Testing Standards
ASTM B117: The Complete Guide to Salt Spray Testing
What is ASTM B117? Everything you need to know about the salt spray test standard — test setup, duration, specimen preparation, and how it differs from ISO 9227.
Published 2026-03-13 · 8 min read
Tags: astm-b117, salt-spray, corrosion-testing, salt-fog, ISO-9227
What is ASTM B117?
ASTM B117 — formally titled Standard Practice for Operating Salt Spray (Fog) Apparatus — is a test standard published by ASTM International that specifies the conditions for conducting a neutral salt spray (NSS) corrosion test. First published in 1939 and regularly revised, ASTM B117 does not define pass/fail criteria. Instead, it defines the test method — the apparatus, the salt solution, temperature, and procedure — so that results from different laboratories are reproducible and comparable.
ASTM B117 is the world's most widely used salt spray (fog) test standard, referenced by thousands of product specifications across automotive, aerospace, marine, hardware, and consumer goods industries.
What Does ASTM B117 Test For?
ASTM B117 is used to assess the corrosion resistance of materials and surface coatings. It creates a controlled, accelerated corrosion environment by continuously exposing test specimens to a fine mist of salt solution. While it cannot precisely predict real-world service life, it is an excellent comparative test — allowing engineers to compare the relative corrosion resistance of different coatings, materials, and surface treatments under identical, repeatable conditions.
ASTM B117 Test Setup: The Key Requirements
1. Salt Solution
The test solution is a 5% (±1%) sodium chloride (NaCl) solution by weight, prepared using reagent-grade or better NaCl dissolved in distilled or deionised water. The pH of the solution as collected in the chamber must be between 6.5 and 7.2 at 25°C.
2. Test Temperature
The exposure zone of the salt spray chamber must be maintained at 35°C ±2°C. This temperature is critical for reproducibility and must be continuously monitored and controlled.
3. Fog Collection Rate
The fog should be dense enough to collect at a rate of 1.0 to 2.0 mL per 80 cm² of horizontal collection area per hour, averaged over the test duration. This is verified using fog collection funnels placed at multiple locations within the chamber.
4. Specimen Placement
Flat panels are placed at 15–30° from the vertical. Specimens must not touch each other, and their arrangement must not affect the fog distribution. Scribed or scratched specimens are used when evaluating coating adhesion and under-film corrosion resistance.
5. Test Duration
ASTM B117 does not specify a test duration — this is defined by the product or specification being tested against. Common test durations include:
- 96 hours — many hardware and fastener specifications
- 240 hours — general industrial coatings
- 500 hours — automotive OEM requirements (e.g., GM, Ford specs)
- 1,000 hours — premium automotive and aerospace coatings
- 2,000+ hours — high-performance marine and offshore coatings
How to Prepare Specimens for ASTM B117
- Clean specimens thoroughly to remove oils, fingerprints, and contaminants before testing.
- Apply scribe marks (if required by the specification) using a carbide-tipped scriber to a controlled depth.
- Record initial condition with photographs where applicable.
- Label specimens clearly using methods that will survive the test (corrosion-resistant labels or engraving).
ASTM B117 vs ISO 9227: Key Differences
ISO 9227 is the international equivalent of ASTM B117 and is the preferred standard in Europe and much of Asia. While both standards specify salt spray testing, there are some key differences:
| Parameter | ASTM B117 | ISO 9227 |
|---|---|---|
| Test types covered | NSS (Neutral Salt Spray) only | NSS, AASS (Acetic Acid), CASS (Copper-Accelerated) |
| NaCl concentration | 5% ±1% | 50 g/L ±5 g/L (~5%) |
| pH range | 6.5–7.2 | 6.5–7.2 (NSS), 3.1–3.3 (AASS/CASS) |
| Chamber temperature | 35°C ±2°C | 35°C ±2°C |
| Primary use region | Americas, global OEM specs | Europe, Asia, international tenders |
In practice, a salt spray chamber meeting ASTM B117 requirements will generally also meet the ISO 9227 NSS requirements. For AASS and CASS testing — which use acidified solutions and copper chloride additions — ISO 9227-compliant chambers are required.
Common Materials Tested to ASTM B117
- Electroplated coatings: zinc, cadmium, nickel, chrome plating on steel
- Organic coatings: paints, primers, powder coatings, and e-coats
- Anodised aluminium and chromate conversion coatings
- Hot-dip galvanised and zinc-alloy coated steel
- Fasteners: bolts, nuts, washers, and screws per ASTM F1137, F2329, etc.
- Automotive components: body hardware, brackets, springs, and connectors
Evaluating Results: What to Look For
At the end of the ASTM B117 test, specimens are evaluated for corrosion according to the applicable product standard. Common evaluation criteria include:
- Red rust formation on bare metal or through a coating (failure criterion in most specs)
- White rust on zinc or zinc-alloy coatings (less severe than red rust)
- Blistering, loss of adhesion, or undercutting from scribe marks
- Percentage of corroded surface area (rated using ASTM D610 or ISO 4628-3)
How to Choose a Salt Spray Test Chamber for ASTM B117
When selecting a salt spray test chamber for ASTM B117 compliance, look for:
- Proven temperature uniformity: chamber should maintain 35°C ±2°C across the entire test zone
- Fog collection rate verification: must deliver 1.0–2.0 mL/hr/80 cm²
- Corrosion-resistant construction: PVC or FRP-lined interior to prevent chamber self-contamination
- Traceable calibration: chamber should be calibrated with a certificate traceable to national standards
- Capacity: size the chamber to your typical specimen dimensions with room for proper spacing
Looking for an ASTM B117-compliant salt spray test chamber? Explore Indeecon's range or request a quote.
Frequently Asked Questions About ASTM B117
- Does ASTM B117 predict real-world corrosion life?
- No. ASTM B117 is a comparative test, not a prediction tool. Results are useful for comparing different coatings or materials under identical conditions, but hours in a salt spray chamber cannot be directly converted to years of real-world service life.
- Can plastics be tested to ASTM B117?
- Plastic components are sometimes tested to ASTM B117 to evaluate the corrosion resistance of any metal inserts, fasteners, or plating on the plastic. The plastic itself is not susceptible to salt fog corrosion but may be evaluated for dimensional or surface effects.
- Is ASTM B117 the same as a 'salt spray test'?
- 'Salt spray test', 'salt fog test', and 'ASTM B117 test' are all commonly used to refer to the same type of neutral salt spray corrosion test. 'Salt mist test' is another term used, particularly in IEC standards.
Summary
ASTM B117 is the foundational salt spray test standard — defining the conditions under which corrosion testing must be conducted to produce repeatable, comparable results. While it does not set pass/fail criteria, it provides the universal framework that product-specific specifications build upon.
Indeecon manufactures ASTM B117-compliant salt spray test chambers and offers calibration and maintenance services to keep your equipment performing to standard. Contact us to discuss your requirements.