One popular question we receive from our customers is that of the best practices for joining stainless shapes to shapes made from other alloys to prevent galvanic corrosion or contamination at the joint. To come up with solutions to prevent this problem, one must first understand what galvanic corrosion is and how it can be contained.
Galvanic Corrosion
In general terms, galvanic corrosion is the corrosion induced when two different types of metals or materials are joined together in an electrolyte. This corrosion can occur when connecting stainless steel to aluminum, carbon steel or other types of metals and it is one of the most common and destructive forms of corrosion. When galvanic corrosion occurs, it is due to the difference in electrode potential because one of the metals becomes the anode and the other the cathode. The anode will always corrode faster than it normally would.
For many industrial, construction, or architecturally exposed applications the electrolyte that causes the galvanic corrosion is water or moisture caused by things like humidity and the metals actually sweating. This is especially true when structures are built outdoors near water sources like oceans and rivers or in climates with a lot of snow and ice. With the presence of the electrolyte, galvanic corrosion will occur. The driving force for this type of corrosion is the actual difference in potential of the metals.
Best Practices to Prevent Galvanic Corrosion
There are a few tried and true methods used when combining different materials that will help prevent galvanic corrosion, such as:
- When possible during the design phase, foresee the joining of materials with similar electrode potential (e.g. 304/304L with 316/316L)
- Breaking the electrical path in the metallic or electrolyte parts of the system. This can be achieved by the use of high-density special primers to shield the joint and isolate the electrolyte from the joint. It is important to note that when using a primer or coating that both materials should be coated. If it is not possible to coat both than the primer should be applied to the metal with the greater susceptibility to corroding. Other water repellant compounds such as grease, plastics, suitable paints or varnishes and other impermeable coatings have also had success in preventing galvanic corrosion. Another method used to prevent galvanic corrosion is by electrically insulating the two metals from each other by using non-conductive materials such as plastics because if the two metals are not in electrical contact, no corrosion will occur.
- Adding inhibitors to the electrolyte
- Cathodic protection by: applied current or sacrificial anode.
Working with Stainless Structurals America
At Stainless Structurals, one of our primary benefits is our ability to provide fully customizable stainless steel and carbon steel profiles. With our laser fusion technology, we are able to combine carbon steel and stainless steel materials within one specific profile. We can also mix and match stainless alloys together to make profiles. For example we have produced beams with the more exposed flange in grade 316/L and the other flange and web in 304/L to reduce costs for the customer. For the Coors Brewery in Golden, Colorado we produced a custom profile from 2205 duplex and 304/L stainless.
The possibilities are endless when working with Stainless Structurals America. If your design calls for a combination of stainless steel and carbon steel, we can do it. Let us assist you in making your complex design a reality. We are ready to help. Please contact us today for more information.
