Protecting Infrastructure – What’s the Difference Between Coatings and Linings?
Per the Association for Materials Protection and Performance (AMPP; formerly National Association of Corrosion Engineers or NACE) definition, a coating is a pigmented material that protects the surface to which they are applied from the effects of the environment. The thickness of the coating can vary depending on the type and condition of the substrate and the service environment. Some 100% solids epoxies and polyurethanes can be applied up to 0.300 inches (< 300 mils) in thickness that develops an adhesive bond with the surface of the material to be protected. The term coatings is generally used for protective materials on a valve, pipe, tank, or sheet pile exterior. The term lining is usually used to describe the protective materials on the interior surfaces of a valve, pipe, tank, or concrete structure. Now that we know the technical difference between the two let’s talk more about the subtle nuances between the two and what is typically seen in real-world applications.
Protective coatings and linings are regularly discussed in the corrosion, water, and wastewater industries. Often, coatings and linings offer the first line of defense against a corrosive environment's harmful effects on infrastructure. We previously described the typical harsh operating environments in which infrastructure, such as pipelines, tanks, vessels, and structures, must be able to survive in this article.
Coatings
Coatings are films applied to the exterior surface of the infrastructure to protect from corrosion, abrasion, and other types of external damage. Coatings are typically composed of paint or polymer resins and applied using brushes, rollers, or spray guns. Coatings can be applied to various substrates and often provide a protective barrier against different conditions, including weather, physical impact, chemical spills, and UV damage.
Paint coating applied to the exterior of a welded steel water tank.
The thickness of a coating can vary depending on the substrate's specific requirements and the coating type being used. Typically coatings are designed to be as low as two mils (0.002 inches) for a primer to 300 mils (0.300 inches) thick for newer 100% solids products. The exact thickness depends on factors such as the substrate being coated, service environment, operating conditions, and required protection level.
Generally speaking, thicker coatings are applied to deteriorated concrete and can be challenging to apply because it requires specialized equipment and training. Thinner coatings may be easier to apply but may not offer the same level of protection. The appropriate thickness for a given application will depend on the project’s specific requirements.
Linings
Linings applied to the interior surface of the water and wastewater infrastructure, such as inside a pipe or walls of a wet well structure, can be field applied or cast in place with the concrete. Linings help prevent substrate corrosion and improve the infrastructure's durability and longevity. Linings are usually made of ceramics, PVC, HDPE, polymers, glass, or even special mortars and are applied using a spray, trowel, or casting method. Linings are likely to be constantly exposed to a highly corrosive or harsh chemical environment; therefore, ensuring the lining is impermeable to the operating environment is crucial.
The thickness of a lining can vary depending on the specific project requirements and the type of lining being used. Similar to protective coatings, the exact thickness of a liner depends on factors such as the material being lined, operating conditions, and the level of protection required. For example, linings for chemical storage tanks may be several mils thick to provide a high level of protection against corrosive chemicals. In contrast, linings for pipe interiors may only be a few mils thick to provide adequate protection. The type of coating and linings being specified will also depend on the capabilities of the applicator, such as a pipe manufacturer or field coating crew.
PVC liner applied to interior of pipe.
It’s important to note that the thickness of the coating or lining is just one factor in its overall performance. Other factors, such as the material composition, surface preparation, and application method, can also play a role in the durability and performance of the protective coating or lining over time. Stay tuned for follow-up articles discussing the importance of adequately written coating or lining specifications, surface preparation, and application methods.
At V&A, infrastructure preservation is at the core of our mission. Coatings and linings offer the first line of defense in extending and preserving infrastructure service life. Our coatings experts assist water and wastewater clients nationwide select the proper coating or lining system to mitigate damage caused by corrosive environments. We welcome your coatings and lining questions in the comment section below.
Learn more about our Coatings Services here.
And as always, feel free to contact our engineers for more information.