How to determine the Performance of VCI Protection?
The time required for active corrosion-inhibiting molecules from VCI products to saturate a package is a result of the volume and temperature of the package. Protection begins as soon as corrosion-inhibiting molecules reach the metal surfaces, and maximum protection is achieved when the entire environment of the package is saturated with the corrosion – inhibiting molecules. VCI saturation in typical factory environments and packaging applications runs from 12 to 24 hours. When parts in an already corroded condition are packaged in VCI products, the corrosion process is slowed. However, the VCI products cannot remove the corrosion that already happened.
The performance of VCI products can be determined in a number of ways. The first one is by acting as a protective barrier from external dirt and abrasion, as well as a barrier to help block the diffus of corrosive acid gas pollutants from outside (such as sulphur dioxide or hydrogen sulphide), thereby preventing contact of these corrosive gases with enclosed metal surfaces. The second one is by vapour corrosion inhibitors that passivate the electron flow between the anodic and cathodic areas on metal surfaces and interrupt the electro-chemical corrosion process. The last one, is by adding water repulsion properties to the metal surface, which inhibit water from permeating the metal surface and providing the electrolyte for corrosion reactions.
Tests performed with electron scanning (ESCA) microscopy show that 2-4 hours after a steel test panel is removed from a VCI package, all traces of the corrosion inhibiting molecular layer are gone from the surfaces of the part. The period of time before corrosion is expected to occur on a part depends on the cleanliness of the part and the environment around the part (relative humidity, presence of pollutants or wood, temperature, etc).