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Selecting the right corrosion test for your HVAC/R protective coating

There are several tests that can be used to measure the effectiveness of protective coatings for HVAC/R coils. These testing processes have evolved over the years as various organizations have tried to provide the most accurate information to engineers, manufacturers, and businesses that need to protect their HVAC/R investment.


ASTM B-117

Originally developed in 1939, ASTM B-117 was the first internationally recognized salt spray standard. For years, it was considered to be the gold standard is corrosion testing. ASTM B-117 is a non-cyclic test, which means that the surface is continually exposed to “salt air.” In this test, the panels are exposed at a 15 to 30 degree angle from vertical to continuous deposition of an atomized 5% NaCl (sodium chloride or salt) solution at 35 degrees Celsius and 97% humidity. Although ASTM B-117 remains a commonly used test, its major fault is that there is limited correlation to a real-world environment in which weather conditions fluctuate.



ISO-9227 is nearly identical to ASTM B-117. The biggest difference between the two tests is that ASTM B-117 is a U.S. standard, while ISO-9227 is recognized nearly worldwide. Like ASTM B-117, in the ISO-9227 test is a continuous test in which the testing atmosphere doesn’t change. Although it is also a widely accepted test, it suffers from the same fault found in ASTM-B117 – it does not mimic real world conditions.



Published in 1998, ISO-12944-6 is a standard originally developed to evaluate corrosion protection of steel structures.  This standard is an improvement over ASTM B-117 and ISO-9227 because it is a cyclic test.  Test panels are exposed to water condensation, salt spray, and in some cases, 168 hours of chemical spot testing consisting of 10% Sodium Hydroxide, 10% Sulfuric Acid, and 18% Mineral Spirits. The length of exposure is dependent upon the corrosivity category of C1 – C5-I or C5-M. (C5-I/M is the most severe).


ISO 20340

ISO 20340 is the most demanding corrosion testing standard available for marine/salt air environments. It is a cyclic test and better correlated to the real-world environments of harsh marine conditions than other standards. ISO 20340 has been adopted as the pre-qualification offshore performance standard for barrier coatings that may be broken down due to long term exposure to sunlight, moisture, sea water spray, and wind chills. We believe it should be the baseline test for HVAC/R systems in offshore and coastal marine environments. This test runs for 25 weeks (4,200 hours). During the test, the environmental conditions cycle between 72 hours of UV, 72 hours of salt spray, and 24 hours of low temperature exposure (-20 – 2 degrees Celsius).

HVAC/R coils and units that are frequently exposed to corrosive environments, particularly harsh marine environments, will provide an extended lifespan when a protective coating has been applied to the equipment. Although any of the standards above indicate that the coating has been subjected to a harsh environment, understanding which test offers the best correlation to the real-world environment your equipment will experience can help you determine the coating’s potential benefit for your units.