Exploring the Myths
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.
Prevention of corrosion
Education is the first step to preventing corrosion. Once engineers are aware of the prevalence of corrosion in their business, they can take steps to select the best anti-corrosion products and apply them in the most effective ways. Engineers must define the mechanisms of corrosion in the environment and then do their homework to select the correct material for the application.
To begin, the material of choice must be given equal consideration as the design itself. Choosing the wrong material can result in frustrating or even dangerous situations. Defining the corrosive agents and determining the concentration can be a complex process. Usually several corrosive elements are present and interactions are not always well documented. Water is the most common corrosive element and usually presents itself in one form or another, such as humidity. Adjacent processing operations or other intermittent activities such as industrial cleaning and the general plant environment may expose the product to a variety of corrosive agents and temperatures. Each environment is unique and all possible corrosive agents should be identified for the intended application.
Aluminum, for example, should not be used in high-mineral acid environments. Stainless steels also should be avoided when there halogens such as fluorine, chlorine, bromine, and iodine are present. Should the decision be made to use one material over another without in-depth investigation, the user may be looking at a very short life span for his or her most vital electrical systems. Next, the engineer must take into account some of the compliance issues and standards for the project.
Understand policies, regulations, standards, and management practices to increase corrosion savings through sound corrosion management. Below are some of the most relevant polices, regulations, and standards for the electrical industry.
UL: The UL mark is one of the most recognized symbols of safety in the world. UL is an architect of U.S. and Canadian safety systems. UL tests more than 19,000 types of products, and 21 billion UL marks appear in the marketplace each year.
ASTM International: ASTM International is one of the largest voluntary standards development organizations in the world—a trusted source for technical standards for materials, products, systems, and services.
National Electrical Manufacturers Association (NEMA): It is NEMA’s belief that standards play a vital part in the design, production, and distribution of products destined for both national and international commerce.
National Electrical Contractors Association (NECA): The NECA Codes and Standards Committee are involved with development, administration, and enforcement of installation codes, safety standards, product standards, and other related industry regulations. This includes, but is not limited to, the National Electrical Code (NEC), National Electrical Installation Standards (NEIS), National Electrical Safety Code (NESC), various NFPA standards, UL safety standards, and OSHA regulations.
Many products meet some or all of these standards; however, this does not guarantee that the product will perform as promised. There is a new need for independent product performance verification as distinguished from verification of product safety compliance.
So how do you differentiate between similar certified products?
Start by using empirical data to compare product longevity and accurately assess factors related to the risk of product failure from companies like Intertek. Intertek is the world's largest independent testing, inspection, and certification organization, that provides independent testing results. In many cases, ASTM test methods are just that—test methods. Regulated standards like Intertek’s ETL Verified put context around these test methods that establish test criteria and determine a grade of pass or fail based on the results.
When a manufacturer enters a product into a verification program, it must provide an initial qualification sample to Intertek. The sample is then independently tested to the specifications of the appropriate standard. If the sample is found to meet the requirements, an Intertek field representative will visit the manufacturer's location to independently select a final qualification sample for further independent testing. Once the second sample is found to meet performance requirements, the product may be marked by the manufacturer as
“ETL Verified.” The manufacturing facility is then subjected to quarterly audits to ensure ongoing compliance.
Consulting and specifying engineers must understand corrosion and how to improve specification of products to avoid the high cost, and sometimes disastrous effects, of product failure caused by corrosion. As evident from this article, there is a pressing need to look for, appreciate, and accept specification-related third-party verification standards that reach beyond traditional or historic ways of qualifying products intended to help fight the high cost of corrosion damage. Solid empirical product data—that is, documentation of product performance that is independently validated by recognized, objective, third-party sources—should be considered and used to control the cost of corrosion in order to produce long-term cost savings on projects.
Article courtesy of Plant Engineering.