ASTM B117 is the oldest, most widely recognised, and universally used standard for salt spray testing. First published in 1939, it provides a standardised method for creating and maintaining a controlled, accelerated corrosive environment within a salt spray test chamber.
It is important to note that ASTM B117 is a practice, not a complete test specification. It details the mandatory parameters for the test apparatus and procedure, but it does not specify the test duration or what constitutes a “pass” or “fail.” These criteria are typically defined by the end-user, the material specification, or the organisation requesting the test.
The primary purpose of the test is to evaluate the relative corrosion resistance of metals and coated materials. It is an excellent quality control tool for comparing the performance of different samples or for checking the consistency of a production process.
Key Parameters of the ASTM B117 Test:
- Test Method: It specifies a single, continuous exposure test known as the Neutral Salt Spray (NSS) test.
- Salt Solution: The test uses a solution of 5% (by weight) sodium chloride (NaCl) mixed with Type IV reagent grade water.
- pH Level: The pH of the collected solution must be maintained in a neutral range, specifically between 6.5 and 7.2.
- Temperature: The test chamber is kept at a constant, elevated temperature of 35°C (+1.1 to -1.7°C).
- Fog Collection Rate: The atomised salt fog must fall out onto collection funnels at a rate of 1.0 to 2.0 mL per hour (per 80 cm² of collection area).
- Specimen Orientation: Test specimens are typically supported at an angle between 15° and 30° from the vertical.
Due to its long history and widespread use, especially in North America, ASTM B117 is a benchmark for industries such as automotive, aerospace, paints and coatings, and general manufacturing. For all practical purposes, its Neutral Salt Spray (NSS) procedure is functionally equivalent to the NSS test described in ISO 9227.
