Salt mist testing verifies resistance to corrosion in salt-bearing environments. Automotive and outdoor products are exposed for long periods to rain, salt mist and industrial atmosphere, and metal plating, connector contacts and structural parts all suffer corrosion.
The three salt mist tests
Neutral salt mist (NSS): sodium chloride solution at pH 5.0-6.5, reproducing a neutral corrosive environment such as coastal salt mist.
Acetic acid salt mist (AASS): acidified to pH 3.2-3.5 on top of NSS, reproducing industrial exhaust and acid rain environments, where corrosion is faster.
Cyclic salt mist: adds heating, cooling, drying and immersion stages on top of salt mist, forming wet-dry cycles that are closer to real outdoor service.
Selection advice for automotive electronics
Metal parts and coatings → neutral salt mist, to verify the corrosion resistance of the base protective layer.
Connectors and terminals → cyclic salt mist, since wet-dry alternation exposes unstable contact resistance more readily.
Seals and structural parts → cyclic salt mist plus a water-tightness check afterwards.
Export products → follow the target-market standard; the European market commonly cites the relevant ISO 9227 clauses.
Post-test checks
Corrosion rating: rate the extent and area of corrosion per ISO 9227.
Contact resistance change: compare terminal resistance before and after the test.
X-ray and cross-sectioning: confirm whether corrosion has penetrated the plating or the base material.
Seal condition: verify that water tightness is retained after cyclic salt mist.
Visual inspection: rust spots, discolouration, white bloom, coating blistering and flaking.
Protection design essentials
Design plating thickness and density to avoid pin holes and thin plating at edges.
Isolate dissimilar metals at contact points to avoid galvanic corrosion.
Design gap structures as a labyrinth to obstruct ingress of the corrosive medium.
Match connector shell and terminal plating to avoid porosity at the contact surface.
Combine cavity sealing with a breather valve, balancing internal and external pressure while blocking moisture.
Frequently asked questions
Can salt mist results be converted into service life?
No. Salt mist testing is accelerated testing, and its corrosion mechanism is not identical to real outdoor atmosphere. Results are used to compare the relative merit of protection designs, not to project years of service life. Life data requires corrosion life assessment or actual exposure data.
Why does the product still rust in service after passing salt mist?
There are three common reasons: the test conditions differ considerably from the real environment, which is more complex (acid rain, UV, pollution); the protection design passes under test conditions but the seal fails or is scratched during actual assembly; or low-grade protective materials were selected. Analysing the actual failed part is recommended.
Service notes
Our laboratory holds both CMA and CNAS accreditation, covers about 10,000 m2 and runs more than 500 sets of equipment. All testing is carried out in our own laboratories — nothing is subcontracted. Plant visits and on-site witnessed testing are welcome.
Scheduling follows the actual project pipeline. You can state your preferred lead time when you submit samples; we will confirm a feasible plan against current capacity and keep you updated at each milestone. Once the report is issued we send the electronic copy; corrective-action advice can be arranged separately.
