ASTM G85 Acidified and SWAAT Testing
Key facts
| Annex | Test | Principle |
|---|---|---|
| A1 | Acetic acid salt spray | Neutral fog acidified with acetic acid, continuous |
| A2 | Cyclic acidified salt fog | Acidified fog alternating with dry and humid phases |
| A3 | Seawater acidified test (SWAAT) | Acidified synthetic seawater, cycled spray and soak |
| A4 | SO₂ salt spray | Salt fog with sulphur dioxide introduced in cycles |
| A5 | Dilute electrolyte cyclic fog/dry | Dilute salt and ammonium sulphate, alternating fog and dry-off |
Why modify the salt spray test
Neutral salt fog (ASTM B117) is gentle on aluminium compared with real coastal and industrial sites. G85 changes the chemistry or the cycle to reproduce specific kinds of attack — acid rain, marine atmospheres, industrial sulphur or wet–dry cycling.
How SWAAT is run
The A3 test uses synthetic sea salt acidified with acetic acid. Instead of a continuous fog, the chamber alternates short spray periods with longer high-humidity soak periods, so the panels or coil samples stay wet but see changing conditions. HVAC manufacturers often run it on complete coil samples, not only flat panels.
Reading the result
As with any accelerated test, a G85 result needs the annex, the substrate, the film thickness and the failure criterion. “1,000 h SWAAT” without the sample type and criterion cannot be compared with another supplier’s result.
Limits
G85 annexes are still accelerated laboratory tests. They rank coatings under one set of conditions and do not convert into years of service.
Reading a supplier report
Check that the report names the annex, not just “G85”. Acetic acid salt spray to ISO 9227 or GB/T 10125 (AASS) is similar in principle to Annex A1 but is a different standard; PG-S1’s ≥ 800 h acetic acid result is to GB/T 10125.
Related
- CoatingsWaterborne Polysiloxane (Sol-Gel) Coil Coating
- EquipmentMicrochannel Coil Corrosion Protection
- StandardsASTM B117 Neutral Salt Spray: What the Hours Mean
- GuidesHow to Verify a Supplier's Salt Spray Claims
- CoatingsBaked Polysiloxane-Urethane Clearcoat
- StandardsSalt Spray vs Cyclic Corrosion Testing
Is SWAAT harsher than ASTM B117?
For aluminium, generally yes, because the acidified seawater and wet–soak cycle drive the pitting and intergranular attack seen in the field. The hours are not comparable between the two tests.
Do PG systems have SWAAT results?
No. Current PG data is from neutral, acetic acid and copper-accelerated salt spray to GB/T 10125, listed in the test data library.
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