Direct answer
First work out which type of salt mist you need: neutral (NSS), acetic acid (AASS), copper-accelerated acetic acid (CASS) or cyclic. The solution, temperature and acceptance basis differ for all four, so confirm the laboratory runs the type your customer specified, and that the cabinet volume can accommodate your samples.
Four types of salt mist — they cannot be lumped together
| Type | Solution | Typical application |
|---|---|---|
| Neutral salt mist (NSS) | 5% sodium chloride, neutral pH | General metal parts, platings, surface treatments |
| Acetic acid salt mist (AASS) | Acidified with acetic acid | Decorative plating (copper-nickel-chromium systems) |
| Copper-accelerated acetic acid salt mist (CASS) | Acetic acid with copper chloride | Accelerated assessment of plating corrosion resistance |
| Cyclic salt mist | Alternating salt mist, drying and damp heat | Automotive components (closer to the real environment) |
The corrosion mechanism and acceleration factor differ across the four, so results cannot be converted from one to another. If the customer standard specifies cyclic salt mist and you test with neutral salt mist, the report will not be accepted.
The acceptance basis is not "is there rust"
There are four common ways of judging, and you should agree with the customer on which one applies before commissioning:
- Appearance rating: protection rating and appearance rating scored per the GB/T 6461 system
- Corroded area proportion: the percentage area of blistering, flaking and rust spots
- Unilateral creep from a scribe: commonly used where a cross-cut or scribe is required
- Functional status: for electronic and powered parts, whether electrical performance has drifted
Sample preparation: four things easily done wrong
- Cleaning method: must not damage the original surface condition, and must not leave oil or grease that affects wetting
- Scribing: many standards require a cross-cut or scribe before testing; without it the conditions do not match the standard
- Orientation: samples are usually set at an angle to the vertical; the wrong angle changes how condensate runs off
- Spacing: samples must not shield each other from the spray and must not touch the cabinet walls
Three questions to ask when choosing a laboratory
"Do you run NSS, AASS, CASS or cyclic salt mist?" "What are the internal dimensions of the cabinet, and can my sample go in without shielding anything?" "Which standard do you judge against, and do you provide rating photographs?"
The third question is practical: judgement in salt spray testing depends heavily on photographs, and if the shooting conditions (lighting, angle, whether the sample was cleaned) are not consistent, the conclusions from two laboratories cannot be compared.
Test duration versus turnaround time
The test duration of a salt spray test is a technical parameter specified by the reference standard (for example a number of hours or a number of cycles), set by the customer or the product specification, and is part of the test conditions. The turnaround time is the actual time from sample receipt to report issue, arranged according to the project; if you have a target date, mention it when submitting samples and we will check it against the current schedule and confirm a feasible plan with you.
These two are often confused in the same question, and separating them helps both sides.
Where we stand
TMC LAB holds both CMA and CNAS accreditation and covers neutral, acetic acid, copper-accelerated acetic acid and cyclic salt mist, with site visits and witness testing available. Send us the sample dimensions, the material and the customer standard, and we will confirm the salt mist type and the acceptance method first.
Related pages for this question
Last updated Technical criteria follow the current standards and the agreed scope; please confirm the specific project with the lab.
