Letter 25021

Penetration of Olive Green Passivation [India] 

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WE USE OLIVE DRAB PASSIVATION FOR ONE OF OUR COMPONENT . THIS IS USED IN THE ENDS OF HOSE AS JOINTS. THE COMPONENT PASSES SALT SPRAY TEST OF 96 HRS. BUT SUDDENLY AFTER STORAGE FOR 2 MONTHS,WE NOTICED RUST ON THE INNER WALLS. OUR PLATING MAN SAYS THAT THE DEPOSITION IN THE INNER WALLS IS ALMOST NIL. CAN ANYONE EXPLAIN THE PHENOMENA.

REGARDS,

D.B.Prabhu ram
Auto Ancillary - Coimbatore, Tamil Nadu, India

Unfortunately the only phenomenon is that the parts passed the salt spray test :-)

Remember that you don't chromate steel, you only chromate the zinc plating. And it is very common for the plating on the inside walls of parts to just barely "cover" the steel. You need to get this plating thicker by switching from barrel plating to rack plating, or from acid zinc to alkaline or cyanide zinc, or by specifying a heavier plating.

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

Dear Mr Prabhu, The rust marked by you does not look good, I must admit. It is also not that deeply recessed that it should rust. I also advise you not to get any more Salt Spray testing done in the same chamber unless you have the corrosivity of the chamber verified. Also have you verified the plating thickness on the part that rusted and the part that passed the Salt Spray test?? Pull your plater up by his ears !! Khozema Vahanwala Automaxx   Bangalore, Karnataka, India

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