Modes of Corrosion Protection |
| There are three primary modes of corrosion protection by Polymet high performance protective coatings; generally use all three in synergistic combination to achieve superior protection. |
Barrier Protection |
| Barrier Protection is the simplest form of corrosion protection. An impermeable coating over a corrodible substrate prevents environmental factors from attacking the base metal. Unfortunately, if the coating is damaged, the substrate will begin corroding and the protective coating will lift off along the edges of the damaged area. In addition, no coatings are truly impenetrable; many other coatings have a high water transmission rate, allowing water to penetrate through the coating, thus allowing corrosion. Due to fact that Polymet has cathodic protection and sacrificial behaviour, it act as barrier protection of metal. |
Sacrificial Protection |
| Sacrificial Protection is the application of a sacrificial metal (i.e., one that is more active or higher in the electromotive force series) to the substrate. This more active metal then sacrifices itself to protect the less active metal. Thus, for example Polymet Zinc al flake base coatings will protect steel. |
Inhibitive Protection |
| Inhibitive Protection is the incorporation of an inhibitive agent in the Polymet coating. Inhibitive agents prevent corrosion by migrating to the molecular corrosion site and intervening in the corrosion mechanism. |
Salt Spray Protection by Polymet™ |
| Because of the Polymet coatings last for years under environmental conditions, accelerated testing procedures are used to evaluate coatings. The most common test is the ASTM B-117 Salt Spray (or Salt Fog) test. In this test, the parts to be tested are exposed to a mist of 5% sodium chloride at 950 F. When red rust is evident the part is deemed to have failed. While zinc plating or phosphate and oil generally provide protection in the 50 hour to 200 hour range, some of these products are able to achieve protection in excess of 1000 hours of salt spray protection. |
Other corrosion Protections by Polymet™ coatings |
| The Polymet™ coating protects substrate from various forms of corrosion like |
| Group 1 - Readily identifiable by ordinary visual examination |
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Uniform corrosion |
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Pitting |
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Crevice corrosion |
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Crevice Model
Pack Rust |
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Galvanic corrosion |
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Lamellar corrosion |
| Group 2 - may require supplementary means of examination |
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Erosion corrosion |
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Cavitation |
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Fretting corrosion |
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Intergranular corrosion |
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Exfoliation |
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Dealloying (selective leaching) |
| Group 3 - Verification is required by microscopy (optical, electron etc.) |
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Environmental cracking |
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Stress Corrosion Cracking (SCC)
Corrosion fatigue
Hydrogen embrittlement |
