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Corrosion Maintenance 101

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  • SIMA
- Posted: April 7, 2017

By George Melchior, ASM

The snow and ice management industry continues to mature, and its growth is no more evident than in the equipment market. More manufacturers are touting high-efficiency low maintenance environmentally friendly products while evangelizing the vision of tomorrow’s perfect snow and ice management fleet.

Although this vision sounds nice, we need to remember that 80% of tomorrow’s fleet is here today, and a focus on service life is critical to keeping that fleet operational. As such, equipment maintenance and specifically the fight against corrosion must be a prominent component of snow and ice management operations.

Numerous studies and articles have been published on maintenance and corrosion prevention for snow and ice equipment, with recommendations like bumper-to-bumper hot wash downs after every use; encapsulating truck chassis with rubber coatings; enclosing systems in stainless steel or composite enclosures; replacing steel with poly-manufactured products; and, my favorite, storing equipment in warm, dry environments. If you’re a large outfit, all of these recommendations may be feasible. But for smaller outfits with limited resources, scarce overhead, and operators who may be chief cook, bottle washer, and everything in between, it may be more difficult.

Chemistry lesson
As with everything, action is precluded with an understanding of how the system works, and corrosion is no different. We’ll start with a quick chemistry lesson. Corrosion is the common word for a chemical process called oxidation. When we talk about oxidation of metals, we are really talking about reduction-oxidation reactions (redox). The reaction involves the transfer of electrons from the oxidizing agent to the reduction agent, which yields oxides (bind to metal; reduce ductility) or hydroxides (expand; flake off, exposing more metal to oxidizing agents) depending on the chemicals involved. The process is irreversible. To that end, there are two important concepts to keep in mind when combating corrosion:

  • Corrosion is diverse.
  • Separation is prevention.

Different types of corrosion impact materials and functions differently. For example, when copper oxidizes, it forms a layer of patina, which spreads evenly across the surface of the copper and bonds to the metal to create a protective layer that prevents further corrosion of the copper underneath. When the structural integrity or performance of the material is important, prevention of section loss, or mass loss, is imperative, and protective corrosion like patina is preferred.

However, when copper is used for wiring, patina would be problematic. Electrical current travels along the surface of copper wiring. So, corrosion on the surface of copper wiring would encumber electrical flow and would also reduce the effective surface area of the wire. Additionally, the corrosion would reduce the copper’s ductility, making it more brittle and more susceptible to facture failure under stress or vibration.

Oxidation (300x169)
Oxidation (rust) of salt conveyor chain and drive assembly. Oxidation is the formation of ferrous oxides on the surface of the metal exposed to oxygen and water.

Know what you’re dealing with
Corrosion maintenance starts with understanding the type of corrosion and its impact on the intended function. When we’re dealing with structural elements, we’re concerned with material section loss. For dynamic components, such as augers or spinners, we’re concerned with section loss, but we’re also concerned with expansion. With components exposed to vibration and other dynamic stress, we’re concerned with hardening and brittle failure.

Section_Loss (178x300)
Material section loss on salt box damper. The presence of chlorides with water and oxygen promotes the formation of hydroxides, which do not bond, causing the surface layer of rust to flake off, which exposes fresh metal for further oxidation. Section loss leads to structural failure under load or vibration.

Most of the materials used in snow and ice removal equipment are metal. Examples include electrical wiring, valve bodies, fluid manifolds, hose clamps, nozzles, augers, spinners, pumps and motors, shafts, blades, vehicle chassis, etc. These metals are exposed to oxidizing agents such as oxygen and water, as well as our common deicers: sodium chloride (NaCl); magnesium chloride (MgCl); and calcium chloride (CaCl).

It’s debatable which salt is more detrimental to which metal. NaCl is more stable than the other two when mixed with water, but releases more chlorides on a per-weight basis. MgCl and CaCl are Lewis Acid Complexes, meaning when they’re mixed with water to form a solution, and they reduce the solution pH from neutral to acidic, it adds another layer of complexity to the redox reaction.

One day we will recognize the snow and ice management fleet of tomorrow, with poly-composite everything; lightweight and fuel efficient; drone-propelled chemical delivery systems; and environmentally safe materials. Until then, and as long as metals are used with salts, operators must employ a corrosion maintenance protocol that acknowledges the diversity of corrosion; its impacts to functionality of various metal components; and methods of separating corrosive oxidizing agents from those components. 

Expansion (258x300)
Material expansion and section loss on conveyor drive chain. When metal rusts, it expands to four times its original volume before flaking off. The material expansion causes mechanical systems with tight tolerances to bind and seize up.


Corrosion maintenance checklist
For systems with multiple functions and multiple forms of corrosion, there is no silver bullet that will protect everything. However, there is a methodology of progressive prevention that can greatly reduce the top three areas of corrosion and doesn’t require an inordinate amount of time and resources to apply.

Preseason

□ Inspect the equipment and knock down any rust or other corrosion with an appropriate brush and solution.
□ Wash the equipment with a neutral detergent, and cold galvanize exposed steel (blade frame and motor mount, salt box, etc.). Cold galvanizing is the application of a heavy zinc coating (93% or more) to the metal surface at a 4- to 6-mil thickness. These products separate the steel from the oxidizing agents (water, oxygen, chlorides) and provide a sacrificial layer of corrosion before the oxidizing agents can get to the steel surface.
□ Seal the coating with a commercially available automobile paint or preferably a urethane. By doing so, you separate the zinc from the oxidizing agents, further protecting the steel.
□ Apply an inhibitor to the equipment, especially the vehicle chassis. Inhibitors go on easy in the preseason, and can get you through a moderate winter with just one application.
□ Grease all fittings and hit all of your exposed mechanical and electrical connections with dielectric grease.
□ If possible, shrink-wrap open electrical connections where practical to reduce exposure and maintenance.

In-season

□ Wash down the equipment with a standard 100 psi nozzle after each use. Do not power wash since heavy pressure can push oxidizing agents into hard-to-reach crevices and strip off inhibitors and other preventive systems put on during the preseason.
□ If possible use a neutralizing agent since rinsing only removes excess chlorides; it doesn’t help with chlorides that are bonded to the surfaces. A simple, cost-effective way to neutralize chlorides is to flush the equipment with vinegar (a base, which neutralizes acid). After washing the equipment with water, simply run a vinegar solution through the dynamic equipment (auger, spreader, motor shafts, etc.).
□ During wash downs, try not to use soap or detergents that attack grease and oil. If you do, reapply dielectric grease to electrical connections, grease fittings, etc.
□ If possible, convince your clients of the importance of anti-icing, which will reduce chemical usage, which, in turn, will reduce your equipment’s exposure to corrosive oxidizing agents.

Postseason
□ Complete a hot-water wash down of all equipment.
□ Wash the equipment with a neutral detergent, and cold galvanize exposed steel (blade frame and motor mount, salt box, etc.). Cold galvanizing is the application of a heavy zinc coating (93% or more) to the metal surface at a 4- to 6-mil thickness. These products separate the steel from the oxidizing agents (water, oxygen, chlorides) and provide a sacrificial layer of corrosion before the oxidizing agents can get to the steel surface.
□ Seal the coating with a commercially available automobile paint or preferably a urethane. By doing so, you separate the zinc from the oxidizing agents, further protecting the steel.
□ Unless you are able to store your equipment indoors or out of the sunlight, do not apply inhibitors since some break down in prolonged UV exposure.
□ Grease all fittings and hit all of your exposed mechanical and electrical connections with dielectric grease.
□ If possible, shrink-wrap open electrical connections where practical to reduce exposure and maintenance.
□ Exercise dynamic equipment. That is, dry run the equipment once every month or two to revolve and rotate the mechanical systems to shift static stresses on components like chains, gears, belts, etc.


Corrosion in snow & ice equipment
Few pieces of equipment are immune from corrosion in snow and ice operations. The chart below shows the approximate breakdown of the types of corrosion most likely to impact snow operations.

Corrosion in Snow& Ice Equipment
 
George Melchior, ASM, is a registered architect and professional engineer and owns GVM Consulting, based in Portsmouth, NH. Contact him at gwmelchior3@gmail.com.

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