2.1 Effects of the Environment
Acidic atmospheres are of increasing concern, especially for materiel in the vicinity of industrial areas or near the exhausts of fuel burning devices. Examples of problems that could occur as a result of acidic atmosphere exposure are as follows. The list is not intended to be all-inclusive, and some of the examples may overlap the categories. Paragraph 6.1, reference a provides further information.
- a. Chemical attack of surface finishes and non-metallic materials.
- b. Corrosion of metals.
- c. Pitting of cement and optics.
2.2 Test Procedure
When an acidic atmosphere test is deemed necessary, the procedure included in this method is considered suitable for most applications. The tailoring options are limited.
2.3 Sequence
- a. General. Use the anticipated life cycle sequence of events as a general sequence guide (see Part One, paragraph 5.5).
- b. Unique to this Method. There are at least two philosophies related to test sequence. One approach is to conserve test item life by applying what are perceived to be the least damaging environments first. For this approach, generally apply the acidic atmosphere test late in the test sequence. Another approach is to apply environments to maximize the likelihood of disclosing synergetic effects. For this approach, consider acidic atmosphere testing following dynamic tests, such as vibration and shock. Perform acidic atmosphere testing after any humidity or fungus testing, and before any sand and dust testing or other tests that damage protective coatings. Because this test is similar in severity to the salt fog test, recommend separate test items be used for each.
MIL-STD-810H METHOD 518.2
- (1) Sand and dust testing deposits may inhibit acid effects as well as abrade protective coatings.
- (2) Acid deposits may inhibit mold/fungal growth.
- (3) Residual deposits may accelerate chemical reactions during humidity testing.
2.4 Determine Test Levels and Conditions
Having selected this method and relevant procedures (based on the test item's requirements documents and the tailoring process), complete the tailoring process by identifying appropriate parameter levels and applicable test conditions and techniques for these procedures. Base these selections on the requirements documents, the Life Cycle Environmental Profile (LCEP), and information provided with this procedure. Consider the essential parameters for defining the acidic atmosphere test that include exposure temperature, exposure time (duration), test item configuration, chemical composition of the test atmosphere, and concentration of the test solution.
2.4.1 Temperature Severities
The test method and the exposure temperature used in this procedure are similar to that used in the salt fog test.
2.4.2 Test Duration
Two severity levels are defined (paragraph 6.1, reference b). In view of the complexity of naturally occurring corrosion processes, no strict equivalencies with real exposure can be quoted. Use severity "a" below for simulating infrequent periods of exposure, or for exposure in areas of much lower acidity. Use severity "b" below to represent approximately 10 years natural exposure in a moist, highly industrial area, or a shorter period in close proximity to vehicle exhaust systems, particularly ship funnel exhausts where the potential acidity is significantly higher.
- a. Three 2-hour spraying periods with 22 hours storage after each.
- b. Four 2-hour spraying periods with 7 days storage after each.
2.4.3 Test Item Configuration
The configuration of the materiel is an important factor in how an acidic atmosphere affects it. Therefore, during the test use the anticipated configuration of the materiel during storage or use. As a minimum, consider the following configurations:
- a. In a shipping/storage container or transit case.
- b. Protected or unprotected.
- c. Deployed (realistically or with restraints, such as with openings that are normally covered).
- d. Modified with kits for special applications.
2.4.4 Chemical Composition and Concentration
Unless otherwise specified, for atomization, use a test solution containing 11.9mg (6 µl) sulfuric acid (95-98 percent)/4 liters (4.23 qt) of solution, and 8.8mg (6 µl) nitric acid (68-71 percent)/4 liters (4.23 qt) solution in distilled or deionized water. This will produce a solution with a pH of 4.17 that is representative of some of the worst rain pHs recorded for rainfall in the eastern United States and other heavily industrialized areas with acidic emissions. Paragraph 6.1, reference c, provides information regarding the more common chemical environmental contaminants together with some consequent likely forms of corrosion that material could encounter.
WARNING: Strong acids are hazardous. The solution to be sprayed is harmful to people and clothing. Operators carrying out the test must take suitable precautions.
WARNING: Refer to the supplier’s Safety Data Sheet (SDS) or equivalent for health hazard data.
MIL-STD-810H
METHOD 518.2
- a. Do not enter the chamber during atomization and, before entry after exposure, purge the chamber with clean air to a level that will satisfy local safety requirements. Continue purging at intervals if necessary to ensure the concentration of noxious fumes remains at a suitably low level.
- b. Wear a suitable respirator and/or eye protection. Use rubber gloves to handle materiel.
- c. See paragraph 4.1b for hazardous waste disposal information.
2.4.5 Operational Considerations
The test item will not normally be required to function during the test, but may be required to do so upon completion of the test, or on completion of a representative sequence of environmental tests.