Corrosion presents manufacturing industries with extraordinary challenges when dealing with metallic alloys. From oil and gas processing to transportation infrastructure and beyond, corrosion can significantly impact metal structure longevity, performance, cosmetics and even safety. An extremely effective way of combating corrosion is to use a Zinc Rich Coating System which we'll discuss in depth in this latest article on Industrial Coatings.
Corrosion results from the deterioration of material when it reacts with its surrounding environment. While corrosion can happen with any type of material, it's most common with metallic alloys. Typically, corrosion is caused by reactions between moisture, hydrogen, electrical currrents, bacteria and even stress can induce corrosion when steel cracks under pressure.
One type of corrosion most are familiar with is rust, a specific type of corrosion that occurs from moisture and air oxidizing with one another. Often the first signs of rust appear as small specs on the surface yet they are actually tiny pits which grow from condinued oxidation.
Zinc coatings are crucial these reasons and more:
- Protection against corrosion and undercutting resulting from damage when using standard coating systems.
- Prevention of rust through extended exposure or inadequate corrosion resistance.
- Avoidance of crevice corrosion due to poor coverage or the use of standard coating systems.
Zinc coatings provide two levels of corrosion protection when applied directly to a steel surface. Being an electro-positive element, zinc forms a cathodic protective barrier with a low corrosion rate of less than .01 mil per year, offering extended service life. Furthermore, zinc is sacrificial and protects steel from atmospheric conditions that produce corrosion.
Zinc-coated bolts demonstrate the sacrificial properties and superior protection offered by zinc coatings. See below for an example of how zinc coated bolts remain clean of all forms of corrosion even after a decade plus of use in incliment weather:
To get the most out of zinc primer, we recommend following these steps:
The below photo is an example of what not to do! Always properly prepare the metal alloy surface prior to putting on any type of protective coatings.
There are several methods used to apply zinc coatings, each with their own pros and cons as we'll cover below:
Electroplating is a metal finishing process in which a thin layer of metal, such as zinc, is deposited onto the surface of a substrate, typically a metal object, to provide a protective coating or decorative finish. The process involves immersing the object to be coated in a solution called an electrolyte, which contains ions of the metal to be plated. The object acts as the cathode (negative electrode), while a piece of the plating metal serves as the anode (positive electrode).
During the electroplating process, an electric current is applied to the electrolyte solution, which causes the metal ions to be reduced and adhere to the surface of the object being plated. The thickness of the deposited metal layer can be controlled by adjusting the duration and intensity of the electric current.
Electroplating with zinc, also known as zinc plating or zinc electroplating, is commonly used for corrosion protection of steel and iron components. The zinc layer forms a barrier between the substrate and the environment, preventing direct contact with corrosive elements such as moisture, oxygen, and salts. In addition, zinc acts as a sacrificial anode, meaning that it will corrode preferentially to the underlying substrate, thereby further protecting the base metal from corrosion.
Overall, electroplating is a widely-used method for applying zinc coatings to metal substrates, providing corrosion protection and enhancing the appearance of the finished product. However, the process may not be suitable for all applications, and alternative methods such as galvanizing or zinc-rich paint may be more appropriate depending on the specific requirements.
Galvanizing, also known as hot-dip galvanizing, is a process where a steel or iron object is coated with a layer of zinc to protect it from corrosion. The method involves dipping the object into a molten zinc bath, typically at a temperature of around 840°F (450°C). The zinc forms a metallurgical bond with the steel, creating a durable and robust protective coating.
During the galvanizing process, the steel or iron object is first cleaned of any impurities, such as oil, grease, and mill scale, through a series of pre-treatment steps. These may include degreasing, pickling in an acid solution, and fluxing to promote the formation of a clean, reactive surface. The object is then immersed in the molten zinc bath, where the zinc reacts with the steel to form a series of zinc-iron alloy layers. Finally, the object is cooled, either by air or quenching in water, to solidify the zinc coating.
Hot-dip galvanizing is a widely used method for providing long-lasting, effective corrosion protection for steel and iron objects. The process ensures complete coverage and forms a strong bond between the zinc and the substrate. However, the method may not be suitable for all applications due to its limitations in size, shape, and compatibility with certain materials.
Inorganic zinc coatings, also known as inorganic zinc-rich primers or inorganic zinc silicate coatings, are a type of paint-like coating system that provides excellent corrosion protection to steel and iron substrates. The coating consists of zinc particles suspended in a silicate binder, which, when applied and cured, creates a highly adherent and durable protective layer on the metal surface.
The inorganic zinc coating is typically applied using spray equipment, such as airless or conventional air spray systems. The surface of the substrate must be thoroughly cleaned and prepared, usually by abrasive blasting, to ensure proper adhesion of the coating. The inorganic zinc coating can be applied as a single coat or as part of a multi-layer coating system, depending on the desired level of corrosion protection and the specific application requirements.
Inorganic zinc spray coatings offer excellent corrosion protection and durability for steel and iron substrates, particularly in challenging environments or where high-temperature resistance is required. However, the application process can be more complex and demanding compared to other coating methods, requiring careful attention to surface preparation and application conditions.
Organic zinc-rich coatings, also known as organic zinc-rich primers, are a type of corrosion-resistant coating system for steel and iron substrates. These coatings consist of zinc particles dispersed in an organic binder, such as epoxy, polyurethane, or acrylic. When applied and cured, the organic zinc-rich coating forms a protective barrier on the metal surface, providing galvanic protection through the sacrificial action of the zinc particles.
Organic zinc-rich coatings are typically applied using spray equipment, such as conventional air spray or airless spray systems. Proper surface preparation, like abrasive blasting, is essential to ensure good adhesion and performance of the coating. The organic zinc-rich coating can be used as a standalone system or as a primer in a multi-layer coating system, depending on the desired level of corrosion protection and specific application requirements.
Organic zinc-rich spray coatings offer excellent corrosion protection and a smoother finish for steel and iron substrates, making them suitable for a wide range of applications. However, they may have limitations in high-temperature environments and may require careful surface preparation to ensure optimal performance.
The best system depends on factors like equipment cost, part size, EPA restrictions, ease of application, and required service life.
Baril Coatings' zinc products have undergone rigorous testing, meeting high-performance standards. The company has a 50+ year history of providing high-performance zinc products for C1-C5 marine environments, with applications ranging from DOT light poles to oil and gas equipment.
SteelKote® 826 Epoxy Zinc Primer: This high-solids, two-component epoxy zinc primer is designed for OEM manufacturing and commercial vehicles. It offers easy application, good flow, excellent corrosion protection, and long-term durability. When applied, the ready-to-spray VOC is 2.8 lbs. per gallon.
SteelKote® 829 Zinc-Rich Epoxy: This high-solid, two-component, 84% zinc-rich epoxy primer is designed for OEM manufacturers and commercial vehicles. It offers easy application, good flow, and superior corrosion protection against undercutting, and creepage, and has passed 5,000 salt spray resistance. Its mixed VOC is 2.5 lbs. per gallon, and it meets the ASTM D520 classification.
DualCure® 306 Zinc-Rich Urethane: This high-solid, 86% zinc-rich urethane primer is designed for OEM manufacturers and commercial vehicles. It offers easy application, high build, and superior corrosion protection. This product has passed 10,000 salt spray hours, 9A gravelometer, and 5,000 hours of magnesium chloride testing. It also meets the ASTM D520 classification.