Chloride pitting in hard chrome plating?
Chloride pitting in hard chrome plating?
(OP)
Someone told me that hard chrome plating is susceptible to pitting from chlorides. Is this true? I thought hard chrome plating was pretty corrosion resistant. We have heavy hydrocarbon stream with up to 5000 ppm chlorides at 210-250F. The pump rotors are plated with 0.010" and we are worried what the chloride pit depth would be.





RE: Chloride pitting in hard chrome plating?
You allude to a "heavy hydrocarbon stream". Do you mean organic chlorides in it, such as perchloroethylene? In that case, you should be fine.
If you mean water with dissolved chloride ions, that is something else again.
Dave Wichern
http://www.dedalusenviro.com
Science is a business of empiricism.
RE: Chloride pitting in hard chrome plating?
RE: Chloride pitting in hard chrome plating?
RE: Chloride pitting in hard chrome plating?
Is the aqueous phase very acidic? Acidic media with high levels of chlorides are truly, the Olympics of corrosion resistance.
I've looked into this, a little, and haven't found any real hard information. My sense is that if the pH is above, say, 4 - 5, that you should be alright.
Any stray currents, or intermetallic galvanic potentials generated could cause trouble in a hurry, however.
Dave Wichern
http://www.dedalusenviro.com
Science is a business of empiricism.
RE: Chloride pitting in hard chrome plating?
RE: Chloride pitting in hard chrome plating?
I did a little looking up, and apparently the substrate in hard chromium plating is not invariably nickel plated, as it must be in decorative nickel plating. Also, some degree of micro porosity is often considered desirable, for lubricant retention. Though, if I were making pump rotors, I think I'd specify a nickel underlayer.
Dave Wichern
http://www.dedalusenviro.com
Science is a business of empiricism.
RE: Chloride pitting in hard chrome plating?
Steel that has been plated with hard chromium does not possess outstanding corrosion resistance in chloride containing environments. The best quality hard chromium will resist ~ 100 hours of continuous salt spray before the appearance of pits. This is difficult to achieve on complicated parts with changes in section, crevices, corners, etc. I would expect that pump rotors will experience pitting on the edges in your environment.
RE: Chloride pitting in hard chrome plating?