The CASS test procedure is given in ASTM B368-97 Standard Test Method for Copper-Accelerated Acetic Acid-Salt Spray (Fog) Testing (CASS Test). “This method is applicable to evaluating the corrosive performance of decorative copper/nickel/chromium or nickel/chromium coatings on steel, zinc alloys, aluminum alloys, and plastics designed for severe service,” so it seems like the proper test.
However, ASTM B368 just tells how to run the test. The sample specimen and failure criteria are given in the referring document, e.g., the plating specification. I suggest you see ASTM B456-95 Standard Specification for Electrodeposited Coatings of Copper Plus Nickel Plus Chromium and Nickel Plus Chromium.
“This specification covers requirements for several types and grades of electrodeposited copper plus nickel plus chromium or nickel plus chromium coatings on steel, nickel plus chromium coatings on copper and copper alloys, and copper plus nickel plus chromium coatings on zinc alloys for applications where both appearance and protection of the basis metal against corrosion are important.”
Table 7 of ASTM B456-95 tells how many hours to run the corrosion test for various coating thicknesses (Service Conditions). Paragraph 6.6.2 then describes the visual examination for corrosion. “Any basis metal corrosion or blistering of the coating shall be cause for rejection” all though a few, widely scattered pinholes may be considered acceptable. It references ASTM B537 if you need to quantify the corroded area.
