All metals are susceptible to corrosion. Naturally, that poses a problem for businesses that sell metal products that operate in highly-corrosive environments, or come into contact with corrosive materials.
Corrosion can cause the loss of equipment, reduce the appearance of buildings and structures, create environmental health hazards, contaminate fluids, and cause injury to employees and end-users.
It is estimated that the cost of metal corrosion across all industries around the world is $2.6 trillion per year.
Because of this, businesses that deal with metal should seriously consider taking preventative measures to manage, slow down, and stop corrosion.
By doing so, they will help increase the effectiveness and longevity of their metal applications, as well as reduce any potential safety issues caused by corrosion damage.
In the following sections, we will cover different corrosion prevention methods you can use to secure your material investments and ensure the safety of your employees, end-users, and the environment.
Preventing corrosion will always begin with choosing your materials.
Selecting the right metal for your project is not easy and could be costly upfront. However, in the long run, the right option will increase the longevity of your material and reduce maintenance and service costs.
Before making the selection, you must have a clear understanding of the conditions and environment your application will be exposed to. Otherwise, you will not be able to match the material to the role it has to play.
The general process of corrosion occurs when the atoms on a metal surface oxidize, i.e., lose electrons due to oxygen exposure.
Oxidation damages the surface of the metal.
There are eight different forms of corrosion that can damage metal surfaces.
These are:
The above forms of metal corrosion are the result of various chemical reactions induced by environmental factors.
These are, for instance, oxygen and hydrogen exposure, condensation of water vapor, and corrosive gases in the surrounding atmosphere such as chlorine, ammonia, sulfur oxides, and hydrogen oxides.
Once you analyze the environmental conditions that cause it and identify the resulting form of corrosion, you can choose the correct metal alloy.
The most effective metal alloys for corrosive environments will always be the ones with high anti-corrosive properties.
There are four main types of corrosive-resistant metals: stainless steel, aluminum alloys, nickel alloys, and red metals.
A short description of each is given below.
Stainless steel has outstanding resistance to all forms of corrosion due to its high nickel and chromium content.
Its chromium content is directly responsible for the formation of an anti-corrosive protective layer (chromium oxide) on its surface when it is exposed to oxygen.
These alloys are known for their natural anti-corrosion properties.
When aluminum is exposed to very strong acids and alkaline environments (pH range: 4-9), a process called self-passivation occurs. This means that aluminum oxide naturally forms to protect the surface from corrosion.
Since aluminum is lighter and more inexpensive than stainless steel, it is highly prized by industries that need lightweight, strong, and cheap material to build its applications and products.
Some examples of such industries include aerospace and the production of food and beverages.
As the name suggests, nickel-based alloys are primarily composed of nickel. However, they also include other alloying elements that help add to their corrosive-resistant nature.
Nickel naturally forms a passive surface film that helps reduce corrosion rates.
Even though nickel-based alloys contain nickel’s natural and spontaneous anti-corrosion film, they are still susceptible to localized forms of corrosion like crevice corrosion and pitting.
To prevent this, elements like iron, chromium, and molybdenum are added to protect against these forms of corrosion.
When we talk about red metals, we talk about copper, brass, and bronze.
All three forms of red metals have excellent corrosion-resistant properties.
Copper has a naturally-formed protective film that forms on its surface, which nullifies corrosion in underground surfaces.
Brass is made up of copper plus zinc, which not only enhances its anti-corrosive properties but also adds other beneficial properties such as strength, malleability, and a high melting point.
Bronze is made up of copper and tin, giving it excellent anti-corrosive properties, as well as good strength and resistance to fatigue.
Applications made from red metals can last up to 100 years even when operating in highly-corrosive environments.
Corrosion resistance can be further enhanced by incorporating additional preventative coatings and layers to the metals chosen.
These additional coatings and methods will be the topic of the remaining sections.
Most metal manufacturers will provide a variety of protective coatings to enhance the corrosion protection of your metal alloy.
The main aim of metal protective coatings is to create a barrier between metal surfaces and the corrosive effects of air and moisture.
There are different kinds of protective coatings that are available to businesses seeking metal parts for their applications.
These include:
A brief description of each is given below.
Powder coatings contain an electrical charge that helps mitigate the process of corrosion on metal surfaces.
The powder is first painted (sprayed) on and then baked to secure the adhesion.
There are many advantages to using powder coating as a protective coating.
They include:
Powder coatings are often used for applications within the automotive, construction, architectural, farming, and manufacturing industries.
An epoxy coating is a mixture of epoxy resin and a polyamine hardener.
When these two elements are mixed, a chemical reaction is produced that links them together, producing a metal surface that is durable and contains its original mechanical properties.
The advantages of using epoxy coatings include:
Epoxy coatings are widely used for applications in the construction, energy, manufacturing, farming, and oil and gas industries.
This is a process whereby steel is coated with zinc for the primary purpose of increasing corrosion resistance.
This process utilizes zinc to increase steel’s corrosion resistance levels.
Hot-dip galvanizing creates a thick and durable anti-corrosive surface on stainless steel.
This process is especially beneficial where galvanizing corrosion occurs frequently. This is largely in environments where salt water, humidity, and industrial pollution are the norm.
The advantages of using the hot-dip galvanizing process are as follows:
Galvanized steel is used in many applications in the manufacturing, marine, solar, farming, water treatment, and oil and gas industries.
Paints, or more specifically, anti-corrosive paints, can be used to increase corrosion protection of metal alloys.
Anti-corrosive paints are a combination of paint and corrosion-resistant elemental pigments like zinc (chromate, oxide, and dust) and lead (red).
Anti-corrosive paints can be used on all forms of metallic surfaces, as well as on ferrous metals. They offer extra-corrosion protection against moisture, oxidation, salt spray, and harsh weather conditions.
Some added benefits of using paints to protect metal alloys include:
Anti-corrosive paint coatings are mostly used for applications in the construction, housing, and architectural industries.
In general, protective metal coatings provide long-lasting protection against corrosion damage.
However, the coating used should fit the specific environment the application will have to work in to get the maximum anti-corrosion benefits.
Sacrificial coatings corrode quicker than the metal they are applied to, thus “sacrificing” themselves for the sake of the metal surface they are protecting.
Let’s take a look at how the process works.
A sacrificial coating is a thin layer of metal that has a lower electrode potential than the metal surface it covers and thus it absorbs corrosion first, before it has a chance to reach the underlying surface.
These coatings are applied directly to metal to steer the corrosive process away from the areas on the metal surface that are most susceptible to corrosion.
In other words, they are put on the areas on the surface they are meant to protect to deter corrosion.
While sacrificial coatings can help reduce corrosion of all forms, they are especially resistant to chemically corrosive substances like sulfuric acid, hydrogen peroxide, and glycolic acid.
Sacrificial coatings are made up of the following substances:
All of the above substances are relatively cheap. Also, they are often combined with aluminum and zinc to give an added layer of protection to the metal substrate.
There are many benefits to using sacrificial coatings to protect metal surfaces, aside from corrosion prevention.
Some of these include an invisible finish (metal surface appears the same after application), application that’s easy and quick, as well as low cost.
Since these are water-based substances, they are also environmentally friendly.
Sacrificial coatings are quite popular in the marine, industrial, heating, and oil and gas industries.
A list of applications that utilize this form of anti-corrosive coating are listed below:
While sacrificial coatings are relatively inexpensive to produce and can be quickly applied on metal surfaces, they do require periodic inspections and replacements. Therefore, there are minor maintenance costs that may appear over time.
This method of corrosion protection utilizes other metals to cover weak areas across a substrate.
During the metal plating process, either zinc, gold, silver, chrome, nickel, copper, tin, rhodium, or chromium is deposited over a base metal to prevent corrosion and improve the look of the material.
The process itself consists of three steps.
The first is cleaning and preparing the metal, which encompasses the following:
What follows is the metal-plating procedure:
We will examine the four types of metal plating in the following section.
Finally, there is the finishing treatment:
A description of the four methods of metal plating is given below.
Let’s take a closer look at each type of metal plating.
In the process of electroplating (a.k.a., electrodeposition), other metals are deposited into the substrate of the base metal using an electrical current.
Electroplating’s main purpose is to enhance the corrosion protection, wear and tear strength, thickness, and aesthetic appeal of metal surfaces.
The electroplating process requires four primary components: anodes and cathodes, the solution in which the electroplating process occurs and the electrical current that triggers it.
Anodes, or positively charged electrodes, form the metal plating, while their opposites: cathodes, or negatively charged electrodes, are located on the substrate (the surface area that requires plating).
The electrodeposition itself occurs in the electrolytic solution consisting of metal salt, into which a power source introduces an electrical current.
Although this process may sound advanced, it is in fact very old, dating back to the late 17th and early 18th centuries. Therefore, it is a tried and tested way of protecting metal surfaces from corrosion and other forms of damage.
Unlike electroplating, electroless plating does not use electricity to convert and deposit metal ions into substrates.
Electroplating utilizes aqueous solutions to produce a negative charge on metal surfaces.
During this process, a reducing agent releases hydrogen into the substrate. When oxidized, it creates a negative charge on the surface of the metal, forming a protective plate on top of it.
One of the main features of this method is the consistent dispersion of metal ions on the substrate. This consistent and even dispersion helps cover hard-to-reach places like edges, cracks, and holes.
Some of the other advantages of using electroless plating include:
Electroless plating is used for many consumer goods because of its ability to produce thick and durable surfaces that have an attractive finish.
During the mechanical plating process, a coating of metal particles is applied to a metal surface through cold welding.
Mechanical plating is perhaps the most popular among all the protective coating methods since it can be used to coat wider and thicker surfaces.
The coating that is used in this process is a mixture of metal powder, water, media, additives, and one or all of the following materials:
There are five steps to this process.
First, components are placed in a tumbling barrel that contains catalysts or reagents.
Then, the metal surface in the barrel is hosed down and cleaned, and metallic powder is added to the barrel to form the coating.
The metallic powder that forms the coating is mixed in the barrel, and additional lubricants are added, if needed.
Mechanical plating offers a variety of advantages for many applications and components:
The most common metal parts to utilize mechanical coating are nails, nuts, screws, washers, springs, clips, stampings, and sintered iron components.
Hot dipping (or hot-dip galvanizing) can be used to coat and protect steel, iron, and other ferrous metals from corrosion.
The process of hot dipping involves passing metals through molten zinc at a temperature of 460°C (860°F).
While passing the metal substrate through molten zinc, a protective layer of zinc carbonate is formed over the surface, which protects it from all forms of corrosion and damage due to stress.
The major advantage of using the hot dipping method is the ability to coat metal surfaces in large batches at a very affordable price.
Other advantages include:
The hot-dipping method can be used for applications that require the corrosion-resistant properties of stainless steel without the added costs or the increased life cycle.
The methods of metal coating described above will increase resistance to corrosion, rust, and wear and tear on most metal surfaces, including stainless steel and iron.
Like the other forms of plating and coatings, corrosion inhibitors also form barriers on metal surfaces to protect them from corrosion.
Such inhibitors consist of chemical compounds like aluminum oxide, copper carbonate, titanium oxide, and metallic chrome (chromium oxide).
The inhibitors form a thin layer of oxygen above the base metal surface, protecting it from corrosion.
The oxygen that forms on aluminum, copper, titanium, and metallic chrome mixes with metal to form metal oxide.
There are four kinds of corrosion inhibitors; a description of each type is given below.
Anodic inhibitors create anti-corrosive layers on metal surfaces by forcing anodic reactions within metal cells.
Anodic inhibitors can alter anodic reactions and thus form protective layers by blocking strong anode sites in metallic cells (electromechanical cells), forcing an outer protective coating to form.
Some examples of anodic inhibitors are:
The only problem with using anodic inhibitors is that, in low doses, they can cause corrosive damage instead of preventing it.
Cathodic compounds form a passivation layer that inhibits corrosion from coming into contact with metal surfaces.
When they come into contact with corrosive liquids and gasses, cathodic inhibitors slow down their corrosive power (rate of corrosion).
There are three types of cathodic inhibitors:
In short, cathodic inhibitors work by slowing down the cathodic reactions limiting the spread of corrosive compounds on metal surfaces.
These inhibitors are compounds that slow down and diminish anodic and cathodic reactions by forming a protective film on metal surfaces.
Phosphates and silicates are the most popular mixed inhibitors used on metal surfaces.
Mixed inhibitors are mostly used to prevent the formation of rust on metal that comes into contact with water. Because of this, they are often mixed with water softeners.
Silicate and phosphate inhibitors are ideal protective coatings for water pipes situated in water distribution systems.
An added benefit of using mixed inhibitors is that they are harmless to the human body. Therefore, they can be safely used to protect the public water supply from contaminants due to corrosion.
Volatile corrosion inhibitors are chemical substances that reduce corrosion and rust by aligning themselves on the surface of metals forming a protective barrier that passivates the surface’s electrical charge.
The formation of VCI barriers prevents corrosion cells from attaching themselves to metal substrates.
VCIs come in many forms, including coatings, oils, and cleaners, and can provide corrosion protection for a variety of metal applications, including ferrous and non-ferrous material.
One of the major benefits of using VCI coatings is that they can reach inaccessible places on metallic surfaces.
These coatings all have corrosion-preventative and reduction properties.
The one you choose will depend on the type of system and application that you are going to use and the environment it will be used in.
The result of corrosion on metal surfaces is material deterioration which produces many safety hazards and a loss of money and time.
To prevent such waste and mitigate dangerous occurrences from happening, specific corrosion prevention methods can be employed.
The purpose of this article was to provide you with the most effective methods of corrosion prevention and reduction for your metal applications and systems.
By implementing these methods, you can help create a safe working environment, promote safety and health to end-users.
As a result, you will save on both money and time, since the longevity of your metal parts will increase, whereas the replacement and maintenance costs will go down.
Contact Bunty LLC
We can help you select the material with the most suitable anti-corrosion properties for your specific application and environment. Contact us via the convenient website form or submit a request for quote directly.
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