3 Steps To Preventing Corrosion

Corrosion does not play favorites. All unprotected metal surfaces will ultimately succumb to corrosion. Thankfully we can use different types of surface preparation and coatings to reduce or nearly stop corrosion. We recommend adding the below steps to your process.

What Is Corrosion?

Corrosion is defined as, "processes of gradual destruction of the metal structure as a result of its chemical reactions with environmental components or electrochemical processes. In many cases the direction of changes and their speed depends on physical factors (e.g. stresses in elements of the leaded structure, external electric field, radiation) or microbiological." It is a natural process that metals go through as they age. The susceptibility to corrosion is determined by the time over which the structure is used and by variable conditions to which it is exposed.

Basically, materials in nature like to be in their simplest form. For corrosion over steel, this is rust. So, a metal refined into manufactured substrates (for example, structural steel used in buildings) wants to rust.

Add a metal surface, oxygen and moisture together... and you get rust.

To stop the corrosion process, you need to use coatings. Paint acts as a barrier to the moisture and an insulator to keep current in the restricted paths.

Step 1: Know Your Risks

Depending on your substrate and the surrounding conditions, you may be risking one or more types of corrosion. We see several types of corrosion frequently occurring. Knowing your risks will help you make an informed decision on the coating and process that you need.

The first type of corrosion is Pitting. "Pitting corrosion manifests itself in the form of holes on the surface." Pitting forms when chloride ions come in direct contact with the material. Below is picture of corrosion pits on the surface:

Another type is Crevice corrosion. "Crevice corrosion is usually localized in crevices or gaps in the surface or places where local stagnation of condensates may occur and the circulation of electrolytes is hindered." Sudden damage can happen when crevice corrosion goes unchecked. Rivets, welds, joints; contact places between a metal and a non-metal, such as composites and glass rubber are all areas this can appear.

Galvanic corrosion is also a possibility. "This occurs when there is connection of two dissimilar metals in the system." (Check out my recent article about why zinc protects steel. Hint: It provides galvanic protection.)

"Intergranular corrosion occurs along the grain of the material when stresses are applied perpendicularly to the grain boundaries."

"Exfoliation corrosion occurs along the longitudinal grain boundaries in the direction of rolling." When this happens, the metal grain layers can begin to separate.

The worst can happen. Consider the Mianus River Bridge Collapse of 1983. This is a span of Interstate 95 that crosses over the Mianus River in Connecticut. The bridge collapsed, killing three motorists. "The collapse was caused by the failure of two pin and hanger assemblies that held the deck in place on the outer side of the bridge, according to an investigation by the NTSB. Rust formed within the bearing of the pin, exerting force on the hanger which was beyond design limits for the retaining clamps."

Step 2: Know Your Resin

Resin is the portion of your coating that binds all of the paint's ingredients together and makes the paint stick to the substrate. The industrial paint industry is built around four basic resin types. There are modified versions and variants of each. Frequently they are blended together to make hybrid products (consider Axalta's Tufcote 2.8 HG 3100, which is an Acrylic-Alkyd).

Alkyds

• Good exterior durability
• Good gloss retention
• Good adhesion to most surfaces
• Saponification can occur (check out my recent article about how to avoid saponification)

Acrylics

• Better exterior durability
• Easy to apply
• Fast dry with proper air movement & lower humidity
• Will freeze in very cold temperatures (if you are painting in cold temperatures, be sure to check out this guide)

Epoxies

• Excellent corrosion resistance (find out why epoxies have such great adhesion here)
• Excellent adhesion
• Excellent abrasion resistance
• Poor gloss retention

Urethanes

• Exceptional exterior durability
• Low temperature cure (down to 35°F)
• Ultra low VOC options (learn about VOCs here)
• Sensitive to moisture during application & cure

Step 3: Know Your Resources

As a painter and Blend Supply partner, you have a lot of resources available. Are you using the most efficient tools available? Do you take into account the effects of fatigue on yourself and your employees? Think about how much more efficient would your shop be performing if productivity didn't go down 10% every afternoon when your employees get tired. Have you ever tracked your spray gun's transfer efficiency? How efficient is your surface preparation? You should also be aware of cost-saving abrasives like 3M's 775L Cubitron II.

Are the coatings that you are using helping you meet your VOC goals? Are they performing in the sun the way your customers expect? We want to help make that happen.

You also have local Blend Supply Representatives available to help you with your specific application. If you are not sure who your representative is, please give us a call at (800) 647-9279.

Here are a few of your favorite Blend Reps at a training in December:

Sources

Czaban, Magdalena. “Aircraft Corrosion – Review of Corrosion Processes and Its Effects in Selected Cases.” Fatigue of Aircraft Structures, vol. 2018, no. 10, 2018, pp. 5–20., doi:10.2478/fas-2018-0001.