ISO 9227 “Salt spray Test for corrosion in artificial Atmosphere” specifies the equipment, reagents and operating procedures for the use of neutral salt spray test (NSS), acetate spray test (AASS) and copper accelerated acetate spray test (CASS) to evaluate the corrosion resistance of metallic materials with or without permanent or temporary corrosion protection.
A Preface
ISO(International Organization for Standardization) is a worldwide association of national standardization bodies (ISO member bodies). The development of international standards is usually carried out by the technical committees of ISO. Each member institution is entitled to participate in a technical committee if it is interested in a subject identified by the Committee. ISO related international organizations, government organizations, non-governmental organizations also participate in the work. ISO works closely with the International Electrotechnical Commission (IEC) on electrotechnical standardization.

International standards are prepared in accordance with the regulations established in Part 2 of the ISO/IEC Directives.

The main task of the technical committee is to develop international standards. The draft international standard adopted by the Technical Committee is then circulated to the member state bodies for voting. Publications as international standards are subject to approval by a vote of at least 75% of the member bodies.

It is important to note that some parts of such documents can be patent issues. ISO shall not be responsible for the identification of any or all patent rights.

The international standard ISO 9227 was developed by technical committee ISO/TC 156(Corrosion of Metals and Alloys).

The third edition cancels and replaces the second edition (ISO 9227:2006) and its published revisions.

ISO 9227-0 Artificial atmosphere corrosion test Salt spray test

The Introduction
There is rarely a direct relationship between salt spray resistance and corrosion resistance in other media because several factors affecting corrosion progression, such as the formation of protective films, vary greatly with the conditions encountered. Therefore, the test results cannot be used as a direct guide to the corrosion resistance of the tested metal materials. Similarly, the performance of the different materials during the test period cannot be taken as a direct guide to the corrosion resistance of these materials in use.

Nevertheless, the method provides a means of detecting the relative quality of metallic materials with or without corrosion protection.

Salt spray test is generally suitable for rapid analysis of discontinuities, holes and damage in organic and inorganic coatings corrosion protection test. In addition, for quality control purposes, comparisons can be made between samples coated with the same coating. However, as a comparative test, the salt spray test is only applicable when the coating properties are similar.

Because the corrosion stresses during the test are significantly different from those encountered in practice, the results obtained from salt spray tests are usually not possible as a comparative guide to the long-term properties of different coating systems. Corrosion test in artificial environment — salt spray test

ISO 9227-0 Artificial atmosphere corrosion test Salt spray test

1 Scope
This INTERNATIONAL standard specifies the equipment, reagents and operating procedures used in the neutral salt spray test (NSS), acetate spray test (AASS) and copper accelerated acetate spray test (CASS) to evaluate the corrosion resistance of metallic materials with or without permanent or temporary corrosion protection. The standard also describes the methodology used to assess the corrosion of the test chamber environment.

The standard does not specify the size of the sample, the exposure time of the specific product or the description of the test results. These details are provided in the appropriate product description.

The salt spray test is particularly suitable for detecting continuity, such as pores and other defects in certain metallic, organic, anodic oxide and conversion coatings.

Neutral salt spray test is a test method in which 5% sodium chloride solution with pH value in the range of 6.5 ~ 7.2 is atomized in a controlled environment. Its specific application is:

ISO 9227-0 Artificial atmosphere corrosion test Salt spray test

Metals and their alloys;

※ Metal coating (anode and cathode);

※ Conversion coating;

※ Anodic oxide coating and organic coating on metal materials.

Acetate spray test is a test method in which 5% sodium chloride solution added glacial acetic acid solution with pH value in the range of 3.1 ~ 3.3 is atomized under controlled environment. It is especially suitable for testing copper + nickel + chromium or nickel + chromium decorative coatings. It is also suitable for testing anodic coatings on aluminum.

Copper accelerated acetate spray test is a test method in which 5% sodium chloride solution with copper chloride and glacial acetic acid in the pH range of 3.1 ~ 3.3 is atomized under a controlled environment. It is suitable for testing decorative coatings of copper + nickel + chromium or nickel + chromium. It is also suitable for testing anodic coatings on aluminum.

The salt spray method is suitable for testing the relative quality of metal materials with or without corrosion protection. They cannot be used as comparative tests to evaluate the relative corrosion resistance of different materials to each other.

ISO 9227-0 Artificial atmosphere corrosion test Salt spray test

2 References
The following documents are required for the application of this document. For dated cited documents, only the cited version applies. For undated citation documents, the new version of the citation document (including all amendments) applies.

ISO 1514, Paints and varnishes — Standard sample for testing

ISO 2808, Paints and varnishes — Determination of film thickness

ISO 3574, commercial grade and press grade cold rolled carbon steel sheet

ISO 8407, corrosion of metals and alloys — Removal of corrosion products from corrosion specimens

ISO 17872, Paints and varnishes — Introductory Guide to scratch marking on coatings of metal plates for corrosion testing

ISO 9227-0 Artificial atmosphere corrosion test Salt spray test

3 Test solution
3.1 Preparation of sodium chloride solution
A sufficient amount of sodium chloride was dissolved in distilled or deionized water to obtain a concentration of 50 ± 5g/L, and the conductivity of water was not higher than 20 Ms /cm at 25 ± 2 ° C. The sodium chloride concentration of the collected spray solution should be 50±5g/L. The specific gravity range of 50±5g/L solution is 1.029 ~ 1.036 at 25℃.

The mass fraction of copper and nickel in sodium chloride should be not less than 0.001% and 0.001%, respectively, when measured by atomic absorption spectrometry and another analytical method of similar sensitivity. Contains not more than 0.1% sodium iodide by mass fraction or 0.5% of total impurities by mass fraction calculated as dry salt. Note 1: If the prepared solution has a pH outside the 6.0 to 7.0 range at 25 ± 2 ° C, investigate the presence of undesirable impurities in salt and/or water.

3.2 Adjustment of pH value
3.2.1 pH value of salt solution

According to the pH of the collected spray solution, the pH of the salt solution was adjusted to the desired value.

3.2.2 NSS test

The pH of the salt solution (3.1) was adjusted so that the pH of the spray solution collected in the test chamber (4.2) was between 6.5 and 7.2 at 25 ± 2 ° C. The pH value can be detected by electrical measurement or precision PH test paper with an accuracy of 0.3pH. Necessary corrections are made by adding hydrochloric acid, sodium hydroxide solution, or analytical grade sodium bicarbonate solution. Spray will cause the loss of carbon dioxide from the solution, which may cause a change in pH. It can be avoided by reducing the amount of carbon dioxide in the solution. For example, heat the solution to more than 35 ° C before placing the device, or prepare the solution with just boiled water.

3.2.3 AASS test

A sufficient amount of glacial acetic acid solution was added to the salt solution (3.1) to ensure that the pH of the spray solution samples collected in the test chamber (4.2) was 3.1 to 3.2. If the pH of the initially prepared solution is 3.0 to 3.1, the pH of the spray solution may be within this specified range. At the temperature of 25 ± 2℃, the pH value was detected by electrical measurement method, or the precision pH test paper with an accuracy of 0.1pH was used for routine detection. Necessary corrections were made by adding analytical grade glacial acetic acid or sodium hydroxide.

3.2.4 CASS test

A sufficient amount of copper (II) chloride dihydrate (CuCl2·2H2O) was dissolved in salt solution (3.1) to a concentration of 0.26 ± 0.02g/L(equivalent to 0.205 ± 0.015g/L of CuCl2).

Adjust the pH according to the process described in 3.2.3.

3.3 Filtering
If necessary, filter the SOLUTION professionally before placing IT IN the reservoir of the device to remove any solid material that may clog the nozzle of the spray device.

ISO 9227-0 Artificial atmosphere corrosion test Salt spray test

4 Installation
4.1 Component Maintenance
All components in contact with the spray or test solution shall be made of or lined with a material resistant to corrosion of the spray solution and shall not affect the corrosion resistance of the spray test solution.

4.2 Spray test chamber
The test chamber should meet the condition of uniform spray distribution. The upper part of the spray test chamber is designed so that spray droplets formed on its surface do not fall on the test sample.

The specification and shape of the spray test chamber shall meet the following requirements, that is, the collection rate of the solution in the chamber is within the range specified in Table 2 and the measurement is within the range specified in 8.3.

For environmental reasons, devices with appropriate treatment techniques for post-test fog to prevent it from being released outside the building and water absorption techniques to prevent it from entering the drainage system should be preferred.

Note 2: Appendix A shows a schematic diagram of a feasible salt spray test chamber design.

ISO 9227-0 Artificial atmosphere corrosion test Salt spray test

4.3 Heater and temperature control
An appropriate system shall maintain the spray chamber and its contents within the specified temperature range (see Table 2). This temperature should be measured at least 100mm from the wall.

4.4 Spray Device
The device for spraying the salt solution includes a clean air supply to control the pressure and humidity, a memory for holding the spray solution, and one or more atomizing nozzles.

The compressed air supplied to the atomizer should first pass through the filter to remove all trace amounts of oil or solid matter, and the atomization pressure should be in the overpressure range of 70 to 170kPa. The pressure should be 98 ± 10 kPa.

Note 3: Atomizing nozzles can have a “critical pressure”, at which pressure, the corrosion of salt spray appears to increase abnormally. If the “critical pressure” of the nozzle is not determined, the fluctuation of the air pressure is controlled within ± 0.7kPa by installing an appropriate pressure regulating valve to minimize the possibility of the nozzle operating at its “critical pressure”.

In order to prevent the evaporation of water from the spray droplets, the air should be humidified by a saturation tower containing hot distilled water or deionized water at a temperature 10 ° C higher than the temperature of the test chamber before entering the atomizer. The appropriate temperature depends on the pressure used and the type of sprayer nozzle, and should be adjusted to keep the spray collection rate in the test chamber and the concentration of the spray collected within the specified range (see 8.3). Table 1 shows the guiding values of the hot water temperature in the saturated tower at different pressures. Water content shall be automatically maintained to ensure adequate humidity.

ISO 9227-0 Artificial atmosphere corrosion test Salt spray test

Atomizers should be made of inert materials. A baffle is provided to prevent the direct effect of spray on the test sample, and an adjustable baffle is used to help evenly distribute the spray in the test chamber. For this purpose, dispersion towers equipped with atomizers may also be useful. The salt solution level in the salt reservoir shall be automatically maintained throughout the test to ensure consistent spray supply.

4.5 Collection Device
At least two suitable collection devices shall be provided, including a funnel made of chemically inert material, a calibrated round bottom cylinder or other similar container. A suitable funnel diameter of 100mm corresponds to a collection area of about 80cm2. The collection device shall be placed in the area where the test sample is placed in the spray test chamber, one near the inlet of the spray and the other away from the inlet. This allows only the spray to be collected and not the liquid from the sample or from the part of the test chamber.

4.6 Recycling and Reuse
If the test chamber has once been used for the AASS or CASS test, or for any other purpose using a solution different from that specified for the NSS test, it will no longer be used for the NSS test.

Once used for AASS or CASS tests, it is almost impossible to clean the test chamber to make it available for NSS tests. In such cases, however, the device should be effectively cleaned and checked according to the method described in item 5 to ensure that the pH of the solution collected is correct, especially during the spraying process. After this process, the sample to be tested is placed in a spray test chamber.