Salt Spray Hours, Narrowing The Gap

My salt spray tests are running anywhere from 51 hrs up to 376 hrs for .0005 chrome bar. What can I possibly do to narrow the gap. The bars are cleaned the same way each time. When they fail, it is almost always due to a blister that appears to be coming from under the chrome. The bath is HEEF and it goes from a caustic clean tank into rinse tanks before etching and then the chrome tank.

Are you sure the salt spray testing is being conducted as consistently as possible? ASTM ASTM B117 calls out a few variables that needs constant monitoring including salt fog collection rate, chamber temp, bubble tower temp, solution pH, and solution specific gravity. Make sure your salt spray testing is being done well before you blame the inconsistency on your part.

A cup of coffee says that you have a variability in the plating thickness. Measure some that pass and some that fail on the same location, same lot and the same saltspray run. Measure with an instrument that will accurately read in your range to 0.0001"