Fastener Salt Spray Test Method and Result Judgement

Fastener Salt Spray Test Method and Result Judgement

Salt spray testing is the most common way to rate fastener plating. Contracts often specify "48/72/96 hours no rust." Without understanding method and judgement, the number can be misread. This article covers key points of neutral salt spray.

Types and Equipment

Fasteners usually use neutral salt spray (NSS) per GB/T 10125, ISO 9227 or ASTM B117. The chamber continuously sprays 5% NaCl solution at about 35°C, with specimens angled. Acetic acid/CASS tests accelerate decorative plating; ordinary fasteners use NSS.

Duration is set by coating: clear zinc often 48-96h, dacromet 500-1000h, hot-dip galvanized longer.

Sampling and Placement

Use unused, unscratched production parts; sample count per standard or agreement. Place specimens at 15-30° from vertical so chamber condensation does not drip directly on them. Clean specimens with solvent before testing; don't touch surfaces with bare hands.

Judgement

At duration, rinse gently, dry and inspect. Judgement usually keys on "white rust" (coating corrosion products) or "red rust" (base metal rust). Contracts generally specify no red rust. White rust does not equal substrate failure; red rust marks coating failure. Area, density and scratches affect results, so compare under agreed conditions.

Reports should record method, concentration, temperature, duration, specimen condition and observations, with photos.

In-Service Notes

Salt spray is an accelerated lab rating, not directly equal to outdoor life. Real outdoor corrosion depends on humidity, acids, temperature and installation. Coastal projects should raise requirements and re-inspect periodically.

Zhuhai Jiali provides salt spray reports and samples for various finishes.