Typical Causes of Corrosion on Structural Steel and 5 Steps for Prevention

Published November 25, 2015 by Whirlwind Team

structural steel corrosion

Structural steel is incredibly durable and will last several lifetimes. That statement is true, but there are some caveats that should be added to increase its accuracy.

Structural steel is incredibly durable and will last several lifetimes if, and only if, there are certain protective features and practices put into place. Steel is certainly durable in its own right, but it is also highly susceptible to moisture damage. Once a little rust settles in, the corrosion that ensues can be extremely costly to repair and, in worst case scenarios, it can become a serious safety hazard to the building's occupants and neighbors.

For this reason, it's important that building owners, architects and builders take proper precautions to prevent rust and corrosion. The good news is that protecting metal building components is a very simple and straightforward process. 

There are several different types of corrosion that can occur on steel and metal building components.

Basic corrosion

The process of basic corrosion is part chemical and part electrical. It requires a combination of moisture and oxygen. Once those two elements - both of which are a constant presence throughout any building's life cycle - come together, and in contact with steel, a multi-stage process begins:

  1. First, the iron (Fe) atoms that comprise steel lose some electrons and become positively charged. Positively charged ions attract negatively charged ions.
  2. Second, water (H2O) and oxygen (O), mix together and become even more negatively charged, thus attracting themselves to the positively-charged iron atoms mentioned above. The result is a chemical called iron hydroxide (4Fe(OH)2).
  3. Iron hydroxide continues to react with oxygen, yielding 2Fe2O3.H2O - also known as hydrated iron oxide OR brown rust.

As long as there is no barrier between the iron and the water/oxygen molecules - and as long as the electrochemical reaction is allowed (via poor design, materials selection and/or neglect) to take place, the steel will continue to react until all that is left is a pile of brown rust and the rest of the building rubble all around it.

Bimetallic Corrosion

A second type of corrosion that affects steel members is called bimetallic corrosion. This type of erosion occurs when a chemical reaction is caused by two metals coming in contact - or close contact - with one another. This type of corrosion is more common in metal alloys and is quite complex as there are multiple variations, but it is partly dependent upon any two metals' respective positions in the galvanic series.

Bimetallic corrosion occurs most frequently in steel structures that are submerged or buried, but working with a reputable metal building supplier will ensure you building is designed with respect to any potential bimetallic corrosion, using proper precautions where necessary.

Environmental Corrosion

Certain environmental pollutants, toxins and compounds can exacerbate either one of the above forms of corrosion, which is why your building's location plays a key roles in the types of materials and protective coatings that are used. Buildings most susceptible to environmental corrosion are those in an industrial or manufacturing areas where off-gassing and toxic emissions are higher than normal, as well as buildings located in coastal environments, exposed to higher levels of salinity.

Thus, the typical causes of corrosion on structural steel members include:

  • Uncoated steel.
  • Steel that has not been coated with respect to the particular environment.
  • Steel that has not been properly maintained.
  • Lack of a vapor barrier and/or adequate insulation inside the building.
  • Unaddressed maintenance issues such as leaky roofs, plumbing leaks, standing water, etc., that lead to chronic exposure to moisture.
  • Incorrect design/construction of the building foundation.

While the corrosion process is relatively complex, the solutions are not.

Prevent Corrosion in Your Steel Building with Five Steps

The following outlines five very simple and straightforward ways to prevent corrosion that can lead to long-term building damage.

  1. Work with a reputable metal building supplier. This is, by far, the single most important step you can take to design and construct a building with corrosion-proof structural steel. The supplier will work closely with you during the building's design, keeping in mind your location, potential environmental threats, climatic risks and your local building code. They can also make suggestions and recommendations based on their years of experience supplying buildings for locations and applications just like yours.

    Plus, they are experts regarding metal corrosion and can easily spot areas in the building design where materials choices would have led to bimetallic or environmental corrosion. You'll also have access to the highest-quality materials and coating options, and will continue to have a frame of reference and assistance throughout the building's lifetime.

  2. Choose the highest-quality materials. The saying, "you get what you pay for," couldn't be more true. This doesn't mean you should go with the highest-price options, but it does mean you should be wary of the lowest-priced versions. The extra money you invest now in high-quality materials, coatings, venting and insulation as well as accessories and features that assist with moisture-prevention will be more than paid for within a decade or two of low maintenance and zero parts repairs and/or replacements.

    Additionally, the higher-quality materials typically come with longer warranties; in the world of metal building design those warranties last as long as 40-years, which provides further protection to both builders and building owners in the event that unexpected corrosion takes place.

  3. Understand five general principals for avoiding corrosion. There are five general design principals used to avoid corrosion in a metal building's design, before coatings, accessories and other structural elements are considered. These are:
     - Avoid entrapped dust and water by choosing angles and finishes that align out and down, rather out and up.
     - Pat attention to column bases, taking advantage of protective features such as sealing plates.
     - Encourage air movement, allowing spaces between layers and room for ventilation.
     - Using "breaks" at junction plates to further prevent the retention of water/dirt.
     - Avoid open crevices.
    You can view building details illustrating these principals at steelconstruction.info.

  4. Hire an experienced metal building contractor. An experienced contractor will understand the above principals and will implement best practices for preventing corrosion throughout all phases of the building process. Additionally, building materials' warranties are more likely to hold up when a licensed metal building contractor performs the construction and/or any repairs or replacements later on.

  5. Observe moisture protection practices at every step. Materials selection and coatings are of primary importance, but moisture-prevention is a close second. There is a long list of items that enhance moisture-control in metal buildings, including things like:
     - Water-shedding  or water-proof roofing materials
     - Adequate ventilation
     - Vapor barriers
     - Insulation
     - Gutters and downspouts
     - Awnings, eves and overhangs
    Each of these items works to either move water away from the building, or to prevent moisture build-up that leads to condensation and then chronic moisture exposure.

While corrosion may be a complex process, preventing it is not. Perform due diligence during the design phase, and then implement corrosion prevention materials and techniques throughout each phase of the building's construction. By doing so, you will benefit from a corrosion-free building that lasts for decades and even centuries.

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