The relative performance of the various corrosion protection methods is determined by standard laboratory testing. While these tests cannot predict installed service life, they are an important part of the fastener manufacturer’s quality control program and help the fastener specifier understand the relative performance of various coatings.
Salt Spray Test.
In this test, fasteners are placed in a sealed cabinet and exposed to an atmospheric mixture of distilled water (H2 O) and 5% sodium chloride (NaCl). One hundred percent relative humidity is maintained in the test cabinet at a temperature of 100 uF. The testing is continuous 24 hours per day, all per ASTM standard B-117. Fasteners are periodically inspected for corrosion. The test results are reported as hours of exposure to the first appearance of rust.
Mebon Prohesion Test.
This test is similar to the Salt Spray Test but utilizes alternating wet and dry cycles of one hour each. The test is meant to more closely simulate long-term natural exposure. Researchers believe that the corrosion of iron occurs most rapidly during drying and rewetting episodes, not during the actual wet period. Only a few jurisdictions and manufacturers currently utilize this test.