Technical FAQ’s on Metal Corrosion Protection
1. What is Corrosion?
Corrosion is a process that takes place when properties within a given material begin to deteriorate, after exposure to elements that are present in the environment. Most often, this deterioration is noticed in metals and referred to as rust. What happens in this case is the chemical reactions that are set up by an exposure of the electrons in the metal to the presence of water and oxygen.
Usually corrosion is the oxidation of metals in the presence of water or water vapor, and is known as rust (iron, steel), white rust (galvanized steel), and other terms of corrosion failures such as tarnish, pitting, flaking and spalling.
2. What type of metal corrosion protection exists?
A. Physical corrosion protection (essentially the withdrawal of humidity)
Transport packaging in the form of PE-bag usually in combination with desiccants
Aluminium foil in combination with desiccants
B. Chemical corrosion protection (modification of the physical process)
Oils and fluids
Acids and bases
Corrosion Protection Inhibitors (VCI films, VCI papers, VCI cardboards etc.)
Protective gases (oxygen scavenging and ethylene absorbing)
3. How do VCI’s offer metal corrosion protection?
VCI products prevent corrosion in several ways.
1. By acting as a protective barrier from external dirt and abrasion, and also as a barrier to help block the diffusion of corrosive acid gas pollutants from outside the packaging material (such as sulfur dioxide or hydrogen sulfide) – thereby preventing contact of these corrosive gases with enclosed metal surfaces.
2) By vapor corrosion inhibitors that passivate the electron flow between the anodic and cathodic areas on metal surfaces and interrupt the electro-chemical corrosion process.
3) By adding water repulsion properties to the metal surface, which inhibit water from permeating the metal surface and providing the electrolyte for corrosion reactions.
MetPro‘s Vapor Corrosion Inhibitor products are made of proprietary chemical formulations that are invisible, odorless, non-toxic, non-reactive, non-flammable and non-allergenic. These chemical formulations release a corrosion inhibiting vapor that diffuses throughout an enclosure and settles on exposed metal surfaces to form a microscopic or monomolecular corrosion inhibiting layer.
This protective layer will remain on the surface of the metal as long as there is no significant, continuous exchange of air within the enclosure. Once the metal part is removed from the enclosure, the corrosion inhibiting layer is no longer kept in place by equilibrium and it dissipates from metal surfaces (typically within about an hour) leaving the metal part clean, dry and corrosion-free.
VCI products offer metal corrosion protection without having to be in direct contact with or coated onto the parts that are being protected. Metal parts merely need to be enclosed in or with a VCI product (where airflow is minimized) for protection to occur. With VCI, it is no longer necessary to apply messy oils, greases and other corrosion protection compounds and incur the cost of their removal.
4. What can be anticipated when parts that are already corroded are packed in VCI products?
When parts in an already corroded condition are packaged in VCI products, the corrosion process is slowed. However, our packaging products cannot remove corrosion that has already formed.
5. How long does it take for the VCI in a package to reach its optimum metal corrosion protection capability?
The time required for active corrosion inhibiting molecules from the VCI product to saturate a package depends on the volume and temperature of the package. In lower temperatures, the corrosion rate is lower and alkso the absolute quantity of VCI molecules in the enclosed space is much smaller. With increasing temperatures, the partial vapour pressure increases so does the amount of VCI in the space which helps to protect the metals quicker in more difficult conditions. 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.
Saturation in typical factory environments and in typical CKD packaging applications runs from 12 to 24 hours.
6. What is the best way to store VCI products before use?
We recommend keeping VCI packaging products clean, out of direct sunlight and away from water while in storage. Simply keep the products in their original shipping cartons, bags or containers. If a carton is opened, cover the products with a sheet or bag of plain polyethylene to protect the products from dust and dirt. It is also recommended that VCI products be stored in moderate temperatures, typical of most indoor workplace conditions to minimize exposure to excessive temperatures and outside elements such as direct sunlight, rain or snow. Storing VCI products correctly ensures that the products will meet or exceed their estimated shelf life.
7. What is the difference between “shelf life” and “in-service life”?
The shelf life is the duration of time that unused VCI products can be stored prior to use without losing their effectiveness. The in-service life is the duration of time that VCI products will protect clean metal objects from corrosion if used properly.
8. What is the Shelf life of MetPro VCI products?
Most MetPro metal corrosion protection solutions have a shelf life of up to two years when the product is properly stored in an external bag or box, out of direct sunlight and under appropriate shelter.
9. What is the in-service life of MetPro VCI products?
Most MetPro VCI products have an in-service life of up to five years when protecting clean metal surfaces and when the applications and guidelines followed by our technical specialists are followed.
10. What are the advantages of MetPro VCI Packaging?
Cost effective Metal Corrosion Protection guaranteed
Safe and environmentally friendly
Easy to apply
No need to use grease or oils
Vapours replenish contained package and penetrate recessed, inaccessible areas ensuring good Corrosion Protection throughout the package.
No need to remove VCI protection layer before using or welding product.