Letter 22011

ASSURING STEEL IS UNPASSIVATED [Canada] 

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1. I AM USING GALVANIZED STEEL, I WANT TO TAKE OFF THE PASSIVATION, WHAT PRODUCT SHOULD I USE?

2. IS THERE A TESTING METHOD TO MAKE SURE THE METAL IS UN-PASSIVATED?

THANK YOU,

SERGE DORE
MOELLER ELECTRIC INC - GRANBY, QUEBEC, CANADA

The meaning of the word "passivation" is very tricky in this instance. Generally the term "passivation" is applied to stainless steels, and refers to the building of a chrome-rich surface skin. The term "passivation" is also sometimes used, however, to refer to the chromate conversion coating that is applid to zinc plated and zinc galvanized surfaces. But the way you are using the term, it seems like you are really asking how to remove the zinc, not just the chromate?

The zinc will almost instantly dissolve in hydrochloric acid; in fact the reaction can be violent.

If you are trying to remove just the chromate conversion coating, so that paint will stick better, I think scrubbing it with tri-sodium phosphate and pumice will do it. There are ASTM standard "spot tests" for the presence of the chromate.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

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