Carbon gouging Aluminum and stainless?

By - Date 02-24-2006 15:12

Addressing the stainless steel only, carbon arc gouging is not the first recommendation for ss. Carbon wil become impregnated in the grain structure of the ss, and must be removed by careful grinding before welding.

By pipewelder_1999 (****)

Date 02-24-2006 17:54

Is there any tests you have done or documentation you have seen that indicates how much Air Carbon Arc Gouging contaminates the base metal and subsequent deposited weld metal ?

I have disagreed with this opinion that carbon IS ALWAYS impregnated in an amount significant enough to show an increase in C content in deposited weld metal. I am ready to be corrected :) . If the gouging process is improperly done outside of parameters, I agree that some carbon could be deposited.

Any information would be helpful and I would be very grateful (And of course would have to go on a few forums and post corrections to my opinion).

The chemical analysis I have seen done showed no increase in carbon content above the norm for the deposited weld metal. However these were not done as scientific tests with control tests.

Have a nice day and I really appreciate your input on this forum.

Respectfully

Gerald

By - Date 02-24-2006 20:29

Gerald,
As Lawrence stated, plasma is probably the safest and cleanest way to cut or gouge SS. I only know that there have been tested and documented evidence, which I don't have in front of me, that indicate that Carbon Arc Gouging SS is not recommended UNLESS all the contamination is carefully removed by grinding. With the heat of the gouging process, carbon can becoome trapped into the grain structure of the SS. When the SS cools down and the molecules close back up, the contamination can be trapped in the microstructure. The same scenario can be presented as if you are using a carbon steel file to file off the surface of SS, or using a CS grinding wheel. Gerald, respectfully, I don't think we can compare the carbon contamination to the carbon that is added as an element in the mixture of the melt used to produce SS as being the same thing.

Chuck

By pipewelder_1999 (****)

Date 02-26-2006 02:48

Thanks for the input. I understand all the precautions. I am just curious if this is theory based, or based on actual engineering.

By - Date 02-26-2006 15:32

Gerald,
The carbon that is induced during a carbon arc gouging process is not the same as the carbon that is added to the melt. Carbon added to a melt is carefully distributed throughout the whole melt and very evenly distributed. This is nowhere the same as carbon added by the gouging process. This type of carbon contamination can be achieved by carbon arc gouging or even when inducting carbon from carbon steel chain falls. This type of carbon contamination can be exposed to the atmosphere and cause IGA under a corrosive environment, among other detrimental scenarios. In my opinion, this is a little more than just theory. I think this has been proven and documented. Actually, I think it is proven in fab shops on a daily basis if the carbon from the gouging process is not removed carefully. I believe what is being stated in this thread is that carbon from the gouging process (or grinding with a CS grinding wheel, or CS file, or any form of inducing foreign carbon into the steel) has a much greater propensity for carbon contaminated problems than if using other recommended means of metal removal.

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

Date 02-26-2006 16:58

For those of you who are not familiar with pure chemistry, when Chuck speaks of "CS grinding wheel", by CS he means silicon carbide (the actual chemical formula is SiC); and when he speaks of "CS file" he means carbon steel.
I've thought this explanation was important to avoid confusions.
Giovanni S. Crisi

By pipewelder_1999 (****)

Date 02-26-2006 19:11

I agree that the process has a greater propensity for carbon contamination.

I just haven't seen the proof or documentation. Not because its not there, I just haven't been exposed to it in my experience.

Is there an IN SHOP test that can be performed on deposited weld metal to measure carbon contamination ? Or a way to verify that a backgouge is FREE from carbon ?

Again , I appreciate the information.

Gerald

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

Date 02-24-2006 19:50

I'll add the following precaution to Chuck's recommendation: grinding should be done with an aluminum oxyde disk, not with a silicon carbide (Carborundum) one. In this case, the carbon that makes part of the silicon carbide will in turn impregnate the stainless steel.
Giovanni S. Crisi
Sao Paulo - Brazil

By Lawrence (*****)

Date 02-24-2006 15:42

I agree with Chuck about Carbon arc being a secondary choice.

So what may be a better choice?

Take a look at this;

Most manual Plasma Arc cutters with 90 degree cutting heads also come with gouging tips that might serve your purposes.

Here is a link to video clip
http://www.millerwelds.com/education/video_library/

Here is a very nice article devoted to plasma arc gouging with images by the folks at Hypertherm
http://www.hypertherm.com/company/gouging_feature.pdf

By agong

Date 02-24-2006 15:59

Thanks a lot guys!

Gong

By aevald

Date 02-24-2006 18:07

Hello agong, I would only add one small note to the comment regarding use of a gouging tip on a plasma cutter. If the plasma is running compressed air you will need to do some grinding to prepare the area prior to welding and even if the plasma is of the type that is using mixed cutting gases you will still need to do some grind prep to avoid contamination issues in the finished weld. My comments are in regard to the preparation of stainless steels, if I were working with aluminum I would tend to avoid the carbon arc and plasma altogether and go with a mechanical means of preparation. Just my 2 cents. Regards, aevald