Salt spray testing is a laboratory simulation of a corrosive saltwater environment. It is used as an accelerated means of testing the ability of surface coatings to withstand atmospheric corrosion. Also known as the Salt Spray Test, it is one of the oldest testing methods used in the HVAC-R coating industry, therefore, it is often mentioned when selecting HVAC-R coatings.
Protective coatings use salt spray testing in two ways when developing and evaluating HVAC-R and radiator coatings. The salt spray test is used as a stand-alone corrosion resistance test and also as an integral part of ISO 12944-9 (formerly known as ISO 20340). For both tests, the salt spray procedure was handled the same way, per ASTM B-117.
First, prepare a small panel (typically 3 by 5 inches or 4 by 6 inches) with the coating to be tested. The edges and back of the panels are protected, usually with tape. The front of the panel is then "scribed" with a sharp tool to scratch the metal substrate through the coating.
After the panel is ready, it is placed in the test cabinet. The cabinet contains shelves to hold the panel in the position specified by ASTM B-117 - tilted back from vertical 15 to 30 degrees.
The cabinet was then closed and 5% saline solution was delivered into the cabinet at a constant rate and temperature through the nebulizer. The salt spray is sprayed upwards, causing the droplets to descend and settle on the panels.
Following this, the test panels are regularly inspected and the salt spray cabinets are monitored to ensure they are functioning properly throughout the test period. During these brief evaluations of the panels, it is determined whether the tests performed as expected or whether the coating on the test panels failed prematurely.
While both ASTM B-117 and ISO 12944-9 are used to measure corrosion protection, there are some notable differences between the two tests. Unlike B-117 which is only a static salt spray test, ISO 12944-9 is a cyclic test where panels are tested to 72 hours of UV exposure, then 72 hours of salt spray, then 24 hours of freezing (168 hours/week in total. This cycle (UV/salt spray/freeze) is repeated for 25 weeks for a total of 4,200 hours. While neither test is an actual outdoor environment, ISO 12944-9 is more like what HVAC-R units are regularly exposed to in the real world extreme weather cycles. For this reason, SSPC (Society for Protective Coatings) concludes: “The corrosion/weathering combination is a substantial improvement over the traditional salt spray test (ASTM B117) in terms of accelerating the reproduction of atmospheric corrosion. You can Learn more about the difference between the two tests and why we test according to ISO 12944-9 by reading the study showing that the ASTM-B117 salt spray test has nothing to do with the actual environment.
Once the exposure required by ASTM B-117 or ISO 12944-9 is achieved, the lab will evaluate the panel for blistering, rusting and scratch creepage. Results are documented and shared in our technical data sheets. The test times reported on our technical data sheet are based on these results
