Salt Fog | Nebbia salina

MIL STD 810 G – Test Method 509.5 – Salt Fog

 

SCOPE

 

Purpose
The salt fog method is performed to determine the effectiveness of protective coatings and finishes on materials. It may also be applied to determine the effects of salt deposits on the physical and electrical aspects of materiel.
Application
Use this method for screening purposes only to evaluate the effectiveness and quality of protective coatings and finishes on materiel and material coupons, and to locate potential problem areas, quality control deficiencies, design flaws, etc., in a relatively short period of time. Although not representative of the natural environment (see paragraph 1.3b), this test has been used to provide an indication of potential problem areas associated with the salt (marine) environment. In general, only apply this method to materiel that will experience significant exposure (as opposed to infrequent or irregular) to high levels of salt in the atmosphere.
Limitations
This method does not attempt to duplicate the complex environment but, rather, it provides a generally stressful situation that may reveal potential problem areas in materiel. Testing in the natural environment, whenever practical, may provide more valuable results. Specifically, this method does not address:
  1. There is no relationship between this test and any real world exposure duration. The test is not intended to duplicate the effects of a marine atmosphere due to variations in chemical composition and concentrations of the various marine and other corrosive environments.
  2. It has not been demonstrated that a direct relationship exists between salt fog corrosion and corrosion due to other media.
  3. It has not been demonstrated that withstanding the effects of this test guarantees materiel will survive under all corrosive conditions. For acidic atmosphere tests, see Method 518.1. Consult ASTM G85, “Standard Practice for Modified Salt Spray (Fog) Testing” (paragraph 6.1, reference a) for information on introducing a sulfur dioxide environment. Caution: Introducing sulfur dioxide in the salt fog chamber may contaminate the chamber for future salt fog tests.
  4. This test has proven to be generally unreliable for predicting the service life of different materials or coatings.
  5. This test is not a substitute for evaluating corrosion caused by humidity and fungus because their effects differ from salt fog effects and the tests are not interchangeable.
  6. This test is not intended to be used for sample or coupon testing in lieu of assemblage testing.

 

TEST PROCESS

 

Procedure
  • Step 1. With the test item in the chamber, adjust the test chamber temperature to 35°C, and condition the test item for at least two hours before introducing the salt fog.
  • Step 2. Continuously atomize a salt solution of a composition as given in paragraph 4.5.1.1b into the test chamber for a period of 24 hours or as specified in the test plan (see paragraph 2.2.3). During the entire exposure period, measure the salt fog fallout rate and pH of the fallout solution at least at 24-hour intervals4/. Ensure the fallout is between 1 and 3 ml/80cm2/hr.
  • Step 3. Dry the test item at standard ambient temperatures and a relative humidity of less than 50 percent for 24 hours, or as otherwise specified (see paragraph 2.2.3). Minimize handling the test item or adjusting any mechanical features during the drying period.
  • Step 4. If the 48/48-hrs option has been chosen, proceed to Step 5. Otherwise, at the end of the drying period, repeat steps 1 to 3 at least once.
  • Step 5. After completing the physical and any electrical checkouts, document the results with photographs. See paragraph 5 for analysis of results. If necessary to aid in the follow-on corrosion examination, use a gentle wash in running water that is at standard ambient conditions, conduct the corrosion examination, and document the results with photographs.
  • Step 6. Visually inspect the test item in accordance with the guidelines given in paragraph 4.5.1.2.

 

NOTE: Tailoring is essential. Please, ask to your confidence laboratory for further details about tailoring of test methods.

 

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