Are VCI Bags Effective?

Corrosion is a serious problem for anyone who works with metal, particularly ferrous metals. From precision engineers to vehicle manufacturers, every metal part can be at risk from the first cut, between each machining, when stored before assembly, during shipping and while waiting to be put into service. Even parts protected by oil during use can start to corrode when left standing for too long as the oil drains away and damp air infiltrates the system. There are many ways to prevent corrosion, including Volatile Corrosion Inhibitors (VCIs) which protect sealed or capped systems, contact corrosion inhibitors which are applied by dip, spray, brush or swab and packaging infused with corrosion inhibiting products. A relative newcomer to the corrosion prevention market is the VCI bag. These plastic bags can be supplied as individual bags with a zip fastening or on a roll to be cut to size and heat sealed. They have a VCI product incorporated into the material and are marketed as a way to protect parts in storage and in transit – it sounds like an ideal solution: parts do not need to be coated so it reduces labour costs. The plastic bag protects from moisture and corrosive chemicals, like salt in marine air or acetic acid from packing cases, and the VCI present should add an extra layer of protection. Unfortunately, VCI bags are not as effective as the manufacturers claim and are actually a very costly form of packaging with limited benefits. A VCI works by building up an effective concentration of vapours in an enclosed space. The vapours react with metal surfaces at a molecular level, preventing corrosion from starting. Providing the space remains closed, capped or sealed, the VCI remains effective indefinitely. By definition, a VCI needs to be able to evaporate in order to do its job and, once it is bound up in a plastic material, it cannot escape. In reality, the major benefit of using VCI bags is that clean, dry metal parts are sealed in plastic which protects them from moisture and environmental corrosives. If the bag itself becomes damaged or the parts are removed from the bag for inspection on arrival and stored loose, they are immediately at risk of corrosion again. The same level of protection would be afforded by simple HDPE plastic bags at a fraction of the price and, where additional corrosion protection is required, the application of a contact corrosion inhibitor like Steelgard would ensure the part is fully protected until it is put into use. Shipments of multiple parts or complex assemblies can benefit from VCI protection by adding VCI liquid or a piece of VCI paper to the packaging, thus avoiding the need to treat hard to reach areas or encase each part in its own plastic bag. At Vapor-Tek we manufacture a wide range of high performance corrosion preventatives. Our Steelgard range is clean, quick and simple to apply. It leaves an ultra-thin film which protects metal parts between machinings, in storage and transit and usually does not need to be removed before they are put into service. No matter how parts are handled or stored, the protection remains in place. Our VCIs are extremely versatile. They can be added to engines, gearboxes, fuel tanks and packing cases before storage or shipping to protect the contents. They are used by packaging companies: printed onto cardboard boxes to keep the contents protected or soaked into VCI paper which is traditionally used to wrap products like razor blades to keep their edge and to protect small, machined parts and toothed or threaded components. VCI paper can also be cut to size and inserted into any packaging to ensure the contents stay protected, where it is preferable to a liquid VCI. We strongly recommend applying corrosion preventatives early in the manufacturing process. Pinprick rust can set in just 4 hours after casting, forging or machining and, while difficult to see, it can affect the appearance and integrity of components and lead to significant corrosion over time. By relying solely on packing parts in plastic VCI bags at the end of the manufacturing process, there is a strong chance that corrosion will have begun before they are shipped, leaving customers at risk of losing stock to corrosion if the packaging is opened or damaged. It puts the onus on the recipient to take steps to apply protectives as soon as parts arrive and are taken out of the bags for inspection or to be stored and could mean the parts you supply are seen to suffer corrosion more easily than those which arrive with a protective coating.

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