Duplex passivation

Date 01-28-2007 22:18

I'm the Technical Service Manager for Avesta and am VERY familiar with Avesta RedOne 140 pickling paste. Let me ease your concerns just by saying that when you pickle a weldment, you are automatically putting it in the passive state. In other words, by pickling, your surface will also be passivated. Contact me if you need further assistance with any of the pickling products. chuck.meadows@avestawelding.com

Chuck

By Geese_howard (*)

Date 01-28-2007 23:01

Thank you Mr. Meadows, perhaps you can give some info or link on recommended practice for the application, like reaction time and and product removal

Best regards

By chuck meadows (***)

Date 01-29-2007 12:53

Send me your e-mail address and I'll send you a procedure for applying the pickling paste. It will be this afternoon before I can send itsince I'm traveling to Tulsa, Oklahoma in a few minutes. I'll send it this afternoon.

Chuck

By Shane Feder (****)

Date 02-02-2007 22:37

Good morning Chuck,
Greetings from Noumea in New Caledonia.
I am presently reading a Technical Note from the Australian Welding Research Association on Pickling and Passivation and after reading your post above I am a bit confused.
" Pickling involves dissolution of surface iron deposits and other contaminants using acids such as sulphuric and hydrofluoric.
Passivation involves establishment of surface passivity with nitric acid solutions.
The exception is welds cleaned by descaling agents which contain nitric and hydrofluoric acids. These function as both descaling (pickling) and passivating agents."
It is a very old technical note so things may have changed greatly since it was written.
Are all products produced these days dual pickling / passivating agents ?
Regards,
Shane

By chuck meadows (***)

Date 02-02-2007 23:01 Edited 02-02-2007 23:05

Hi Shane,
Greetings from Dallas, Texas. Stainless steel, when it is melted at the mill, and upon cooling, it has a black colored scale on the surface from the intense heat. At this time it goes through a huge pickling bath. When the pickling removes the surface oxides, it is now in the passive state. In other words, the chromium surface is restored sufficiently to be corrosion proof. This is done with the acids you mentioned. So, after this pickling process, it is in the passivated state. Pickling put it in this passive state. Nitric acids "re-enforces" the surface of lightly rusted surfaces, only on the surface. Pickling removes the oxides on the surface and immediately below the surface. So, when you pickle a weld, for example, you are removing the oxide from the weld heat and putting the steel back in a passive state, or anti-corrosive state. Pickling involves the use of hydrofluoric, sulphuric, and nitric acid, all working together in one solution, to remove the oxides from welding or other rusting oxides. This fully restores the steel to the passivated state. Nitric acid alone does not do this. Nitric more or less removes the free iron from the surface. In actuality, pickling removes the oxides that prevent the steel from being fully anti-corrosive. The result of this process puts the steel in a passive state. Passivity means anti-corrosive surface. I guarantee you, when you pickle a stainless steel, you are restoring it to its natural anti-corrosive state, or passive state. Avesta also makes a passivating agent that contains nitric acid, but it is not a pickling solution. It is only used to remove slight rust and re-enforces the already passive layer of the steel.

By Shane Feder (****)

Date 02-03-2007 00:58

Thanks Chuck, much appreciated.
Regards,
Shane

By GRoberts (***)

Date 02-03-2007 22:50

The way I understand it is that pickling removes the contamination, whether it be free iron or scale. At that point, the surface is not protected because it is the Chromium oxide that forms protecting the surface. Creating this Chromium oxide layer can be done quicly with chemicals, or over a longer period of time with air. One example I have experienced is that a corrosion test that is pickled and immediately tested failed, but a test that was pickled and air-passivated for 48-60 hours passed. So in my experience, both Chuck and Shane are correct. While the stainless can be passivated with chemicals, it can also be passivated by just sitting in air.

By chuck meadows (***)

Date 02-04-2007 14:37

Very simply put, pickling is done to remove the chromium depleted oxide layer that prevents the oxidation in the air from reacting with the chemistry in a stainless steel enabling it to re-form (self heal) the chromium protective layer. After pickling is done, the oxidation in the air starts forming the protective layer immediately. The surface of the steel needs to be free of contaminants for the pickling to work effectively. Removal of free iron is normally done with a nitric or phosphoric solution prior to pickling. It is a much quicker and less hazardous way of removing free iron and light rusting, or rouging.

By ssbn727 (*****)

Date 02-07-2007 21:45 Edited 02-07-2007 22:57

Here's another interesting perspective with respect to passivation...
http://www.pfonline.com/articles/119806.html

Please see attached also.

Respectfully,
Henry

Attachment: passivation.pdf (747k)

By ssbn727 (*****)

Date 02-07-2007 22:57 Edited 02-08-2007 00:47

Oh Yeah I almost forgot!!!
Here's a link to Euro - Inox, otherwise known as the European Stainless Steel Development Association...
once one get's there, click the linkthat reads: "The self passivation of stainless steel"...
once you're in the the second link, browse around because there are more than one streaming videos such as "Stainless Steel - Alloyed for lasting value" & "The Self-Passivation of Stainless Steel"...
There are also some interesting and educational .pdf documents on stainless steel for both instructors and students if one cares to do so.("Stainless Steel Properties" is the only one .pdf document written in another language other than english. It's written in czech or polish language which can easily be translated to english by using one of the many online trnaslation services via an app extension called "Fox Lingo" which is added & used with either Mozilla's Firefox 2.0 or SeaMonkey's newest version. No need to open up another separate web browser app like with IE.) The rest of the .pdf documents are written in english. You can also request them to send some of the .pdf's via your e-mail address directly in order to avoid prolonged download times!!! *Note: There are two or more articles in which one has to fill out a request form so that the articles can be sent to you directly... Free of charge of course!!!

Before one does visit this website, Please let me explain that there is a streaming media video which needs Flash player 7 in order to play it for both 56K & DSL... Let the streaming video upload completely to your player and then run or play it again to look/listen to the content appropriately otherwise, it will look/sound like it's breaking up or not working properly.

This link covers many aspects in working with, and designing with stainless steels and it has some cool educational videos on some different types of corrosion also.

http://www.euro-inox.org/htm/p_20_EN.html

Also, check out this link including the "Multi Criteria Search", "Correspondance EN/AISI", "Grade/Data Sheet", "View/Print Tables" and "Extras":
http://www.euro-inox.org/technical_tables/index.php?navi=gradedata

Enjoy the videos, .pdf documents, (PAL Country code 2) DVD's and whatever else you might find useful to request a printed copy of *free of charge.
*Note: There is one or two books for sale that are more than likely well worht it for only 20 Euros.

Respectfully,
Henry

By CWI555

Date 02-10-2007 16:41

Chuck,

Could you post the name of the product you refered to as a passivation agent. The project I am on now could benifit from it.

By chuck meadows (***)

Date 02-10-2007 19:02

Gerald,
I was referring to a product called (Avesta's name) Passivating Agent-601.

CHARACTERISTICS:
** secures the reformation of the corrosion resistance after mechanical surface treatment of stainless steel
** accelerates rebuilding of the protective layer of chromium oxide
** removes surface contaminants and iron particles from the steel's surface

This is a nitric based chemical, but is not intended to have the same effects as a pickling agent. Unlike this passivation agent, pickling contains a different chemical base that is designed to remove the oxides formed during the welding or heat treatment of stainless steel. The passivation agent is normally used after any kind of mechanical treatment is done to the steel, such as bead blasting, grinding, or buffing is done.

By chuck meadows (***)

Date 02-10-2007 19:26

Gerald,
There is also another Avesta product called Avesta Original Finish-Rust Remover. That is designed to remove lime stains, calcium deposits, and light rust or rouge stains. It comes in a spray bottle like a Windex Bottle. Anyway, not sure exactly what you're looking for, but here are two things that you might be looking for. Let me know if there is a specific application you need.

Chuck

By chuck meadows (***)

Date 02-10-2007 22:57

Gerald,
The passivation product is 630, not 601. I'm sorry, the 601 is the old product code. The rust (light rust) remover is the 410 Rust Remover.

By CWI555

Date 02-11-2007 22:11

Specific application: We've had some cross contamination on some 304L and 316L stainless pipe. (caused by grinding and working carbon steel in proximity of the stainless pipe) The source problem is rectified, however; certain individuals have it in their heads to either sand or grind to clean. I am of the opinion that's not the smartest path that could be taken. We may need both for other reasons. if you could email me a source and price it would be appreciated.

By chuck meadows (***)

Date 02-11-2007 22:33

Gerald,
E-mail me directly and we can talk more, or give me a phone number to call and we can talk directly.

Chuck

By Ted.Chungli (*)

Date 02-17-2007 08:35

Chuck!

We had some 316 and 316L welded pipes, we used your agent for passivation , there is a question for me , we had different colours around the welds cuased by welding heat, from yellow to dark purple, as I know these colour heat tints are formed based on amount of abosorbed heat of welding in surface oxid layer, pickling pastes remove this layer and passivate stainless steel, means anticorrosion properties will be recovered, that's all.
Some guidelines - specially in food industries - recommend that "NOT using of welded stainless with dark heat tint" e.g. dark blue or purple even if passivated!!! do you have any idea?

Ted

By chuck meadows (***)

Date 02-17-2007 13:57 Edited 02-17-2007 14:01

Ted,
Just to make sure that I understand your question correctly..Are you saying that some food industry guidelines will not allow welded stainless steel that had a dark heat tint even if it was pickled? The thing to remember is that pickling only removes the surface heat tint and restores it to it's natural state. If thinner metal is welded and it discolors the steel all the way through the thickness, then pickling or passivating the steel will not remove all of that color, only on the surface. I have visited food industries and sanitary milk producing facilities that use only TIG process for welding because it leaves a minimal discoloration, and that is easily removed with pickling. I'm not surprised that a sanitary facility will not allow welded stainless steel if it still has the darker discoloration on it, though, even if it has been pickled. It could be the perception that the steel is corroded, or degraded, because of the color that is still there, I don't know. I'm sure different facilities have different color requirements. You are certainly correct in saying that the darker the oxide layer, the thicker it is. And, you are right, that is directly proportional to the heat input. But, even if a thin sheet of SS has the heat tint all the way through, and I'm sure that whole thickness has gone through some metallurgical changes, the surface can still be returned to it's natural anti-corrosive state. The heat tint can still be seen because it penetrates through the entire thickness, but it can still be put back to corrosive resistance on the surface. Remember, that is all pickling does. Maybe a request for clarification to the NSF (National Sanitary Foundation) would answer your question. This is the Foundatioon that certifies products and cleaning methods for the sanitary food conditions.

By rebekah (**)

Date 04-26-2007 12:42

Hey Chuck and all,

I have read all the posts about stainless steel pickling/passivating and want to make sure that I understand correctly.

When welding stainless steel, I was always told to try and keep the discoloration/heat input to an absolute minimum--straw being best, grey meaning a bad weld. Does the pickling/passivation make this no longer true? I have been confused on this point for a while. Usually the stainless I weld is thick--minimum of o.5-2.0", hardly ever any sheet so this is not the case of the discoloration going all the way through the piece--and exposed to highly corrosive environments. If the weld is grey, is it a "bad" weld or does the passivation return its anti corrosive properites.

I think I am missing something when I read through the posts because I am sure the question has been asked and answered.

Thanks

Rebekah

By chuck meadows (***)

Date 04-26-2007 15:05

I'll call you and we can discuss.

Chuck