Service Life Expectancy
Thermal Spray Coatings: Materials & The Environment - Service Life Expectancy
The corrosion protection of Thermal Spray Coatings (“Metalizing”) has been thoroughly examined and documented in hundreds of reports and journals, both domestically and internationally. The following excerpts briefly describe the incredible protection Metalizing can afford your company’s equipment and infrastructure for decades.
American Welding Society Subcommittee on Metalizing
The AWS evaluated more than 4,000 test panels exposed to various parameters, such as coating thickness, surface preparation, and sealer coatings, in long-term exposures in several environments. Sealed metalized-coated panels (80 microns at Wrightsville Beach, North Carolina) showed no damage to the underlying steel after 19 years exposure, with many them “looking as though they would continue to succeed for another 19 years.”
St. Andrews Lock and Dam Corrosion Protection System.
TSCs have “the ability to revolutionize the coating industry since they are an extremely durable, single coat system which can offer life spans in excess of 50 years with little or no maintenance.”
ECCS and U.S. Air Force, SAIC.
Coating lives in the field exceeding 20 years in highly corrosive marine environments with unsealed zinc and aluminum metalized steel structures have been demonstrated. These same coatings have exhibited even longer protective lifetimes when sealed with conventional topcoat. Life cycle analyses of TSC systems predict significantly lower costs than those incurred by even the best epoxy/polyurethane corrosion protection coatings available today.
U.S. Navy Port Hueneme Harbor, California
Determined the successful performance of a 125 micron unsealed TSC after a 15-year exposure and a 100 micron TSA coating after 18-1/2 years on the West Coast of California.
1977 British Standard (BS 5493)
Concluded that sealed TSA will protect steel from corrosion for 20 years or longer without maintenance in seawater splash-zones. It should be noted that the TSA coatings in 1977 would not be the same quality as those used today – they are better!
LaQue Centre (Kure Beach, North Carolina)
Both 80 and 150 micron aluminum coatings showed no corrosion of the steel substrate after 34 years of exposure on the North Carolina beach.
Bethlehem Steel Corp.
Documented results with 25 years of testing experience with Al-Zn alloys coatings. First rusting of the substrate was 15 years for severe marine (25 m from the ocean) and 25 years for moderate marine (250 m from the ocean). This was the case for alloys with a 45 to 70% Al content.
Norwegian Institute for Air Research
Published results that metalized-coated steel, after 14-1/2 years of exposure in a marine splash zone (Tananger, Norway), had insignificant damage.
With experience in TSC systems, showed that a 120 micron Al coating could perform effectively for 20 to 25 years in salt water; a 150 micron thick dual Zn-Al coating (5 microns of Zn - 145 microns of Al) could last 40 years or more in a humid atmosphere; and a 200 micron Al coating could withstand the corrosive effects of the splash zone for a service life of 50 years or more.
Tests in natural seawater, gave free corrosion rates of 2 to 3 microns/y after 11 months of exposure for both 99.5% Al and Al-5%Mg. This would imply a service life in excess of 60 years for a 200 micron TSA coating.
Germany (Southern North Sea) Program Study
Predicted that 99.5% Al-coated steel (200 microns) exposed to various submerged and splash zones would have a minimum 10-year service life.
U.S. Army: Buzzard's Bay, Massachusetts
Found no rust undercutting in the areas protected by sealed TSA piles after 18 years of exposure; TSA coating was rated to be the best of the 24 systems tested.
U.S. Army: La Costa Island, Florida
Observed TSA coatings (150 microns) with sealer (vinyl) in excellent condition after 10 years of harsh exposure in the splash zone.
U.S. Navy Standard (1981)
TSA coatings approved as standard DOD-STD-2138 (SH) for U.S. Naval ships for high-temperature service (780 degrees C), a 250 to 375 micron coating, two coats of a heat-resistant Al sealer, and adhesion strength of 13.8 MPa (2,000 psi). This coating is expected to give more than 10 years service.
Nat’l Cooperative Highway Research Program Project
Depending on the corrosion environment and with the right amount of dry film thickness metalizing can protect a steel surface for 50 years or more. See Table.
CONCLUSIONS: THERMAL SPRAY COATINGS
Materials: INDIVIDUAL PROPERTIES
99.9% pure Zn:
- excellent cathodic protection
- service life proportional to thickness
- not ideal for acid (pollution) environments or high temperatures
99% pure Al:
- low self-corrosion rate
- good seawater performance
- high-temperature resistance
- acid (pollution) resistant
Materials: COMMON PROPERTIES
- Long-term corrosion protection in excess of 20 years common, in both industrial and marine exposures, supported by extensive documentation
- Provide sacrificial corrosion protection to steel substrates, even when areas are exposed to the corrosive environment
- Considering their relatively low corrosion rates and their sacrificial corrosion protection properties, these TSC metals and metal alloys are suitable for use even in the harshest of environments.