Best Practices in Preventing Galvanic Corrosion on Stainless Steel

If you work with structures that incorporate joins between stainless steel and another metal or alloy, chances are you'll need to manage the risk of galvanic corrosion. This particularly destructive form of corrosion forms when there is a difference in electrical potential between two surfaces that are connected by an electrolyte. The potential difference results in one surface acting as an anode (the electrode that "gains" electrons and becomes oxidised), whilst the other surface becomes the cathode (the electrode that "donates" electrons). Oxidation is a corrosive process. The metal/alloy acting as the anode experiences accelerated corrosion. In galvanic corrosion, the most common electrolyte will be moisture that penetrates between the two surfaces.
 
Protecting joins from galvanic corrosion is a priority for many industries. Here we detail best practices to minimise the risk of the conditions developing which would facilitate galvanic corrosion.

For a potential difference to occur between the two surfaces in a join, each surface needs to have a different electrical potential. The closer the values are, the less corrosion will occur. When designing a new structure, considering the electrical potential of the materials used enables the elimination of joins that will result in a significant potential difference between surfaces.
 
Where there isn't an alternative to joining two surfaces that have markedly different electrical potentials, recognising that the risk exists provides the opportunity to provide a suitable solution to the problem.

The use of a sacrificial anode is already a common practice, typically when a coating of zinc is applied to an iron or steel core. The zinc corrodes first, protecting the core from damage. Galvanising steel surfaces with zinc or some other sacrificial coating means that even if corrosion does occur, the integrity of the core material is maintained. Used as part of a suite of preventative measures, the use of a sacrificial anode can significantly prolong the life of the joint.

Galvanic corrosion can only occur if an electrical circuit between the two surfaces and the electrolyte can be maintained. Breaking the circuit eliminates the possibility of galvanic corrosion. 



There are several ways that this can be achieved, including the use of insulating primers. Applying a barrier, such as grease, between the two surfaces is also a way of preventing the electrical connection from occurring.

Few joins start their life with an electrolyte already present. In most cases, the electrolyte is water that's penetrated a joint exposed to adverse weather conditions, seawater or other challenging environments. Minimising exposure to the weather reduces the risk of galvanic corrosion significantly. If this isn't possible, a pre-emptive inhibitor can be placed in between the two joint surfaces. In the event that moisture does penetrate into the joint, the inhibitor acts to slow the development of electrical potential difference between the surfaces.
 
Following some or all, of these suggestions, should go a long way to reducing or even eliminating the likelihood of galvanic corrosion. Hardrok Engineering have experts that provide care for stainless steel here in Mount Isa, have a corrosive free stainless steel and make your work easy. Contact us on 07 4749 1770 today!