1 Scope
This test is to be applied to compare the resistance to deterioration from salt mist of specimens of similar construction.
It is useful for evaluating the quality and the uniformity of protective coatings.
The following restrictions shall be taken into account:
a) The test is unsuitable as a general salt corrosion test;
b) It is considered to be unsuitable for the evaluation of individual specimens intended for use in salt-laden atmospheres.
For equipment and components, test Kb is considered to provide more realistic conditions and to provide means of assessment of individual items. If however, for particular circumstances, the relevant specification requires this test (Ka) to be applied to individual specimens for qualification purposes, then the specimens should be tested as part of the overall assembly or equipment in which they are to be used and be complete with any protection devices (cases, covers, shields, etc.), as in practice.
2 Test Apparatus
2.1 Test chamber
The chamber for this test shall be constructed of such materials that will not influence the corrosive effects of the salt mist.
The detailed construction of the chamber, including the method of producing the mist, is optional provided that:
a) The conditions in the chamber are within the limits specified;
b) A sufficiently large volume with constant, homogeneous conditions (not affected by turbulence) is available; these conditions should not be influenced by the specimens under test;
c) No direct spray impinges upon the specimens under test;
d) Drops of liquid accumulating on the ceiling, the walls or other parts cannot drip on the specimens.
e) The chamber shall be properly vented to prevent pressure build-up and allow uniform distribution of salt frog. The discharged end of the vent shall be protected from squalls which can cause strong air currents in the chamber.
2.2 Atomizer(s)
The atomizer(s) used shall be of such a design and construction as to produce a finely divided, wet, dense mist. The atomizer(s) shall be made of material that is non-reactive to the salt solution.
3 Salt Mist
3.1 Salt solution
3.1.1 Concentration
The salt used for the test shall be high quality sodium chloride (NaCl) containing, when dry, not more than 0.1 % sodium iodide and not more than 0.3 % of total impurities.
The salt solution concentration shall be 5±1% by weight.
The solution shall be prepared by dissolving (5±1) parts by weight of salt in 95 parts by weight of distilled or demineralized water.
3.1.2 PH value
The PH value of the solution shall be between 6.5 and 7.2, at a temperature of 35±2℃.
The PH value shall be maintained within this range during conditioning; for this purpose, diluted hydrochloric acid or sodium hydroxide may be used to adjust the PH value provided that the concentrations of NaCl remains within the prescribed limits.
The PH value shall be measured when preparing each new batch of solution.
The PH value may need to be adjusted, within the limits specified above, to meet the requirements of Chapter 6.
