A salt spray test places plated parts in a closed cabinet filled with a fine fog of salt solution for a set number of hours, then checks them for corrosion. It is the most common way to check that plating on brass and steel parts is thick, continuous and well applied.
The test is a quality control check, not a forecast. A number of hours in the cabinet does not translate into a number of years in use.
The standards
- ISO 9227 is the international standard. It covers three methods: neutral salt spray (NSS), acetic acid salt spray (AASS) and copper-accelerated acetic acid salt spray (CASS).
- ASTM B117 is the American standard for neutral salt spray and is broadly similar to the NSS method in ISO 9227.
- ISO 10289 gives a rating system for judging corrosion on metallic coatings after the test.
Which method suits which finish
Neutral salt spray is used for most coatings, including zinc, tin and many nickel finishes. Decorative nickel-chrome finishes on sanitary fittings are often tested with CASS, which is faster and more aggressive. Your product standard may name the method and duration.
Neither ISO 9227 nor ASTM B117 sets a pass mark. You must state the method, the number of hours and the acceptance criteria. For example, you might specify no base-metal corrosion on significant surfaces after a set number of hours.
How to use it in your order
- Put the test method, duration and acceptance criteria on the drawing or purchase order.
- Ask for the test on samples from each production lot, not just the first sample.
- Use an accredited laboratory for disputes or certification, and ask for photos before and after the test.
- Combine it with thickness checks, because a thin but intact coating may pass a short test and fail in use.
Limits of the test
Results vary between cabinets and laboratories, so compare results only within one lab where possible. The test also does not reproduce real conditions such as wet and dry cycles, UV or cleaning chemicals.
Parts are also sensitive to handling. Fingerprints, packing oil or scratches from bulk packing can start corrosion early and make a good coating look poor. Agree with the lab how parts are cleaned, positioned and inspected, and use parts taken straight from the packed lot.
If you need a closer match to field use, ask the lab about cyclic corrosion tests, which alternate salt fog, drying and humidity. They take longer and cost more, but they rank coatings more realistically.
For electrical parts, also check solderability and contact resistance. See nickel, chrome, tin and silver plating for how to specify each finish, and the guide to reading a lab certificate before you accept a report.
Next step
We arrange testing of production lots and check the reports before shipment. To set up plating tests for your parts, book a free sourcing review.