Salt Spray Test
Salt Fog Test
Salt Spray Test is one of the key methods used to study corrosion, which remains one of the most persistent challenges affecting materials and coatings across industries ranging from automotive to marine, construction, electronics, and consumer goods. To address this, standardized laboratory tests like the Salt Mist Test have become essential tools for evaluating a material’s or coating’s resistance to corrosive environments.
The Salt Fog Test is an accelerated corrosion testing method designed to simulate the effects of long-term exposure to moist, salty environments. This test is commonly used to assess the protective performance of coatings, such as paints, platings, anodized layers, and conversion coatings. The test exposes samples to a fine mist or fog of salt water under controlled conditions in a sealed chamber to induce corrosion. This method provides rapid feedback on how a coating or material will perform in harsh, real-world conditions, especially in marine, coastal, or winter-weather environments.
While primarily used on metallic substrates, Corrosion Testing can also be relevant for non-metals such as plastics and composite materials that are coated or painted. Corrosion can affect not just unprotected metal, but also tempered steels, high-alloy materials, and even surfaces with protective coatings, if the coating is improperly applied or damaged.
Standards Followed in Salt Mist Test:
- ASTM B117
- ISO 9227
- IEC 60068-2-11
- MIL-STD-810H Method 509.7
- EN ISO 7253
Purpose of Salt Spray Testing
Salt Spray Testing is often used for:- Quality control during production
- Benchmarking and comparison of coatings
- Evaluating coating integrity after physical damage (e.g., scratches)
- Research and development of new surface treatments
It is important to note that while Salt Spray Testing is extremely useful for comparing performance and identifying defects or weak spots, it does not directly predict the exact service life of a material in a real-world environment. Actual environmental exposure conditions may vary greatly, involving factors like UV light, temperature fluctuations, air pollutants, and mechanical wear, which are not always simulated in salt fog tests.
Purpose of Corrosion Testing
Samples to be tested are placed inside the salt spray chamber, usually at a 15° to 30° angle from vertical. The salt solution is atomized using pressurized, purified air, creating a dense fog of salty droplets that settle on the samples’ surfaces. Exposure durations can range from a few hours to over 1000 hours, depending on the requirements of the test or the specification being followed.
In some cases, artificial defects, such as cross-hatch cuts or scratches, are deliberately introduced into the coating to test how well the material resists corrosion at vulnerable points. As corrosion progresses, dendritic patterns or “corrosion creepage” can form along the scratch lines. The length of these dendrites is often measured as a quantitative indication of the coating’s ability to prevent corrosion from spreading.
Salt Spray Testing is commonly applied in industries such as:
- Automotive – Testing car parts, underbody coatings, and chassis components
- Marine and Offshore – Evaluating metal components exposed to seawater
- Construction – Ensuring durability of exterior fasteners, railings, and fixtures
- Electronics – Assessing the corrosion protection of connectors and enclosures
- Consumer Goods – Testing decorative or functional finishes on appliances, tools, and hardware
Standard Test Protocol – ASTM B117
The most widely accepted procedure for conducting Salt Spray Testing is defined by the ASTM B117 standard. Developed by ASTM International, this standard outlines how to create and maintain a corrosive environment using pressurized air to atomize a 5% sodium chloride (NaCl) solution, producing a consistent and fine salt mist inside a closed chamber.
- Temperature Range: Typically maintained between 35°C and 50°C, with the standard condition being 35°C.
- Humidity Level: Approximately 95% Relative Humidity (RH) is maintained in the chamber.
- Salt Solution: A 5% NaCl solution with a pH between 6.5 and 7.2.
- Spray Rate: Typically 1 to 2 ml of salt solution per 80 cm² per hour.
These tightly controlled conditions ensure repeatability and reliability across laboratories and testing facilities worldwide.
Results are evaluated based on:
- Appearance of rust, blistering, or coating delamination
- Time taken for corrosion to appear
- Corrosion coverage or penetration
- Length of corrosion creep from damaged areas
Visual inspection is commonly used, often in accordance with ISO 10289 or ASTM D610 for rating corrosion and rust grades. Some organizations also apply more advanced methods such as microscopic examination, weight loss measurements, or electrochemical analysis to supplement visual assessments.
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