Scenario: a coating datasheet says “500 hours salt spray”. Direct answer: that number describes how a specimen behaved in a defined test chamber. It is not a number of winters. ASTM B117 itself says so in plain terms.
What the standard says about itself
The standard describes its own scope, and that scope is narrower than most buyers assume.
- Scope (1.1, 1.2): the practice covers the apparatus, procedure and conditions needed to create and maintain a salt spray (fog) environment. It does not prescribe the type of specimen, the exposure period for a given product or how to interpret the results.
- Use (3.1): it provides a controlled corrosive environment used to produce relative corrosion-resistance information for metals and coated metals in a given chamber.
- Limits (3.2): prediction of performance in natural environments has seldom been correlated with salt spray results used as stand-alone data, and correlation or extrapolation is not always predictable.
- Repeatability (3.3): results depend heavily on specimen type, evaluation criteria and control of operating variables, and variability has been observed between chambers.
I read the current B117-26a store page (updated September 22, 2026). The full text is paid, so I cite only the public scope and significance text.
What to ask when a supplier quotes hours
| Question | Why it matters |
|---|---|
| Which edition of the standard, and which lab? | Results vary between chambers |
| What was tested: bolts, plated nuts or a flat panel? | Shape and coating thickness differ |
| What failure criterion ended the test? | “No red rust” and “5% rust” are different results |
| Was the coating scratched before testing? | Plow hardware gets scratched in use |
| Is there real-world history on a similar part? | The standard itself stresses long-term exposure data |
An example of the difference
Suppose two suppliers each quote a coating with the same number of hours. One tested a flat panel to first sign of red rust; the other tested threaded bolts to a percentage of rust coverage. The numbers look equal but do not measure the same thing. This is an illustration of how criteria differ, not data about real products.
A practical reading
Hours are only comparable between tests run the same way.
- Treat hours as a way to compare two coatings tested the same way, not as a lifetime.
- Weigh it against salt-brine exposure, road chemicals and abrasion on your own routes.
- Keep a corrosion note in your edge log. Your own trucks are the best long-term test.
Boundary: I make no statement about what any specific plow bolt or coating achieves in chamber hours or in service.
Sources and further reading. External references are dated; where a figure is quoted, the link shows where it came from.
ASTM International: ASTM B117-26a Standard Practice for Operating Salt Spray (Fog) Apparatus (store page: scope and significance) (B117-26a, updated Sep 22, 2026) ↗Hardware Corrosion and Seizing on Plow Blades: Prevention Practice ↗Salt, Brine and Abrasives: Choosing De-Icing Materials for a Fleet ↗Carbide snow plow blades ↗
