Galvanic Corrosion: Avoidance and Risk Mitigation Explained
While galvanic corrosion is a serious threat, understanding why it occurs can make avoiding this common corrosion type simpler.
Corrosion is a critical concern when choosing piping materials and designing piping processes. While stainless steel is highly resistant to many forms of corrosion, being mindful of risks is essential to safe long-term operation and reducing costs over the life of your system.
In this guide, we’ll discuss galvanic corrosion, where and when it might occur, and how you can minimize the risk of or prevent galvanic corrosion when using stainless steel pipe.
What is Galvanic Corrosion?
Also known as bimetallic corrosion or dissimilar metal corrosion, galvanic corrosion is when corrosion damage occurs due to two dissimilar metals coupling in the presence of an electrolyte.
So, breaking that down, it means three conditions must be met for galvanic corrosion to become a concern:
Multiple metals must be present with varying electrode potentials or nobility. The greater the difference, the greater the risk of galvanic corrosion.
These metals must be in electrical contact.
Exposure to an electrolyte -- such as saltwater -- must occur.
In the process, one metal -- the anode -- will corrode faster than it would alone while the other -- the cathode -- will corrode slower than it would alone.
Preventing Galvanic Corrosion
Much of minimizing galvanic corrosion risks is simply avoiding combinations of the three elements listed above. However, for many industries -- such as those processing chemicals or operating off-shore in salt-rich environments -- this is easier said than done.
Consider the following when designing or maintaining piping processes where galvanic corrosion is a concern.
The Galvanic Series (Electrode Potential) Explained
One of the foundational steps to preventing galvanic corrosion is choosing metals with similar electrode potentials or nobility.
As highlighted in the image above, many stainless steel alloys rank toward the cathodic end of the scale. This means they are less likely to suffer damage from galvanic corrosion. However, if used with highly anodic fasteners, structural elements, valves, or other components, the large difference in nobility can lead to rapid degradation of the other components.
This is commonly seen when carbon steel or aluminum is used alongside stainless steel piping.
Understanding Environmental Components of Galvanic Corrosion
It is important to note that galvanic corrosion risks will also vary based upon the electrolyte connecting both metals. For example, the risks of galvanic corrosion in very pure water are minimal. Yet, deploy the same metals in a marine or chloride rich environment and you could see corrosion occur very rapidly.
While your exact experience will depend on many factors and you should always consult an engineer for accurate information relating to your specific needs, the following chart offers examples of what galvanic corrosion risks to expect from common metal combinations.
Options to Reduce Galvanic Corrosion Risk
Even with the ideal materials chosen, it may not be possible to completely eliminate galvanic corrosion risks. If so, insulating components and breaking the electrical path where possible are effective options to further boost corrosion resistance and ensure a long operational life.
Options include:
Insulating dissimilar materials using non-conductive material coatings, greases, paints, treatments, or primers. Optimal protection is offered by insulating both materials. However, insulating just the anodic material can help to slow galvanic corrosion progress even if it does not completely prevent it.
Using buffers -- such as pipe wraps, clamp liners, and wear pads -- between dissimilar metals to eliminate galvanic cell creation and interrupt electrical paths.
Plating, or galvanizing, is also an effective means of reducing galvanic corrosion risks or altering the electrode potential of components without completely changing their structure. For example, it is common to plate carbon steel fasteners with zinc to greatly improve corrosion resistance. However, any noble metal -- such as chrome, nickel, or gold -- can be used as well.
Key Takeaways
While stainless steel pipe and piping components are a popular choice due to their excellent resistance to corrosion, this same resistance can also make pairing other metals with stainless tricky when galvanic corrosion is a concern.
Galvanic corrosion requires two dissimilar metals, in electrical contact, in the presence of an electrolyte to occur.
Metals further apart on the Galvanic Scale (or with greater electrode potential) are at higher risk of galvanic corrosion.
Environmental factors (such as electrolyte concentrations, flow rates, and temperatures) can further impact galvanic corrosion risks.
Insulation, buffers, and plating all offer effective ways to minimize corrosion risks when pairing other metals with stainless steel products.
As a leading provider of stainless steel pipe and other stainless steel components throughout Canada and North America, Unified Alloys understands the complexity involved in choosing the ideal materials for piping processes and other stainless steel projects across a range of industries. Whether you’re in the oil industry, food processing, or healthcare, our expert sales analysts have the expertise to help you find the ideal solutions for your needs. Contact us today for more information.
References
Unified Alloys expressly disclaims any liability for loss or damage caused by use of any information contained in this publication, including any special, incidental or consequential damages arising from such use.
Nothing in this publication shall create or imply any warranty whether expressed or implied.