Материал: Стандарт MIL-STD-202G

MIL-STD-202G

CLASS 100

ENVIRONMENTAL TESTS

MIL-STD-202G

METHOD 101E

SALT ATMOSPHERE (CORROSION)

(formerly Salt Spray (Corrosion))

1.PURPOSE. The salt-spray test, in which specimens are subjected to a fine mist of salt solution, has several useful purposes when utilized with full recognition of its deficiencies and limitations. Originally proposed as an accelerated laboratory corrosion test simulating the effects of seacoast atmospheres on metals, with or without protective coatings, this test has been erroneously considered by many as an all-purpose accelerated corrosion test, which if "withstood successfully" will guarantee that metals or protective coatings will prove satisfactory under any corrosive condition. Experience has since shown that there is seldom a direct relationship between resistance to salt atmosphere corrosion and resistance to corrosion in other media, even in so-called "marine" atmospheres and seawater. However, some idea of the relative service life and behavior of different samples of the same (or closely related) metals or of protective coating-base metal combinations in marine and exposed seacoast locations can be gained by means of the salt atmosphere test, provided accumulated data from correlated field service tests and laboratory salt atmosphere tests show that such a relationship does exist, as in the case of aluminum alloys. (Such correlation tests are also necessary to show the degree of acceleration, if any, produced by the laboratory test). The salt atmosphere test is generally considered unreliable for comparing the general corrosion resistance of different kinds of metals or coating-metal combinations, or for predicting their comparative service life. The salt atmosphere test has received its widest acceptance as a test for evaluating the uniformity (specifically, thickness and degree of porosity) of protective coatings, metallic and nonmetallic, and has served this purpose with varying amounts of success. In this connection, the test is useful for evaluating different lots of the same product, once some standard level of performance has been established. The salt atmosphere test is especially helpful as a screening test for revealing particularly inferior coatings. When used to check the porosity of metallic coatings, the test is more dependable when applied to coatings that are cathodic rather than anodic toward the basic metal. This test can also be used to detect the presence of free iron contaminating the surface of another metal, by inspection of the corrosion products.

2.APPARATUS. Apparatus used in the salt atmosphere test shall include the following:

a.Exposure chamber with racks or fixtures for supporting specimens.

b.Salt-solution reservoir with means for monitoring an adequate level of solution.

c.Means for atomizing the salt solution, including suitable nozzles and compressed air supply.

d.Chamber-heating means and controls.

e.Means for humidifying the air at a temperature above the chamber temperature.

2.1 Chamber. The chamber and all accessories shall be made of material that will not affect the corrosiveness of the salt atmosphere, such as glass, hard rubber, or plastic. All parts of the test setup that come in contact with test specimens shall be of materials that will not cause electrolytic corrosion. The chamber and accessories shall be so constructed and arranged that there is no direct impinging of the spray or dripping of the condensate on the specimens, so that the atmosphere circulates freely about all specimens to the same degree, and so that no liquid which has come in contact with the test specimens returns to the salt-solution reservoir. The chamber shall be properly vented to prevent pressure build up and allow uniform distribution of salt spray. The chamber shall have a suitable means of heating and maintaining the required test temperature.

2.2 Salt solution reservoir. The salt solution reservoir shall be made of material that is non-reactive with the salt solution, e.g., glass, hard rubber, or plastic. The reservoir shall be adequately protected from the surrounding environment and shall have a means to monitor the solution level. The reservoir shall include a means to filter the salt solution in the supply line to the atomizers. When long duration test conditions are specified (e.g. test condition D), the reservoir may be refilled via auxiliary reservoirs so that the test cycle shall not be interrupted.

METHOD 101E

8 February 2002

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