ISO 9227:2017 download.Corrosion tests in artificial atmospheres – Salt spray tests.
Introduction
There is seldom a direct relation between resistance to the action of salt spray and resistance to corrosion in other media, because several factors influencing the progress of corrosion, such as the formation of protective films, vary greatly with the conditions encountered. Therefore, the test results should not be regarded as a direct guide to the corrosion resistance of the tested metallic materials in all environments where these materials might be used. Also, the performance of different materials during the test should not be taken as a direct guide to the corrosion resistance of these materials in service.
Nevertheless, the method described gives a means of checking that the comparative quality of a metallic material, with or without corrosion protection, is maintained.
Different metallic substrates (metals) cannot be tested in direct comparison In accordance to their corrosion resistances in salt spray tests. Comparative testing Is only applicable for the same kind of substrate.
Salt spray tests are generally suitable as corrosion protection tests for rapid analysis for discontinuities. pores and damage in organic and inorganic coatings. In addition, for quality control purposes. comparison can be made between specimens coated with the same coating. As comparative tests, however, salt spray tests are only suitable if the coatings are sufficiently similar in nature.
It is often not possible to use results gained from salt spray testing as a comparative guide to the long-term behaviour of different coating systems, since the corrosion stress during these tests differs significantly from the corrosion stresses encountered In practice.
by the method in 522 and the corrosivity of the cabinet ventled by the method in tIau,e2 to not be significantly affected by previous tests.
NOTE It is very ditlicult to clean a cabinet sufticiently that was once used for AASS or CASS testing so that It can be used loran NSS test.
7 Method for evaluating cabinet corrosivity
7.1 General
To check the reproducibility and repeatability of the test results for one piece of apparatus, or for similar Items of apparatus In diflerent laboratories, it is necessary to verify the apparatus at regular intervals as described in 7,2 to 24.
NOTE During permanent operation, a reasonable time period between two checks o( the covrrosivity of the apparatus is generally considered to be 3 months.
To determine the corrosivity of the tests, reference specimens made of steel shall be used.
As a complement to the reference specimens made of steel, high-purity zinc reference specimens may also be exposed in the tests in order to determine the corrosivity against this metal as described in Annex B.
7.2 Reference specimens
To verify the apparatus, use at least four reference specimens of 1,0 mm ± 0.2 mm thickness and 150 mm * 70 mm of CR4-grade steel in accordance with ISO 3574 with an essentially faultless surface2) and a matt finish (arithmetical mean deviation of the profile Ru = 0,8 tni ±0.3 aim). Cut these reference specimens from cold-rolled plates or strips.
Clean the reference specimens carefully, immediately prior to testing. Besides the specifications given in 62 and 6.3. cleaning shall eliminate all those traces (dirt, oil or other foreign matter) that can influence the test results.
Thoroughly clean the reference specimens with an appropriate organic solvent (such as a hydrocarbon with a boiling point between 60°C and 120 °C) using a clean soft brush or soft cloth, non-woven lint free cloth, that does not leave any remains or an ultrasonic cleaning device. Carry out the cleaning in a vessel full of solvent. after cleaning, rinse the reference specimens with fresh solvent and then dry them.
Determine the mass of the reference specimens to ± I mg. Protect one face of the reference specimens with a removable coating, for example. an adhesive plastic film. The edges of the reference specimens may be protected by the adhesive tape as welL
7.3 Arrangement of the reference specimens
Position at least four steel reference specimens in four quadrants (if six specimens are available, place them in six different positions including four quadrants) in the zone of the cabinet where the test specimens are placed. with the unprotected face upwards, and at an angle of 20° t 5° from the vertical. The support for the reference specimens shall be made of or coated with, inert materials such as plastics. The lower edge of the reference specimens shall be In level with the top of the salt spray collector.
The cabinet should be verified du ring the testing of test specimens. If this is the case, great care shall be taken that the specimens do not affect each other. Otherwise, the cabinet shall be filled with substitute specimens to maintain the homogeneity of the cabinet. The verification procedure shall be performed using the same settings as for the test runs.
10.5 During operation, the tank for the salt solution shall be covered by a lid to prevent dust or other contaminants from Influencing the solution and to prevent the concentration of sodium chloride and the pH from fluctuating.
11 DuratIon of tests
11.1 The period of test shall be as designated by the specification covering the material or product being tested. When not specified, this period shall be agreed upon by the Interested parties.
Recommended periods of exposure are 2 h, 6 h. 24 h. 48 h, 96 h. 168 h. 240 h, 480 h. 720 hand 1 008 h.
11.2 Interruptions of the test shall be minimized. The cabinet shall be opened only for brief visual inspections of the test specimens in position and for replenishing the salt solution in the reservoir, if such replenishment cannot be carried out from outside the cabinet.
The total opening time per day shall not exceed 1 h.
11.3 lIthe end-point of the test depends on the appearance of the first sign of corrosion, the test specimens shall be inspected frequently with the requirements of ill.
11.4 A periodic visual examination of specimens under test for a predetermined period may be carried out, but the surfaces under test shall not he disturbed, and the period for which the cabinet is open shall be the minimum necessary to observe and record any visible changes.
12 Treatment of test specimens after test
12.1 General
How to treat test specimens after testing should be included in the test specification or material specification given by the customer. It shall be agreed with the test parties before starting the test.
12.2 Non-organIc coated test specimens: metallic and/or Inorganic coated
At the end of the test period, remove the test specimens from the cabinet and allow them to dry for 0.5 h to I h before rinsing, in order to reduce the risk of removing corrosion products. Before they are examined, carefully remove the residues of spray solution from their surfaces. A suitable method is to rinse the test specimens gently In clean running tap water, at a temperature not exceeding 40 C, and then to dry them Immediately In a stream of air, at an overpressure not exceedIng 200 kPa and at a distance of approximately 300 mm.
NOTE ISO 8407 can be used for treatment of the specimen after the test.
12.3 Organic coated test specimens
12.3.1 Scribed organic coated test specimens
Clean the surface of the organic coated test specimens under running tap water directly after removing the test specimens out of the salt spray cabinet. A soft sponge may be used to remove dirt and salt rests out of the scribed area but not to remove evaluable corrosion phenomena. Remove the delaminated area around the scribe by one of the following methods:
a) using a knife, Carefully remove the loose coating using a knife blade held at an angle, positioning the blade at the Interlace between the coating and the substrate and forcing the coating away from the substrate.
b) using an adhesive tape.