ISO 9227 VS ASTM B117: SALT SPRAY TEST DIFFERENCES
ISO 9227 NSS and ASTM B117 create similar neutral salt-fog environments, but the standards are not interchangeable.
Both establish a continuous neutral salt spray exposure using approximately 5% sodium chloride, a 35 °C exposure zone, and controlled fog collection. The important differences are in the details: specimen angle, cabinet verification, solution preparation language, reporting requirements, and the additional AASS and CASS environments included in ISO 9227.
If a product specification calls for one standard, run that standard. Similar conditions do not make an ISO 9227 NSS report an ASTM B117 report—or the other way around.
ASTM B117
The ASTM practice for operating salt spray apparatus, generally used for continuous neutral salt fog.
Closest comparison
Compare ASTM B117 with the NSS portion of ISO 9227—not with AASS or CASS.
ISO 9227
One international standard covering NSS, AASS, and CASS salt spray exposures.
Current references: ISO 9227, its amendment, and ASTM B117. Always use the revision required by the governing specification.
ISO 9227 vs. ASTM B117: Side-by-Side
| Comparison Point | ASTM B117 | ISO 9227 |
|---|---|---|
| Scope | Practice for creating and maintaining a salt spray environment. | Specifies the apparatus, reagents, and procedures for NSS, AASS, and CASS. |
| Neutral salt spray | Continuous neutral salt fog. | NSS is the closest ISO 9227 counterpart. |
| Additional environments | AASS and CASS are covered by separate ASTM documents, not B117. | Includes NSS, AASS, and CASS in the same standard. |
| Neutral solution | 5 ± 1% sodium chloride by mass. | 50 ± 5 g/L sodium chloride. |
| Neutral collected-solution pH | 6.5 to 7.2. | 6.5 to 7.2 for NSS. |
| Exposure-zone temperature | 35 ± 2 °C. | 35 ± 2 °C for NSS and AASS; 50 ± 2 °C for CASS. |
| Specimen angle | Generally 15° to 30° from vertical unless otherwise specified. | Generally 15° to 25° from vertical unless otherwise specified. |
| Fog collection | 1.0 to 2.0 mL/h per 80 cm² of horizontal collecting area. | 1.5 ± 0.5 mL/h per 80 cm² of horizontal collecting area. |
| Cabinet corrosivity | Controls operating variables and warns that results can vary between chambers. | Includes a defined method for checking cabinet corrosivity with reference specimens. |
| Exposure duration | Established by the governing product or material specification. | Established by the governing product or material specification. |
| Pass/fail criteria | Not supplied by B117. | Not supplied by ISO 9227. |
| Service-life prediction | Stand-alone results should not be converted directly into field life. | Not intended to predict long-term corrosion resistance or rank unlike materials. |
The practical answer: ASTM B117 and ISO 9227 NSS are close enough that the same properly configured chamber can often run both. They are not close enough to ignore the standard named on the drawing, purchase order, qualification plan, or customer specification.
Auto Technology M Series Size 22 salt fog chamber.
ISO 9227 Covers Three Salt Spray Environments
The largest structural difference is simple: ASTM B117 addresses the basic salt spray practice, while ISO 9227 places three continuous salt spray exposures in one document.
NSS — Neutral Salt Spray
NSS uses a neutral sodium chloride solution and a 35 ± 2 °C exposure zone. It applies broadly to metals and alloys, metallic coatings, conversion coatings, anodic oxide coatings, and organic coatings on metal. This is the ISO 9227 environment that most closely resembles ASTM B117.
AASS — Acetic Acid Salt Spray
AASS acidifies the sodium chloride solution with acetic acid. The collected solution is maintained at pH 3.1 to 3.3, while the exposure zone remains at 35 ± 2 °C. ISO identifies AASS as particularly useful for decorative copper-nickel-chromium and nickel-chromium coatings and for certain anodic and organic coatings on aluminum.
CASS — Copper-Accelerated Acetic Acid Salt Spray
CASS adds copper(II) chloride to the acidified salt solution and raises the exposure-zone temperature to 50 ± 2 °C. It is used primarily for decorative copper-nickel-chromium and nickel-chromium coatings and can also be used for anodized aluminum and other applications specifically calling for CASS.
In the ASTM system, the closest separate counterparts are ASTM G85 Annex A1 for continuous acetic acid salt spray and ASTM B368 for CASS. They should not be represented as automatically interchangeable with ISO 9227; use the document named by the governing specification.
Differences That Matter in the Laboratory
Specimen Position Is Not Identical
ASTM B117 generally permits the surface of interest to be positioned 15° to 30° from vertical. ISO 9227 generally uses 15° to 25°. If racks are fixed at one angle, confirm that the angle falls within the standard actually being run and any tighter requirement imposed by the product specification.
ISO 9227 Includes Cabinet Corrosivity Verification
ISO 9227 includes a procedure for evaluating the corrosivity of the cabinet environment with reference specimens. This is separate from routine measurement of temperature, collected volume, concentration, and pH. Use the prescribed reference material, preparation, exposure, cleaning, and mass-loss procedure from the applicable ISO 9227 revision.
ISO 9227 Requires More Than One Temperature Capability
A chamber intended only for B117 or ISO 9227 NSS operation at 35 °C may not be equipped for CASS at 50 °C. CASS also requires compatible wetted materials and strict control of an acidified, copper-containing solution. Confirm the chamber configuration before assuming that NSS capability includes CASS.
The Standards Describe Similar Quantities Differently
ASTM B117 expresses the neutral solution as a mass percentage. ISO 9227 expresses its sodium chloride concentration in grams per liter. The fog-collection limits are numerically equivalent, but the standards present them differently. Copying values from one document into a procedure for the other is an unnecessary source of audit problems.
The Report Must Name the Standard Actually Run
Record the standard and revision, exposure type, specimen preparation and orientation, exposure duration, interruptions, operating conditions, collection results, post-exposure handling, evaluation method, and deviations required by the applicable documents. Do not report “ASTM B117 / ISO 9227” as though one exposure automatically certifies compliance with both.
Can the Same Chamber Run Both Standards?
Usually, yes—for ASTM B117 and ISO 9227 NSS. Both use a continuous neutral salt fog at 35 °C with similar collection and chemistry requirements. The chamber still has to be operated and documented according to the selected standard.
AASS and CASS require more scrutiny. Acidified solutions change the material-compatibility and cleaning requirements, while CASS requires a 50 °C exposure zone. A chamber configured only for neutral salt spray should not be assumed to support them.
| Required Exposure | Chamber Consideration |
|---|---|
| ASTM B117 or ISO 9227 NSS | Continuous neutral salt fog at 35 °C with compliant collection, conditioned air, and solution control. |
| ISO 9227 AASS | Acidified-solution compatibility, controlled pH, suitable solution handling, and thorough changeover procedures. |
| ISO 9227 CASS | Acidified copper-containing solution, compatible wetted materials, and a chamber configured to maintain 50 ± 2 °C. |
Auto Technology’s Salt Fog & Humidity chambers can be configured around the standards and exposure types your laboratory actually needs. For the larger equipment-selection discussion, see ASTM B117 salt spray chamber requirements. For operating details, see How to run ASTM B117 salt spray testing.
Need testing instead of equipment? Auto Technology’s materials and corrosion laboratory performs salt spray exposures for qualification, research, and independent testing programs.
Send the standard and revision, exposure type, specimen dimensions and quantity, required duration, and reporting requirements.
Frequently Asked Questions
Are ISO 9227 and ASTM B117 the same test?
No. ASTM B117 and ISO 9227 NSS create similar continuous neutral salt-fog environments, but their detailed requirements are not identical. ISO 9227 also includes AASS and CASS, which are not part of ASTM B117.
Can the same chamber run ASTM B117 and ISO 9227?
A properly configured chamber can usually run ASTM B117 and ISO 9227 NSS. AASS and CASS require compatible wetted materials, appropriate solution handling, and—for CASS—the ability to maintain a 50 ± 2 °C exposure zone.
Which is more severe: ASTM B117 or ISO 9227?
ASTM B117 and ISO 9227 NSS use similar neutral salt-fog conditions, so neither is simply the “more severe” version. ISO 9227 AASS and CASS are more aggressive acidified environments intended for particular coatings and materials. Test severity should not be confused with relevance to the product’s service environment.
Does either standard specify how many hours a test must run?
No. ASTM B117 and ISO 9227 establish exposure procedures but do not assign one universal duration or pass/fail criterion. Those requirements come from the governing product, material, coating, customer, or purchase specification.
What are the ASTM counterparts to ISO 9227 AASS and CASS?
ASTM G85 Annex A1 is the closest ASTM practice for continuous acetic acid salt spray, while ASTM B368 covers CASS. Similar exposure names do not make the documents automatically interchangeable; use the standard required by the governing specification.
Can salt spray hours be converted into years outdoors?
No universal conversion exists. ASTM warns against using stand-alone B117 results as a direct prediction of natural-environment performance, and ISO 9227 states that its methods are not intended to predict long-term corrosion resistance.