Nuclear Stainless Grinding

Date 02-04-2011 13:49

Good Morning Everyone!

I currently work as a QA Engineer and Welding Engineer building parts, mostly 300 series stainless steel, for the nuclear power industry. Many customer contracts restrict grinding media to aluminum oxide or silicon carbide or sometimes just aluminum oxide. Our shop’s preference is to use zirconia alumina grinding media as it has a better life and more aggressive metal removal rate. I’ve done a lot of research into the matter and cannot find a basis for the restriction. At most I can find a linkage from ASTM A-380 (industrial standard for cleaning) to the ASM Handbook, Volume 5, Surface Engineering, that recommends the use of aluminum oxide or silicon carbide for stainless steels, but does not restrict anything else.

Does anyone know why this exists?

By OBEWAN

Date 02-04-2011 14:22

What about carbon contamination? In the oil industry codes that is why we have the same restriction. Any carbon pickup at all could cause loss of corrosion protection.

By JustinT (*)

Date 02-04-2011 14:23

I don't think that's it because they always further go on to say to use stainless steel wire brushes and not to use items previously used on carbon steels.

By rlitman (***)

Date 02-04-2011 15:18

There was another thread that brought this up:
http://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=201425

The carbide left behind by silicon carbide can activate the stainless.

I've got no idea why zirconia is not accepted.

By G.S.Crisi (****)

Date 02-04-2011 19:20

Silicon carbide is not the best material to grind austenitic stainless steels because it contaminates the material with carbon, giving way to intergranular corrosion.
Austenitic stainless steels should be ground with aluminum oxyde or zirconia grinding wheels. I can't see any reason why zirconia shouldn't be used. May be your customer has a special reason that we don't know. If I were you, I'd ask him what reason is it.
Giovanni S. Crisi
Sao Paulo - Brazil

By 99205

Date 02-07-2011 22:19 Edited 02-08-2011 05:09

Found this interesting so I Google'd it and found some info about zirconia and Nuke plants. http://www.3rd1000.com/elements/Zirconium.htm
Last time I worked a Nuke plant they controlled the type of Sharpis we could use because normal Sharpies had a corrosive effect on some of the alloys being used there. Zirconia may have the same issues.

By MBSims

Date 02-08-2011 02:58

The Sharpy markers contain halogens which can initiate stress corrosion cracking in austenitic stainless steel. The zircalloy cladding used in fuel pellets is not particularly susceptible to corrosion induced by halogens, by can have other issues such as hydriding. The nukes use mostly 304/304L and 316/316L/316NG stainless steels in the piping systems that are connected to the reactor vessel cooling or cleanup systems. Not many "exotic" alloys in a nuke compared to fossil units or gas turbines. The choice of aluminum oxide or silicon carbide abrasives is to ensure no corrosive particles (such as iron or iron oxides) become embedded in the stainless steel during grinding and later initiate corrosion sites.

By Metarinka (****)

Date 02-13-2011 17:56

Hello JustinT,
I'm a welding engineering working the nuclear field, however I do government work and we are not subject to commercial standards. Zirconium is generally used inside reactor vessels, but seeing as this is 300 SS work, I'm guessing it's the steam and piping side. Hence I don't think it would be a poison or criticality issue.

I've never heard of a restriction on zirconia alumina grinding, I know the effects of SS on zirconium (negative) but not the other way around. The easiest thing would be to request engineering information. There could be some obscure reaction going on here, or zirconia could help contribute to corrosion or stress corrosion. I found that in the nuclear industry a lot of things that sneak into the code have been there for decades, probably were put in for a good reason but few if any know why they were there.

In the short run the cost of consumables should be built into the product or bid. I'm sure a few dollars in grinding consumables isn't killing profits.

By JustinT (*)

Date 02-08-2011 12:13

I don't think the issue is contaminates, either in the form of halogens or impurities such as sulfur or iron. I say this because you can find manufacturers of contaminate free grinding wheels for all three grinding media such as Sait, Norton or Pferd. It's always specifically limited by the grinding media and not just by one customer but the vast majority.

The closest reason I can find is because ASTM A-380 is the industry standard for the cleaning of stainless steel. ASTM A-380 points to the ASM Handbook Vol 5. Surface Engineering which "recommends" the use of AO or SC grinding media. That's all well and good but that seems like a silly reason to make it a contract requirement.