EN
Quick Answer: Salt spray testing (per ASTM B117 or ISO 9227) is an accelerated corrosion test that exposes metal auto parts to a continuous fine mist of 5% sodium chloride solution at 35°C. Standard duration ranges from 48 hours for decorative chrome to 720 hours for severe-duty under-hood components. For aluminum valve covers, oil pans, and metal inserts, 240 hours of salt spray exposure with no red rust is the typical aftermarket benchmark. Ranmi's QC lab includes a salt spray test chamber for routine validation.
What Salt Spray Testing Measures
The test simulates years of exposure to:
- Coastal humidity and salt air (Middle East coastal regions, Florida, Mediterranean)
- Winter road salt in northern climates (Russia, Canada, Northern Europe)
- Industrial atmospheric pollution
The test does not perfectly correlate to real-world corrosion (laboratory and field conditions differ), but it provides a reproducible benchmark for comparing materials, coatings, and surface treatments.
Test Standard References
|
Standard |
Body |
Notes |
|
ASTM B117 |
ASTM International |
Most widely cited |
|
ISO 9227 (NSS) |
International Organization for Standardization |
European/Asian preferred |
|
JIS Z 2371 |
Japanese Industrial Standards |
Japanese OEM applications |
|
GB/T 10125 |
Chinese national standard |
Domestic applications |
ASTM B117 and ISO 9227 NSS (Neutral Salt Spray) produce nearly identical results.
Test Procedure
- Sample preparation — clean part, mark exposed surface, mask cut edges if needed
- Chamber loading — parts mounted at 15–30° from vertical so spray drains
- Salt solution — 5% NaCl in distilled water, pH 6.5–7.2
- Chamber conditions — 35°C ± 1.1, continuous fog, collection rate 1–2 mL/h per 80 cm²
- Exposure duration — varies by part class (see table below)
- Inspection — periodic photo documentation, final rating per ASTM D1654
Typical Duration Requirements
|
Part Type |
Duration |
Acceptance Criterion |
|
Decorative chrome plating |
48 hours |
No visible corrosion |
|
Cadmium-plated fasteners |
96 hours |
< 5% white rust, no red rust |
|
Zinc-coated steel brackets |
120 hours |
No red rust |
|
Galvanized exhaust components |
240 hours |
< 10% surface corrosion |
|
Aluminum die castings (uncoated) |
240 hours |
< 5% pitting |
|
Aluminum + ED coating |
480 hours |
No red rust through coating |
|
Underbody steel components |
720 hours |
< 10% red rust |
For Ranmi aluminum valve covers (Toyota 2KD, Honda METTS, Ford Windsor), the typical specification is 240 hours of NSS with no red rust visible to unaided eye.
Coating Strategies
To pass demanding salt spray durations, aluminum and steel parts use:
- Anodizing (aluminum) — controlled oxide layer, 5–25 µm thick
- Cataphoretic ED-coating (e-coat) — electrostatically deposited primer, 20–30 µm thick
- Powder coating — robust topcoat for visible parts
- Zinc-rich primer — sacrificial protection for fasteners
- Trivalent chromium passivation — replacement for hexavalent chromium (RoHS)
Test Reporting
A complete salt spray test report should include:
- Test standard and revision
- Sample identification (part number, lot, date code)
- Coating system description
- Chamber conditions (temperature, pH, collection rate)
- Inspection intervals and observations
- Photos at start and at each interval
- Final pass/fail with rating per ASTM D1654
FAQ
Q1: Do plastic valve covers need salt spray testing? No — plastic itself does not corrode. However, copper bushings and steel bolts inside a plastic valve cover are tested separately.
Q2: How long does a 720-hour test take? 720 hours = 30 days. Plus 1–2 days for sample preparation and final evaluation. Total typical lab time: 32 days.
Q3: Is salt spray performance correlated with field corrosion? Approximately. A common rule of thumb is that 240 hours of salt spray ≈ 5 years of moderate climate exposure, but this depends heavily on coating system and field conditions. Salt spray is best used for relative comparisons, not absolute lifetime prediction.
