Salt spray testing is one of the most quoted — and most misquoted — corrosion tests in hardware specification. It places specimens in a chamber where a saline solution is atomised into a continuous mist, then inspects them for corrosion after a set number of hours. The widely used neutral version is described in ASTM B117.
What the Test Actually Does
A prepared specimen is placed in a closed chamber held at an elevated temperature, and a salt solution — commonly a sodium chloride solution around five percent — is atomised so that it settles continuously on the surface. The chamber is not cycled: exposure is constant, which is precisely why the result should be read carefully.
The outcome is normally recorded as the number of hours before a defined level of corrosion appears, such as the first sign of red rust on steel or white corrosion products on a plated surface.
Comparative Tool, Not a Life Prediction
Continuous fog is not what real equipment experiences. Outdoors, surfaces alternate between wet and dry, are washed by rain, and are exposed to sunlight — and the drying phase is when many corrosion processes actually accelerate. Because the test removes that cycling, the hours correlate poorly with calendar life in service.
Use it the way it was intended: to compare finishes, plating systems or stainless grades against each other under identical conditions, and to catch process problems such as poor plating adhesion or inadequate passivation.
Why Hardware Fails Before the Shell
A polymer shell does not rust. What corrodes on a protective case is the metal content:
- Latches and hinges — the highest-stress items, and the ones handled every use.
- Springs and pins — thin sections with little material to lose before function is affected.
- Fasteners — often the first visible rust, and the least specified item on a case.
- Plated components — corrosion begins where the plating is damaged or thin.
A corroded latch is a functional failure, not a cosmetic one: it stops clamping the lid, and the seal loses the compression it needs.
Specifying for Marine and Coastal Service
| Environment | What to specify | Why |
|---|---|---|
| Inland, dry industrial | Standard plated hardware is usually adequate | Exposure is intermittent and washdown is rare |
| Outdoor, regular rain | Corrosion-resistant plating plus drainage design | Water must not sit against metal |
| Coastal, salt-laden air | Stainless hardware, compatible fasteners, rinsing access | Salt deposits keep surfaces wet and conductive |
| Marine, spray and washdown | Marine-grade stainless, isolation of dissimilar metals | Galvanic corrosion accelerates when mixed metals meet electrolytes |
Two design details matter as much as the metal choice. First, avoid trapping water: recesses that hold salt water against a fastener will corrode it regardless of grade. Second, avoid dissimilar metals in contact, because joining metals far apart in the galvanic series in the presence of an electrolyte drives corrosion in the less noble one.
Practical Maintenance
Even well-specified hardware benefits from simple routines in coastal use: rinse with fresh water after salt exposure, dry before storage, keep latches and threads lightly lubricated, and inspect springs and pins at regular intervals. These cost little and extend service life more than upgrading every fitting.