“Passes 96 hours salt spray” sounds precise, but it is not a complete
specification. A useful corrosion requirement must identify the test
method, specimen, exposure time, evaluation point and acceptance
criteria.
ISO 9227:2022 specifies procedures for neutral salt spray, acetic
acid salt spray and copper-accelerated acetic acid salt spray testing.
ASTM B117-25 covers the apparatus, procedure and conditions for
operating a salt-spray fog environment. Both are controlled laboratory
practices—not universal formulas for converting chamber hours into years
of outdoor service.
What the standards say
ISO 9227 states that it does not specify the exposure period for a
particular product or the interpretation of results; those details
belong in the product specification. It also says salt-spray tests are
useful for detecting coating discontinuities, pores and defects, but are
not intended to predict long-term corrosion resistance.
ASTM B117 similarly states that the practice does not prescribe the
specimen, exposure period or interpretation. It notes that correlation
with natural environments is seldom predictable when salt-spray data is
used alone.
A complete salt-spray
specification
| Item | Example of what to define |
|---|---|
| Method | ISO 9227 NSS or ASTM B117 |
| Specimen | Finished production part, flat panel or assembled component |
| Sample count | Number of parts and batches |
| Preparation | Cleaning, masking and handling before exposure |
| Exposure time | Buyer-defined number of hours |
| Evaluation | Red rust, white corrosion, blistering, pitting or coating failure |
| Inspection area | Functional surface, cut edge, rack mark or all visible areas |
| Acceptance | Maximum affected area, first-corrosion time or visual grade |
| After-test function | Gate movement, spring return, swivel movement or buckle fit |
Why hardware geometry
matters
A flat coated panel and a finished snap hook do not present the same
risk. Formed edges, welds, holes, springs, rivets and recessed areas can
retain solution or expose thinner coating. Plating thickness may also
vary with current density and part orientation.
For moving hardware, corrosion appearance is only one outcome. The
buyer may also need to check whether the gate opens, the swivel rotates,
the tongue engages and the webbing-contact surface remains smooth after
exposure.
Avoid the “hours equals
years” shortcut
Natural exposure includes wet-dry cycles, temperature changes,
sunlight, pollutants, abrasion, sweat, cleaning agents and maintenance.
A continuous salt-fog chamber does not reproduce every one of those
mechanisms. Two finishes can change ranking when the environment
changes.
Use salt-spray testing as a repeatable quality-control or
coating-screening tool. For critical applications, combine it with
application-specific ageing, outdoor exposure, wear testing or buyer
field validation.
What buyers should include
in an RFQ
State the base material, coating system, colour standard, salt-spray
method, hours, corrosion type, acceptable area, functional checks and
whether the criterion applies before or after assembly. Require the
report to identify the tested sample and drawing revision.
Jinxing Hardware can review buyer-defined finish and inspection
requirements during sampling. Test scope and acceptance criteria should
be agreed before quotation and production.
Frequently asked questions
Does 96 hours salt spray equal one year
outdoors?
No universal conversion exists. ISO 9227 and ASTM B117 do not provide a
general hours-to-service-life formula.
Which is better, ISO 9227 or ASTM B117?
Neither is automatically “better.” Use the method required by the buyer,
market or product specification and define the missing product-specific
details.
Should assembled hardware be tested?
Often yes, when geometry, joints, springs or movement are relevant. The
agreed specimen should represent the risk being evaluated.
Sources
- ISO 9227:2022: https://www.iso.org/standard/81744.html
- ASTM B117-25: https://store.astm.org/b0117-25.html
