MIL STD 810 G – Test Method 518.1 – Acidic Atmosphere
Use the acidic atmosphere test to determine the resistance of materials and protective coatings to corrosive atmospheres, and when necessary, to determine its affect on operational capabilities.
Use this test method when the requirements documents state that the materiel is likely to be stored or operated in areas where acidic atmospheres exist, such as industrial areas or near the exhausts of any fuel-burning device.
This method is not a replacement for the salt fog method, nor is it suitable for evaluating the effects of hydrogen sulfide that readily oxidizes in the test environment to form sulfur dioxide. Consult ASTM G85, (paragraph 6.1, reference a) for information on introducing a sulfur dioxide environment. Caution: Although salt fog chambers are usually used for this test, introducing an acidic or sulfur dioxide atmosphere in a salt fog chamber may contaminate the chamber for future salt fog tests.
Step 1. With the test item installed in the test chamber in its storage configuration (or as otherwise specified in the requirements documents), adjust the test chamber temperature to 35°C, and temperature condition the test item for at least 2 hours before introducing the acid solution.
Step 2. Expose the test item to one of the two following severities as specified in the test plan. (See paragraph 2.4.2.) During either the a or b (below) options, continuously atomize the acidic solution (of a composition as given in paragraph 2.4.4). During the entire exposure period, measure the acidic solution fallout rate and pH at least at 24-hour intervals1/. Ensure the fallout is between 1 and 3 ml/80cm2/hr.
Four 2-hour exposure periods with 7 days storage after each.
Three 2-hour exposure periods with 22 hours storage after each.
Step 3. At the completion of Step 2, stabilize the test item at standard ambient conditions.
Step 4. Using appropriate protective clothing, visually examine the test item to the extent practical.
Step 5. If required, place the test item in an operational configuration and conduct an operational check of the test item. See paragraph 5 for analysis of results.
Step 6. If required, test items may be cleaned by rinsing with a dilute sodium bicarbonate solution (to neutralize any acidic residue), followed by distilled/deionized water, and dried by the application of heat (up to 55°C (131oF)), where this is acceptable, or by other means. Collect the rinse water and check it for hazardous substances prior to disposal (see paragraph 4.1b also).
Step 7. At the end of this test, and in conformity with the requirements documents, examine the test item for corrosion and deterioration of parts, finishes, materials, and components. Document the results.
NOTE: Tailoring is essential. Please, ask to your confidence laboratory for further details about tailoring of test methods.