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ASTM B117 and ISO 9227 Neutral Salt Spray testing are often considered broadly comparable because they both use a NSS, generally maintained at approximately 35°C. This similarity means many organizations use the two standards interchangeably for basic corrosion screening. However, ISO 9227 provides additional options that significantly increase corrosive severity. AASS introduces acidic conditions that accelerate attack on decorative coatings, while CASS further increases corrosion rates through the addition of copper ions and higher test temperatures.
IEC 60068-2-11 differs because it typically incorporates exposure and assessment approaches intended to replicate environmental contamination of electrical equipment rather than solely maximizing corrosion rates. RTCA DO-160G introduces exposure regimes intended to simulate aircraft operational environments. The test sequence includes consideration of salt deposition and post-exposure effects that may continue after the chamber exposure itself has ended. The resulting failure mechanisms often involve electrical connectors, bonding interfaces, grounding points, moving assemblies, and electronic systems rather than simply coated surfaces.
The table below shows the differences between each standards solution:
| Standard | General | pH (Measured Temp) | Specific Gravity | Conductivity in µS/cm | Notes |
|---|---|---|---|---|---|
| ASTM B117 | 5% Solution, 50g/l +- 5g/l, with max 0.3% Impurities by mass. | 6.5 to 7.2 @ 23°C +-3°C | *Using Salinity Hydrometer* 4 to 6% @ 25°C | No more than 5.0 µS/cm | Type IV Water from D1193 (Deionised, Electrodionisation, Reverse Osmosis Water. pH 5.0 to 8.0) NaCl Reagent Grade NaOH or HCl if pH needs adjustment |
| ISO 9227 (NSS) | 5% Solution, 50g/l +- 5g/l, with max 0.5% Impurities by mass | 6.5 to 7.2 @ 25°C | 1.029 to 1.036 @ 25°C + - 2°C | No more than 20 µS/cm | Deionised Water NaCl HCl or NaOH or if pH needs adjustment |
| ISO 9227 (AASS) | 5% Solution, 50g/l +- 5g/l, with max 0.5% Impurities by mass | 3.0 to 3.3 @ 25°C | 1.029 to 1.036 @ 25°C + - 2°C | No more than 20 µS/cm | Deionised Water NaCl HCl or NaOH or if pH needs adjustment |
| ISO 9227 (CASS) | 5% Solution, 50g/l +- 5g/l, with max 0.5% Impurities by mass | 3.0 to 3.3 @ 25°C | 1.029 to 1.036 @ 25°C + - 2°C | No more than 20 µS/cm | Deionised Water NaCl HCl or NaOH or if pH needs adjustment. |
| IEC 60068-2-11 | 2-11 5% Solution, 50g/l +- 5g/l, with max 0.5% Impurities by mass | 6.5 to 7.2 @ 25°C | 1.029 to 1.036 @ 25°C + - 2°C | No more than 20 µS/cm @ 25°C +- 2K | Deionised Water NaCl HCl or NaOH or if pH needs adjustment |
| RTC DO 160G Section 14 | 5% + - 1% Solution, with max 0.5% Impurities by mass | 6.5 to 7.2 (Can be measured electrometrically or by bromothyl blue or via litmus paper) | Refer to Figure RTC-DO-160G, Section 14, Pg 14-7, Fig. 14-1 | N/A | Distilled or Demineralised water |
The most misunderstood difference is the way results are evaluated.
ASTM B117 contains no universal pass or fail requirement. A specification may call for 500, 1,000, or 2,000 hours of exposure with limits on red rust, white corrosion, blistering, or coating degradation. The acceptance criteria come from a separate document. ISO 9227 operates similarly, the standard describes how testing is performed, but product-specific requirements determine what constitutes success or failure. Different industries may demand entirely different performance levels despite using the same test method.
IEC 60068-2-11 evaluates whether environmental exposure has adversely affected the intended function of the equipment. Corrosion observations remain important, but equipment performance increasingly becomes part of the assessment.
RTCA DO-160G places the greatest emphasis on functionality. After exposure, equipment is typically inspected and evaluated to verify that operational requirements continue to be met. Corrosion may be recorded, but the decisive factor is whether the product still satisfies its performance and safety requirements. For aerospace certification, an apparently minor defect that affects reliability or functionality can become far more significant than visible corrosion.
A component that passes 1,000 hours of ASTM B117 testing may still fail IEC 60068-2-11 if salt contamination causes electrical degradation. Similarly, a product that satisfies IEC requirements may not automatically comply with RTCA DO-160G because the aerospace standard requires demonstration of continued airborne functionality under a specific qualification framework.
Likewise, a successful ISO 9227 CASS test does not mean a product is qualified for aircraft service. It merely demonstrates resistance to a highly aggressive corrosion environment. Aerospace qualification requires a much broader assessment of operational performance.
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