How To Protect Structural Beams From Corrosion

It's ironic: Steel needs protection.

It first appeared in Asia the third century BC. And it's been preferred for building, machinery and equipment applications ever since.

That isn't surprising. Steel is light, strong, versatile, durable and safe for the environment. That makes it an ideal material for structural beams.

But for all their strength and value, steel structural beams are subject to corrosion. Rust, caused by exposure to water and oxygen, is the best-known risk factor.

But there are other factors that may be less well-understood.

For example, airborne pollutants like sulfur dioxide can speed up the corrosion process. They come from marine environments or industrial sources like refineries and deicing operations.

Solid airborne particles actually absorb moisture from the air. That ability can make them the source of local damage, like pitting.

An electrical current between a corroded and a protected metal can also cause corrosion.

And a structure's design can be a contributing factor.

For example, stressed steel or other metals are more subject to corrosion. So are freshly cut steel and steel brought into contact with another metal.

Structures with lots of small or dissimilar pieces tend to be harder to protect than structures with big, flat surfaces.

But properly coating your exposed steel can stop corrosion in its tracks. Here's how to do it.

Coating Alternatives

There are several ways to prevent or stop corrosion in structural beams. The best choices depend partly on the source of the corrosion.

For example, to prevent corrosion caused by an electrical current, apply an equally strong current flowing in the opposite direction.

This kind of solution is applied to pipelines and buried equipment. It requires careful engineering in order not to promote more corrosion.

Sacrificial metals can also prevent or stop corrosion. Hot dip galvanizing is a good example. Here, cleaned steel is dipped in a chemical that promotes good contact between the steel and the coating. It's then dipped into a vat of molten zinc.

The galvanized steel is completely covered with a coating of zinc, which protects the steel.

Primers and coatings also can create a barrier between steel and corrosives like moisture and pollutants.

Surface Preparation is All-Important

Remember that water soluble particles can cause fast deterioration. That means surfaces must be free of dirt, dust and all pollutants before applying the coating.

Obviously, that's hard to do properly in a construction environment.

Ideally, coatings are applied before beams are shipped to the construction site. This is usually done in heated, enclosed workshops. More coating material can be applied later if necessary.

Picking the Structural Beams Protection System

The best system for your structural beams application depends on several factors:

Desired Durability

One way to rate the durability of a protective coating is "life to first maintenance." That is, how long the coating will last before touch-up or additional coating becomes necessary.

For the greatest durability - the longest life to first maintenance - you'd start with hot-dip galvanized structural beams or beams that have received a thermal metal spray.

In either case, the beams would then get a sealing coat of paint.

Hgh performance paint systems will deliver a medium to long life.

Paint systems based on drying oils are appropriate for short life in tough environments. And they're suitable for long to medium life applications in unpolluted exterior environments.

If the original finish is intact, a thicker coating can also extend durability.

Finally, one or two coats may be enough for steel that's been blast-cleaned to a high standard.

Other Factors to Consider

Appearance - In industrial settings, this may be relatively unimportant. In other applications, you may want paint that retains its color or its glossiness.

Price - Consider not only the quality of the paint but the implications for maintenance. A lower quality coating may cost less but need more frequent or extensive touch-ups.

Environment - Regulations vary depending on location. And federal regulations may be changing. Research local and applicable federal regulations to ensure that your coating complies.

For More Help

Choosing and applying protection to structural beams can be a complicated process. It's also important to ensure the longest possible life for your project.

When you need expert help for coating needs, contact us.

1 Response

  1. need to coat previously painted, now rusted i-beams supporting a bridge deck over a borrk. What products and procedured do you recommend?
    Harry S

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