Salt Spray Testing of Hot-Dip Galvanized (HDG) Steel
Accelerated corrosion test methods such as salt spray testing (ASTM B117, ISO 9227) and other similar tests have been widely used in the construction and manufacturing industries to evaluate or compare the corrosion resistance of various protective coatings. However, coating performance in natural environments has seldom been correlated with salt spray test results. When salt spray test results are more favorable than real world results, misleading claims about the comparative performance of coatings in marketing materials can result.
Galvanizing associations around the world alongside the International Zinc Association (IZA) advise against using salt spray tests to compare different types of coatings. ASTM B117 explains the prediction of performance in natural environments has seldom been correlated with salt spray results when used as standalone data. Further, ISO 9227 recommends salt spray tests are suitable only as quality control tests for rapid analysis for discontinuities, pores and damage in paint or some metallic coatings.
See detailed information sheet developed by the European General Galvanizers Association (GAA) and supported by the American Galvanizers Association (AGA) on salt spray testing and why it should not be used to compare different types of coatings:
Specific to hot-dip galvanized (HDG) steel, salt spray testing is not appropriate for predicting performance in real-world environments, comparing HDG steel to other corrosion protection systems, determining HDG steel material acceptance, nor galvanizing facility qualification. These tests often lead to false conclusions about the corrosion resistance of HDG steel in addition to deceptive marketing claims against HDG steel. For these reasons, the AGA does not acknowledge nor participate in research programs involving salt spray testing.
While accelerated tests are appealing, they are never a substitute for the valuable performance data gained from long-term exposure testing and real-world case studies. Since 1926, organizations like ASTM, ISO, and others have conducted exposure testing in various environments to determine corrosion rates of HDG steel. Extensive corrosion data paired with advanced corrosion modeling techniques allows the prediction of corrosion rates in a much wider range of real-world conditions, far beyond what limited salt spray tests can offer.
To assist in predicting the life of HDG coatings in atmospheric environments of North America, please consult the following resources:
- AGA Time to First Maintenance Charts
- Zinc Coating Life Predictor (ZCLP)
- Service Life of Galvanized Steel Articles in Soil Applications
- The Performance of Hot-Dip Galvanized Steel in Water Environments
- Dissimilar Metals in Contact with Zinc
AGA's Project Gallery and Galvanized Steel Studies (GSS) videos also offer a vast collection of HDG steel case studies among many industries and applications. For other applications, AGA maintains a searchable knowledgebase or you can contact the AGA Technical Department.