Everybody is familiar with the results of the corrosion on metals which are observable as red-brown or green-blue rust (iron oxide). The actual process of corrosion is less noticeable and research still conducted today for better understanding of the mechanisms and how to control it. Although corrosion engineers faced with a difficult challenge, there are several tools that can be implemented in the corrosion control designs, including:
- Design of Structure
- Corrosion Inhibitors
- Material Selection
- Cathodic Protection
- Alteration of the Environment
- Protective Coatings
Design of Structure
How a structure is designed can influence its resistance to corrosion. Generally speaking, corrosion control designs:
- Eliminate possible entrapment of water, chemical salts and other matter that could promote corrosion “hot spots”. Hot spots are areas particularly conducive to accelerated corrosion, and are often referred to as “critical areas”.
- Eliminate complex shapes like back to back angles and orientation of members that could serve as “traps”
- Provide access for maintenance activities allowing operators to implement corrosion control systems
- Eliminate sharp edges, crevices, and other difficult-to-protect elements
A corrosion inhibitor is a substance that, when added to an environment, decreases the rate of corrosion. Corrosion inhibitors are typically added in small amounts to the electrolyte, most commonly in closed systems such as piping. They can also be used in the form of vapor phase inhibitors and migrating corrosion inhibitors.
There are alternatives to construction materials that may not corrode as fast as steel. Choosing a corrosion resistant material may be required in certain applications on the structure to be protected.
Cathodic protection as corrosion control measure uses sacrificial anodes made of more active metals such as aluminum, zinc, or magnesium. When connected to the steel structure being protected, these anodes then corrode, in preference to the steel structure. When the anode is completely depleted, it must be replaced. An alternate form of cathodic protection is an impressed current which provides an external current to offset the current of the corrosion cell.
Alteration of the Environment
The environment can be modified to make it less corrosive. This primarily means dehumidification. While this is common practice for interior applications, or in temporarily installed containment, it does not play a major role in on-going corrosion control.
Protective coatings represent the most common and extensively used corrosion control system for industrial structures. The mechanism for protection varies depending on the particular material used. The chosen mechanism can isolate the substrate being protected from the environment (the electrolyte). This is generally known as barrier protection. The protection afforded by protective coatings can be greatly influenced by:
- Defects in the protective coating film (discontinuities, misses, holidays)
- The type of protective coating system
- Protective coating system thickness
- The nature of the electrolyte
- Presence of mill and other scales
Working with a coatings professional you can identify the specific corrosion control needs of your infrastructure and select the appropriate coatings that will best serve your business.
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