Avoiding corrosion in electrical systems

Properly specifying electrical products for highly corrosive environments will reduce overall long-term cost and risk of failure.

02/17/2014


Figure 1: Corrosion was found on conduit placed underground at a gas station. Courtesy: Robroy IndustriesProduct failure due to corrosion is estimated to cost $1 trillion annually. A key role of consulting and specifying engineers is to help ensure effective specification of products. This responsibility is especially critical when applications are in highly corrosive environments where product failure not only is extremely costly, but also raises the risk of catastrophe and human harm. There is reason to believe that many professionals, although aware of general facts specific to corrosion, do not maintain adequate knowledge of how and why diverse methodologies for corrosion prevention work well in some applications but are ineffective in others. 

The foundation for preventing corrosion damage is continuous education in the causes of corrosion. Understanding product life predictions as well as performance assessment methods is essential for determining which products will truly survive in a corrosive environment. Last, knowing how to follow through with proper specification using third-party product testing results will result in tremendous long-term cost savings.

Short course: Corrosion

A basic knowledge of corrosion is essential for prevention. It starts with a definition of corrosion; this one is from the National Association of Corrosion Engineers (NACE): 

Corrosion is the deterioration of a substance, usually a metal, or its properties, because of an undesirable reaction with its environment. 

Corrosion is a natural and inevitable process that once understood can be mitigated so that preventive measures and controlled outages can take place. 

The next task is to consider the environmental conditions in which the electrical components will be placed. Conditions such as moisture, dust, and temperature can affect the rate of corrosion. 

Moisture: The level of corrosion typically increases with moisture content. Common atmospheric sources of moisture are rain, dew, and condensation. 

Dust: Dust particles can cling to surfaces and retain moisture. Typical sources of dust include soil/sand, smoke, and soot particles or salts. 

Temperature: Increasing the temperature of a corrosive environment will generally increase the rate of corrosion. For every 10 C rise in the temperature, the corrosion rate can double.

Common types of metal corrosion

Knowing common types of corrosion will aid in determining the best methods of prevention. Here are just a few of the types of corrosion that consulting and specifying engineers might face on the job.

  • General corrosion attack is the most common type of corrosion. It is typically caused by a chemical reaction that results in the deterioration of the entire exposed surface of a metal in a uniform manner. Ultimately, the metal deteriorates to the point of failure.
  • Galvanic corrosion occurs between two dissimilar metals. If these metals are placed in contact (or otherwise electrically connected), this potential difference produces electron flow between them, causing corrosion. 
  • Crevice corrosion is a localized corrosion that is associated with a stagnant solution located in material flaws, holes, gasket surfaces, lap joints, surface deposits, and crevices under bolt and rivet heads.
  • Pitting is a form of corrosion caused by a localized attack resulting in holes in the metal.
  • Erosion corrosion results when a protective layer of oxide on a metal surface is dissolved or removed by wind or water, exposing the underlying metal to further corrode and deteriorate.
  • Corrosion fatigue is the mechanical degradation of a material under the joint action of corrosion and cyclic loading or alternating stress.
  • High-temperature corrosion can be caused by compounds that are very corrosive toward metal alloys normally resistant to corrosion, such as stainless steel

Once corrosion is discovered, it must be addressed. However, corrosion is unpredictable, and the most effective way of controlling corrosion is by preventing it. A recent study by the Executive Branch and Government Accountability Office determined that the annual cost of corrosion could be decreased by as much as 40% (or $400 billion) by preventing corrosion instead of treating it as it occurs. 


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