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How to quantify the increased hardness from adding hard chrome plating?

adv.    

I am assisting a client who is experiencing extremely rapid wearing of a knife gate valve blade due to abrasion from cement being blown through the line. We are recommending that the 316 SS hardened face blade be replaced with a hard chromed 304 SS blade; but I cannot find any technical information that documents the increased hardness rating of the two stainless steels with and without the hard chrome coating. Any suggestions on where I could find this data?

Richard M [last name deleted for privacy by Editor]
consulting engineer - Olmsted Falls, Ohio
2004

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Several questions came to mind when I read your letter.

1- How can you recommend something when you don't have "any technical information" that compares it to the actual situation? You just "feel" chrome is better?
2- What kind of "hardening" are you talking about on the face of a 316SS blade? It certainly is not a heat treatment. Could it be nitrided, coated or what?

Unless we understand more about the actual condition we would be making the same mistake.

Guillermo Marrufo
Monterrey, NL, Mexico
2004

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That information is available from several sources including libraries and the internet. The optimum would be to own the appropriate AMS volume.

Hardness is not the same as wear resistance. Also, nothing is said as to exactly what is failing, the existing knife or the throat. If it is the knife, I have some doubts as to the longevity of the plate. What thickness of chrome are you considering ? Are you aware that it will have to be ground after plating or the edges will be oversize? Further, since both 316 and 304 are plateable, what is to be gained by switching to 304? Some thought might be given to using S-2 or D-2 which is certainly higher in wear than 316 and probably last longer than plated SS.

James Watts
- Navarre, Florida
2004

adv.