Galvanic Reaction: Incompatible Metals Responsible for Corrosion

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During a maintenance check in the 1980s, workers discovered that the Statue of Liberty had a serious structural issue: the statue’s internal wrought iron support system was rusting over because the insulating layer of shellac between the iron and copper had failed and allowed for galvanic corrosion to occur. Although this was not a surefire recipe for structural disaster, it was still a serious structural issue that took millions of dollars and months of work to ensure Lady Liberty’s structural integrity was better prepared to stand the test of time.

While atmospheric and crevice corrosion are some of the most common causes of metal deterioration in structural components, galvanic corrosion, another common culprit of metal deterioration, is just as widespread. Nonetheless, this pernicious chemical reaction is often misunderstood by many members of the construction industry.

As a designer, builder, engineer, or architect who works with exterior metals, you may have heard of the term galvanic corrosion (also known as bimetallic corrosion), or perhaps at the very least, are familiar with the concept of galvanized metals – such as steel coated with a thin layer of zinc to prevent rust – which employ a “controlled” form of galvanic corrosion to achieve their corrosion resistant properties. 

While most people know that galvanic corrosion is dangerous, not many know how it works, how its real world consequences play out in terms of structural safety, and what can be done to avoid it.

This article provides important information about galvanic corrosion and related safety considerations.

 

What is galvanic corrosion?

Simply speaking, galvanic corrosion is the damage or deterioration of metal that takes place between dissimilar metals because of an electrochemical reaction. Specifically, it occurs when two different metals come into contact with each other and have either been submerged or moistened by an electrolyte, with the corrosion taking place around the point where the two metals meet. Additionally, this reaction can be catalyzed by substances that increase the conductivity of water, like salt, and thus the rate of corrosion can vary based on the environment where the reaction takes place.

Galvanic corrosion occurs because each metal has its own electrical conductivity potential. This difference in electrode potential in turn drives a corrosive attack on the positively charged metal (anode), forcing it to dissolve into the electrolyte.

Most commonly, galvanic corrosion can be seen in plumbing systems where a copper pipe is directly connected to a steel or iron pipe. Once in contact both metals can undergo galvanic corrosion because of the electric or galvanic current that takes place at the anode and cathode of the pair of metals.

In addition to environmental salinity, the severity of galvanic corrosion that occurs when two metals come into contact is dependent on several other factors as well, including:

  • The dissimilarity of the two participating metals and the difference between the electrode potentials of each of them.
  • The surface of each of the metal and whether or not it has a protective film.
  • The properties of the electrolyte, including the flow rate, volume, temperature, ionic species, conductivity, and pH.
  • Presence of nearby concrete sealed with sodium acetate.
  • The humidity, moisture, sun exposure, temperature variation, etc. of the local environment.
  • Geometric and physical factors such as surface area, contact point, and the distance between the metals.
  • Metallurgical properties such as the alloy mix, mechanical disturbance, and heat treatment.
  • Other factors such as reversible electrode potentials, chemical reactions, and microbiological contributors.

 

Examples of galvanic corrosion

In addition to the example involving the Statue of Liberty cited at the beginning of this article, there have been several other high-profile examples of galvanic corrosion affecting a structure’s integrity.

Another one of these famous examples involves St. Mary’s Cathedral in Tokyo, a prominent Catholic church built in 1964 with a unique metal design. In 2002, a photograph of the building was released, which showed its stainless steel roof, and while it was dirty, it was totally corrosion-free. However, just a few years later, the building’s roof peeled off during a storm. How did this happen? Well, in the intervening years the non-metal separator between the metal roof and metal structure deteriorated significantly. Once this inert separator was lost, galvanic corrosion caused the carbon steel support system to fail. Unfortunately, this is a common theme among lots of these prominent examples: designers often fail to realize that if a cladding or roof system is designed to last throughout the building’s life, then the same should apply to the structural support too.

Now of course not all of us do work involving ultra modern metal churches in Japan, so what are some more real-world examples of the safety implications of galvanic corrosion that the average architect or designer might face? Let’s say, for example, you want to build a stainless steel facade that’s fastened with screws. Now, if you opt for screws coated with zinc, then the stainless steel will aggressively corrode the zinc because fasteners coated with zinc are attacked by this dissimilar metal from all directions. Obviously this is not good: screws and anchors are vital to structural integrity and with the screws corroding, it could lead to structural failure. Not to mention the ugly rust trails and white corrosion that will bleed down the skin of the building as the metals corrode.

Therefore, it’s only a good idea to choose fasteners coated with zinc on metal if your metal is also the same or has similar nobility to that of zinc. In other words, you can choose zinc-coated fasteners for use with aluminum since it’s much closer to zinc on the galvanic series (a ranking of the molecular similarity of different metals), and therefore less dissimilar which in turn means there won’t be a lot of corrosion. However, you can completely avoid galvanic corrosion by choosing matching metal anchors. So, for example, choosing zinc on zinc would have the lowest risk for corrosion. Use this chart below to better understand what metals will work best together without potential for galvanic corrosion:

Click to Enlarge
Click to Enlarge

 

How to prevent galvanic corrosion

While keeping the reactivity and nobility of metal structural materials in mind when choosing building components is one way to prevent corrosion from galvanic interaction, it isn’t the only way. It is possible to prevent galvanic reaction in metal structures and materials through the choice of proper building materials and components too. Here are some examples:

 

  • Preventing electrical connections: In cases where two dissimilar metals must be joined together, it’s best to separate them with any non-conductive component, like dielectric fittings on pipes.
  • Making use of corrosion-resistant connectors: When joining two dissimilar metals, such as in cases where copper is used with iron pipes, it’s better to use a soldered or brazed joint instead of a threaded or mechanical one since the former is more durable than the latter.
  • Choosing the right size or area of the joined metals: When it comes to joining two dissimilar metals, the higher-noble metal should have a smaller area, and the less-noble metal should have a larger area.
  • Use antioxidants: when working with copper or aluminum use antioxidant pastes.
  • Prevent electrolyte contact: coating metals with hydrophobic substances like grease prevents electrolyte contact, slowing any potential corrosion.
  • Using protective coatings in the right manner: If you’re using an anti-corrosive paint or coating, then make sure that both of the metals are coated instead of just one.
  • Using a sacrificial anode: In some cases, you can also cover the component with a material that serves as a “sacrificial anode.” So when corrosion does occur, it will only chip away the sacrificial anode and not harm the component underneath until all of the sacrificial anode has been corroded (as is the case with galvanized iron or steel which uses a thin layer of zinc as a sacrificial anode to prevent rust).

 

Is galvanic corrosion always harmful?

While galvanic corrosion is generally something that is avoided at all costs, in some industries, a controlled galvanic reaction can be used for extending the asset’s life. Combining a metal to such as one that is higher on the galvanic series can spur the corrosion of the anode while protecting the anode’s cathodes that would have been at risk otherwise. This technique is known as cathodic protection, and while it is expensive, it’s a popular choice for hard-to-reach areas like buried pipelines or ships’ hulls.

 

Conclusion

Galvanic corrosion is an expensive issue which can not only result in ugly rust stains and metal finishes, but is also a serious safety consideration that can lead to catastrophic and deadly structural failure if left unchecked. However, by taking a few measures, it’s possible to ensure that your buildings stay safe from galvanic corrosion. Remember to keep these factors in mind to help prevent and control galvanic reaction and ensure the safety and longevity of your building.

If you need further information about the corrosive properties of the metals we use in our products, please give us a call at (631) 750-3000.

3D Printing Metal: The Advantages of Direct Metal Laser Sintering

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Did you know that metal parts can be 3D printed? It happens via a process called Digital Metal Laser Sintering or DMLS. DMLS is a form of additive manufacturing that uses metal powders and precision lasers to create the desired part. The technology operates on the basis of a 3D CAD file which specifies how complex a design should be.

So, how exactly does DMLS printing work? What happens is this: a thin layer of metal powder is evenly distributed across the bed of the printer. By following a CAD file, a precision laser sinters (heats and fuses) the metal powder particles to replicate the specified design. This process is repeated with additional layers of metal powder until the desired shape and size is achieved. In essence, parts are produced one metal cross section at a time.

Now that you know how DMLS works, let’s have a look at some of its advantages:

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5 Things You Didn’t Know About the Metal Fabrication Process

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Basic metal fabrication involves the forming, shaping, or joining of metal. Typically, this happens through deforming or removing some portions of the raw material.

To many, metal fabrication may seem like a simple one or two step process. But the fact of the matter is, it’s much more detailed and comprehensive than simply pulling metal pieces off the inventory shelf. Here we’ll explore different aspects of metal fabrication to help you be more informed the next time you need to rely on the services of a fabricator:

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8 Tips for Making Any Woodworking Project Successful

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If you’re a new woodworker, safety and precision are likely two things you keep top of mind at all times. But that’s only the tip of the iceberg. As many a skilled woodworker will tell you, any project requires your attention in several different places at once…and this can be difficult as well as dangerous.

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The Hidden Health Dangers of Sawdust

Let’s put it this way: investing in a dust collector can really go along way, especially when it comes to your health. If you regularly spend time working wood, you know how much of a nuisance sawdust can be. It flies all over the place, gets into your power tools, coats your hand tools, and keeps you from breathing clean, fresh air. But that’s not all it does.

Experts and OSHA agree that sawdust poses a serious health risk to those who are overexposed to it. Not only is sawdust an irritant that affects your eyes, nose, and throat, but it’s a known carcinogen that may cause cancer.

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The Future of Manufacturing: Are We in the Midst of a Robot Takeover?

Robots often get a bad rap. Sci-fi novels and films have painted them as evildoers looking to take over our lives and our jobs. Pundits and politicians have largely done the same. But today’s innovative technology is proving that quite the opposite is true. Not only are robots creating jobs but they’re also making existing jobs more convenient. And, to top it all off, they work side-by-side with humans in a relatively peaceable manner.

They’re helping manufacturers turn bigger profits and making operations more efficient. They’re powerhouse machines that can work hour after hour without fatiguing to the point of needing a break. They don’t require salaries or benefits which prompts manufacturers to allocate money for other uses–such as hiring a robot operator or maintenance technician.

And because these machines can do repetitive tasks endlessly with a high degree of accuracy, they boost employees’ productivity in other areas that require a human touch.

Simply put: Robots act as a cost-effective and complementary component on the warehouse floor which makes for a higher quality product that consumers are compelled to by.

Types of Robots

While entertainment of the Sci-fi variety has conditioned us to believe that most or all robots take on human-like forms, the reality is that in manufacturing this simply isn’t true. Sure, some have arms and even “eyes” but for the most part, industrial robots are just…well, machines that help people get stuff done.

Here’s a look at some of the robot types on warehouse floors today:

  1. Cartesian Robots:  Typically used in the automotive and auto component industries, Cartesian robots are noted for their linear movement and ability to move and carry heavy loads. Manufacturers rely on them for accuracy and repeatability when cutting drilling, stamping, or welding materials. Because of their versatility, especially in metal fabrication operations, these robots are gaining popularity in the metal and food/beverage packaging industries.
  2. Articulated Robots:  Articulated robots are distinctly different than Cartesian robots in that they use rotating movement to achieve a full range of motion. They’re most often used in the automotive industry for assembling and material handling but they can also be used for welding, picking, cutting, and spraying materials.
  3. SCARA Robots:  Selective Compliance Assembly Robot Arms or SCARA robots have a parallel axis joint that acts as an arm and are used to for assembly, pick and place, and loading/unloading operations. In comparison to Cartesian robots, SCARA robots are cleaner and faster and more suited to high speed assembly. They’re often used in the automotive, electrical, and electronics industries.

Companies Making a Splash in Robotics

Many companies have happily adopted robotics as a key component in their business strategy. These are just a few:

1. Amazon Robotics LLC

Formerly known as Kiva Systems and acquired by Amazon in 2012, Amazon Robotics LLC uses robots to provide smarter, faster, and more consistent customer service. The robots, which move autonomously around the warehouse floor, are used to make warehousing operations like picking and packing quicker, easier, and more efficient all around.

While Amazon has no plans to share the technology with competitors, the Kiva Systems acquisition opened up a world of robotics possibilities for other companies to explore.

2. Kuka Robotics

Kuka Robotics produces a number of industrial robots designed specifically to aid manufacturers in production. Kuka strives to customize a manufacturer’s robotics experience by tailor-making robots to a specific need. Altogether, there are eight types of Kuka robots:

  • Six axis robots
  • Welding
  • Cleanroom
  • Shelf-mounted
  • Palletizers
  • Heat-resistant
  • Press-to-press
  • High accuracy

Each one comes equipped with a dependable, programmable PC-based system that manufacturers can use to streamline their production processes.

3. Rethink Robotics  

Rethink Robotics provides manufacturers with robots that can easily adapt to real world variability. Using embedded cameras that work as “eyes,” these robots–called Baxter and Sawyer–can change applications quickly as well as ‘feel’ their way through any task. As such, they can perform a wide variety of tasks and work around obstacles that may hinder progress on a job.

All in all, technology has advanced to the point where industrial robots can be an asset to manufacturing companies. While robots are changing the way companies do business, they are largely acting as collaborators that can work side-by-side with humans to help meet or exceed goals. This isn’t a bad thing. In fact, it should be embraced as a mark of progress that helps companies and workers alike expand their knowledge of industry and the possibilities that lie ahead.

 

Job Training Programs: How 4 Companies are Closing the Manufacturing Skills Gap

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Over the next decade, an estimated 3.4 million jobs will need to be filled in the manufacturing sector. The problem? Candidates with the right skills to fill those positions will be few and far between.

To close this skills gap, these four companies are taking matters into their own hands:

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Do Metals Contribute to Sustainable Building? You Bet They Do

IMG_1393-2 While you may think of wood as the main source of sustainable building material, various metals actually play an integral role in keeping the green building industry going. Here’s how metals contribute to the bigger sustainability picture: They’re RecyclableRecycle Metal Metals like copper, stainless steel, and aluminum are 100% recyclable which means they can be remade into the same product without sacrificing quality. Recycling metal also reduces emissions and uses less energy than mining, milling, and refining new material. Just to give you an idea of how useful recycled metal can be, here are a few stats you might find interesting:
  • 90% of end-of-life stainless steel is recycled into new products and most stainless products contain about 60% recycled content.
  • Of all the aluminum produced in the United States, around 75% of it is still in use today.
  • Approximately 75% of all copper based products contain recycled copper.
So, from the very start, these metals reduce waste and are energy efficient no matter their form. They Have Long Lifespans In essence, sustainability is all about maintaining longevity, reducing waste, and making the environment better for the next generation. Metals like stainless and aluminum contribute to the longevity of a project because, in most cases, they last for decades before they need to be replaced and recycled. Aluminum AngleThey’re Durable and Versatile Metals like stainless steel and aluminum are durable and malleable, making them some of the most versatile materials to work with. They can be used on all aspects of green building projects, from core construction and interior design to outdoor applications like solar energy panels. One of the contributing factors to a metal’s versatility is its content. For instance, the chromium and nickel content in stainless steel protect against rust and corrosion which can happen in high temperatures or severe environmental conditions. Aluminum, on the other hand, naturally forms a layer of oxide that is impermeable and repairs itself when damaged. This kind of efficiency in application and resistance to the elements makes these materials ideal for sustainability. Other Sectors Rely on Them The appeal of metal in sustainable building permeates multiple sectors, including those that enable sustainability to continue. Automotive, construction, transport, and tool industries all depend on metals to function. And it’s the innovations of these industries that help green building forge ahead.

Is New Technology Fueling the New-Shoring Trend?

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Innovations in technology are making it easier than ever to manufacture products right here at home. From 3D printing and computer aided design to the Internet of Things and data analytics, modern technology is transforming the way manufacturers think and create.

But something else is transforming, too: production. While many established companies have chosen to produce goods in lands far and away over the years, newly launched start-ups and independent manufacturers are using innovative technologies to keep production all American. This trend, called new-shoring, started to pick up just a few years ago and is now a way of business for many manufacturing newcomers.

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