ASTM B117 Salt Spray Testing Requirements: A Practical Compliance Guide

What ASTM B117 Covers—and What It Does Not

ASTM B117 is titled Standard Practice for Operating Salt Spray (Fog) Apparatus. It is a practice, not a performance specification. Section 1 (Scope) makes clear that the standard describes the apparatus and procedures for creating a controlled salt fog environment. It does not tell you how long to test, what corrosion rate is acceptable, or whether a coated panel passes. Those decisions belong in the product specification, purchase order, or a separate evaluation standard such as ASTM D1654 or ASTM D3359.

This distinction matters because ASTM B117 salt spray testing requirements are often quoted in material certificates and supplier declarations. A supplier may state "passed 500 hours ASTM B117," but that statement is incomplete unless the acceptance criteria and evaluation method are also defined. For a broader view of how test documentation should be structured, see our guide to ASTM Material Test Certificate Requirements.

Section 3 (Significance and Use) explains that salt spray testing is useful for comparing materials or coatings under a fixed set of conditions. It is not a direct predictor of service life in every environment. Coastal, de-icing, and industrial exposures differ. Use ASTM B117 when you need a repeatable, standardized corrosion screen—not as a universal corrosion warranty.

Core Chamber and Solution Requirements

Section 4 (Apparatus) and Section 5 (Reagents and Materials) contain the hardware and chemistry rules. The chamber must be made of materials that do not affect the corrosive environment. It needs a fog atomizer, air supply, temperature control, and exhaust. The salt solution is prepared from sodium chloride and water. ASTM B117 specifies a 5% sodium chloride solution, with limits on impurities that can change corrosion behavior. The water must be sufficiently pure; typical lab practice uses distilled or deionized water that meets a recognized purity grade.

The collected solution must have a pH between 6.5 and 7.2 at 25°C. The chamber temperature is maintained at 35°C (95°F). The fog collection rate is 1 to 2 mL per hour per 80 cm² of horizontal collection area. These three checks—pH, temperature, and collection rate—are the daily heartbeat of a compliant salt spray run.

pH, Temperature, and Fog Collection Checks

ASTM B117 requires the pH to be measured on the solution collected in the chamber, not just the supply reservoir. That is because dissolved gases and evaporation can shift pH during operation. Adjust the pH with hydrochloric acid or sodium hydroxide before the test, and verify it again from collected fog. Temperature must be stable at 35°C; a fluctuation of a few degrees can change corrosion rates. Collection rate confirms the atomizer is producing a proper fog and that the chamber is not drying out or flooding.

Air pressure at the atomizer is also controlled, typically in the range of 83 to 123 kPa (12 to 18 psi), depending on the apparatus. The exact value is less important than consistency. Calibrate pressure gauges, thermometers, and pH meters on a schedule. Record every reading. If a reading drifts outside the ASTM B117 limits, stop the test, correct the condition, and document the deviation.

Specimen Preparation and Placement

Section 6 (Preparation of Apparatus) and Section 7 (Procedure) cover how specimens enter and sit in the chamber. Clean specimens before testing. Remove oils, fingerprints, and debris with a method that does not leave a protective film. Handle coated panels by their edges. If you are testing a machined or metallic part, know its surface condition and whether edges or cut faces should be masked. Masking is allowed when it reflects the real application, but it must be reported.

Specimens are supported at an angle of 15 to 30 degrees from vertical. This angle lets the fog condense and run off without pooling. Do not let one specimen drip onto another. Do not let specimens touch the chamber walls or each other. Use inert supports such as plastic or glass; metal racks can corrode and contaminate the fog. If you need to compare materials, run a control specimen with a known response. Replicates are strongly recommended because salt spray results can vary across chamber positions.

For metallic materials, the base metal specification still matters. If you are testing steel coupons, review the ASTM A36 chemical composition limits and ASTM A36 tensile strength requirements to confirm the substrate is what you think it is. Corrosion performance is only meaningful when the material identity is controlled.

Duration, Evaluation, and Reporting

ASTM B117 does not set a default duration. Common exposure periods include 24, 48, 96, 168, 720, and 1,000 hours. The correct duration comes from the product standard, customer requirement, or internal qualification plan. For packaging and distribution testing, do not confuse salt spray with transport conditioning. Our ASTM D4169 distribution testing schedule guide explains how distribution cycles are selected separately.

After exposure, evaluate specimens using the method called out in the test plan. Painted or coated panels are often rated for blistering, rust creep, and scribe creep under ASTM D1654. Adhesion may be checked with ASTM D3359. Uncoated metals may be rated for mass loss, pit depth, or visual corrosion. Section 8 (Evaluation of Results) and Section 9 (Report) require a clear record of the apparatus, solution, temperature, pH, collection rate, test duration, specimen orientation, and any deviations.

A useful report includes:

• Standard designation and edition (as cited in the test plan)
• Salt solution concentration and pH readings
• Chamber temperature and collection rate data
• Specimen description, preparation, and orientation
• Exposure duration and interruptions
• Evaluation method and results
• Operator, date, and equipment calibration status

Because ASTM B117 salt spray testing requirements are a practice, the report must connect the operating conditions to the acceptance criteria. A statement that a part "passed ASTM B117" without duration, evaluation method, and limits is not a complete compliance claim.

Common Pitfalls and Compliance Tips

The most common mistake is treating ASTM B117 as a pass/fail standard. It is not. Another is letting pH drift because only the reservoir is checked. A third is poor specimen spacing, which creates shadowing or cross-contamination. Keep the chamber clean, rinse it between campaigns, and verify the fog collection rate before every long test.

Use calibrated instruments. Log daily readings. Train operators on Section 6 and Section 7. If a customer asks for ASTM B117 salt spray testing requirements, provide the test parameters and the evaluation criteria, not just a duration. That is the difference between a meaningful corrosion test and a number on a certificate.