This case study on corrosion provides lessons learned from the Smithfield Beef Group Food Processing Company.
The food processing industry is one of the largest manufacturing industries in the United States, accounting for approximately 14 percent of the total U.S. manufacturing output.
As you walk through a typical food processing plant, you can see equipment of varying ages, constructed of a myriad of materials, including carbon steel, aluminum, stainless steel and plastics. Corrosion – an attack on a material due to a chemical or electrochemical reaction with a surrounding medium – can be an enemy of many of those materials.
Typical food processing plant maintenance departments must constantly battle the effects of corrosion on metals in the plant, especially because of the necessary food quality requirements. These food quality requirements lead most plants to select stainless steel as a material of choice. Assuming that the stainless steel consumption and cost in this industry is entirely attributed to corrosion, a total annual direct cost of corrosion is estimated at $2.1 billion.
Battling corrosion should start up front with proper material selection for the plant. However, a course in corrosion often is not part of standard electrical educational programs. Therefore, an additional course like the one offered by Corrosion College can improve any electrical maintenance department knowledge of corrosion and methods to prevent it.
Corrosion College : A unique, hands-on opportunity
Offered monthly in Gilmer, Texas, Corrosion College provides the following unique features and benefits:
Additionally, Corrosion College grants 1.5 CEUs to participants for participation and successful completion. CEUs are available from either Kilgore College or Purdue University.
Metal material lessons highlighted
Corrosion College includes valuable instruction on metals and their resistance to corrosion. Metals with high potential energy are called active and corrode more easily. Some metals, like gold and silver, can be found in nature in their pure metallic form. They require little added energy to change them into a useable form. As a result, the balance of energy is relatively stable and these metals corrode very slowly. Metals with low potential energy are called passive.
Metals can be ranked by their relative energy potentials. This can be thought of as a listing by the amount of energy that is required to convert them from their natural state to a metallic useable form. This listing is called the Electromotive Force Series, or EMF, for short.
Metals such as aluminum, iron, steel, chromium and titanium form a thin oxide film under oxidizing conditions. This oxidizing film increases the resistance of the metal to corrosion. The basic resistance of stainless steel occurs because of its ability to form a protective coating on the metal surface. This coating is a "passive" film, which resists further oxidation, or rusting. The formation of this film is instantaneous in an oxidizing atmosphere such as air, water or other fluids that contain oxygen. Once the layer has formed, we say that the metal has become "passivated" and the oxidation or rusting rate will slow down to less than 0.002 inches (0.05 millimeters) per year.
Unlike aluminum or silver, this passive film is invisible in stainless steel. It's created when oxygen combines with the chrome in the stainless to form chrome oxide that is more commonly called "ceramic". This protective oxide or ceramic coating is common to most corrosion resistant materials.
Methodology for prevention of corrosion
A step to economically enhance corrosion resistance and prevent corrosion is the selection and use of a corrosion-resistant coating material. Steel is so widely used that some form of coating protection must be used in order to increase the life expectancy of steel structures, piping or conduit. Because the anode, cathode and metallic path are quite often on the same piece of material, isolating the material from an electrolyte is the easiest method of prevention.
Metallic coatings provide a layer that changes the surface properties of the piece to those of the metal being applied. The piece becomes a composite material exhibiting properties generally not achievable by either material if used alone. The coatings provide a durable, corrosion-resistant layer, and the core material provides the load bearing capability. The most widely used metallic coating method for corrosion protection is galvanizing, which involves the application of metallic zinc to carbon steel for corrosion control purposes. Hot-dip galvanizing is the most common process, and as the name implies, it consists of dipping the steel member into a bath of molten zinc.
In applications where more severe or heavy corrosion conditions exist, the galvanized steel is often coated with paint or other polymer coatings such as PVC for additional corrosion protection. Robroy polyvinyl-chloride (PVC) externally coated rigid steel conduit has been successfully used to protect sensitive wire and cable systems in extremely corrosive environments for several decades. However, Corrosion College helped to inform our department that proper surface preparation such as the two-part proprietary system used by the Robroy Conduit Division and a rigorous quality assurance program are necessary to achieve reliable coating protection.
When coating adhesion fails due to improper surface preparation, the underlying zinc becomes the primary corrosion protection. In this case, only the galvanized coating protects the rigid steel conduit; the PVC or polyurethane coating is no longer an effective corrosion protection. In the case of adhesion failure, the galvanized zinc coating will probably have a shorter service life than plain galvanized rigid steel conduit.
If you have the opportunity to select anti-corrosion material, ensure you have investigated the material and coating as the most appropriate for the expected type of environment. In other words, do not use aluminum if mineral acids are going to be used; do not use stainless steels within a salt environment.
Immediate results at Smithfield Beef Group-Plainwell
The knowledge gained at the college was transferred immediately into the Smithfield Beef Group’s Plainwell plant. Prior to the Corrosion College course, the electrical maintenance department often painted some of the metal housings on its lighting system to prevent corrosion. However, it seemed to be only a short-term solution because within a relatively short time, the units needed to be replaced and the peeling coatings were a source of food contamination on the production line. Now the department knows that another selection of metal material and coating for the lighting system could save the company hundreds of thousands of dollars.
Confronting another corrosion issue with a section of conduit within the plant was also made quicker. This section of conduit had become corroded and wires were now exposed. With the lesson learned at the college, we understood that two different metals having contact with each other caused the corrosion. The two metals are now properly protected so corrosion and the chance of having exposed electrical wires again are now reduced significantly.
The Corrosion College education significantly helped the electrical maintenance department at Smithfield Beef Group-Plainwell to switch from a short-term to a long-term view of corrosion. The long-term view is one that will offer our plant a significant reduction in the amount of material and labor costs in the plant.
About the Smithfield Beef Group Food Processing Company
Based in Green Bay, Wis., Smithfield Beef Group is the nation's fifth-largest beef processor, with an 8,000-head-per-day harvest. The company was established in 2001 after Smithfield Foods acquired and then merged Moyer Packing Company (acquired June 2001) and Packerland Packing Company (acquired October 2001).
For more information on Corrosion College or coated conduit, check out these Web sites: