Using Zinc-Nickel as a Barrier to Corrosion on Naval Vessels
According to a study completed by the National Association of Corrosion Engineers, the costs of corrosion were expected to exceed $2.5 trillion globally in 2016. It was estimated in 2012 that upwards of $20 billion was spent within the American defense industry. In the Navy alone, 25% of the maintenance expenditures and 38.2 days of ship availability are lost due to corrosion. These facts, along with increased congressional mandates, the need for longer deployments, and the reductions in fleet size, has made it clear that an effective method of corrosion control must be found. Another group which has historically suffered the same issues with corrosion as the defense industry is the automotive industry. Since 1975, a concerted effort has been made by the major manufacturers of automobiles to decrease the costs of corrosion within the industry. Since implementing these improvements, these companies have realized cost savings on operating costs, manufacturing costs, and longer life of their products to the public. These improvements were done through a variety of corrosion prevention methods. One of the main advancements was done in the area of galvanic corrosion prevention. By depositing a layer of a less noble (more reactive) metal on the surface of the substrate, a sacrificial coating is provided which will preferentially corrode over the base metal. One of the main sacrificial coatings used within the automotive industry is zinc. Because of increased demands within the industry, steps forward are being made in the market. The sacrificial coatings which were traditionally pure zinc are being made into alloy deposits which provide more protection by creating an immediate galvanic effect within the protective coating. Because the alloy is consistent throughout the whole deposit, a spider web of micro-corrosion sites will form over the entire part instead of the macro-corrosion pit formed in a pure zinc deposit. One of the most successful alloy coatings being used in the industry is zinc nickel. Testing has been completed which has shown that zinc nickel alloys can provide protection that is up to 3 times as effective as zinc alone. Taking this technology to the defense sector, specifically within the navy would be beneficial as the main corrosion prevention technology currently used is simply paint over steel. We have proposed applying a sacrificial layer of zinc nickel alloy over the base steel to be painted. In our testing, we have shown that the adhesion of paint to the sub layers is unaffected and that once the organic paint layer is compromised, the substrate is protected longer the unprotected substrate. These gains in protection can be translated into huge cost savings for the government agencies which are responsible for the maintenance and repair of these vessels.