What the salt spray test is
The salt spray test (ASTM B117) places parts in a cabinet fogged with 5% salt solution at a controlled ~35°C to accelerate corrosion, recording the time until rust appears.
It is the international standard for comparing the corrosion performance of different coatings.
What “hours” means
Two values are usually reported: time to white rust (the zinc layer) and time to red rust (the base steel). Red rust is the real indicator of protective life.
E.g. “Cr3+ yellow, 200h to red rust” means red rust appeared after 200 hours — higher is better.
Limitations to know
Salt spray is a comparative lab test; it does not convert directly into years of real service, which is more complex. It remains an excellent way to set specs and accept work.
FAQ
200 hours = how many years?+
There is no fixed conversion; use it to compare coating quality. Real life depends on environment.
White rust vs red rust?+
White rust is the zinc layer corroding (still protecting the steel); red rust means the base steel has begun to rust.
