Salt spray corrosion test

Salt spray is an artificial condition created in the laboratory to simulate a highly corrosive environment, typical of marine or industrial areas, where materials are exposed to high levels of sodium chloride (salt). Salt spray testing, also known as salt spray corrosion testing, is a standardized procedure used to evaluate the corrosion resistance of materials and coatings.
This test involves exposing the specimen to a fine mist of salt water, inside a test chamber, for a specified period of time in order to observe the reaction of the material and detect any signs of degradation. Its importance lies in its ability to simulate in an accelerated manner the corrosive stress to which a material and/or coating is exposed during normal service life.

There are several international standards, such as ISO 9227 and ASTM B117, that regulate the conditions under which these tests are performed to ensure consistency and repeatability of results. The technical elements of salt spray testing include strict control of salt concentration, temperature and humidity, which are crucial aspects of accurate and effective salt spray analysis.

Salt spray test: what it is

Salt spray testing is an accelerated environmental test in an artificial atmosphere used to evaluate the corrosion resistance of materials, coatings and finished products. But what is salt spray? It is a simulated laboratory condition that recreates a highly corrosive environment, typical of coastal or industrial areas, where materials are exposed to high concentrations of sodium chloride (salt). During the test, also known as salt fog analysis, specimens are placed inside a test chamber at a specific angle to the vertical, where they are exposed to a fine fog composed of an atomized salt solution. This continuous exposure to salt spray accelerates the corrosion process, allowing observation of how the material reacts over time. The salt spray test concludes with a visual inspection and, if necessary, further analysis to identify any signs of oxidation, corrosion, or degradation of the material. This salt spray test is essential for predicting the durability and quality of materials in environments that simulate the actual corrosive conditions they will be subjected to during their lifetime. To determine the simulation conditions for this type of corrosion test, reference is made to specific industry standards.

Salt spray testing is essential for predicting the durability and quality of materials in environments that simulate the actual corrosive conditions they will be subjected to during their lifetime. Specific industry standards are referenced to determine the simulation conditions for the corrosion test.

Why salt spray analysis

Salt spray testing is critically important for evaluating the corrosion resistance of materials and coatings that will be exposed to aggressive environmental conditions, such as those found in coastal areas, industrial environments, or on vehicles exposed to weathering.

This type of salt spray corrosion testing is essential to ensure that materials used in these settings maintain their structural and functional integrity over time. Performing a salt spray test allows early identification of potential corrosion problems, preventing costly failures and ensuring the safety and durability of products. It is especially important for industries such as automotive, aerospace, biomedical, shipbuilding, and construction, where materials are often exposed to severe corrosive conditions. In addition, this test is crucial for meeting industry regulations that require specific testing for corrosion resistance, making salt spray analysis an indispensable tool for certification and marketing of products in regulated markets.

Types of salt spray tests

There are different types of salt spray tests, and the difference lies in the chemical composition of the fog:

Neutral salt spray uses sodium chloride in solution at 5% concentration
Acetic salt spray to 5% sodium chloride solution adds acetic acid. It is used for coatings: copper-nickel-chromium, nickel-chromium and anodized aluminum.
Cupro acetic salt mist consists of 5% sodium chloride solution with acetic acid and the addition of copper chloride. It is used for coatings: copper-nickel-chrome, nickel-chrome and anodized aluminum.

Salt spray regulations

There are hundreds of specific standards that require both quantitative and qualitative analysis.
Standards such as ISO 9227 and ASTM B117 regulate the conditions under which salt spray testing is performed to ensure consistency and repeatability of results.

In particular, ASTM B117 regulates neutral salt spray.

Instead, the UNI EN ISO 9227 standard regulates the three different types of salt spray:

neutral salt spray
acetic salt spray
cupro acetic salt mist

In the evaluation of metallic coatings, the most widely used reference standard is UNI EN ISO 10289.
For the evaluation of coatings with electrolytic zinc, UNI EN ISO 2081 is used.

For painted surfaces, there are various types of defects that can occur:

Occurrence of blisters (blisters) – the degree of blistering is calculated UNI EN ISO 4628-2
occurrence of corrosion – the degree of corrosion is calculated using UNI EN ISO 4628-3
appearance of cracking – the degree of cracking is calculated using UNI EN ISO 4628-4
occurrence of flaking – the degree of flaking is calculated using UNI EN ISO 4628-5
Presence of delamination and subfilm corrosion for calculation using UNI EN ISO 4628-8

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Salt spray in TEC Eurolab: our tests

In the next subsections, all technical aspects related to salt spray testing will be discussed in depth, providing a detailed overview of how this salt spray corrosion test is performed and what are the key parameters that influence the results. The operational steps and relevant regulations will be reviewed, as well as describing the technologies and machinery used to conduct salt spray analysis accurately and in accordance with international standards. It will also illustrate how these techniques are applied at TEC Eurolab, ensuring that each salt spray test is performed with the utmost rigor and professionalism, offering reliable results for proper corrosion resistance assessment.

Test execution procedure

At TEC Eurolab, the procedure for performing the salt spray test follows strict protocols to ensure the accuracy and reliability of the results. The process begins with the preparation of samples, which are placed inside a special chamber where they are exposed to a fine mist composed of a sodium chloride solution. If required in product or process specifications, the samples are placed inclined at an angle between 15° and 30° from vertical as specified by standards. This salt spray corrosion test is performed by carefully monitoring the parameters of temperature, pH, conductivity, solution density, rainfall constant and salt solution concentration in accordance with international standards. During salt fog analysis, samples are constantly monitored to observe how they react to the corrosive environment, allowing any signs of degradation or corrosion to be identified. At the end of the salt spray test, the samples are examined and analyzed to determine corrosion resistance and provide certification of compliance by referring to the material’s industry standards.

Tools and equipment used

To carry out salt spray tests, we use specific machines in TEC Eurolab: salt spray test chambers. Certain conditions are then required under which the test must take place. In this section we explain how salt spray chambers work and what the test conditions are.

Salt spray test chamber

Salt spray chambers consist of a test compartment made of inert material that does not affect the corrosivity of the machine, closed by a canopy-shaped cover such that the condensed solution cannot drip onto the samples inside the test compartment. Next to the test compartment is the reservoir where the 5 percent salt solution is prepared with enough volume capacity to cover sufficiently long test periods. The salt solution prepared in the reservoir goes into the chamber via a pump for continuous replenishment of the required amount of solution to the salt solution atomizing nozzle. In addition to the reservoir, there is a saturation tower used to humidify the compressed air to about 95 percent relative humidity. Only distilled water is used within the chamber circuits and in the preparation of the solution. There is also a thermoregulation device of the test chamber to reach the temperature of 35±2°C in accordance with the requirements expressed in the reference standards UNI EN ISO 9227 and ASTM B117. The machine is equipped with a control system to check the temperature ramp-up in such a way as to avoid exceeding the minimum maximum threshold allowed by the standards. All described components of the process are subject to periodic calibration.

Test conditions

Water: water for the preparation of the solution is obtained through appropriate treatment of mains water. The mains water is subjected to distillation, demineralization and finally reverse osmosis. Such that it has a conductivity of no more than 20 µS/cm at 25°C and a pH between 5 and 8. These limits are always in reference to the standards governing the salt spray process UNI EN ISO 9227 and ASTM B117.
Salt solution: the test solution must have a concentration of 5 wt% analytical grade sodium chloride. The following solution in and out of the chamber is analyzed by checking the solution density, pH, conductivity and rainfall constant.
- Density is measured through a digital Densimeter properly calibrated with its standard reference solution.
- The pH is measured with a pH meter, where the probe is present, which is calibrated with appropriate standard solutions covering the ranges required by the test.
- Conductivity is coupled to the pH meter with its conductivity probe, which is also in turn calibrated with its standard reference solution.
- The rain gauge constant is calculated by measuring the volume of rain gauges collected by dividing by the operating hours of the climate chamber.

Supports for samples in the chamber

The holders in turn are also made of inert material so as not to interact with the corrosive properties of salt spray. Different specimen holders are available depending on the type of specimens to be tested such as screws, laminations, data, bars, plates, etc… Specimens are placed inside the specimen holders inclined at a specific angle, usually it is between 6° and 30°. The inclination is indicated in the customer’s product specifications. The arrangement of the specimens is such as to ensure that the salt spray can circulate freely and evenly around them so as to prevent stagnation of the solution on the specimens themselves. Each sample holder is identified by a code to which a calibration certificate corresponds.

Applications and industries involved

Salt spray testing is widely used in many industries to ensure the corrosion resistance of materials and components exposed to aggressive environmental conditions.

Major applications of this salt spray corrosion test include theautomotive industry, where it is critical to test the durability of coatings and metal components.

Theaerospace industry also frequently uses salt spray testing to verify the strength of materials used in aircraft and equipment, which often operate in environments with high exposure to corrosion. In addition, salt spray testing is crucial in the marine and construction industries, where structures and components must resist corrosion caused by salt water and adverse weather conditions. This type of testing is therefore essential to ensure that products and materials used in these sectors are reliable and durable, preventing premature failure and ensuring safety and structural integrity over time.

Regardless of the area of application, each component in its technical drawing-if it will be used in areas of high corrosive risk-submits the hours of salt spray resistance and the standard according to which its corrosion resistance compliance must be certified.

Test results and interpretation

Salt spray test results provide crucial information on the corrosion resistance of materials and coatings.

After completing the salt spray test, samples are carefully examined for signs of oxidation, discoloration, blistering or other indicators of degradation.Salt spray analysis allows for an assessment of how effectively a material can withstand corrosive environments, and the results obtained are compared to relevant regulatory standards to determine product compliance.

Interpretation of the results of a salt spray test is critical to identify potential weaknesses in the materials tested and to make any improvements to manufacturing processes or protective coatings. This evaluation process is essential to ensure that products are able to maintain their performance and structural integrity over time, even under extreme conditions.

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