the past several years, we’ve received more inquiries about vapor corrosion inhibitors (VCI) than any other packaging technology. It’s no wonder. Corrosion of metals is an annual $340 billion dollar problem in the United States and VCI has become an important tool in curbing the corrosion process. Though literature on VCI has often been complicated unnecessarily, packaging resellers with VCI subject matter expertise are finding profitable new business that didn’t exist a few years ago.
It’s estimated that only about 1/3rd of all corrosion damage can be avoided by using current available practices, so there is no silver bullet for maintaining metals. But VCI has found a place among several prevailing methods of handling vulnerable parts because each process has its drawbacks.
- Dessicants protect metals only in well-sealed containers that include the right amount of dessicant.
- Paint can defend exposed metals only if all vulnerable surfaces can take paint and be stripped as needed.
- Oil coatings on metals are cleaned by solvents that must be removed and disposed of properly.
VCI products represent a growing $400 million dollar segment of the prevention market primarily because they primise to be simpler, faster, and more environmentally friendly than these methods. To better understand this opportunity, let’s take a deeper look at the mechanism of corrosion and the VCI technology itself.
THE CORROSION PROCESS
Corrosion is a continual, naturally occurring process that occurs to all metals. It is erosion by chemical action, or oxidation. And it is electrochecmical in nature (see image below).
Corrosion happens whenever a gas or liquid attacks the exposed surface of a metal. Most metals corrode on contact with water, salts, acids, bases and other liquid chemicals. But metals will also corrode when exposed to gaseous materials like water vapor, chlorides, acid vapors, formaldehyde gas, ammonia gas and sulfur containing gases.
Think of corrosion as a surface phenomenon. The more surface area, the more opportunity for oxidation. Then, like an electrical circuit, anything that can speed up the transfer of electrons will accelerate the problem.
Heat makes it worse. Temperature helps to speed up the movement of molecules and ions. Corrosion happens twice as fast for every 50 degree rise in temperature.
Moisture makes it worse. Water is an electrolyte (that is, charged partides can exist freely in it), so it facilitates a “corrosion current.”
Pollutants make it worse. Sodium chloride (salt), acids, sulfur, hydrogen and ammonia each make for better conducting electrolytes. They make the corrosion current stronger.
Sometimes corrosion happens uniformly over a surface. The dulling or oxidation of jewelry, for example. That’s uniform corrosion. It accounts for about 1/3rd of all failures. Other times it’s a more localized problem, like a rusty spot. Typically more severe, locvalized corrosion accounts for the balance.
VCI’S IN ACTION
In an attempt to preserve military equipment, the U.S. Navy tested the first vapor corrosion inhibitors on boilers and other materials from war ships in the late 1940’s. Their attempts to preserve mothballed items used amine nitrate solutions. Nitrates have since been shown to form nitrosamines – a carcinogenic material – when exposed to certain types of amines and heat. In the 1970’s newer generations of VCI’s were introduced and most of today’s chemistries are more environmentally sound and nitrate-free.
Vapor Corrosion Inhibitors are materials that have enough vapor pressure under normal, everyday circumstances to become a gas. Picture under a metal part stored in a polyethylene bag. Contained within a bag’s plastic film, VCI additives are able to fill the interior with vapor which in turn readily absorbs onto the surface of the metal component.
As an ion layer, VCI molecules form microscopic, protective barriers to the oxygen, water and other contaminants that facilitate corrosion. In that way, VCI’s prevent reactions on metal surfaces. They work to interrupt the corrosion circuit – halting corrosion itself.
Once designed for ferrous (iron-based) materials, most current VCI’s boast performance for ferrous, non-ferrous and mixed metal materials. These include aluminum alloys, zinc, brass, silveer, copper-nickel and stainless, galvanized and aluminum steels.
Clearly, not everyone uses VCI bags. It is an important and useful technology, but there are several limitation you should know.
Higher Product Costs. Alongside paints, oils and desiccants, VCI raw materials can be expensive. Manufactured bags may cost twice their standard bag counterparts.
Limited Performance Life. Unlike paints or barrier oils, VCI’s don’t last forever. Published shelf lives of 2 years or more are common.
Heavier Gauge Requirements. Unlike desiccants, VCI’s require a thicker bag. The heavier the gauge, the more VCI actives will be available. You’ll find typical minimums to be 3-4 mils.
Greater Temperature Sensitivity. Unlike most other solutions, the volatile nature of VCI’s makes them sensitive to extremes in temperatures. The higher the temperature, the faster VCI materials will dissipate. At very low temperatures, VCI actives will slow or cease to work.
Most VCI bags will cite conformance to MIL-B-22019C and MIL-B-22020D for type I (heat-sealable) corrosion inhibitor bags. These specs, reference material, construction and performance standards, including the American Society for Testing and Materials (ASTM) methods for corrosion inhibition efficacy.
VCI’S IN YOUR MARKETPLACE
With a basic understanding of the technology and its limits, conversations about VCI packaging can create terrific opportunities. And as VCI’s acceptance alongside other methods of preservation continues to grow, expect to have many more of those conversations.
Have questions? We would love the opportunity to talk with you!
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