ASTM B117 Salt Spray Test Standard Explained

What Is the ASTM B117 Salt Spray Test Standard?

In industries such as automotive components, metal processing, electronic equipment, aerospace, and surface treatment, corrosion remains one of the key factors affecting product reliability and service life. To evaluate the corrosion resistance of materials and protective coatings under accelerated laboratory conditions, the salt spray test has become one of the most widely used accelerated corrosion testing methods worldwide.

Among various salt spray test standards, ASTM B117 “Standard Practice for Operating Salt Spray (Fog) Apparatus” is one of the most commonly referenced standards. It is widely used by manufacturers to evaluate the corrosion resistance of metal materials, coatings, plating systems, and corrosion protection processes.

It is important to understand that ASTM B117 is not a product performance specification. It does not define how many hours a material or product must withstand salt spray exposure to be considered qualified. Instead, it specifies the operating procedures, environmental conditions, and testing requirements for salt spray testing equipment to ensure consistent and repeatable test results.

ASTM B117 Salt Spray Test Principle and Key Test Conditions

The ASTM B117 salt spray test accelerates corrosion by simulating a high-salt, high-humidity environment. During the test, a sodium chloride solution is atomized using compressed air to create a continuous salt fog atmosphere. The salt mist settles on the surface of the test specimens, and chloride ions gradually break down protective layers on the metal surface, accelerating electrochemical corrosion processes.

The typical test conditions specified in ASTM B117 include:

• A 5% ± 1% sodium chloride (NaCl) solution;

• A salt solution pH value maintained between 6.5 and 7.2;

• A test chamber temperature maintained at 35°C ± 2°C;

• A controlled salt fog collection rate within the specified range;

• Continuous salt spray exposure during the test period.

Maintaining stable test conditions is essential for reliable salt spray test results. Variations in temperature, salt concentration, or spray volume can affect corrosion rates and lead to inconsistent test outcomes.

How Is an ASTM B117 Salt Spray Test Conducted?

When performing a salt spray test according to ASTM B117, the test specimens must first be properly prepared. This includes cleaning the surfaces, removing contaminants, and recording the original condition of the specimens. For products with coatings, plating layers, or corrosion protection treatments, additional information such as coating type, thickness, and surface defects should also be documented.

During installation, specimens must be positioned to ensure uniform exposure to salt fog while avoiding shielding effects between samples. Throughout the test, the salt spray chamber must continuously maintain the specified temperature and spray conditions until the required exposure time is reached.

After the test is completed, specimens are cleaned and inspected to evaluate corrosion performance, including:

• The appearance of red rust;

• Formation of white corrosion products;

• Coating blistering or peeling;

• Surface cracking or corrosion propagation.

These evaluation results help determine the corrosion resistance of materials and protective systems.

How Long Should a Salt Spray Test Last?

There is no universal duration for a salt spray test. The required exposure time depends on the product type, application environment, and specific industry standards or customer requirements.

Common salt spray test durations include:

• 24 to 96 hours: Typically used for basic corrosion resistance verification;

• 240 to 500 hours: Commonly applied to industrial components and surface-treated products;

• 1,000 hours or longer: Often required for automotive parts, high-performance equipment, and products with demanding corrosion resistance requirements.

It is important to note that salt spray exposure time does not directly represent the actual service life of a product. For example, a 1,000-hour salt spray test does not mean that a product can operate in a real-world environment for 1,000 hours. Instead, it is an accelerated method used to compare the corrosion resistance of different materials and protective systems.

Therefore, the appropriate test duration should be determined based on product specifications, service conditions, and customer requirements rather than simply using exposure time as the sole indicator of product quality.

How Are ASTM B117 Test Results Evaluated?

A common misconception is that a longer salt spray test duration automatically indicates better corrosion resistance. However, this is not always accurate.

ASTM B117 itself does not specify how many hours a product must pass to be considered acceptable. The exposure duration is only one test parameter, while final acceptance criteria are determined by the applicable product standards or customer specifications.

Common evaluation methods include:

• Corrosion rating evaluation: Assessing the appearance of red rust, white corrosion products, and the percentage of corroded area;

• Coating performance evaluation: Checking for blistering, peeling, cracking, or coating degradation;

• Appearance evaluation: Examining color changes, gloss reduction, and other visible defects.

For example, two products may both undergo a 500-hour salt spray test but have completely different acceptance criteria depending on their intended application and industry requirements. Therefore, test results should always be interpreted within the context of the product’s actual operating environment.

What Is a Salt Spray Test Chamber Used For?

A salt spray test chamber is laboratory equipment designed to simulate corrosive salt fog environments and evaluate the corrosion resistance of metal materials, coatings, plating layers, and corrosion protection systems.

By continuously spraying a controlled salt solution inside a sealed test chamber, a salt spray test chamber accelerates the corrosion process and helps manufacturers identify potential failures that may occur during long-term product use.

Salt spray test chambers are widely used in industries including:

• Automotive components;

• Fasteners and hardware products;

• Electronic components;

• Metal structures;

• Aerospace products;

• Coatings and surface treatment industries.

It should be noted that a salt spray test chamber is not intended to completely reproduce all real-world environmental conditions. Instead, it provides a standardized and repeatable accelerated corrosion test method for comparing the performance of different materials and protection systems.

How to Select a Salt Spray Test Chamber Compliant with ASTM B117?

When selecting a salt spray test chamber, long-term stability and testing consistency are critical factors that directly influence test reliability.

First, the chamber should provide precise and stable temperature control to maintain the required test environment of 35°C ± 2°C throughout the entire testing process.

Second, the spray system should ensure uniform salt fog distribution so that all specimens receive consistent exposure conditions. The internal materials of the chamber should also have excellent corrosion resistance to prevent degradation, contamination, or premature equipment failure during long-term operation.

In addition, as laboratory automation continues to advance, many manufacturers are placing greater emphasis on intelligent equipment features, such as:

• Automatic water replenishment;

• Automatic salt solution control;

• Test data recording;

• Remote monitoring;

• Laboratory information system integration.

These capabilities improve testing efficiency, enhance data reliability, and support better quality management.