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Up Topic Welding Industry / Technical Discussions / Stainless Oxidation with GMAW
- - By Metarinka (****) Date 09-05-2008 19:05
Hello all

I've run into some issues with stainless oxidation on GMAW welds 304L with 308L filler if memory serves me correct. I'm wondering what there is in the way of options to reduce oxidation with the GMAW process especially since our machines do not have a back purge etc option.

I believe this is due to the increased heat and travel speed as opposed to GTAW.
I was able to correct this distortion problem by running extremely slow and cold ~20V 200WFS in the short circuit transfer mode but that produces unsatisfactory welds.

Any help on what's out there? the oxidation is bad we're talking reddish at best but more that nasty grey colour.
Parent - - By Lawrence (*****) Date 09-05-2008 21:42
Some folks have good results with GMAWP which has an overall lower heat input than traditional spray transfer. It is also a good tool to improve distortion.

Other have excellent results with a shield gas mixture of 98/2  Argon/Co2.  The Carbon Dioxide will provide good spray and is reported to leave a bit less oxidation... This is an engineering type decision and metellurgical issues also need to be considered.  Ed Craig at www.weldreality.com  has some pretty good data on Argon/Co2 with GMAW and stainless.
Parent - - By Metarinka (****) Date 09-05-2008 22:43
funny you mention 98-2 lawrence, as part of my internship/Job  one of my reponsibilities was to evaluate welding procedures and suggest changes. last week I was doing test plates and macro's on welds done with tri-mix and 98-2,  on stainless steel I suggested 98-2 partly on some of Ed craigs writing and because of economics. Having never witnessed stainless still GMAW at this particular shop I was surprised to the level of oxidation with both gases. The ultimate goal was to achieve indentical results with the cheaper 98-2 which I was able to achieve by turning up the voltage and WFS. What Ed craig said about tri-mix is true helium definetly does run hotter than argon at Identical settings, however for our purposes this didn't always appear as a negative with stainless as it helped foster fluidity and fusion at low temperature settings.

However to get similar bead appearance to tri-mix this required higher voltage to encourage fluidity and in turn higher WFS. The skilled welders compensated by increasing travel speed and my calculated energy density was similar but the oxidation was slightly worse under 98-2 which I believe has more to do with coverage than heat input at this point.  As of right now both offer unacceptable oxidation but tri-mix offered slightly better prosepcts as it allowed the bead to wet out better at low voltage settings which reduced oxidation, unfortunately I forgot my camera so I won't have a chance to take a picture any time soon of the test plates.

so I'm back at the same point, I was able to achieve very similar welds under each gas but having been focused on other tasks I had never noticed how bad the oxidation was until I ran the tests, which led me to ask around  about ways to reduce oxidation on GMAW stainless.
Parent - By aevald (*****) Date 09-06-2008 03:26
Hello Metarinka, I don't know if you noticed that the 98/2 that Lawrence was referring to was 98%Ar and 2%Co2 instead of the more commonly used 98/2 which is 98%Ar and 2%O2. If you already picked up on that, forgive me for pointing it out, I wasn't quite sure by your response. It is somewhat interesting that you are talking of oxidation. I was at a seminar that the late Chuck Meadows of Avesta put on in Spokane, Wa., a fair amount of discussion was done surrounding "surface oxidation", I came away with the sense that once welding has taken place and cleaning and passivation have been completed the surface oxides will have been taken care of and are not an issue. The only times you will need to be concerned with these oxides are when you aren't planning on cleaning and passivating as this could leave the surfaces open to attack by whatever fluids or materials might come into contact with them that are corrosive or otherwise damaging. If I misunderstood this I am open to correction. Best regards, aevald
Parent - - By Stephan (***) Date 09-06-2008 10:05 Edited 09-06-2008 10:08
Metarinka,

now it was me who was "fence sitting" (quote aevald :-)) before stepping in here, even though - to be honest - the statements coming from "Mr weld39" are still acting hardly as a thorn in the side and I have considered if all this what I have tried to learn or meant to have understood over the years in terms of welding physics was none but male bovine excrement.

But since I am not that vain I'd like to venture making a short predication upon your post.

As there were some very interesting discussions over the time here in the forum in regard to the choice of what kind of shielding gas should be used in GMAW, I would even as well consider to use 98Ar/2CO2 or - being mainly used here in Germany - 97.5Ar/2.5CO2.

Due to I have tried to describe the benefits of these shielding gas mixtures here in the forum both from the arc-physic's side and from the economical point of view I'd like to avoid to repeat it again.

However, there were different points I found interesting in your descriptions and - in particular - in Allan's questions, which I want to begin with.

It is very interesting what Allan has stated in regard to the term "oxidation". What I have missed a bit concerning the use of even this term is a little more precise explanation about what you are meaning by "oxidation" in this particular GMAW application.

Is it the oxidation Allan describes by using the term /quote/ "..."surface oxidation..." /unquote/ or is the oxidation you are meaning rather the result of the metallurgical reaction between the active shielding gas constituents and the liquid weld pool?

The first named "problem" can be resolved of course by /quote Allan/ "...cleaning and passivating..." /unquote/ whereas the second one leads to the products we know well as "slag". This again must be removed accurately from the weld seam or - if necessary - the adjacent areas of the seam to avoid possible material damage by corrosion.

This however, as a very general question, to understand what you would like to reduce actually.

Coming then to your descriptions in terms of the differentiation between tri-mix - correct me when I'm wrong but I guess this mix has a higher Helium content - and 98Ar/2CO2 or 2O2 (by the way, there's not that great difference in welding characteristics between the latter).

As you state /quote/ "The ultimate goal was to achieve indentical results with the cheaper 98-2 which I was able to achieve by turning up the voltage and WFS" /unquote/ please let me ask. Did you have to increase the voltage by using 98Ar/2O2 in comparison with the high Helium containing tri-mix to achieve similar results?

Then it would be interesting to understand what Ed Craig means by /quote/ "What Ed craig said about tri-mix is true Helium definetly does run hotter than Argon at Identical settings." /unquote/.

It would surprise me when comparing Argon with Helium and finding out that it were feasible to use identical settings for getting the Helium to run hotter.

But I guess you have already answered the previous question by stating /quote/ "However to get similar bead appearance to tri-mix this required higher voltage to encourage fluidity..." /unquote/.

However, what surprises me as well is /quote/ "...but tri-mix offered slightly better prosepcts as it allowed the bead to wet out better at low voltage settings...".

Does this mean that you could run the tri-mix with lower voltage settings compared with the 98Ar/O2?

Please forgive me, but due to here in Germany shielding gas compositions containing higher amounts of Helium, are rather not being used for welding high-alloyed steels, due to the outstanding high costs for these gases. This again is the reason that 2-component shielding gases as 97.5Ar/2.5CO2 are being used to achieve comparable results both in weld process stability and economical aspects.

That's the reason I am humble questioning these details and would be grateful if you or someone could shed a light on these questions.

By the way, are you using the pulsed arc mode or as Lawrence assumed spray arc, what is the wall thickness, joint design,...?

Thanks a lot in advance for a short feedback and best regards,
Stephan
Parent - - By aevald (*****) Date 09-06-2008 16:33
Hello Stephan, I knew that the terminology that was used would draw out some responses. If my memory serves me somewhat correctly there are actually some differences between the visible and physical deposits that are left after making welds on SS materials. I'll try some new terminology that I hope correctly describes the conditions that I am speaking of and you have talked of in your response. After the completion of a weld on SS there are deposits of soot, there are some discolorations adjacent to the weld bead which can somewhat indicate the amount of heat input that has been applied during the course of the welding, the surface of the weld bead can display various colors from silver, gold, reddish gold, blue, gray or black, typically these colors result from how well the shielding is in place at the time of the weld and also how hot the weld area was when the shielding passed beyond it and there can, in some instances, be deposits of a glassy type material, likely some form of silica. As I believe you also eluded to, most of these items can be cleaned mechanically by some form or another and then chemically processed to passivate them in order to restore the chromium layer that is the trademark of protection for a SS material. If cleaned and left to it's own the SS will eventually replace the protective chromium layer yet this may take more time than would be advisable depending upon the time between welding and introduction to service, thus the suggestion to passivate. Second item would probably cover a more major issue of mechanical soundness of the weld as related to another term that is sometimes used by welders called "sugaring". This condition indicates a more major flaw as it is readily recognizable upon the completion of a weld and is likely the result of insufficient shielding or some other form of weld metal contamination, ie, dirt, oil, chemicals, etc. I don't believe that any sort of shielding gas issue that is related to suggested cover gases would introduce this into the picture. These are just a few more thoughts of mine, hopefully they will spark some additional discussion and either support or refute my statements, either way, I will certainly learn along with everyone else. Best regards to you Stephan and thank you for exercising my brain matter, Allan
Parent - - By Stephan (***) Date 09-07-2008 15:55
Hello Allan,

first of all, thanks a lot for these additional and - as usual - excellent descriptions which hopefully "...will spark some additional discussion...".

It would be great if Metarinka might give us somewhat more details about which kind of "oxidation" was meant of those ones you have described.

After that, one could consider the further thoughts on this very interesting question.

Even though I guess that Metarinka might have meant the (as you have named it) "... discolorations adjacent to the weld bead which can somewhat indicate the amount of heat input that has been applied during the course of the welding...", I guess also there are a plenty of factors to be considered with this issue - although you have given a very important hint (heat input) towards what the crucial points were.

Looking forward to an interesting discussion with you and the others!

Best regards to you,
Stephan
Parent - - By aevald (*****) Date 09-07-2008 20:30
Hello Stephan, have been rather surprised by the lack of comment on this one. As you say though, hopefully Metarinka will add some other information or comment to narrow things down. I can certainly add this though, since my start in the welding field, the specifics of welding and working with the various grades of SS have changed considerably and as a result of my association with the forum I feel much more comfortable that I have made some really good corrective steps when I work with it now. Hope life is treating you and your family well and you are still enjoying the change in your position. Best regards, Allan
Parent - By Stephan (***) Date 09-08-2008 08:42
Hello Allan,

thanks for replying and asking!

I'm doing good so far and I truly hope you may as well!

As you say: "...have been rather surprised by the lack of comment on this one...".

Hmmm... you know what?

Even though I'm no old-timer here in this forum, I have the strange feeling that something has changed within the very recent past.

It's nothing more but an impression and as funny as it sounds, neither I can explain nor define it accurately.

I'm truly missing the input of some of the great ones (js55, ssbn727, jon20013, 803056,..., to name only a few of them) whose opinions and experiences are most valuable in particular topics as e.g. the discussed one.

Hopefully they are doing good and they are just busy currently and thus finding no time for attending the forum at the moment.

Or just taking a short "time-out" before enriching the forum again.

But anyhow... most probably I'm wrong by having this impression!

Sometimes it's rather hard to find even time to participate, so let's wait if Metarinka will add something or even not.

Thanks again Allan and best regards,
Stephan

P.S. Good link, Dave!
Parent - - By Metarinka (****) Date 09-09-2008 02:52
oh sorry! distracted with school work and I had to play in a regional Table tennis tournament!

I was using 98 argon 2% CO2.

The complete setup is 3/16" SS type 304L  flat horizontal and V-down. filler is 308L
As of this writing welding takes place with tri-mix, I switched out to 98-2 Argon CO2 at which point I noticed the oxidation. Furthermore 98-2 exhibited more oxidation which I believe was due to the higher settings it was run at in order to mimmick the slightly better wetting action I observed under tri-mix.

from the sounds of it, unlike GTAW there is expected to be some surface colouration and oxidation due to the mechanics of GMAW mainly the fact that filler input(and by proxy) heat input is higher so the weld bead cools at a slower rate. Thus the weld bead has a chance to oxidize prior to cooling.

Maybe it is my own over reaction then?  having cut my teeth welding stainless steel GTAW I'm of the opinion that any oxidation is generally not a good sign, especially when the color is in the dark blue to greyish colours associated with heavy surface oxidation.  The surface oxidation can be removed by mechanical means and not all of this material will be in a corrosive environment I was just hoping I missed something obvious and the oxidation was a matter of poor technique or practice.

p.s: Stephan as I heard you mention the scarcity of helium in Germany, interestingly enough the US government used to keep a large reserve of helium mostly for wartime use of balloons and I believe it was needed in the refinement process of nuclear material. however the Us government liquidated it's helium assets http://en.wikipedia.org/wiki/Helium#Extraction_and_use  gives a partial history of the us involvment in helium. I hear it's still very scarce in other parts of the world though.

double p.s: I've used solar flux for GTAW pipe and other full pen open root welds, however this is plate welding and root oxidation is not the problem. useful stuff, but as mentioned shielding gas or a backing is preferred in my books.
Parent - By aevald (*****) Date 09-09-2008 06:55
Hello Metarinka, the aesthetics of welding can likely be the basis for your concern. When we learn, I believe we are all striving for the best, most uniform, well shaped, "straight", correctly placed, "pretty" and any other number of descriptive terms that we can deliver. If you are trying to compare a SS GTAW weld bead to a SS GMAW weld bead it is likely that you will pull your hair out trying to end up with the same "look". The processes are certainly different enough to prevent this from happening. I have always been taught to try to avoid having the blue, gray, and black colors when welding SS with the GTAW process, now I'm understanding that these aren't quite the monsters that I thought. Most SS GMAW welding will display those "dreaded colors, coloring, or surface conditions that many of us have been told aren't right as well. After following many articles, technical bulletins, and informational documents that are available on the topic, I have had to alter my thoughts somewhat as to what is acceptable, tolerable, and rejectable. I don't think there are black and white delineations for describing the acceptable vs. the unacceptable when you are looking at coloring of SS weld beads or the HAZ. There have been numerous debates on the forum here along those same lines. I believe many experts have voiced opposing opinions on many occasions, I also believe that this is likely affected somewhat by the area of use, application, and process as well. What might be acceptable for one form of service is not workable for another. To me it boils down to a few things, are the mechanics of the weld or the HAZ acceptable for the application, do the end surface conditions present any issues with the service that is expected from the fabricated component, and are there any long-term delayed conditions that may come about as a result of a particular choice or application of a welding process. If you feel that these sorts of conditions or requirements have been met for your particular work or job, you're probably in pretty good shape. Hope this has made sense and doesn't stray too far from the actual technical issues that are present. Best regards, Allan
Parent - - By Stephan (***) Date 09-17-2008 23:28 Edited 09-18-2008 15:13
Hello Metarinka,

even though Allan and Lawrence have given their excellent input to this matter of subject and even though a bit time has passed meanwhile, please let me nonetheless add two or three words to this interesting topic.

First of all, thanks for both the comprehensive explanations on the type of application and the background of your thoughts.

You know what made the issue so interesting for me? It was the relation between the general technical term "oxidation" and the extended descriptions coming from Allan and Lawrence.

Let me try to clarify what's driving me...

You know, here in Germany - as I guess in other European countries as well - "stainless" steels are designated as "High Alloyed Steels" what fits - in my opinion - better than "stainless". The latter leads from my personal opinion often to an understanding which is simply risky. Even that "stainless" steels cannot rust. Now all of us know very well, that this is illusive - at least as far adverse circumstances can be observed. Thus it's not my intention to "philosophize" about the nature of "stainless" steels or how they are manufactured for even achieving and assuring the corrosion resistance they undoubted have. But nonetheless, as that welding - and in your particular case GMAW can negatively affect this corrosion resistance - it should be allowed to speak about the mechanisms being in charge for making "stainless" steels being "stainless". And as I have seen Lawrence has posted a great conclusion for both the explanation for the existence of a "thin film..." (called passivity) and the explanation for even the "discolorations" Allan has explained. Thus, it's certainly unnecessary to repeat these information given already along the thread. But... as far as we speak of "oxidation" at a general view we can say that even an oxidation process has already occurred as a reaction between a metal and the element oxygen. Without even this "oxidation" we won't have achieved the passivity of a "stainless" steel. Hence we might say, that even the passive layer of a high alloyed or "stainless steel" is the result of an oxidation. The reaction between Chromium (Cr) and Oxygen (O) or Cr + 2O2 + 2 e- gives [CrO4]2- and this layer is adsorbed by the metal's surface.  Due to even the little thickness of this layer (0.05... 0.1 µm = 10... 15 molecule layers) the metal appears to be shiny. However, and before treating the question of how the shielding gas composition may influence the grade of oxidation or "discoloration" it drives me to understand what the mechanisms are behind the passivity or passive layer, making even the metal corrosion resistant? You know, here in Germany there exists the term "Edelstahl" which means as much as "noble steel" and is used very often in the relation of "stainless" or high alloyed steels. I guess the etymological origin of this term "Edelstahl" has to do with the term "Edelmetall" which is "noble metal" in English. Most likely the originators of the word had the idea that the "steel" behaves like "gold" by not corroding and thus the corrosion resistance were based upon the same chemical a/o physical mechanisms. However the metal (steel) itself is base and thus in no way comparable with a "noble metal" like gold, as we all know. "Noble Metals" are comparable with "Noble Gases" which are inert in their chemical character. This inert character is based again upon the complete saturation of their outmost valence electron orbital. Stainless steels however have a passivity or passive layer which is not "inert" in the sense of the word, but they are acting like a "semiconductor" allowing electrons but not large metal ions to pass the layer's barrier. Hereby the normal "electrical corrosion current circuit" is quasi interrupted and corrosion doesn't occur. What's interesting by the way as well, is to having a look upon the statistical distribution of Chromium in iron. I could find out that the statistical distribution with a steel containing 13% Cr is approx. that each 7th atom at the steel's surface is a Chromium atom. Now one could ask why there's a that high dense passive surface layer having that great resistance against corrosion while there's that incomplete distribution of Chromium across the metal's surface. The explanation could be found by having a look at the affinity of Chromium to oxygen which is quite high, so to speak. Since Chromium has - compared with iron and under normal conditions - the highest affinity to oxygen, the passive layer can be seen obviously as an overlapping of single "insular" disks. And even the content of > 13% Cr in iron enables a rather complete overlapping of those "chromium oxide disks". Hard to imagine but apparently true. However, due to the little thickness of this layer and the base character of the metal alloy (stainless steel) itself underneath the layer, it is quite susceptible against damage what means again that the passive layer - once damaged by e.g. a base iron or even nonmetallic contamination - cannot regenerate itself and the "stainless" but actually "base" steel corrodes as far as there is an electrolyte present. I have tried to find a picture of what could prove these statements but unfortunately I haven't succeeded. But what I have found is an interesting metallographical picture showing the surface of a "stainless" steel contaminated with aluminum oxide (Al2O3), see also the attached Al2O3_jpeg. Here one can see fairly clear the overlapping insular aluminum oxide layers upon the stainless steel surface.

So far so good, excuse me the sidestep to this matter.

Coming thus now to the "discolorations" adjacent to the seam and which are a function of temperature over time or in other words, how long does a particular amount of heat do treat a particular alloyed material. As known these layers are oxide layers as well and thus finally the result of an "oxidation" process as well. Due to their different thicknesses they do have a different light reflection behavior and thus they appear to have different colors. It's known that these layers do have a different behavior in respect to the corrosion resistance what means that they do not protect the metal itself against corrosion. This is based on that they are having a different structure compared with the "thin" and actual protective passive layer structure and the "darker" (red, blue, brown) ones (iron oxides) are the "thicker" ones and are having a quite lower corrosion resistance than the "brighter" and "thinner" ones (straw yellow) which are mainly chromium- a/o chromium-nickel oxides. These oxides - normally rather not generated under room temperature conditions - are generated by dropping their oxygen affinity by increasing the temperature - even by the welding process itself.

Resume...

Now talking about the shielding gas composition. When comparing both "He/Ar/CO2" and "Ar98/2.0CO2" in particular regard to their influence to generate "discolorations" or even non protective oxide layers. To be honest and to say this previously. It appears a bit strange to me that both shielding gas compositions should have different effects with the coloring of the heat affected areas besides the weld seam. Why..?

Well, first of all one should presume that we are not talking of the "metallurgical" reactions taking place within the molten metal of the weld pool - and droplet of course - by the intensive contact between the shielding gas constituents and the molten metal. That was the reason for me to question what kind of "oxidation" was meant by you. The seam itself has very often a dark color which is to be seen as the result of a high energy content of the melt and a kind of imbalance between this energy (heat) content and the conditions of welding speed and shielding. In other words - please apologize when I have problems to express clearly what I mean - the higher the heat content the slower the welding speed should be for improving the shielding effects of the solidifying and down cooling weld seam. This however, is ineffective in regard to economical aspects. Since the higher the welding speed the faster the job is done. So presumed you're using "tri-mix", containing a high amount of helium, making sure that you can generate a high arc- or even use a high welding performance respectively, you may assume that you can thus increase the welding speed. The higher the welding speed whereas the lower the reaction time between the active components of the shielding gas and the weld pool volume. This means - at least in my understanding - even though you have a "dark" or "black" weld seam - generated by a higher average heat content and lower  "shielding time" - due to higher welding speed - you may have a lower amount of slag. Otherwise there should be a difference between the "tri-mix" and Ar/CO2 to be observed since the arc shape is a different one as well. Due to there's a more bell shape profile having a more or less similar depth of fusion with the high helium containing shielding gas to be expected, there should be likewise a greater weld pool volume to be expected. I.e. a greater volume of molten metal is available to let occur a metallurgical reaction between the active shielding gas constituents and the melt. Thus, perhaps, a more or less similar quantity of slag - or even the products of the metallurgical reactions between shielding gas and the molten pool/droplet - might be observed. This however, is just an assumption and certainly some of you fellows may correct me when I'm wrong.

But this should not be the main topic, since as we know now, we are taking about "discolorations" as a result of "oxidation" but not about the "oxidation" of the weld pool itself based on even the metallurgical processes within the melt yielding a weld seam appearance as to be seen in the attached stainless_steel_oxidation_jpeg, which I have - gratefully - taken from Ed Craig's " weldreality.com " website.

You are rather talking of the oxidation yielding even discolorations or the layers as already described above and which are to be found adjacent besides the weld seam. And this is most interesting...

Hence, let's assume that you have chosen a particular welding speed under using "tri-mix" i.e. high helium containing shielding gas. Dependently to the thermal energy input into the base material you'll achieve a very specific heat accumulation which is depending again to the thermodynamic properties of the material itself. As far as the heat source - e.g. the arc -stands still, the equal temperature fields or the isotherms respectively, are formed rotationally symmetric around the heat source. A moving heat source however, distorts this rotationally symmetric condition, all this is well-known. What can be said is, the faster the heat source is being moved, the lower the peak temperature of a specific volume unit of the melt. And the lower the peak temperature the lower the material's unit volume's heat content. Besides the lower kinetic reaction between the gaseous constituents and the melt, since the lower the temperature the lower the driving force for oxidation, as mentioned above, one might say that the weld seam's adjacent areas are differently affected by the different shaped temperature field's. The lower the welding speed the higher normally the temperature at a specific point adjacent to the weld seam. This however, should yield a higher driving force for oxidation which is strongly affected by the height of temperature or in other words, the higher the material's surface temperature adjacent to the seam the higher the endeavor to oxidation. And the higher the temperature besides the weld seam the greater the thickness of the oxide layer's what can be visually recognized by their darker colors. Please let me attach a file for a better understanding of what I am talking about, see also the Quasi_Stationary_Temperature_Field.pdf. Here I have used the base material's properties to calculate the quasi stationary temperature field when welding with an arbitrary welding power - which should be pronounced to be secondary for the clarification. However, by holding everything but the welding speed - which should be presumed to be doubled - constant, one can see that there is a significant difference in both peak temperature and temperature field or isotherms respectively, around the heat source. This would be an explanation for the lower oxidation when using the tri-mix, as you have described it. Since the higher the welding speed - which should be assumed to be reached when using tri-mix (please correct me when I'm wrong) the lower the surface temperature besides and behind the seam and thus the less the oxide layer's thickness. When now assuming you are using Ar98/2CO2 while remaining at similar wire feed speed I am quite certain of what you have described how you adjusted the performance by changing the welding parameters ("[...]was due to the higher settings it was run at in order to mimic the slightly better wetting action I observed under tri-mix."). As to have an example for the differences between high helium containing shielding gas welding characteristics to an Ar98/2CO2 welding characteristic I have tried to find out what the numbers were to clarify these distinctions. When choosing ~ 9 m/min (354 in/min) wire feed speed one can set the approximate welding current at ~ 240 Ampere and the approximate welding voltage at ~ 33.4 Volts. As the direct reflection when choosing Ar98/2CO2 one has an approximate welding current of ~ 290 Ampere and an approximate welding voltage of ~ 23.3 Volts. So it doesn't matter how you are choosing the direction of what kind of shielding gas is used primarily or secondarily, you will see a difference at all. When choosing the high helium containing shielding gas. When choosing the Ar98/2CO2 shielding gas first and setting the welding parameters for it you will achieve an electrical equivalent of ~ 6757 Watts yielding an appropriate welding result. When now choosing the high helium containing tri-mix without changing the parameters you will achieve an electrical equivalent of ~ 8016 Watts, which is a difference of ~ 1259 Watts compared with the Ar/CO2 gas. I am venturing to assert that you might say "Good Bye" to your contact tip due to the ~ 10 Volts higher arc voltage when not adjusting the parameters when changing from Ar/CO2 to "tri-mix". But all of this just mentioned by the way.

So coming back to the differences in oxidation or "discoloration" when using the two different shielding gases. As you've mentioned that the oxidation appeared to have been increased when using Ar98/2CO2 / quote / "...Furthermore 98-2 exhibited more oxidation..." / unquote / one might ask, where does this behavior come from. And now it comes to the flow patterns of the two different shielding gases. And before I resume, I won't be able to say if there are that great differences between Ar/CO2 and "tri-mix". Let's therefore have a look at the shielding gas flow rate. Argon as the "base gas " of the two component Ar + 2.0% CO2 shielding gas compositions has a particular density which requires a particular flow rate to protect the weld pool and the adjacent areas of the seam against the air. When using now - for comparison - the high helium containing "tri-mix", I suppose that the flow rate has to be increased due to the appropriate lower density of helium which is the "base gas" of even this composition. This should be comparable with the requirement to work with a correction factor when using pure Argon and either helium containing or pure helium when GMA welding aluminum. Thus higher flow rates for "tri-mix" can be assumed. When considering now that the higher flow rate of helium containing "tri-mix" is required to adjust the lower density of the shielding gas and the density is again an equivalent for the number of particles (mass) over the unit volume then one might assume to have a comparable shielding effect in terms of the seam adjacent areas of the weld, since actually the higher flow rate acts just as making sure that a similar number of shielding gas particles is available for shielding the weld pool as the areas before, besides and behind the welded seam. However, and now it's getting complicated, the flow pattern mechanisms for shielding gases in GMAW are extremely intricate. I had the great honor recently to listen to a lecture of Prof. John Norrish who is the head of the welding research at the School of Mechanical, Materials and Mechatronic Engineering at the University of Wollongong Australia. He and his team  have investigated the effects of on-torch fume extraction methods and what they found out was outstandingly impressive. However, what they have used for calculating the flow patterns of shielding gases while GMA welding - it was Computational Fluid Dynamics - showed that the influences of the different forces (impinging- and buoyancy forces) to be observed while welding and their influences when wanting to extract them efficiently are quite complex. As a little addendum I would like to attach a jpeg, see also the GMAW_Induced_Flow.jpeg, showing a visualization of such a simulation and showing the intricate flow pattern of shielding gas under - theoretical - welding conditions. Thus it is hard for me to have an imagine if just the change of the "tri-mix" to the Ar98/2CO2, while holding all other factors (e.g. welding speed, welding power,...) constant, would make that great difference with the formation of oxide layers adjacent to the seam. As I said, it' just a personal thought and perhaps the higher flow rate for the high helium containing shielding gas affects a greater area which is  protected against the air compared with Ar/CO2, and this although helium has a lower density and is lighter than air and thus fairly volatile when loosing rate of flow.

But I guess it will be as always, and the effects are to be seen as a combination of many single influencing factors which have to be examined analytically in relation and specific dependence to your welding application.

Just my humble opinion...

Best regards,
Stephan
Attachment: Quasi_Stationary_Temperature_Field.pdf (201k)
Attachment: Al2O3.jpg (4k)
Attachment: GMAW_Induced_Flow.jpg (45k)
Attachment: stainless_weld_oxidation.jpg (19k)
Parent - - By aevald (*****) Date 09-17-2008 23:58
Hello Stephan, you never cease to amaze me. Even though you speak in technical terms and concepts that are certainly well above the level of my normal understanding, you manage to clear things up and make them understandable. Your descriptions and words have helped me to "visualize" these processes and occurances much more clearly and understandably. Thanks so much for your contributions here. Best regards, Allan
Parent - By Stephan (***) Date 09-18-2008 15:17
Hello Allan!

Words fail me...

You are honoring me outstandingly, Sir!

Thank you very much Allan it is always my greatest pleasure to discuss with you!

All the best to you,
Stephan
Parent - - By Jeffrey Grady (***) Date 09-18-2008 06:58
Stephan,
Wow...Now that was one absolutely eloquent dissertation on the subject matter. Your knowledge is encyclopeadic. Most of it went way over my head, however, I found it to be a very good read. thanks for sharing Your extensive knowledge with us.
Respectfully, Jeffrey
Parent - By Stephan (***) Date 09-18-2008 15:22
Jeffrey!

Thank you so much as well, Sir!

Wow, gentlemen you are truly making my day...

Please let me heartfelt thank all of you for allowing me to participate this the "world's greatest welding forum"*!

It is always a true joy for me to be here as far as I can find a little time to do so! :-)

My best regards to you Jeffrey!
Stephan

* Quote Henry (ssbn727) :-)
Parent - - By jrw159 (*****) Date 09-18-2008 15:53
Stephan,
  WOW!!!

"please let me nonetheless add two or three words to this interesting topic."

When you make this statement, I always know we are in for a doosie of a post, and as always you have come through in spades!

I will not pretend for one minute that I have even as yet absorbed all of your wonderfully educational post, as it will take me reading this at least three times to fully achieve the maximum effect.

OUTSTANDING to say the least.

Thank you,
John
Parent - - By Stephan (***) Date 09-25-2008 20:09
[deleted]
Parent - - By jrw159 (*****) Date 09-25-2008 20:13
Stephan,
  Absolutly no appoligies necessary my friend. I have been very blessed as of late and had an abundance of time, but I do know the "too busy to breath" scene. :-)

You take care, and I as well as many others will look forward to more of your valuable and educational input on this forum.

John
Parent - By Stephan (***) Date 09-25-2008 20:16
Thanks a lot my friend!!!

See you soon and all the best to you and to all the other appreciated ladies and gentlemen!

Stephan
Parent - - By Metarinka (****) Date 09-26-2008 20:22
Thank you very much Stephan you explained very clearly some mechanics I was always aware of but never fully understood in a technical sense.

I believe everything you said confirms what I've witnessed in my years of welding and after discussion I had come to a similar (although not nearly as well described conclusion).  My fears of oxidation were mostly due to being unfamiliar with GMAW Stainless steel having only ever welded it in volume on the GTAW process which has a much smaller energy input per pass than GMAW and does not have the same surface oxidation on the bead.

However I believe your analysis, while correct, isn't perfectly describing the situation I've encountered. What I'm trying to say is I most likely didn't describe the situation in full detail, and you assumed several variables different than what actually happened.

To clarify what was said before:
*  welds were made on identical material and joint detail, 304L 3/16 SS open root square groove weld
*  Several welds were performed under Tri-mix at settings comfortable to the welder.
*  Shielding gas was switched to 98-2 and the welder allowed to perform practice beads and adjust settings until comfortable at which point a more or less identical bead was run on several more identical test plates.   The objective as given to the welder was to create similar quality, size, contour etc beads.
*  Penetration, travel speed, shielding gas flow rate and machine parameters were all open variables the welder was free to manipulate in order to achieve a similar quality bead.  I mention penetration as a variable and I'll come back to that later.

After completion of each test plate machine parameters were recorded, normally I recorded travel speed too, but didn't due to time constraints (I didn't have a stop watch with me). There was no expectation for a large or intrinsic deviation between travel speed for the two shielding gases and so it wasn't considered an important variable.  However I'm kicking myself now as one of your chief theories on base metal oxidation revolves around heat input based on travel speed (which makes perfect sense and I believe most welders are familiar with).

Below are the averaged machine settings between the two shielding gases:
Tri-mix:
21V
220 WFS

98-2:
27V
375 WFS

** this was an analog machine with no meters therefore settings are "knob" settings relative only to each other and not indicative of true machine settings, my feeling is that actual voltage and WFS are much higher. Generally I would physically measure voltage with a multi meter and WFS by measuring wire length over a given time. I didn't have a chance to do this due to time constraints.**

This particular machine the welder had noted as being finicky and more "loose", in retrospect not the best machine to conduct experiments on but the only machine at the time with stainless steel filler material.

The most immediate difference between the two machine settings is the higher voltage and WFS, travel speed however was slightly higher under 98-2. You assumed and I quote,

"Since the higher the welding speed - which should be assumed to be reached when using tri-mix (please correct me when I'm wrong)".

Travel speed under 98-2 would actually be higher (although obviously not by a theoretical factor of 2) When trying to maintain an equal bead appearance under a "colder" less penetrative arc (due to shielding gases). When reacting to a cold weld bead the welder would naturally do one of several things: Reduce travel speed to achieve similar heat input as you theorized and I'm sure we all have done, adjust welding technique, gun angle etc to increase heat focus on welding bead, or adjust machine settings to increase heat input. 

The welder I worked with adjusted machine settings because, at identical machine settings the bead surface was rough and uneven indicating low heat input (fast freezing puddle). However lowering travel speed was not a solution as that would create unwanted surface buildup for the given joint.  Basically at the tri-mix settings the parameters were outside the acceptable range for creating an identical weld under 98-2. The only solution that would increase heat input so as to give good bead characteristics was to raise machine settings by a sizable factor.

Now here is a big detour and in depth explanation on how raising machine settings would increase travel speed. Anyone here with decent welding experience would know that if one raised voltage and WFS naturally travel speed would increase and can probably skip it, but I included some interesting findings

*BIG DETOUR*
Due to my previous efforts on measuring weld performance and weld cost evaluation I have done a lot of experimentation on how welding parameters affect performance.  In conjunction with a statistics class I took as part of my internship I measured the prime variables of every welder at my facility under different settings to accurately estimate welding cost. This was also part of a previous experiment I had enacted to switch all shielding gas for carbon steel GMAW from 100% CO2 to C15 (85% AR 15% CO2). 

As mentioned above experienced welders react to machine and material settings by compensating in several ways. In my experience the prime welding variable for GMAW is voltage, on constant voltage machines V is related to heat input, however if voltage is increased too much than there will be issues of wire burn back and puddle viscosity. Therefore WFS (filler deposition) is also increased to compensate. However WFS also controls Amperage so by increasing WFS net energy levels in the electrode are higher. However, on any individual molten droplet energy density will be roughly the same due to the increased WFS (volume) of metal exiting the nozzle in a given period of time.  In order to compensate for this increased net energy and filler deposition, travel speed is increased

Due to this chain reaction of parameters for any one voltage there is a narrow range of acceptable WFS. Due to this relatively narrow range of heat inputs for a given voltage and filler deposition, there is now  a narrow range of acceptable travel speeds ( to achieve good bead quality) 

Now the whole point of this long detour is that if other variables are maintained and after sufficient experimentation one can accurately predict both WFS and travel speed based on voltage alone!  Attached is two graphs GMAW.jpg that reflects this. After collecting data on a sample of 12 welders a direct correlation can be seen between Voltage and travel speed with the objective being identical, quality bead appearance etc. (sorry for the bad format of this particular chart I don't have access to all my data right now). Additionally is a chart reflecting the observed maximum and minimum Travel speed (TS) for a given voltage which would follow the acceptable parameter range.

In fact with a large enough sample size (the number of welders at my facility) I was able to establish a formula using statistical methods to calculate travel speed for a voltage with about 90% confidence, of course due to the parameter range there is a always going to be variation in weld parameters while still maintaining acceptable bead appearance.  If requested I can dig up and attach this information.

Anyways, although travel speed is increase to compensate for increased heat input the ratio is not exactly 1:1 that is to say welders don't increase travel speed as much as they increase voltage.

So what happens at higher voltages?

Through observation it has been my conclusion that by increasing Voltage, and hence by proxy WFS at a 1:1 ratio, but by not increasing travel speed at the same ratio; filler deposition and heat input is slightly increased. On square grove welds and fillet welds the heat and WFS means more penetration for groove welds and larger leg size for fillet welds.

This also corresponds to a higher heat input "ceiling" for acceptable welds at higher voltages with colder gases. Below is the observed heat input range by switching to a "colder" shielding gas and allowing welders to change all other parameters to ensure acceptable (identical) welds.

*Averaged settings*
22V:  CO2
354 WFS
145-165 A.
Heat input: 10,000-13,600 kJ/in

29V C15
648 WFS
210-240 A.
Heat input: 12,000-16,000 kJ/in

Due to the colder, less penetrative gas heat input (voltage) is raised to the necessary range to insure similar bead fluidity (good bead appearance), which leads to the cascade of events as previously mentioned. From this information we can ascertain that when switching to a "colder" arc situation, heat input will generally be higher even if travel speed is increased!

it should be noted that that when switching between 100% CO2 to C15 this opens the ability to use spray transfer, a higher energy mode of transfer, thus it's impossible to raise CO2 above 24v (erratic globular transfer) and as such this skews data slightly as naturally C15 will have a higher energy input. Tri-mix and 98-2 can both achieve spray transfer at similar Voltages.

To further correlate my findings that a colder shielding gas will increase heat input and, by proxy, penetration; are pictures of two welds taken from the above trials, one of C02 and one of c15 titled (C02.jpg and C15.jpg respectively).  Those are nick break tests from actual welds performed during the formation of the information above, it's easy to see the increased penetration (deposition rate) of C15 if surface appearance is maintained.

What this all means is that one of the metrics welders use to judge non code welds (bead appearance); can improve welding characteristics (travel speed, penetration, distortion) If they switch to a colder shielding gas and try to maintain bead appearance via machine settings! However this would not be the same under all scenarios for instance robotic applications with very high travel speeds may benefit from a "hotter" shielding gas to aid penetration on thick material and "colder" less penetrative shielding gases may be desired on sheet metal applications.

*END DETOUR*

Now how this all relates to the stainless steel situation at hand?

Well as previously mentioned and generally accepted 98-2 is a "colder" less penetrative shielding gas than tri-mix.  If the fixed variable is bead appearance (the metric welders at my company use) than a colder shielding gas will necessitate higher heat input and by proxy, higher penetration, energy density, filler deposition etc. Then by the mechanics you explained so well, increased latent heat in the weld bead will lead to higher oxidation which is also coupled to the increased travel speed under the colder gas.

Basically we came to the same conclusion with two slightly different versions of what transpires under a changed shielding gas.

As you mentioned about heat input into the base material due to higher travel speed and therefore subsequent discoloration. I saw no noticeable change, I suspect a macro cuts and acid etching would more easily highlight HAZ size, which I am assuming would be parallel to surface oxidation in base material and which would correspond to your good explanation of heat input as a function of travel speed.

I think most welders are aware of this phenomena which means that sometimes although a weld can be achieved at lower speeds travel speeds with lower heat settings, over heating of the base metal can occur, which is important on a sensitive metal such as Stainless steel.

Finally you make mention of the complexities of gas flow etc and it's relation to shielding.
Quote, "the high helium containing "tri-mix", I suppose that the flow rate has to be increased due to the appropriate lower density of helium which is the "base gas" of even this composition"
However under the tests the welder actually increased flow rate under 98-2 as opposed to tri-mix. This was his reaction in trying to counter the increased oxidation.  I believe flow rate was around 22 CFH for tri-mix and 28-30CFH for 98-2 but I'm going off of memory of an event a month ago. The only basic guess I have is that some of the welds were performed vertical down in which the lighter than air helium might rise somewhat to cover the trailing weld bead. Similar to its use for back purging in the high areas of a piping loops.  However the rest of the welds were performed in the flat position where I would think the opposite would be true of argon which would dissipate slower and downwards as opposed to the rising helium. Again that is just a guess and I'm not sure how much that would actually influence shielding characteristics.

Very amazing posts Stephan! It made me think quite a bit about fundamentals of welding physics I've always taken for granted. I posted my rather large detour as I thought other forum users might find the experimentation I've been doing on shielding gases informative.

I've attached this reply as a word file in case it's hard to read in the browser
Cheers!
Attachment: 98-2correspondence.doc (42k)
Attachment: c15.jpg (195k)
Attachment: co2.jpg (213k)
Parent - - By Stephan (***) Date 10-03-2008 23:41
Hi Metarinka!

Very first of all, please forgive me the great delay in my response it is as I said once. Quite much to do at the moment and thus as being the inverse opposite, quite less time for this wonderful forum! By the way, it appears unbelievable but a few days or even a few weeks not attending the forum means one is missing hundreds of posts. Wow... this is truly tremendous!

Thank you Metarinka for your excellent reply and the detailed and valuable information contained in it! Please let me try to state two or three words on even your response since I mean you have described some very interesting items deserving to be discussed further.

As one of the first of those please let me come back on what you have attached as my quote and dealing with the assumption of that the travel speed under tri-mix should be presumed to be higher compared with Ar/CO2. You know this assumption was made by me under having considered the statements coming from Ed Craig who - I hope my memory serves me right - has mentioned that helium runs "hotter" that argon under similar conditions. Even this was what made me a bit concerned, so to speak. Since from my humble standpoint it is dangerous to compare both gases - even used as arc welding shielding gases - 1:1 due to their quite different physical properties they are showing within the arc plasma. This means when comparing both shielding gases under similar parameter set ups one will obtain results as I have tried to describe them by having stated the examples with the approximate similar wire feed speed of 9 m/min. Even this however, is nonetheless one of the benefits of the tri-mix, or high helium containing shielding gases in general. Due to the greater performance obtainable by using these shielding gases one may obtain particular benefits as even higher welding speed, improved droplet detachment characteristics or wetting behavior. So what happened when you have tested the shielding gases was - at least in my interpretation - even the proof for this assumption. Due to you have firstly chosen similar conditions - based on the parameter set up for tri-mix (quote: "Several welds were performed under Tri-mix at settings comfortable to the welder") - for both shielding gases, you could not use even these parameters to be used for the Ar/CO2 mix. And honestly I would have been surprised if you would have been able to use them in a 1:1 ratio. And just a short input once again. Statements as e.g. "Helium runs hotter than argon under similar conditions" may awake - at least from my point of view - even the assumption that the welder has just to switch the shielding gases from argon to helium, remain at the same parameters and may run the bead faster since even helium provides more "heat" over the unit time. But this is definitely not the case, as you have recognized and given your welder the chance to freely and experienced adjust the parameters and other variables /quote/

"Penetration, travel speed, shielding gas flow rate and machine parameters were all open variables the welder was free to manipulate in order to achieve a similar quality bead..."

/unquote/.

And even these set-ups were the result of his adjustments:

Tri-mix:
21V
220 WFS

98-2:
27V
375 WFS

And this is the evidence for that no similar conditions can be chosen for both shielding gases, which is however the risk of being assumed when listening to statements as "helium runs hotter than...". Of course runs helium "hotter" than argon but nonetheless it is necessary to change some very important conditions for obtaining approximately similar results. To use different words. Helium provides a higher arc performance with similar conditions where I have to clarify that - at least for me - the only real "constant" in GMAW is the wire feed speed. Even this is - so my assumption - what your welder has experienced when switching to Ar/CO2 and using the similar parameters as been used for tri-mix. And of course it won't work to reduce the welding speed to obtain a similar heat input into the base metal, since there must be an imbalance to be observed between the energy input in general and due to the stronger bead reinforcement you would probably have obtained by decreasing the travel speed you have not obtained an increase in the melting efficiency itself. In other words. One can of course reduce the travel speed to try to obtain a similar "heat input" when using Ar/CO2 but this is just a theoretical approach and the real results will most likely deviate from the theoretical assumptions by showing unacceptable bead appearances. As one of the most influencing factors I believe is the quite different heat conductivity of both shielding gases to be seen. Argon has a lower heat conductivity across the plasma's radial cross section shows thus a "hot" core and a temperature drop across the radius resulting in the well-known finger type penetration profile. Helium whereas shows a higher heat conductivity under showing simultaneously a diffuse arc plasma but having an even more homogenous temperature distribution. However, it requires a higher arc voltage leading under similar wire feed speeds to a higher arc performance hence higher melting efficiency and hence higher welding speed under the assumption to obtain a similar depth of penetration.

Thus again to obtain similar welding results with particular respect to productivity your welder had of course to change the parameter set up which results in those values as been stated by you.

This again makes it entirely understandable what you have stated subsequent to that, namely /quote/:

"Travel speed under 98-2 would actually be higher (although obviously not by a theoretical factor of 2) when trying to maintain an equal bead appearance under a "colder" less penetrative arc (due to shielding gases)." /unquote/.

It appears understandable that a wire feed speed of 375 inches/minute (9.525 m/min) when using Ar/2CO2 compared with a wire feed speed of 220 inches/minute (5.588 m/min) requires a higher welding speed since you have admittedly adjusted the arc performance by increasing the voltage times the current (wire feed speed) but of course you have changed the constant wire feed speed on the other hand and to deposit thus a higher burn off rate - to obtain similar bead shapes - it requires a higher travel speed. This makes sense and does of course lead my assumption that the welding speed under tri-mix was assumed to be higher to be incorrect. But - as I tried to describe - I have assumed the welding speed to be higher under using tri-mix based on the general statement that helium runs "hotter " than argon under similar conditions which I interpreted have included similar welding parameters.

Coming now to your "BIG DETOUR" :-)

Well, what should I say..?

Most interesting what your observations and the explanations for these are. First of all I would like to treat the observation for increased voltage - set by the welder - does require an appropriate increase in wire feed speed to avoid burn back and some other problems. When I am interpreting these observations correctly then you have proved hereby the volt ampere relationship between both crucial values in GMAW. When using a conventional power supply - I am sorry for not knowing the correct English term - what means that I can choose both voltage and wire feed speed independently (i.e. no modern power source providing "synergic" characteristics) one from the other then I mean one could obtain even what you have found by having set the voltage as a main value and adjusting the wire feed speed and proportional to this the current for finding the correct operating point as being the optimal matching point between both values. However, besides this operating point there is a more or less wide range possible depending to the characteristics of the power supply itself and limiting the field where even the parameters can be varied in between. In Germany we call this "Arbeitsbereich" or translated "working range".

In respect to your statement /quote/:

" In my experience the prime welding variable for GMAW is voltage, on constant voltage machines V is related to heat input..." /unquote/

please let me say the following.

I must repeat myself when saying that "heat input" is my personal hobby. Even this makes it so hard for me to say what "heat input" in the most objective sense of the word really is. This, since it is most intricate to define it exactly in general due to the extraordinary amount of variables relating to this issue. What does this mean now..? Well, let me assume that the voltage is the main variable for affecting the heat input and I assume further that the voltage is approximately proportional to the arc length. Then I assume to set a particular range of parameters i.e. voltage and wire feed speed or current, respectively. The result of the electrical efficiency of the arc is thus voltage times current. Now I assume that I have to calculate the "heat input". This is being accomplished by setting the electrical arc efficiency over the travel speed. This is a theoretical approach as well-known. However, even by the moment the arc is ignited the conditions related to the welding process may vary dependent to the particular instantaneous conditions as to be found as a reaction between the solid (base metal) and its specific properties and the arc. The performance from the arc is relating again by having a specific arc length (set by the voltage) and current (set by the wire feed speed). When now obtaining a particular product being set by voltage times current I must consider as well the appropriate length of the wire extension which does stand for an important amount of resistance to be integrated into the product which has been calculated by voltage and current. When now increasing the voltage by holding the wire feed speed or current respectively, constant, one increases the arc length and hereby decreases the wire extension length. This means that one decreases the resistance cohering to even the wire extension but increases the arc resistance which might compensate again the resistance losses of the wire extension. In other words, one might assume that the product remains the same as the wire feed speed remains the same. However the heat input might drop due to greater energy losses by radiation and the penetration profile might change as the cathode spot changes with respect to its unit area. This again means I am transferring an approximate similar product of arc energy (reduced by the increased radiation losses) over a greater area which yields a wider bead having a shallower depth of penetration. Hmmm...

Coming instead to an approach to welding speed and arc or welding performance, respectively. This is being expressed by the term "melting rate" (MR) and can be stated as:

MR = alpha * I + beta * l * I² / a

I is the current, l is the electrical wire extension and a is the cross sectional area of the wire. Alpha and beta are constants. Whereas the first term represents the arc heating effect and the second term represents the resistive heating of the electrode. Wire feed speed - which depends to the current chosen and this again is chosen in relation to the wall thickness of the parts to be welded - is - as I said once - for me the only constant in GMAW since the wire being fed has to be molten and to be deposited onto the workpiece over a particular unit of time. In order to obtain proper bead shapes and penetration profiles one has - proportionally to the wire feed speed which determines the melting rate - to choose an appropriate welding speed. This however is determined again by a maximum melting efficiency what means finally that I cannot increase the welding speed infinitely by increasing the melting rate - or the welding performance - infinitely. In other words, and this is what makes the subject so complex, each base - filler material combination suited under a particular shielding gas composition, under particular peripheral conditions will obtain particular values for welding speed, bead appearance, "heat input", etc. etc. An experienced welder - as you have mentioned - recognizes these conditions instinctively and adjusts the exterior and interior parameters to even obtain a proper result under varying conditions. However, so far that I remind correctly, the relation between welding speed and melting efficiency has been investigated by ROSENTHAL very first time. He has stated that there is s strong coherence between the welding speed and the melting efficiency which is based on the thermomechanical properties of the base material, in particular its heat conductivity. This means that the less time the material has to conduct a particular amount of thermal energy into the adjacent areas the higher the melting efficiency is. In other words, when considering a constant arc performance and changing the parameter travel speed one can presume a higher melting efficiency the higher the travel speed is. Even due to the increasing imbalance between the thermal energy transferred from the arc to melt the base material and the time the thermal energy or the heat source (arc) respectively, can interact with the solid matter.

To come to an end slowly and dealing with two little points thus.

Firstly the "colder" shielding gas.

I have tried to understand what the meaning of "colder " shielding gas might be. Does this mean that pure CO2 is the colder shielding gas when being compared with Ar/15CO2? Normally CO2 provides even great benefits for increasing the depth of penetration due to dissociation and recombination processes delivering additional thermal energy to improve fusion depth and "heat input". Even though I do not really know if this is the right comparison but CO2 reminds me personally always on helium since both shielding gases require higher voltages for GMAW purposes. Both again yields higher arc powers and thus higher heat inputs compared with "colder" shielding gases like argon. Although, and this has been excellently explained by you, CO2 has the restriction of not being able to be used in a spray arc mode. Nonetheless, in Germany we have standardized the so called "Langlichtbogen" (translated best as "Long Arc") which does work as particular arc mode under pure CO2 at ranges the regular Spry Arc does work under high Argon containing shielding gases. It has a high performance obtains deep penetration but is not short circuit free and yields spatter. One particular characteristic is that it burns underneath the base materials surface quasi as a "buried" arc.

Secondly let me say a word to the shielding gas flow rates, you have kindly stated. As I have assumed that the flow rate for the use of tri-mix should have been higher, the opposite was the case /quote/:

"However under the tests the welder actually increased flow rate under 98-2 as opposed to tri-mix. This was his reaction in trying to counter the increased oxidation.  I believe flow rate was around 22 CFH for tri-mix and 28-30CFH for 98-2..." /unquote/.

I have conversed (into liters per minute) the flow rates - under the assumption that CFH = Cubic Feet per Hour - as been stated above and have received:

·  22 CFH ~ 622.97 l/h ~ 10.38 l/min.
·  28 CFH ~ 792.87 l/h ~ 13.21 l/min.
·  30 CFH ~ 849.50 l/h ~ 14.15 l/min.

Hmmm... to be honest with you Metarinka - by the way, may I perhaps call you Joel? - and please this is just a guess. I mean that in particular the values for the tri-mix might be a little too low under the consideration of a significantly reduced shielding gas density. The values for the Ar/2CO2 whereas are - at least from my humble point of view not that high actually when using the rule of thumb: wire diameter x 10 ~ flow rate - but of course not knowing what the diameter of your filler was.

So... and now coming really to an end, it's ~ 1.45 a.m. here. It was great to read your outstanding interesting explanations and it's truly a joy to discuss this with you.

And I thank the good Lord as I thank my beloved wife for having granted me the time finally once again for being allowed to visit this great forum. However, the weekend comes and I am at home this weekend... Perhaps I'll find some additional time to read some of the hundreds of posts been sent in the meantime since I've been here last time.

Last but not least, Metarinka, you have stated /quote/:

"In fact with a large enough sample size (the number of welders at my facility) I was able to establish a formula using statistical methods to calculate travel speed for a voltage with about 90% confidence, of course due to the parameter range there is a always going to be variation in weld parameters while still maintaining acceptable bead appearance.  If requested I can dig up and attach this information." /unquote/.

This sounds extremely interesting! Would you be so kind and provide this information? That were truly great!

Once again thank you for your very knowledgeable and most interesting reply and my very best regards,
Stephan
Parent - - By Metarinka (****) Date 10-16-2008 22:21
Forgive me I somehow missed your post Stephan.

excellent indeed, I can't think of much else to contribute and I've learned some more about the GMAW process

When I am on my personal computer I will post that statistical data.

On a related note: I was presented with the possibility to study abroad for a semester at a german Institution, unfortunately my um..  "Schreckliche deutsche Fähigkeiten"?  would probably prevent me from attending
Parent - By Stephan (***) Date 10-19-2008 17:58
Hello Metarinka,

thanks for replying!

Yes, it were great to get knowledge about your statistical examinations!

Thanks again and best regards,
Stephan

P.S. In terms of your "Deutsche Fähigkeiten"! Wow, I'm truly impressed. Vielleicht können wir uns ja bald in Deutsch unterhalten! ;-)
Parent - By Kix (****) Date 09-19-2008 17:22
Try some ER308Lsi with the 98/2 you are using for better wetting.  That's what I'm running with 98/2 argon/co2 and it does a much better job then the plain ER308L.
Parent - - By DaveBoyer (*****) Date 09-08-2008 06:47
Is this product of any use?     www.solarflux.com  
Parent - - By Lawrence (*****) Date 09-08-2008 17:02
Dave,

Solorflux is not applicable for this conversation in my opinion.

It has limited effectiveness in back side full pen welds in stainless and super alloys.. But I don't recommend it when inert gas is a possibility...

Solar Flux is a paste that is applied to the back side of full pen welds... It then must be removed or the byproduct will become a corrosive agent long term. 

Solar flux does not have a positive effect on heat tint type of oxidation in my experience.

Good stuff in a pinch when gas backup is unavailable... Not the best choice in fabrication when inert gas is a viable alternative.
Parent - - By Stephan (***) Date 09-08-2008 18:32
Lawrence,

does "...heat tint type of oxidation..." mean

/quote Allan/

"...some discolorations adjacent to the weld bead which can somewhat indicate the amount of heat input..."

/unquote/ ?

I'm yet a bit indecisive regarding this topic to say the least.

I'm doubting that different shielding gas compositions - only in terms of their constituents - may have that great amount of influence on the extent of discolorations.

As Allan has already pretty fine described these relations by using the words:

"...typically these colors result from how well the shielding is in place at the time of the weld and also how hot the weld area was when the shielding passed..."

Does it mean thus that not the "metallurgical" reactions between melt and active shielding gas components - yielding slag - are to be treated here but even the "discolorations"?

Best regards,
Stephan
Parent - - By Lawrence (*****) Date 09-09-2008 10:55 Edited 09-09-2008 10:58
Stephen!

Yes.. When I am mentioning "heat tint"  I am talking about oxidation at or near the weld that is a result of depleation of chromium.

Lord Bless Chuck Medows; while he is enjoying God forever now in heaven, I often wish I could depend on his treasure of experience in the world of stainless steels. Now he is a stainless expert in the world without end!

I think "...some discolorations adjacent to the weld bead which can somewhat indicate the amount of heat input..." is a statement that can be true only if we have a situation where shield gas coverage is controlled to a great degree and that degree can be known and recorded.

Now when I spoke of "Solar Flux" I assume that there are at least some active gas components produced when the flux on the back side of a weld is exposed to molten stainless..  There is some chemical reaction, the Solar Flux does not remain simply inert......... As to what the Solar Flux actually does at the molecular level?  Now that is far beyond my understanding.  It is advertized to protect the back side of full pen stainless welds.. and to some extent it does. But it certainly leaves a residue (this you might well refer to as a slag) as well as some of the "heat tint" referred to above......... Keep in mind now that Solar Flux is applied only to the back side of joints... Solar Flux is not designed to protect the weld face or HAZ on the top side of a weld joint, nor should it be exposed to the welding arc or it's plasma.
Parent - - By DaveBoyer (*****) Date 09-10-2008 04:02
    Does the heat tint really come from depletion of chrome ? or is it really from exposure to oxygen at elevated temperature? I have seen chrome plated exhaust pipes on motorcycle engines that showed heat discoloration, but the chrome seemed intact.
Parent - By aevald (*****) Date 09-10-2008 06:11
Hello Dave, in a sense yes, it does mean a depletion of the chrome. Your question about exposure to oxygen at an elevated temperature would result in a form of oxidation and could happen as a result of the loss of shielding before the material has been allowed to cool below the reactive temp.  There is chrome throughout the makeup of the SS in varying levels and is governed by the grade. So if the chromium layer that makes up the surface is altered by oxidation caused by excessive heat or improper shielding it opens up the possibilities of attack, depending on type of service, by various elements or chemicals that might be detrimental to the SS. By using an appropriate form of cleaning and in some cases, chemical passivation you can return the surface to it's natural state. If left untreated it will eventually form it's own chromium layer again, however if it is put into service in an environment that requires this protection immediately it may suffer damage before this happens naturally on it's own. Hope this somewhat answers your question. Best regards, Allan
Parent - - By Lawrence (*****) Date 09-10-2008 06:12
Here is a word for word copy from a post Jim Hughs made on a thread here on the forum that started in 2001 and has continued to 2008. Worth a read itself... He is very clear and concise:

"stainless steels are materials with great corrosion resistance. Chromium is the alloying element that gives stainless steels their ability to resist corrosion by combining oxygen to form a thin film on the surface of chromium oxides. This is called passivity. The oxidation that you see after welding in the form of color inpedes this passivity process and in its extreme form on the back side of a root pass which we call sugar. By simply taking this oxidation off the weld by brushing or grinding the thin film of protection is restored. Even in its exstreme form oxidation does not have much effect on the mechanical properties that I personally have seen, but I'm sure some might beg to differ with me on that point. Remember one of the main reasons we use stainless steels is the corrosion resistance. This invisible film can be restored very easy and quickly by brushing."
http://aws.org/cgi-bin/mwf/topic_show.pl?pid=91630;hl=chromium%20stainless
Parent - By Stephan (***) Date 09-10-2008 20:00
Lawrence, Allan, Metarinka!

Superb!

Thank you all for having replied!

I apologize but I truly don't have time at the moment to join your excellent discussion...

Please let me come back as soon as possible to contribute two or three more words!

My best regards to you gentlemen,
Stephan
Parent - - By DaveBoyer (*****) Date 09-11-2008 04:14
Lawrence, I read with great interest this exerpt from one of Your posts on the thread You linked Me to:

Back to Stainless. Many of those cute new fangled orbital welders have been thoughtfully constructed with integrated argon trailers that keep coverage over the hot zone long enough to make what appears to be a perfectly colored finish on the OD right? As to removing oxides that again is kinda dependent on the function of the weld and the alloy involved. For instance the newly published "AWS D17.1:2001 Specification for Fusion Welding for Aerospace Applications" comes right out in Table 6.1 and says that in the matter of Discoloration of Stainless Steel welds that All oxidation colors are Acceptable in all classes. Food processing and Bio-stuff remove every trace that might be left even in the heat-effected zone. Now there are reasons for these differences. Those tenacious oxides that could be a gathering place for bacteria in a food service situation are actually a corrosion preventative and protector in some aircraft engine hot section components. And as to method, again if you're working to a standard it's prolly going to call out for specifics. I've seen everything from stainless wire toothbrushes to power wire brushes to 80 grit disks, chemicals or bead blasting.
Parent - - By Lawrence (*****) Date 09-11-2008 11:15
Dave,

It is interesting, the differences in how stainless oxides are handled in various service conditions and codes.

The aerospace mettelurgists and engineers tell me those oxides that form on hot sections and afterburners are so tough they are protecting the part.... 

I can see that line of thinking.  That burnt looking Hastelloy X, Waspelloy or Inconel that is pulled out of a hot section has a nice protective coating........ But I would not want to run chardonnay through it eh:)
Parent - - By js55 (*****) Date 09-18-2008 12:34 Edited 09-18-2008 12:36
I might ask, what is it that provides the thin tenacious layers for many alloys?
Ok, I quickly perused Stephens post and not only did he beat me to it, he did a much more thorough job of discussing it as opposed to my concise question.
Parent - By Stephan (***) Date 09-18-2008 15:30
Jeff,

as ususal you hit the nail again directly on the head!

This is - as far as I mean to believe - one of the most tricky questions at all...

Honestly I have hoped that you eventually might enlighten me a bit more with more sophisticated knowledge on this, since what I have learned about this lies a considerable while back, what means that I truly do not know if they have found out somewhat new on this interesting matter.

Please allow me to come back to this later - unfortunately I'm in a hurry at the moment - for discussing this question a little more in depth and to adjust my humble knowledge with your outstanding one.

My best regards,
Stephan
Parent - By Stephan (***) Date 09-25-2008 20:14
Jeff,

please read my response to John.

Sorry for not having come back by now!

Hope you will grant me a bit more time for returning to this topic*?

Have 15 behind and certainly some hours before me today...

Best regards,
Stephan

* I promise to come back as soon as I can!
Parent - - By Stephan (***) Date 10-03-2008 23:47 Edited 10-04-2008 16:59
Jeff,

please let me come back to your most interesting question on what the mechanisms are creating this thin tenacious layer. Before I start please let me beg your understanding for that I am definitely no chemist. Thus - of course - I may truly be wrong by seeing the things as I try them to explain here as we are talking about those interesting topics. And thus I am running the risk, that Mr "weld39" (even though it's quite silent around him since that time) may post another angry statement again on that I should go to a college and earn a degree in chemistry to learn how the things are working before I start to talking about. But however, as I feel the greatest joy by discussing with all of you also these tricky issues and I have gratefully read the excellent predication of our fellow Joe Kane that time, I'd like to venture nonetheless adding a few words to this. I have firstly busied myself with this question in the late 1980's as I have written an article for the German Welding Society's (DVS) trade journal "Der Praktiker". The article dealt with the aim to provide an "understandable" explanation for the theory of Intergranular Corrosion.  However, the mechanisms or better, the theories for this particular issue "passive layer", are numerous what was the reason again, for that I have mentioned that eventually nowadays there are some more sophisticated explanations available, compared with those of even the "late 1980's". And by the way, as we know to have a honored chemistry engineer amongst us (Prof. Giovanni Crisi) he may perhaps have a look at what I am trying to describe hereinafter and perhaps he kindly may correct me when I were wrong.

Anyway, please let me try to describe what I mean to know or better, what I have tried to learn about the most fascinating question of "What is in charge for the creating of a passive layer on that many iron based alloys?" If even this previous asked question is responsible in a whole - what by the way I am hardly disbelieving - then there is one factor which appears for sure to playing a major role... oxygen. 

But before coming to some details please let me go back to the "reaction" I have stated within my post as being responsible for generating a passive layer upon the stainless steel and which was: Chromium (Cr) + 2 Oxygen (2 O2) + 2 Electrons (2e-) yields the Chromate Ion [CrO4]2-. Here - as far as I have learned that time - two negative charge carriers (2 electrons = 2e-) originated from iron - which is the base of a high alloyed steel - react with Chromium - which is the responsible alloy element - and Oxygen - from the air or even from any other surrounding medium (e.g. an oxidizing acid) - to create the negative Chromate Ion [CrO4]2-. This again - so the theory - is adsorbed by the metal's surface and creates the passive or provides the "thin tenacious layer" as you have named it so adequately. 

However, as this is just one theory for the creation of the passivity of high chromium containing "stainless" steels there are of course some others.  Even this was the reason for me to ask if there are some news intermediately. One of the problems with the theory as described above is amongst others that actually chromium has a higher tendency to oxidize compared with iron. This means that iron is actually more noble than chromium and thus it was - at least at that time - doubted that iron can provide the electrons for the reduction of chromium to result as a chromate ion [CrO4]2-. As known one says that - according to the electrochemical series - the less noble element or metal respectively, is being resolved or is what's even named "active" by providing its valence electrons to the corrosion process. Well, how to say? Now, to say the least, it becomes tricky and hardly complicated to treat the subject without using some special equations, what is normally not my intention because those are often complicating the whole subject in an undesired way. I mean it is necessary to use these details to try to explain - at least rudimentarily - the mechanism of the formation of the tenacious passive layer we are talking about. And I ask those of you for forgiveness who are much more experienced in chemistry and who might wonder if that what I try to use herein as even the equations is correct chosen by me. However, to get an idea of what's going on basically in oxidation and reduction between an element which is providing its valence electrons and an element which is absorbing those electrons to obtain a more stable (noble gas) configuration one should use the basics of those processes.

This should be described by having a look at two well-known metals. Copper (Cu) and Zinc (Zn). When connecting these both metals - having a different electrochemical potential - by storing them into a liquid or electrolyte respectively, the following processes are taking place:

} Oxidation:

Zn - 2e- => Zn2+ or more generally M - ne => Mn+

In other words:

Metal minus specific number "n" of electrons "e" => Positively charged Metal Ion (Cation)

} Reduction:

Cu2+ +2e- => Cu or more generally Mn+ + ne- => M

In other words:

Positively charged Metal Ion (cation) plus specific number "n" of electrons "e" => Metal "M"

Copper which reduces the Zinc receives the passive state hereby and is protected against corrosive attack.

As a short sidestep:

Interestingly when alloying steel with very few tenths of percents of copper (e.g. with weathering steel) one obtains a considerable improvement of the steel's corrosion resistance. When these alloys are corrosively attacked both iron and copper are being resolved. In other words, the iron corrodes by forming "rust" as well as the copper is corroding by forming copper oxide. However, while the corrosion process does continue the copper oxide is deposited amongst the iron oxide and is forming a very dense layer protecting the alloy against further mass loss by corrosion. But as I said, this just mentioned by the way and coming back to the chromium effects in high alloyed stainless steels when forming a passive layer.

To using these basics and to clarify the processes between iron and chromium in a more in depth way please let me first of all state hereinafter the electron configurations of iron and chromium. Iron does have four "shells" (1;2;3;4) between which 26 electrons are distributed in the following configuration:

1s2 2s2 2p6 3s2 3p63d6 4s2

When now considering that the 3d orbital can be filled up with ten electrons in general to obtain an "inert" noble gas electron configuration one can presume that iron has to loose three electrons (2 from the 4s orbital and 1 from the 3d orbital) becoming hereby a trivalent positive ion and may combine with another iron ion (having experienced the similar procedure) to form a double ion (2 x 1s2 2s2 2p6 3s2 3p6 3d5) which is... passive. However, the electrons coming from the electropositive metal (iron) have to be attached by another element e.g. oxygen.

Oxygen has a distribution of 8 electrons across the orbital (1s;2s;2p):

1s2 2s2 2p4

Since oxygen is always bivalent electronegative, what means that 2 electrons are missed for filling the 2p orbital completely (maximal 6 electrons), 1 oxygen atom can absorb two electrons to obtain the noble gas electron configuration. Both elements together - the metal (iron) and the nonmetal (oxygen) - can form hereby the very well known oxide "Fe2O3". And this combination is much too often found as its being driven by the force that iron is actually a non precious metal or simply it is base. That's actually the reason what we are discussing herein namely the effort to passivate it by alloying it e.g. with chromium and making it thus "stainless".   By the way, the interruption of the corrosive attack by even a tenacious oxide layer is based on what Dave Boyer has stated as he said /quote/ "Those tenacious oxides (...)are actually a corrosion preventative and protector in some aircraft engine hot section components." /unquote/ and used in heat resistant and non-scaling steel materials for protecting them against further damage. But this mechanism is much better understood than the mechanisms of the passivation of iron by using chromium above a particular amount.

Resume...

Coming thus back to chromium and to compare both metals directly one to each other one should have a look at the specific electron configuration of chromium.

Chromium has a structure of where 24 electrons are distributed across 4 shells or a orbital number of 7 (1s;2s;2p;3s;3p;3d;4s), namely:

1s2 2s2 2p6 3s2 3p6 3d5 4s1 

One can recognize that the chromium atom has to provide 1 valence electron (4s1), becomes a univalent ion and has to combine with another chromium univalent ion to obtain a noble gas structure by filling up the 3d orbital with 10 electrons and forming hereby a double ion ( 2 x 1s2 2s2 2p6 3s2 3p6 3d5). Now what one can see is a similarity to iron as mentioned above, with the little difference that chromium is more active - or even less noble - than iron and thus should show a worse corrosion compared with iron. But it doesn't and this is fairly strange to say the least. Because chromium is acting as becoming the "passive" element and besides this it's acting as well as making the alloyed steel "stainless" by making its surface "passive" as well. As an intermediate conclusion by now one can say that iron-alloys (stainless alloys) containing chromium are acting like the passivation of chromium but not as the passivation of iron (oxygen surface layer by being oxidized through the medium attacking the surface e.g. oxidizing acid). On the other hand however, it is nonetheless comparable what takes place when looking at the passivation of a chromium containing iron alloy, since the oxygen coming e.g. from an oxidizing acid has actually a great influence on the formation of the passive layer. As an example, the passive layer of a stainless steel - containing none but chromium - has great problems or is even impossible to be formed when the surface of the alloy is attacked by a reducing acid, e.g. sulfuric acid. These alloys, resistant against reducing acids must contain other alloy elements, as well-known, e.g. Nickel and Molybdenum. However, this means: The "strength" of the oxidizing activity of the medium attacking the steel plays a major role for the passivation even though the mechanism of the passivation itself is not completely similar to the passivation of e.g. a pure iron surface. And to complicate the whole issue additionally - even though these even are the information I have from the time I have busied myself with this subject - it is or it was at least - quite difficult to define the structures of the passive layer what makes the issue so hard to understand.

To coming back to the differences between the passivation of pure iron, e.g. by using a strong oxidizing medium (acid), and the formation of a passive layer by using the element chromium. One has of course tried to find the reasons for these different mechanisms and to define what is responsible for the formation of the passive layer. One of the problems with the explanation of that the corrosion resistance is based upon a chromium-oxide layer is e.g. - and just mentioned by the way - that the interruption of the corrosive circuit (large ions can no more pass the passive layer to activate the metal) is the fact that some CrNi-alloys can be activated rather earlier by bromine ions than by chloride ions. This is interesting since the bromine ions are quite larger than the chloride ions and should normally not being able to pass the passive layer. But they do.

Hmmm... mother nature even! But as I said, it might certainly be, that meanwhile somebody has found the reason for even these tricky differences in the mechanisms.

To come to an end slowly...

As I said it was tried to find out what the reasons were for the strange behavior when a passive layer is formed. Therefore one has used 18% Cr and 8% Ni steels  (~ AISI 304) and has tried to measure the surface adsorption of the steel for oxygen. And what was found is the detail that normally the mechanism of pure adsorption (formation of an oxide-layer) could not explain the high resistance against the attacking media, e.g. acids. It was found out that this layer were capable to react with the medium itself and this again would mean that the corrosion of the base metal itself would continue. The explanation for these difficulties was - at least at that time and perhaps this has been revised again already - that the high resistance may be rather explained by the mechanism of "chemosorption".  Hereby some very intricate processes between the surface adjacent metal atom valences which are saturated by the layers ions or charged molecule rests should play the major role for the formation and the high corrosive resistance of the passive layer. In other words. Everything thus - at least following these explanations - is based on the exchange of valence electrons of the base metal atoms adjacent to the surface and the valence electrons of the oxygen saturated layer which has a "non measurable" or at least most complex structure finally.

However, I am honest, all these coherences are much too complex for me and way above my head to be understood entirely. All this, what has been mentioned by now - and this is important - does treat iron-chromium alloys. I personally mean that the relations with stainless steels containing even more than just chromium - even Nickel, Molybdenum, etc. - are much more intricate and even this is what it makes it so extremely difficult to define the "ultimate" mechanism for the formation of passive layers on stainless steels.

One has to consider namely that the valence electron reactions between the different elements been added to the base element iron in stainless steels, may be assumed to be much more difficult to describe than only the reactions between chromium and iron. Everything what we have discussed by now is just the theoretical assumption of finding "undisturbed" valence electron structures between the elements and no kind of "distortion" was included. The latter again is additionally to be presumed by the corrosive medium itself attacking the metal's surface. But this is, I request your understanding Jeff, much to complex for me to understand. And to be honest, I have never tried to step further into this matter of subject as even to the low level which can be recognized by my humble tries of an explanation before. Nonetheless, it is as usual. The passive layer subject is surely one of the most interesting ones to be dealt with but surely one of the most tricky ones as well.

I have tried to find out somewhat new on this matter by having spoken and discussed this with a friend who is chemist (I am blessed by knowing all these people :-)). But what he told me was not that different to that what I have stated above and what I have learned that time I have busied myself with it for writing the article I have mentioned at the beginning of this response. My colleague told me that the passivation of stainless steels is based upon a very dense chromium-oxide layer which interrupts the corrosion circuit. This chromium-oxide layer as well as chromium-hydrate-layers which may be formed on the steel surface has a much higher density compared with iron-oxide layers which are - so my fellow - much more less dense or porous to say the least. That again is the reason for that the corrosion circuit is not interrupted by even the "discolorations" consisting of iron-oxide layers and the material itself is damaged finally under the attack of an aggressive medium.

So far my humble contributions to your interesting question.

It were great if you or some others perhaps have more current information, eventually correcting my explanations or even confirm those or whatever else. The important thing were to get some reaction on this which were greatly appreciated, friend(s)!

Thanks again and I wish you very well,
Stephan  
Parent - By electrode (***) Date 10-16-2008 20:12 Edited 02-28-2012 09:29
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Parent - By Metarinka (****) Date 09-26-2008 20:48
Thank you to everyone who's chimed in on this topic, I've mined a lot of valuable information from all of you. It's interesting to see that oxidation acceptance levels are different depending on code and service requirements. I never thought about it that way.

For the record all welding at my facility is not done to code, however the service environment is generally quite corrosive depending on the product line. We only GMAW stainless steel when building a frame or machinery base that will function be exposed to corrosive material outside of the machine. Therefore all our GMAW stainless steel welds are low temperature and don't carry any product or corrosive themselves.

we do work with a lot of corrosives though but those are contained in stainless steel or inconel piping and sheet metal shells that are always GTA welded.
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