|Wednesday, June 19, 2013
There have been numerous tests of metallized coatings over the years. Many of these tests are repeated by owners before using metalizing on a bridge. This testing is often duplicative of earlier work. Here are test reports that establish the effectiveness of metalizing.
This is the single most important test report available. It is internationally recognized as thorough and definitive. It is one of those essential documents for all who use or apply metalized coatings for atmospheric service.
From the Abstract
This report presents the results of a 19-year study of the corrosion protection afforded by wire-flame-sprayed aluminum and zinc coatings applied to low-carbon steel. It contains the results of an inspection of the flame-sprayed coated steel panels made after all panels had been exposed for 19 years.
- American Welding Society 19-Year Report, 1974, pp. 4-7
The report "Corrosion Tests of Flame-Sprayed Coated Steel, 19-Year Report" is known worldwide as the definitive work on the effectiveness of metalized coatings. It is available from the American Welding Society, Miami, Florida.
Another thorough evaluation of metalizing is detailed in Marine Atmospheric Corrosion Museum Report on the Performance of Thermal Spray Coatings on Steel, Robert M. Kain and Earl A Baker, ASTM 1989.
From the Abstract
In the early 1950s, a number of zinc-aluminum compositions were applied to carbon steel using then-current practice and exposed at several test sites in England and the United States. The performance of these test panels was described by Hoar and Radovici following 10-½ years of exposure. In the ensuing years, a number of the original panels remained on exposure at Kure Beach, NC, in the LaQue Center for Corrosion Technology, Inc., marine atmospheric corrosion site.
This paper describes the protection afforded by the various coatings after 34 years of continuous exposure in the moderately aggressive marine location situated 250 m from the Atlantic Ocean. Several electrochemical methods presently in use are reviewed in a reflection of how accurate they might be in forecasting the effectiveness of these coatings.
From the Summary
Examination of the specimens for detectable base metal rust and stain through the coating revealed a broad range in the degree of protection. This varied considerably with alloy content, type of powder, and the method of application.
Although a number of zinc coatings and high zinc containing, mixed and alloy powder, coatings performed well, the greatest number of resident coatings were generally those of high aluminum content. The latter materials typically exhibited less variability as a function of the applicator gun .
Other investigators are presently studying the protection characteristics of thermal sprayed alloy wire coatings with compositions approximating those which have performed well in 34-year tests.
- Performance of Thermal Spray Coatings on Steel, ASTM, 1989
The coatings evaluated in this series of tests were applied by flame-sprayed powder. Todays standard is wire flame-spray or twin wire electric arc spray. These tests evaluated coatings of Zinc-20 Al and Zinc-30 Al mixed powder and other compositions. Today the standard zinc/aluminum coating material is Zinc-15 Aluminum pre-alloyed wire. One could predict even better results using todays standard flame or arc wire equipment and the 85% zinc / 15% aluminum wire.
NOTE: The fiftieth anniversary of this test is in the year 2002. The LaQue Center is planning to evaluate the condition of the metalized coupons still exposed on this anniversary.