Test Conditions
Can be used to test the relative resistance to corrosion of coated and uncoated metallic specimens, when exposed to a salt spray climate at an elevated temperature. Test specimens are placed in an enclosed chamber and exposed to a continuous indirect spray of neutral (pH 6.5 to 7.2) salt water solution, which falls-out on to the specimens at a rate of 1.0 to 2.0 ml/80cm²/hour, in a chamber temperature of +35C. This climate is maintained under constant steady state conditions. The test duration is variable.
Method
Salt fog testing is performed by placing samples in a test cabinet that has been designed in accordance with Paragraph 4 (Apparatus) of ASTM B117 and operated in accordance with Paragraph 10 (Conditions) of ASTM B117.
A 5% salt solution, prepared by dissolving sodium chloride into water that meets the requirements of ASTM D1193 Specification for Reagent Water, Type IV is supplied to the chamber. At the time the samples are placed into test, the cabinet should be pre-conditioned to the operating temperature of 35ºC and fogging a 5% salt solution at the specified rate. The fog collection rate is determined by placing a minimum of two 80 sq. cm. funnels inserted into measuring cylinders graduated in ml. inside the chamber. One collection device is located nearest the nozzle and one in the farthest corner.
Orientation
Unless otherwise agreed upon, the samples are placed at a 15-30 degree angle from vertical (automotive components, however, are often tested in the "in-car" position). This orientation allows the condensation to run down the specimens and minimises condensation pooling. Overcrowding of samples within the cabinet should be avoided. An important aspect of the test is the utilization of a free-falling mist, which uniformly settles on the test samples. Samples should be placed in the chamber so that condensation does not drip from one to another.
Test durations
Test durations are typically in 24-hour increments and can range from 24 hours to 5000 hours (where salt fog exposure is a part of a more complex test method, exposure time can be as little as 15 minutes.) Except for sample rotation and daily monitoring of collection rates, the cabinet should remain closed for the duration of the test.
Appendix X.3
In 1987, Appendix X.3 was added to ASTM B117 to suggest the use of mass loss panels as a means for checking the corrosive conditions in a given salt spray chamber. The procedure calls for SAE 1008 commercial grade cold-rolled carbon steel panels, measuring 76 x 127 x 0.8 mm, to be cleaned, weighed, and placed in the chamber in the proximity of the collector funnels. After an exposure time of 48, 96, or 168 hours, the panels are removed, cleaned, and re-weighed. When conducted on a regular basis, the final mass loss number can be used as a tool for monitoring consistent corrosive conditions within the chamber. The frequency of conducting this test should be determined by the user, but common practice suggests the test be conducted monthly, or whenever any change occurs which might affect the cabinet - such as a change of location, salt, water, operators, etc.
