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Pickle Inhibitors for 300 series Austenic Stainless

January 16, 2017

Q. Hello,
My company has a unique use for stainless where we bond elastomeric coatings to the surface. The chemistry and physical structure of the surface as received from the mill can have a profound effect on the strength of bonding. Most of the mills use a combination of HN03 and HF in the pickling process. I understand that boron is used as an inhibitor. I was wondering if you could confirm this and share with me any of the other inhibitors that are used. Many of these inhibitors would likely lead to bonding issues if not fully removed. Thank you for your help.

Thomas Swasey
Process Development - Ann Arbor, Michigan USA
  ^- Privately contact this inquirer -^

January 2017

A. Hi Thomas. I can tell you that pickling inhibitors are interfacially-active compounds which bind to the steel as monomolecular layers, and shield it, reducing the attack on the steel. I also know that they may contain both organic and inorganic ingredients -- commonly alkenes, alcohols, amines, polymerized aromatics, and heteroaromatics. But that's all I know :-(

This is one of those rare occasions where we must ask people to try to help via citations from published works rather than from their personal knowledge (unless the responder is well known to us). The problem here is that there are many proprietary inhibitors offered by Rodine, Akzo, Stannine LTP, and others, and the formulations are trade secrets. If a person unknown to us starts offering information about the composition of pickling inhibitors, we have no realistic way of knowing that they are an independent researcher with personally developed knowledge rather than a disgruntled employee or former partner trying to devalue someone else's intellectual property :-(

Luck and Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey

January 16, 2017

A. Thomas,
It sounds like you may be better off finding pickling compositions that don't cause problems for you, and specifying on your purchase orders that only those compositions may be used.

The other problem with bonding this, that, or the other thing to stainless steel is how non-reactive the passive layer tends to be. I guess it depends on the coating, some things need the surface to be activated, some things work better if the surface has been very well passivated, and for some things it doesn't matter much either way. I wonder if that's a factor with your coating.

Ray Kremer
Stellar Solutions, Inc.

McHenry, Illinois

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