The acidic atmosphere test used to determine the resistance of materials and protective coatings to corrosive atmospheres, and when necessary, to determine its effect on operational capabilities. This test method used 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.
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.
a. Chemical attack of surface finishes and non-metallic materials.
b. Corrosion of metals.
c. Pitting of cement and optics.
The test method and the exposure temperature used in this procedure are similar to that used in the salt fog test.
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
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.
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.
Procedures Of This Method Are As Follows:
Procedure I - Near-field with an actual configuration. Procedure I is intended to test materiel in its functional mode and actual configuration (materiel / pyrotechnic device physical configuration), and to ensure it can survive and function as required when tested using the actual pyrotechnic test device in its intended installed configuration. In Procedure I, it is assumed that the materiel or a portion of the materiel resides within the near-field of the pyrotechnic device.
Procedure II - Near-field with a simulated configuration. Procedure II is intended to test materiel in its functional mode but with a simulated structural configuration, and to ensure it can survive and function as required when in its actual materiel/pyrotechnic device physical configuration. In this procedure, it is assumed that some part of the materiel lies within the near-field. Make every attempt to use this procedure to duplicate the actual platform/materiel structural configuration by way of a full-scale test. If this is too costly or impractical, employ scaled tests provided that in the process of scaling, important configuration details are not omitted. In particular, only the structure portion directly influencing the materiel may be involved in the test, provided it can be reasonably assumed that the remainder of the structure will not influence materiel response. On occasion, for convenience, a special pyrotechnic testing device may be employed for testing the materiel, e.g., a flat steel plate to which the materiel is mounted and the pyrotechnic charge is attached.
Procedure III - Mid-field with a mechanical test device. Replication of pyro shock for the mid-field environment with a mechanical device that simulates the pyro shock peak acceleration amplitudes and frequency content (other than an electrodynamic shaker because of frequency range and weight limitations of the electrodynamic shaker). Pyroshock can be applied using conventional high acceleration amplitude/frequency test input devices. Paragraph 6.1, reference b provides a source of alternative test input devices, their advantages, and limitations. In this procedure, it is assumed that all parts of the materiel lie in the mid-field of the pyrotechnic device.
Procedure IV - Far-field with a mechanical test device. Replication of pyro shock for the far-field environment with a mechanical device that simulates the pyro shock peak acceleration amplitudes and frequency content (other than an electrodynamic shaker because of frequency range and weight limitations of the electrodynamic shaker).
Procedure V - Far-field with an electrodynamic shaker. Replication of pyro shock for the far-field environment using an electrodynamic shaker to simulate the comparatively low frequency structural resonant response to the pyro shock. On occasion, pyro shock response can be replicated using conventional electrodynamic shakers. In this procedure, it is assumed that all parts of the materiel lie in the far-field of the pyrotechnic device, and the materiel is subject to the structure platform resonant response alone for frequencies less than 3,000 Hz.
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.
a. Four 2-hour exposure periods with 7 days storage after each.
b. Three 2-hour exposure periods with 22 hours storage after each.
Step 3. After 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 the 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).
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