The standard "ISO 16151 Corrosion of metals and alloys - Accelerated cyclic tests by exposure to acidic salt spray, "dry" and "wet" conditions" published by the International Organization for Standardization (ISO) describes two accelerated corrosion test procedures, Method A and Method B, for the comparative evaluation of metallic materials with or without permanent corrosion protection or temporary corrosion protection in outdoor salt/acid rain environments. The standard also defines the apparatus used. The two tests involve cyclic exposure of specimens to acidic salt spray, "dry" and "wet" conditions.
The particular advantages of the two tests over traditional accelerated tests, such as the neutral salt spray test described in the ISO 9227 standard, lie in their ability to better reproduce corrosion occurring in outdoor salt/acid rain environments. They are also useful for assessing cosmetic corrosion.
Method A,
Method B,
When applying Method A, when preparing an acidic 5 percent sodium chloride solution, a sufficient amount of sodium chloride should be dissolved in distilled or deionized water having a conductivity of not more than 25 µS/cm at 2 degrees plus/minus 20 degrees to obtain a concentration of 50 g/L plus/minus 5 g/L. The specific gravity range for a 50 g/L plus/minus 5 g/L solution at 25 degrees should be between 1.029 and 1.036.
Sodium chloride shall contain not more than 0,001 mass percent copper and not more than 0,001 mass percent nickel as determined by atomic absorption spectrophotometry or another analytical method of comparable sensitivity. It shall not contain more than 0,1 mass percent sodium iodide or 0,5 mass percent total impurities calculated for the dry salt.
If the pH value of the prepared solution measured at 25 degrees plus/minus 2 degrees is outside the range of 6,0 to 7,0, the presence of undesirable impurities in the salt or water is investigated.
In the acidification process, the pH value of the solution should be adjusted to 10 degrees plus/minus 5 degrees 25 plus/minus 2 by adding the following reagents to 3,5 liters of prepared neutral 0,1 percent sodium chloride solution:
When applying Method B, when preparing the mixed salt solution, the reagent mass shown in the table given in the standard shall be dissolved in distilled or deionized water having a conductivity of not more than 25 µS/cm at 2 degrees plus/minus 20 degrees to obtain a stock solution with a concentration of 36 g/l plus/minus 3,6 g/l. It shall be diluted 6,0:0,6 to obtain a mixed salt solution with a concentration of 1 g/l plus/minus 6 g/l.
The composition of the stock solution is the same as that of a typical synthetic ocean water, as shown in the test solution for simulating the corrosive effects of ocean water, given in the annex of the ISO 11130 standard.
To prepare the acidic solution, 16,2 g of concentrated nitric acid and 42,5 g of sulfuric acid should be dissolved in water and diluted to a total volume of 1 liter to obtain a 1 N acid solution in terms of equivalent proportions of nitric acid and sulfuric acid.
When preparing acidified salt solution, the prepared acidic solution should be added to the mixed salt solution to adjust the pH value to 25 plus/minus 2 at 2,5 degrees plus/minus 0,1 degrees. The relationship between the amount of mixed acidic solution and the pH value of the acidified salt solution is included in the standard appendix. This solution with a pH value close to 2,5 has no buffering effect.
All components that come into contact with the spray or test solution used in the tests shall be made of or coated with materials that are resistant to corrosion by the test solution and that do not affect the corrosiveness of the sprayed test solution. This device shall contain the following components:
The number and type of test samples are selected according to the specifications specified for the material or product being tested. Unless specified, these details are mutually agreed upon between the parties involved.
Test samples are carefully cleaned prior to testing to remove any traces (dirt, oil or other foreign matter) that could affect the result. The cleaning method used depends on the nature of the material, its surface and contaminants, but should not involve the use of abrasives or solvents that could attack the surface of the samples.
For metals or alloys without organic coatings and inorganic coating materials, samples should be thoroughly cleaned with a suitable organic solvent using a clean soft brush or an ultrasonic cleaning device.
Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, our organization also provides testing services defined in the standard “ISO 16151 Corrosion of metals and alloys - Accelerated cyclic tests by exposure to acidic salt spray, “dry” and “wet” conditions” with its trained and expert staff and advanced technological equipment.
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