The underlying chemistry of corrosion may be complex to understand, but its effects are not: Corrosion-related product and infrastructure failures cause billions of dollars of damage every year and are extremely dangerous.
All metals are susceptible to some form of corrosion, and all corrosion will affect how metallic materials perform in some way. Therefore, expert corrosion testing is an essential part of any manufacturing process that relies on metal materials.
By understanding how and when metal corrodes, and how the corrosion will affect that metal’s performance, experts can determine what a given metal should and should NOT be used for. In the process, they help prevent critical damage and save lives.
To understand just how important corrosion testing is today, this is what you should know about how corrosion works, why it’s so dangerous, and how the right testing can prevent disaster.
What is corrosion?
Corrosion is the natural result of electrochemical reactions between metals or other materials and substances in their environment. Corrosion converts refined metals into more chemically stable oxides via these reactions.
The most common form of corrosion occurs when metal is exposed to oxidants (such as oxygen or hydrogen) in their environment. For example, rusting is a corrosion-based reaction that occurs when iron comes into contact with oxidants in air and moisture.
When refined iron comes into contact with water, water molecules can penetrate microscopic pits and cracks in the surface of the metal. Once inside the metal, oxygen atoms inside the water chemically combine with iron atoms and convert them into iron oxide, which is the characteristic reddish-brown material commonly called rust.
Unfortunately, corrosion isn’t always as easy to define and predict as it is with rust. The chemistry of corrosion can be very complex, and many different types of interactions trigger different types of corrosion. For example, one kind of corrosion Secat commonly tests is called galvanic corrosion, or bimetallic corrosion.
What is galvanic corrosion?
Galvanic corrosion occurs when two types of metals with different electrode potentials come into contact with one another while immersed in an electrolyte (such as water). In these situations, an electrical circuit between the two metals called a galvanic couple forms.
While metals are united in a galvanic couple, their tendency to lose or gain electrons (known as their electrochemical potential) changes. The metal with the more negative electrochemical potential becomes the anode (negatively charged electrode) in the galvanic couple’s electrical circuit and begins losing electrons and undergoing oxidation as molecules in the electrolyte environment rush in to replace them. As a result of this interaction, the metal serving as the anode in the galvanic couple begins corroding at an accelerated rate.
Meanwhile, the metal with the more positive electrochemical potential becomes the cathode (positively charged metal) and begins accepting electrons from the anode. As this occurs, the cathode metal is “protected” from the influence of the electrolyte environment and corrodes much slower than it would otherwise.
Galvanic corrosion is extremely important in metal manufacturing because manufacturers can manipulate the phenomenon to protect critical alloys from corrosion damage. For example, zinc is frequently used as a “sacrificial anode” to protect iron from rusting on seafaring ships.
Zinc has a more negative electrochemical potential than iron. When the two metals are submerged in saltwater, they form a galvanic couple with zinc as the anode and iron as the cathode. Instead of rushing to the iron where they will create rust, oxidants combine with the zinc anode, and the iron itself is protected from corrosion.
What is corrosion testing?
Corrosion testing refers to any processes which professional laboratory testers use to understand a material such as a metal, ceramic, or polymer’s potential to corrode under different circumstances. Analysts perform corrosion testing on products and materials to determine when and how they might corrode, helping to predict, prevent, or reduce any potential corrosion-related issues that could arise during use.
Corrosion testing procedures and results are governed by a series of international standards that are rigorously tested and updated. For example, the accepted gold standard for galvanic corrosion testing is the American Society for Testing and Materials G71, also known as ASTM G71. Secat follows ASTM G71 when conducting all galvanic corrosion testing to ensure our testing follows proper procedure and to accurately contextualize our results.
Why is corrosion testing important?
Corrosion poses a problem because the oxides formed from metal lack the properties of their refined counterparts, such as high strength and durability. For example, iron oxide or rust is brittle and easily broken, so rusted iron can’t perform the kind of functions uncorroded iron can.
As a result, if a metal like iron corrodes while it’s performing a critical function — such as reinforcing a bridge or serving as the hull of a ship — its ability to perform that function will be severely compromised. This frequently leads to costly and dangerous product and infrastructure failure.
Corrosion testing is essential for avoiding these kinds of costly and dangerous failures. By conducting comprehensive corrosion testing on any metallic materials that will be used in service, experts can predict whether those materials will be safe for their intended use cases.
For example, Secat frequently conducts corrosion tests on aluminum alloys used by clients in the construction and automotive industries. By thoroughly assessing how these alloys may or may not corrode under a wide range of conditions, we can evaluate whether aluminum used in products like wheels or door panels will withstand its intended lifecycle without issue.
More advanced forms of corrosion testing, such as galvanic corrosion testing, have even more diverse applications. For example, Secat can test how different metals form galvanic couples and how these couples speed up or slow down each metal’s corrosion. This can help manufacturers understand how to manipulate galvanic couplings and protect their alloys from damaging forms of corrosion.
Further, corrosion resistant polymeric coatings are often applied to the surfaces of metals to prevent corrosion. There are many options for coating systems with a wide array of performances in different environments. Corrosion testing can be used to evaluate the performance of different coating systems and help determine the right coating for the job. Secat follows ASTM standard D1654, “Evaluation of Painted or Coated Specimens Subjected to Corrosive Environments” when conducting these tests.
How does corrosion testing work?
There are many different types of corrosion testing. Secat uses a controlled relative humidity corrosion chamber called a Q-Fog CRH chamber to conduct cyclic corrosion testing.
Cyclic corrosion testing is considered the most accurate and effective form of contemporary corrosion testing for two reasons:
- It offers the best possible laboratory simulation of the natural atmospheric conditions that cause corrosion.
- Experts can use machines such as the Q-Fog CRH chamber to manipulate these conditions, expediting the process of natural corrosion to observe and monitor it much faster than it would otherwise occur.
During Secat’s corrosion testing, our experts place samples of the metal(s) we’re testing inside a 57” x 32” x 18” chamber. Within this chamber, we can subject the samples to fully controllable temperature ramping, relative humidity changes, and electrolyte shower sprays at variable distances, intensities, and lengths of time.
This technology allows us to recreate (and expedite) a wide range of natural corrosion-causing environments and situations the sample may come in contact with and monitor how corrosion develops as a result. Secat regularly uses corrosion testing to evaluate coating integrity, understand the corrosion rates of different metals and metallic alloys, and to study the mechanisms of complex forms of corrosion at an accelerated rate.
Using cycling corrosion testing, Secat’s analysts can tell you how your material will corrode under different circumstances, how quickly that corrosion will occur, how that corrosion will affect its performance, and more.
If you think you need corrosion testing, get in touch with Secat for expert help right away.