relation between humidity and temperature at welding

By Stephan (***)

Date 04-29-2008 19:16

Yusuf,

for the first, have a look upon:

http://files.aws.org/wj/supplement/sept99/HARWIG.pdf

http://www.scielo.br/scielo.php?pid=S0100-73862002000400005&script=sci_arttext

http://www.phx-international.com/fcw_article.html

Regards,
Stephan

By 803056

Date 04-29-2008 21:17

Hello Stephan;

It's good to see you again in the forum. Welcome back.

Best regards - Al

By Stephan (***)

Date 04-30-2008 05:41

Al,

thanks a lot!

Always a great joy to finding the way back home! :-)

Best to you and to all the other appreciated fellows,
Stephan

By yusuf polat Date 04-30-2008 05:48

thank you for helping. but I think I asked my problem in wrong way.
I am going to weld S355J2G3 at the 20 degree celcius temperature.What is the best welding place atmosphere humidty degree to prevent the materials gaining hydrogen from humidty of atmosphere.

By Stephan (***)

Date 04-30-2008 17:01

Yusuf,

no problem at all...

But I beg your pardon for asking: "What is your actual "problem"?"

S355J2G3 according to EN 10025 is "just" a plain and "good-natured" structural steel. And as always the behavior of the material to be welded does not only depend on the material grade of the part itself but as well on its geometry, size, manufacturing-circumstances and those conditions under whose the part is being used finally.

Although the materials within the standard are not abundantly suitable for welding by using the different processes, the steel grades JR, JO, J2G3, J2G4, K2G3 and K2G4 are suitable to be welded by using all welding processes, in common.

However, in my understanding humidity is and remains a very particular issue. I suppose it may differ significantly with the region it is measured. For instance the Amazonian region would yield different values at 20°C for humidity compared with the Central European region at 20°C. The latter again will certainly give different values for the early morning hours compared with the midday conditions.

So now my question: "Is there an issue to expect with increased humidity and eventually moisture upon the part's surface, where you are intending to weld the part?"

In Germany we use for predicting the preheat temperatures for higher-strength structural steels the so-called "Stahl-Eisen-Werkstoffblatt 088" (SEW 088). It is valuable in defining the ranges of risk for hydrogen induced cold cracking in relation to a particular material.

I have calculated the SEW 088 Carbon Equivalent (CET) = C+ (Mn+Mo)/10 + (Cr+Co)/20 + Ni/10 under assuming:

C ~ 0.22
Mn ~ 1.60
Si ~ 0.55

and have achieved a SEW 088 CET of 0.38.

For a wall thickness of 20 mm this yields a preheat temperature of ~ 70°C.

For a wall thickness of 25 mm it yields a preheat temperature of ~ 85 °C and for a wall thickness of 30 mm a preheating temperature of ~ 100 °C is recommended by calculation.

By following however the recommendations of SEW 088 in particular regard of S355 a preheat temperature of 120°C at wall thicknesses > 25 mm (maximum 250°C depending on the wall thickness) is recommended to avoid or at least reduce the risk for flaws as hydrogen induced cold cracking. In terms of the diffusible hydrogen content, see also the ISO standard ISO 3690 (http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=22157).

I have tried to find an US-American steel grade being most likely comparable with the European S355J2G3 and what I found was (most likely) the "ASTM A 656".

So perhaps some of our greatly appreciated United States fellows, or eventually even the most appreciated Prof. Crisi from Brazil, could let us kindly partake on their experiences and hints in welding those steels and their recommendations in reducing moisture upon the materials surface at higher degrees of humidity.

Best,
Stephan

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

Date 04-30-2008 18:12

Thankyou for your kind words, Stephen.
No doubt that Amazonian region conditions, with a relative humidity of 80%, are different than Central Europe ones.
Now let me make a good humored comment. In the Brazilian Amazone we woudn't use S355J2G3 steel (why such a long designation?). Here in Brazil we follow American standards, so we would use an ASTM or SAE equivalent.
And speaking of an ASTM equivalent, why A 656? If it is a plain and good natured structural steel, I'd say that it's similar to A 283.
Regarding the pre-heat temperature, being a low carbon steel (C 0.22%), back in my days of erector engineer it was sufficient to heat them up until they were "warm to the hand", which in practice means about 50 °C.
Giovanni S. Crisi
Sao Paulo - Brazil

By 803056

Date 04-30-2008 21:50

My ignorance is shining through on this inquiry.

I've never considered relative humidity when welding any carbon steel or high strength low alloy steel. The only factors I've considered have been the carbon equivalency, thickness, and degree of restraint.

I can understand the issue if you are welding with a low hydrogen covered electrode and the exposure time of the electrode (covering) to environmental conditions could be a concern, but other than that, I don't understand how the relative humidity is going to affect the weld puddle if sufficient shielding is used to exclude nitrogen and oxygen from the area of the molten weld puddle.

I would assume (maybe incorrectly) that should there be surface moisture on the base metal it is removed by preheating to evaporate it before welding.

What am I missing?

Best regards - Al

By Stephan (***)

Date 05-01-2008 10:03 Edited 05-02-2008 07:58

Al!

First off, once again I must realize: It is a honor to discussing with personalities as you, Giovanni Crisi and all the other great experts here in the forum!

And once again in my opinion you hit the nail!

Normally and under considering what kind of art our colleagues from the "Underwater Welding Party" (= 100% humidity) are performing day by day, one could surely ask what kind of negative impact surface moisture may have when welding these steel grades on shore.

And please permit to agree entirely with you when you say:

"...I don't understand how the relative humidity is going to affect the weld puddle if sufficient shielding is used to exclude nitrogen and oxygen from the area of the molten weld puddle...".

Normally the arc's energy should evaporate any kind of moisture before the actual fusion zone is reached while welding (only exception could be the starting area). This even by the heat flow which generates - under "normal" circumstances - a kind of "preheating front" before the arc.

But on the other hand it could as well appear as a kind of contradiction. Since actually all thinkable measures are undertaken to protect the weld pool or the liquid weld deposit against the contamination with hydrogen (Low Hydrogen electrode use, electrode rebaking,...) while the metal's surface is not taken into account as a possible source for hydrogen.

To be honest, I have never considered yet if hydrogen can be "trapped" within surface constituents, e.g. metal oxides, and if so, what the physical or chemical respectively, mechanisms for even this "trapping" might be. If however, so my humble consideration, the hydrogen could be resolved by metal oxides as it can be resolved by the welding electrode cover compounds (even chemically) and the oxides were "overwelded" (what a term, please don't laugh), then hydrogen could be as well provided from the metal's surface.

For me personally, I would honestly hesitate to weld an HSLA steel part under the requirement to use Low Hydrogen electrodes when seeing that the part to be welded is "contaminated" with surface moisture. I guess this might be the reason for that Giovanni and his colleagues in Brazil have "preheated" the parts to be welded until they were "warm to the hand". By the way we have done often the same as Giovanni did. But perhaps this was finally nothing more than a "cosmetical" measure, only to "silence the conscience", since the "real physical" work is actually certainly carried out by the arc as it evaporates the moisture before hydrogen can reach the weld puddle. But this is only my humble assumption.

I guess Yusuf could clarify everything immediately, if he would be so kind and would share his considerations with us.

Thanks Al and best regards,
Stephan

By Stephan (***)

Date 05-01-2008 09:14

I thank y o u Giovanni!

Firstly of course for the wise and experienced comment in terms of "preheating" those steel grades until they are "warm to hand" but even as well as for the good humored comment in terms of our "short and precise" European standardization system. Though to answer your reasonable question on why we have to use that long designation types is hardly to perform. Sometimes I have the impression that - under considering an international technical standard as the lowest common denominator between all attendees having sat around the table to even create the standard - each country in Europe has got 1 number or character with the designation for proving that they have partaken the standardization meetings. Meanwhile the number of members in the European Union has increased to 27 countries. I assume the worst for the future standards :-).

Thank you as well for the hint in regard to the comparability of steel grades. What I have tried was to find an USA steel grade being quite accurate equivalent with the European S355J2G3 - by the way the former German designation was "St52-3" which was at least, as you can see, a bit shorter. Unfortunately I failed since the US grades - please correct me when I am wrong - often contain additional elements as Copper et al and slightly more Carbon amounts compared with the European ones.

The S355J2G3 however achieves his strength mainly from his Carbon+Manganese ratio and no additional elements as mentioned above are used to improve the mechanical properties. But... of course the magic limit of 0.22% C should be taken always into account when talking about welding suitability of steels. This - fortunately - appears to be a very "universal" and truly short and precise law in welding.

Thank you once more and my best regards to Sao Paulo,
Stephan

By 803056

Date 05-01-2008 22:04 Edited 05-01-2008 22:07

I guess the problem is that "we have a failure to communicate".

The original inquiry was regarding humidity and temperature, so I assume the question is related to the "relative humidity" which is "how much moisture is contained in the air at some specified temperature". As a general principle, the higher the temperature, the more moisture can be held in air (or any gas) before it becomes saturated. As the temperature drops, the air can not hold as much moisture, it reaches the point of saturation and any excess will condense on surfaces as condensate producing a wet surface. It was the moisture in the air that I could not contemplate as having an influence on the welding operation.

I agree that there can be surface moisture in surface contaminates such as hydrates, rust, or residue from cutting operations that use water based coolants and lubricants, but these contaminates can be easily removed as part of the joint cleaning operation prior to welding. Once removed from the surface of the metal, those sources of moisture and the resulting diffusible hydrogen are eliminated.

Once again, I am not aware of any special considerations where preheat is used to counteract the moisture contained in the air provided there is no condensate (surface moisture) on the surface of the metal. So, now that my curiosity has been tweaked, my question is; do you take any special precautions to counter the moisture contained (entirely) in the air (not as surface condensate)?

Best regards - Al

By Stephan (***)

Date 05-02-2008 07:49

Ahaaa... I see!

It was thus my misunderstanding.

It was my problem to interprete Yusuf's predication:

"...the relation between humidity and temperature of welding atmosphere..." first,

then he was so kind to clarify the issue by saying:

"...I think I asked my problem in wrong way. I am going to weld S355J2G3 at the 20 degree celcius temperature. What is the best welding place atmosphere humidty degree to prevent the materials gaining hydrogen from h u m i d t y o f a t m o s p h e r e..."

and I have misunderstood it again!

You are surely right in your - as usual wise - understanding, whereas I interpreted even the terms h u m i d t y o f a t m o s p h e r e as the cause for surface wetness as the result of the relative atmosphere's saturation with moisture. That was the reason for the sidestep to the different geographic regions in the world, which was fortunately kindly confirmed by Giovanni Crisi who is living in a region with rather "higher" relative atmospheric humidity (~80%). This again means - please correct me - that the atmosphere at 20°C is saturated with a share of 8/10 of even that amount of humidity which would be feasible theoretically. This in turn means to me - hopefully I am right - that the amount of condensation (or surface moisture) at e.g. 80% should be higher when decreasing the temperature, than decreasing the temperature equivalently but having lower amounts of relative humidity, e.g. 30%.

However, and to answer for me personally your question if we have taken any special precautions to counter the moisture contained (entirely) in the air prior to welding: "No! Of course we haven't neither tried nor even done somewhat like this."

And to be honest, I cannot imagine something (except generating a vacuum) that should be realized to counter or even reduce the relative moisture content in the atmosphere that surrounds the "...welding place".

I beg your forgiveness for the confusion I have caused! It's even me... :-)

Thanks for your patience and best regards,
Stephan

P.S. I have found and would like to attach two jpeg's showing the general relationship between relative humidity and its influence on the moisture content of basic stick electrode covers as well as the feasibility to use "rebaking" for decreasing relatively high moisture contents of basic stick electrode covers after longer aging periods at different relative humidity values.

Attachment: Relative_Humidity_1.jpg (67k)

Attachment: Relative_Humidity_2.jpg (0B)

By Tommyjoking (****)

Date 05-02-2008 11:31 Edited 05-02-2008 12:17

Jeez Stephan in the midst of "missunderstanding" STILL YET you shine light on unknown things to me"!!!!!

From a bench standpoint I can tell you guys that the "iron" welds a bit different in the morning "first light" then it does at 3:00 pm. And in my experience more welds fail ndt (on ironworking jobs) done early then late, lots of variables, draw your own conclusions. But I bet some of those spud wielding welding pros will back that up!

Moisture has always been a factor for me on the job and now that I am only working with high alloys in a so-called controlled enviorment, I see evidence of it rearing its influence more and more. Just a matter of eliminating possibilities, and it keeps coming down to moisture influencing the weld pool...according to the reading I do. I work in an extremely humid climate...we have seen the effects of it on certain jobs. FOr instance I have seen for myself that applied preheat on 4130 can significantly reduce defects in certain joints. Spent some effort on this very forum trying to resolve that. But in seasonal times fall/spring preheat is not necessary for the same result ...during the summer you better do it or we get probs. Lots of variables here ...but I am convinced that moisture in the air can have an effect on steel welding and its problematic to combat.

ok I tossed in my paltry $.02

Neat thread really (best regards to Al and Stephan...yall are over my head but I enjoy the read)
Tommy

By 803056

Date 05-02-2008 15:04

Hello Tom;

I would think that you would preheat 4130 regardless of the ambient temperature or relative humidity on all thickness. The carbon equivalency for alloys containing 0.3 carbon as well as chrome moly additions would be on the high side to say the least.

I use a book titled "Weldability of Steels" authored by Stout and Doty, copyrighted in 1978 as my bible for preheating and post weld heat treating steels. It tends to be more conservative than ASME construction codes, but so is AWS D1.1 in comparison to the minimum preheat requirements of ASME construction codes. I also use the carbon equivalency equation and guidelines found in Annex I (D1.1-2006) for steels where I know the actual chemistry based on the material test report or actual product analysis. I favor the conservative approach (high preheat) unless there is a reason to minimize preheat, in which case I use preheat in conjunction with temper beads to temper the martensite in the HAZ.

I can't say that I have experienced higher reject rates with welds completed in the morning versus those made in the afternoon. I have found just the opposite to be true if there is a bar near by the facility that is frequented by the welders at lunch time. ;) I have never had a welder pass a qualification test after drinking. I have never had a welder pass a qualification test after drinking, even one beer is sufficient to adversely affect the welder's ability to pass the test!

As always, you shed some interesting light on the subject and I will be more observant of those early morning welds. :)

Stephan, you may interpreted the original question much better than I did. Hence my confusion.

I looked at the graphs you attached and noticed one of them said the electrode was aged for one year. Does that mean the relative humidity of the storage (condition) was held constant for the entire year? The electrodes must have been corroded by the time they determined the actual moisture content of the flux covering. It does show a good job of demonstrating the hygroscopic characteristic of the flux covering. I wonder just how effective long term storage of low hydrogen electrodes at 250 degrees F actually is?

I have a good friend that is a welding engineer in a shipyard that told me electrode storage at 250 deg. F is not sufficient to maintain the low hydrogen characteristics of the flux covering. For that reason, all low hydrogen electrodes are baked at 600 degrees F before use.

I guess the answer is to use GTAW or GMAW where there is no flux component to add hydrogen to the weld puddle.

The attached photograph is a case where the fabricator did not check the chemistry of the steel until after the fact. I am convinced their failure to use sufficient preheat resulted in a hard brittle HAZ. The subsequent hot acid pickling (high concentration of hydrogen ions) prior to hot dip galvanizing resulted in delayed hydrogen cracking. Brittle fracture occurred when the members were erected in mid winter at sub zero temperatures. Based on AWS D1.1 Annex I, the CE was on the order of 0.38 and would have required a preheat temperature of about 300 deg. F rather than the 50 deg. F they actually used when the shop welds were made using GMAW (spray transfer). The fabricator responsible never performed any hardness testing or microscopic examinations, so my comments are conjecture at this time.

It is interesting to see the direction some of these threads take before coming to a conclusion. It shows the more heads involved, the better the solution.

Best regards - Al

Attachment: BrittleFracture.pdf (34k)

By Stephan (***)

Date 05-02-2008 17:29

Tommy!

Thank you so much for both your kind words and your - as Al already stated: always - valuable (for me a $2K) contribution.

Very interesting to read what you have experienced on-site and some very good facts to be stored on my "brain's hard disk". :-)

Al, cheers to you as well for this superior reply again!

I have had a look to the interesting detail again and that far as I can see there were three different grades of relative humidity used as the aging was accomplished (30%, 50% and 70%). Although within the paper from WEYLAND no further explanation was given to this detail I assume that even these grades were held constant over the period of 1 year.

Then the electrodes were rebaked at 300°C (572°F) which is quite good comparable with the statement coming from your friend in the shipyard.

In regard to the 250°F (~ 121°C) storage I would agree with you when you say that this value might be - eventually - too low. From the physical side, so my humble opinion, the reason therefore could be that the contamination of the hygroscopic electrode cover compounds with moisture does not only mean the contamination of the constituent's surface (I hope I'll translate this right now, in Germany we say "Kristallwasser" and I would translate it as "water of crystallization"??) with "water of crystallization" by adsorption but even the contamination by absorption. Whereas the first should probably be vaporized at rather lower temperatures (>100°C = >212°F) the latter can probably only be removed by using much higher temperatures, e.g. 250... 300°C.

I had a good friend who was the Godfather of welding in my hometown at that time. Unfortunately he has meanwhile passed away so may God rest his soul. He had some electrode furnaces in his company and had stored the basic electrodes - different to what the shipbuilding engineer does - at temperatures of ~ 95... 100°C. I have never asked him at that time why he has decided to fix even this temperature range (I was admittely a curious but even as well a young man :-)) For me it was clear that time that water vaporizes at 100°C and thus the range was respectively chosen by him.

Later whereas as I have busied myself with the interesting mechanisms of moisture absorption in hygroscopic materials, I found as I said, that 100°C could rather be too low for rebaking. But... my consideration was as follows:

When one has a "dry" basic or LH-electrode and uses it for welding while the dry electrodes are stored and taken from an electrode carrier, one could suppose that the hydrogen content of the covers might not increase that significantly while being stored in the carrier. This means however on the other hand, when storing now directly the rest or non used (dry) electrodes from the carrier into the electrode furnace and the temperature within the furnace is at ~ 100°C, one could assume that the relative humidity within the furnace' atmosphere is ~ 0% or at least the air within the furnace is extremely dry and thus an increase in the cover's hydrogen contamination should be rather unlikely. This - so was my subsequent consideration - could have be the reason Willi (so was my friend's name) has chosen the temperature at ~ 100°C. However, this is just my humble consideration and unfortunately it is too late to ask him today. By the way, he was my great idol, since he has welded until far above his 70th year of age. Last time I have met him at a lecture at that time, he had a garish red face since he has used a diam. 2.4 mm flux cored wire and had missed to protect his face while operation(!!!). I will never forget him in my life! He was also one of the greatest ones and unfortunately this generation passes slowly away and takes so much irretrievably knowledge with themsleves.

However, Al!

Once again you have impressed me so tremendously deep by describing your outstanding excellent theory:

"I can't say that I have experienced higher reject rates with welds completed in the morning versus those made in the afternoon. I have found just the opposite to be true if there is a bar near by the facility that is frequented by the welders at lunch time." :-):-):-)

This is brilliant! And it simply proves the partially negative influence of "moisture" on the quality of welding seams :-).

But to be serious finally. The photograph you have attached is extremely impressive. Good that it has been recognized early enough!

So far for now.

Ahhh, before I forget, Tommy, please let me agree entirely with you as you said: "Neat thread!"

Best regards to all of you!
Stephan

By 803056

Date 05-02-2008 20:10

Hello Stephan;

As always, your dissertation covers many of the fine points of our technology that I tend to overlook. A pleasure to read because of the elegance of the presentation.

I believe your the term "Kristallwasser" is what we would simply call moisture of hydration.

I did a web search and came up with the following:

Main Entry: water of crystallization
Function: noun
: water of hydration present in many crystallized substances that is usually essential for maintenance of a particular crystal structure.

What comes to mind is the interaction of cement powder and moisture. When I discuss the subject of low hydrogen covered electrodes, I use the analogy that if you were to leave a bag of cement powder in a moist environment, it would absorb the ambient moisture and hydrate to form a solid cement block. Since the main constituent of the flux covering of a low hydrogen electrodes is calcium carbonate (limestone), the reaction to moisture is similar. The limestone covering is hygroscopic an reacts in a manner not unlike cement powder. The reaction, i.e., hydration, is much more complex than simple surface moisture due the fact that hydration is a chemical reaction, thus the high rebake temperatures are necessary to reverse the reaction.

I'm sure most of us can relate to you and your mentor. Most of us are where we are because someone was willing to offer us encouragement and share their knowledge and understanding of our chosen field. I'm fortunate in that the two gentlemen I learned so much from are still alive and doing well, although both have hung up their welding hoods long ago. As our careers change direction we still depend on mentors to provide us with direction and encouragement.

An engineer I do a lot of work with is the person that introduced me to the AWS CWI program. I remember him telling me, "Al, I can always tell a welder, but I can't tell him much."

When I put my hood down and started to burn electrode it dawned on me that he was saying I was one thick headed SOB. I'm afraid it is a common trait for many of us welders.

Here it is some thirty years later and he is still one of my mentors. He's in his seventies and still working every day.

Gotta run and do some work.

Best regards - Al

By Stephan (***)

Date 05-03-2008 07:03

That's it!

Cheers my friend!

Best to you,
Stephan

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

Date 05-03-2008 17:45

Gentlemen, don't be upset if a chemical engineer comes into the discussion.
The covering of a low hydrogen electrode is not calcium carbonate, it's calciuym oxyde. So, the moisture absorbed by the covering will not be crystallization water but it will react chemically with the calcium oxyde to produce calcium hydroxide.
The chemical reaction is CaO + H2O ----> Ca (OH)2
Calcium carbonate is not hygroscopic, i.e., it doesn't absorb water. Calcium carbonate (chemical formula CaCO3) doesn't have crystallization water, unlike many other salts that do. Actually, calcium carbonate is unsoluble in water. Marble is almost pure calcium carbonate and it doesn't dissolve in water.
Giovanni S. Crisi

By 803056

Date 05-03-2008 19:16

Thank you for the clarification Giovanni, but now you have only caused me to think of more questions!

Once again, my brevity is at fault. We say the low hydrogen covering is limestone based, but in fact I believe it is processed before being added to the mix of flux components.

Perhaps you can help clarify how the components of the flux interact for us.

I was under the impression that the limestone (calcium carbonate?) was "baked" to drive out the water and the resulting clinkers ground to powder much as they do to produce cement powder. Is it the dehydrated limestone powder (calciuym oxyde?) added to the flux that is hygroscopic and reacts with water to reform hydrates if the electrode is stored properly? Or is the limestone simply ground and added to the flux. If the limestone is simply ground into a powder, isn't it already hydrated, thus how would it absorb moisture?

This is where the value of so many people with different back grounds and different fields of expertise comes into play and makes this forum so valuable.

I looked in a couple of my references, but they didn't provide much information about the chemical reactions taking place, i.e., how the limestone is processed before being added to the flux covering and the subsequent chemical reactions when the electrode covering is exposed to moist air.

This is where I need your expertise Giovanni. We need to tap into the wealth of information you have acquired over the years.

Thanks - Best regards - Al

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

Date 05-14-2008 01:20

To Al and Stephan,
Calcium oxide reacts with water to give calcium hydroxide. Chemical equation: CaO + H2O ---> Ca(OH)2
This is an exothermic reaction, i.e., it releases heat. The conversion of hydroxide into oxide again is an endothermic reaction, i.e., it absorbs the same heat it has released before. This is why low hydrogen electrodes that have absorbed humidity due to poor (or lack of) storage conditions must be heated in an oven at a certain temperature during a certain time.
Of course, calcium oxide absorbs also carbon dioxide to give calcium carbonate. Chemical equation: CaO + CO2 ----> CaCO3.
This calcium carbonate decomposes when welding, due to the high temperature of the electric arc. Chemical equation: CaCO3 + heat ---> CaO + CO2.
However, this small amount of carbon dioxide is not harmful. Remember that MAG welding is performed in the presence of an inert gas plus a small amount of CO2.

Regarding sodium and potassium silicates, used as binding materials of the electrode coatings, the nickname of "waterglass" in the USA and Germany (and "soluble glass" here in Brazil) is due to the fact that, when pure, it is transparent and very similar to glass; but it's soluble in water, which glass is not.
When sodium silicate is used, the electrode is good only for direct durrent; when potassium silicate is used, the electrode is good for direct and alternate current.

I thank you for your kind words on my person, which I really appreciate.
Giovanni S. Crisi

By Stephan (***)

Date 05-04-2008 22:55

Giovanni,

how could this upset somebody?

On the contrary, it is impressive and it is always a honor to learn from you!

But please let me - additionally to the excellent items coming from Al - ask some humble questions.

As I have mentioned, a longer time ago I have busied myself with the mechanisms of moisture absorption on basic stick electrodes. Hereby I have learned that in particular this type's cover should constist of three different main components:

- Calcium Carbonate CaCO3
- Calcium Fluoride CaF2
- Titanium Dioxide TiO2

Beside the fact that it is entirely new for me, that not CaCO3 - used to reduce the arc voltage as to generate shielding gas and slag - is one of these three major constituents but CaO (which was known to me by now as being used in SAW fluxes), it is as well new for me that these substances are resistant against adsorbing humidity.

All these constituents are as you mentioned not distinctive hygroscopic, which was understood by me as absorbing water above that level of "moisture of hydration" as Al named it, and what we are calling "Kristallwasser" in Germany. The latter whereas is - please correct me when I'm wrong - a mechanism of physical forces, even adsorption. Since however - just as my personal assumption - all electrode covers are to be seen as a capillary interspersed conglomerate and each of the substances used for the cover may have a surface, having itself again a more or less surface roughness and a particular surface energy, moisture of hydration (or water of crystallization) could occur. Hygroscopic mechanisms are whereas - at least as I have thought by now - based upon the chemical resolving of (e.g. hydrogen molecules) into the substance's lattice, even absorption. Since the forces in case of absorption are however much higher than the forces of adsorption, I thought by myself, the "rebake" temperature, which is - at least in my humble understanding - in the widest sense a value for the amount of energy transferred to the electrode cover, should be different for both "absorbed" (hygroscopy) as "adsorped" (moisture of hydrate) kinds of cover moisture. This means, one cannot be certain of having reduced the total amount of water from an electrode cover by only rebaking it at temperatures of ~ 100°C.

But I guess you reply now: "But none of these three substances mentioned above is "hygroscopic" since none of them is soluable in water!"

Well, without knowing what you will answer on Al's fine questions, I just would like to mention that I mean to remember, that not in particular the substances above (CaCO3, CaF2, TiO2) are referenced in the coherence with hygroscopic mechanisms, but very first of all the binders used to form even the mentioned "conglomerate", as there were mainly Sodium Silicate (Na2SiO3) and Potassium Silicate (K2SiO3), we call it "Wasserglas" in Germany but I think it may be a mistake to translate it into "water glass". These substances are -as far as I can remember correctly - hygroscopic substances and here we have thus a case for an absorption of hydrogen which must be removed from the coating by using higher temperatures. But I must truly admit that I haven't tried to find out at that time in how far CaCO3 and the others might be hygroscopic. That's why it was so interesting to read what you have explained so excellently.

But I humble request your correction for everything I have misunderstood as well as I am looking forward to your responses on Al's very interesting questions.

Thank you and my best regards,
Stephan

By DaveBoyer (*****)

Date 05-05-2008 01:27

Stephan, sodium silicate is called "water glass" in the US, informally at least. In the old days, farmers & country folks would keep eggs imersed in a crock of the solution for longer storage.

By Stephan (***)

Date 05-05-2008 09:17

Ahaaaaa!

Thank you very much Dave!

To cite Al: "There's always something new to learn!"

Best regards,
Stephan

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

Date 05-03-2008 17:30

"How much moisture is contained in the air at some specified temperature" is called "humidity ratio" in the USA, and "absolute humidity" here in Brazil. It's measured in grains per pound of dry air in American units or grams per kilogram of dry air in metric units.
As Al correctly says, moisture is not completely soluble in air, and, at a certain pressure, solubility depends on the temperature.
The moisture contained in air at the saturation point is called "specific humidity" in the USA.
Relative humidity is defined as the partial pressure of water vapor contained in air at certain conditions (here, in this room and in this moment, for example) divided by the partial pressure of water vapor contained in the saturated air at the same conditions, multiplied by 100.
A more simple definition of relative humidity, perfectly suitable for practical purposes, would be this: it is the water vapor contained in air at certain conditions (i.e., the humidity ratio) divided by the water vapor contained at saturation (i.e., the specific humidity), multiplied by 100.
For practical daily purposes, the second definition is OK. The first one is used for rigorous scientific purposes.
The unit of relative humidity is "percentage".
Giovanni S. Crisi

By Stephan (***)

Date 05-04-2008 21:22

Giovanni,

great explanations, as usual!

Learned something again!

Thanks and best regards,
Stephan

By 803056

Date 05-05-2008 04:44

I should really be going to bed, its 12:40 and I have a class tomorrow, but there is always something new to learn!

Gentlemen, I have to run along.

Look out Texas, Stephan is on the loose! Step aside partner! :)

Best regards - Al

By ssbn727 (*****)

Date 05-08-2008 07:48

Cumprimentos Giovanni!
Ele é sempre um prazer de ler os seus correios, e eu não quis que você se sentisse ignorado sendo exclusivo em direção a Stephan na conversação com você na sua língua também...

Espero que tudo seja melhor no Brasil desde a erupção recente da febre Dengue lá adiante!!! Todo o melhor para você e os seus estudantes, e olho foward aos seus correios e respostas nesses fios!!!

Finally, I would also like to know from you how well this translator did in Portuguese - if you would be so kind in commenting. ;)
Adeus o meu amigo!!!

Respeitosamente,
Henry

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

Date 05-08-2008 22:51

Cumprimentos, Giovanni! It's a formal phrase in the Portuguese langauge spoken in Portugal. Here in Brazil the greeting would be: Saudações, Giovanni (a formal phrase) or Alô, Giovanni (a colloquial one, perfectly acceptable among long time frequentors of the Forum)
É sempre um prazer ler (erase Ele and de) as suas opiniões (correios means the post office, not a posting), e eu não quis que você se sentisse ignorado ......... (from this point I understood each particular word but not the meaning of the phrase, rewrite it in English).
Espero que tudo tenha melhorado no Brasil desde a recente epidemia de febre dengue (erupção is the eruption of a vulcano. The dengue epidemy is limited to the greater Rio de Janeiro area, but unfortunately is still in course, the situation is still bad). Tudo (tudo, not todo) o melhor para você e seus estudantes (OK in the Portugal Portuguese; in the Brazilian Portuguese would be: Tudo de bom para você e seus estudantes), e estou a espera de suas opiniões e respostas nesses (fios? fio means thread or a thin electrical cable).
Giovanni S. Crisi

By yusuf polat Date 05-05-2008 05:42 Edited 05-05-2008 06:49

Thank you everyone for helping. We are using MIG welding machine with SG2 electrode wire. Protector gas is He and CO2 mixture. Temperature of welding room is 20 degree C. rH of room is between 47-54. Parts preheat temperature is 110 degree C. Thickness of parts are 25 mm. at the end of welding we tested the welding parts and we have great results. when we are using electrode arc welding we heat the electrodes at 400 degree C for 2 hours then keep them in an heat protector that has 200 degree C.
We try to keep the welding room air cold and dry . we use coolers and dryers for this.
we will try to weld high mangan alloy soon. ifwe get an interesting result I will share here
Stephan,Giovanni and Al thank you all for those wonderful explanations.
Best regards;
Yusuf.

By Stephan (***)

Date 05-05-2008 09:24

Yusuf,

don't want to line-jump, but please let me be the first one who says: "Thank you for the information!"

Keep us in the loop... :-)

Best regards,
Stephan

By jon20013 (*****)

Date 05-05-2008 09:39

What a very informative thread!! Professor Crisis (Giovanni) so very good to see you back, I was beginning to think you'd dropped from the planet! Always refreshing reading your highly enlightened threads as well as our young genious Stephan's! Not to discount anyone else's response, I'm just in awe reading some of this heady stuff!!!

By ssbn727 (*****)

Date 05-08-2008 02:07

With all due respect to the participants of this thread...

I had to jump up high enough and hang on for dear life because of all the "moisture" that seemed to rise higher and higher as a result of the conversation...
But then again, that's what you get from someone with a New York City attitude so, forgive me for being so blunt!!! :) :) :)

I'm wearing my "waders" from now on - PERIOD!!! ;) Oh yeah, and a series of rosebud torches in a circumferential configuration in order to evaporate as much of that "moisture" as possible wherever I walk from now on!!! ;) ;) ;) Who knows??? Maybe I'll have to use moisturizers for my feet! :) :) :)

BTW Al, I've passed many a qualification test after I was drinking although, I most definitely do not recommend anyone to attempt it!!! Back in those days I was an enigma and besides, if I tried to do that today, not being able to pass the test would be the least of my worries afterwards...

So, if any of you youngsters want to really learn something about being prepared to pass a qualification test, then stay sober for the test because, I'm one in a million who could pass but, are you willing to gamble as to whether or not you can include yourself as also being a one in a million enigma??? I didn't think so. ;)

Respectfully,
Henry

By Stephan (***)

Date 05-08-2008 03:55

"King" Henry!

So great to hear from you!

I'm sure to speaking on behalf of all the other appreciated fellows. Your reply honors this thread outstandingly*! :-)

I hope everything is good and you're alright!

Best regards,
Stephan

* Just as you said, you're even one in a million! :-)

By ssbn727 (*****)

Date 05-08-2008 07:33 Edited 05-08-2008 07:36

Herr Stephan!!!

Wie ist mein liebster Freund von Deutschland?

Ich hörte, dass Sie ein sehr beschäftigter Mann kürzlich - viel wie ich selbst gewesen sind!

Ich hoffe, dass mein Deutsch erträglich ist, und ich wünsche Sie das Beste vom großen Zustand Pennsylvaniens, der USA...
Das Haus von vielen deutschen Gesellschaften, die Geschäfte in den Vereinigten Staaten machen!!!
Auch nach Hause vielen Personen der deutschen Herkunft.

I'm glad you have a good sense of humor with respect to my previous post because, my intent was not to belittle or insult anyone in this thread. ;)

So, how's my German translator working so far??? I'm asking you because, if it is coming close enough to "hitting the mark" so to speak in translating from English to German, then I'll be sure to post the translator's web site if your reply is favorable... Of course, feel free to critique any shortcomings found in the translation by all means. After all, I trust your judgment. :) :) :)

As always, it's a pleasure to continue our friendship even though we haven't actually met as of yet although, something tells me that Las Vegas is in the cards so to speak - this year!!! So if you're headed to this year's AWS/Fabtech or whatever the title is - convention, then I'll make it a point to formally introduce myself to you - SIR!!!

Until then, Auf Wiedersehen mein Freund!!! :) :) :)

Respektvoll,
Henry

By 803056

Date 05-09-2008 02:10

I saw that test plate and I thought you must have hidden an automatic welding machine in your pants based on the weave pattern of the cover bead. Now I understand it was just you swaying back and forth while you were humming "99 Bottles of Beer on the Wall".

Drink on my friend! :)

Best regards - Al :)

By Tommyjoking (****)

Date 05-09-2008 10:22 Edited 05-09-2008 10:31

BWHAAAAAHA!!!

NEAT THREAD!!!!

I apoligise to AL and Stephan both because sometimes I still need to learn to just "be quiet" and pay attention. I can't comment on the drinking part because that is individual I would imagine applies across the board as far as any kind of testing goes.

Not to distract the thread but since I brought it up...
Can someone lay me a theory or fact as to why since I started preheat routines and laying higher amperage fillet welds against opposite side groove welds....under surface porosity in my 4130 work has dropped some 97%. Everything else being equal. I just want to understand why?

"now your doing it right is not a great answer!"

Thx all you guys
Tommy

Edit yes 97% ...I am competitive as all get out what can I say.

By 803056

Date 05-09-2008 13:11

I'm not sure what you are doing. Please provide some more detail to explain what you mean by "..... fillet welds against opposite side groove welds".

Best regards - Al

By Tommyjoking (****)

Date 05-10-2008 02:36

Hi Al sorry for the poor description

That particular joint is a 1" x .049 SQ tube with a piece of machined bar stock .070 mating with the tube down its length. Both pieces lay flat and join together so there is a fillet weld between tube and machined piece (down one corner of the tube length). After the fillet you flip it over and are left with a groove weld (the round corner of the tube against the squared edge of the machined piece). I hope that describes it ok.....no pics sorry I am home sick today.

Thx to everyone here I got a solution to this joint which was a plague. Porosity was rampant on the backside of this joint (groove/flat side). Preheat coupled with a slightly hotter fillet has eliminated this problem entirely.

I just want to know why or how this happens....I have heard "trapped hydrogen" and moisture content. If there is no clear answer thats fine...I just want to understand it.

Best Regards
Tommy

By 803056

Date 05-10-2008 16:08

A little residual cutting fluid, machining fluids, forming oil/lubricant residuals on the tube or machined part, light rust, etc. could contribute to the problem. Without seeing the conditions of the parts it difficult to guess, however, porosity is typically caused by surface contamination, thus there are gas reactions that can result in porosity. Light rust can contain retain limited amounts of surface moisture and hydrates that can result in moisture.

At this point it is merely a guess as to the cause.

I hope you are at home playing hooky from work and not home sick.

Best regards - Al

By Tommyjoking (****)

Date 05-11-2008 04:08

neg I been puking my guts out but I went in today. As far as the contaminants....the parts are thoroughly bead blasted inside and out then washed in alcohol as well as the filler rods. We also typically make sure our hands are clean before handling the filler. The porosity has always been inside the weld and is found after grinding....it can usually only be seen with magnification. No matter we got a handle on preventing it now so all is good. I am just on a search for a definitive cause and so far have come up with maybes.

Your right some light rust on a tig rod can cause havoc...we got tired of cleaning rods so now they are stored in an oven until point of use to keep the moisture at bay.

Best Regards
Tommy

By 803056

Date 05-11-2008 14:04

I hope you feel better soon.

While I wasn't as sick as you, I had a little problem with a chest cold last week while I was teaching in Orlando. I had to request a microphone so my voice would hold out for the length of the course. I had to use the men's room at one point and as I was standing at the urinal, a though came to mind of Leslie Nielsen in one of his "Police Squad" movies. You know the one where he's at a banquet for the Queen of England and he's in the men's room humming a merry tune while relieving himself? Yep, I just had to do it; I turned the mike on placed it next to the urinal as I flushed it. Sometimes a thought pops into my mind and I simply can't resist the impulse! I've never attached a long streamer of toilet paper to my shoe, but I've thought of it several times over the years!

The only woman in the class said, "Yes Al, we heard the flush!"

Everyone had a good laugh.

Happy Mothers Day everyone!

Best regards - Al

By Stephan (***)

Date 05-11-2008 15:38

Hi Tommy,

I truly hope that you had a quick recovery and you're doing better meanwhile!

I don't know if it's right to ask if I may add some humble words on this, since actually all has been said already, but however I'll venture it.

If I have really understood correctly how the parts are being manufactured, I guess there could be at least an assumption for a possible explanation from my side.

When I have read what you have explained on Al's additional request to detail the application, I thought by myself, that the problem may be based upon an effect, called in Germany "Mechanische Porenbildung".

I guess there will exist a technical term in English as well which I unfortuntely do not know. Thus I would like to translate the German term as mentioned above by using "Mechanically Induced Porosity".

Before resuming we should be keep in mind that "pores" are "nothing more" than gaseous inclusions mainly within the weld metal deposit or - in exceptions - in the HAZ (e.g. Microporosity along the grain boundaries). And thus it is clarified that these gaseous constituents "trapped" within the solid material have to "come" from somewhere.

Now as to my best knowledge "Porosity" and its mechanisms can be separated into two main fields:

1. Metallurgically Induced Porosity (Metallurgische Porenbildung)

2. Mechanically Induced Porosity (Mechanische Porenbildung)

The first named is including all cases of porosity based upon Al's - as usual - excellent explanation which was (quote):

"A little residual cutting fluid, machining fluids, forming oil/lubricant residuals on the tube or machined part, light rust, etc. could contribute to the problem. Without seeing the conditions of the parts it difficult to guess, however, porosity is typically caused by surface contamination, thus there are gas reactions that can result in porosity. Light rust can contain retain limited amounts of surface moisture and hydrates that can result in moisture." (unquote),

which means that the liquid weld metal is contaminated with "gaseous cleavage products" from hydrocarbon containing lubricants (generating hydrogen) or solids (generating in particular nitrogen or oxygen). By being split within the arc plasma, the solid or liquid contaminants generate gaseous constituents which are resolved within the liquid weld pool. As liquids have a higher "disolving power" than solids the gaseous constituents are "harmless" as long as e.g. the temperature does not drop. In case of welding whereas the liquid does - of course - solidify to form the weld seam. By decreasing the temperature the melt's "disolving power" drops as well and it tries to get rid of the gas.

Now for both - solidifying melt and escaping gas - it comes to a kind of "race against the time". This, since the crystallization front of the metal moves with a specific (depending to many different factors e.g. thermal conductivity,...) velocity. As in the amount of that the metal's solidification does proceed the gaseous contaminants solvability in the metal decreases.

And if now the solidifying metal's crystallization front is "faster" than the motion speed of the particular gas on its way towards the seam surface, it is entrapped within the solid metal and forms - pores.

This mechanism is drastically observable in pure metals (having no solidification range but a specific solidification point) and here again the best example is pure aluminum. The solvability for hydrogen in liquid aluminum is 20:1 compared with its solid state of matter. As pure aluminum has defined point of solidification much of the disolved hydrogen can be entrapped and yield porosity.

Nonetheless, metallurgical induced porosity can be created as well as by welding "older" steel grades having higher amounts of impurities or which are unknown by their chemical analysis (e.g. basic Bessemer steel etc.). But I guess to weld these steel grades is rather rarely nowadays.

But however, this all is certainly well-known. The reason I have mentioned it though is to compare these mechanisms with the above second named, the "Mechanically Induced Porosity".

Mechanically induced porosity is based upon the physical volume expansion of gases at higher temperatures. For instance, when welding circumferentially a fillet joint around two parts and between the two parts a cavity exists, the temperature rise by the arc can cause an evaporation of surface moisture, eventually both part surfaces are contaminated with, or can simply cause an extension of the volume amount of air within the cavity, existing between the two parts. I have prepared a s c h e m a t i c representation, please see also the attached Circumferential_Weld.pdf, for a better understanding of what I am trying to describe. By finishing the weld the extended air, gas,..., tries to escape the cavity and the only way is through the solidifying weld bead itself. By even its way across the weld seam's cross section it can thus be entrapped in the weld metal deposit.

Very often I have seen mechanical induced porosity in joining zinc coated thin sheet metals by having a lap joint geometry. By having a gap between the two sheets we have the same problem as mentioned above but severely aggravated by having the additional reactions of vaporized zinc!

By vaporizing zinc between the upper and the lower sheet, which can not escape across the gap between the sheets its way is determined to be through the molten and subsequently solidifying bead.

The result can be seen in the attached Mechanical_Pore.jpeg and I guess this picture says all.

Mechanical induced porosity must have thus a continuous connection to a kind of "reservoir" of gas, or gas generating substances which can be provided to the weld pool. Even this "gas generating substance" in the attached picture was the zinc, which was vaporized and could not early enhough escape through the solidifying weld metal. In other cases this can be e.g. moisture or even the substances Al has named in his excellent post.

Perhaps thus finally my assumption, might this be the case as well in your application and your problem was based upon mechanically induced porosity. Even as well that you have named the porosity found in your application "...under surface porosity..." let me assume that the way for the gaseous constituents trough the weld's cross section might be slightly too long before they can escape entirely from the weld metal.

Though by increasing the temperature (preheating + weld performance) you might have "done even right" since you have caused hereby - perhaps - a slightly extended period of liquid state which may allow the escaping gaseous constituents to "find their way" through the weld before being entrapped within.

So far my humble considerations, as usual please correct me when I'm wrong.

Best regards to you and everyone,
Stephan

Attachment: Circumferential_Weld.pdf (11k)

Attachment: Mechanical_Pore.jpg (0B)

By Stephan (***)

Date 05-11-2008 12:16

Hallo Henry, mein Freund!

Da bin ich aber nun wirklich überrascht, dass ich dies von Dir lesen darf! :-)

As translated: "I'm very surprised to read this, written by you!"

Thanks, I'm doing quite well!

Your German is more than endurable!

Once Al (803056) was so kind to encourage me to continue writing in English here in the forums, thus I truly hope that Al was really honest to me :-) and my English may be at least roughly that good as your German to be sufficient to communicate with all you great ones herein.

All you have written appears understand- and reasonable to me.

I didn't know by now that many German companies are situated in Pennsylvania to be doing good business over there.

Thus I truly hope that my compatriots are at least as kind, as I have experienced all the US American people when I have had the honor to visit your great country!

Take good care and all my best regards,
Stephan

By Tommyjoking (****)

Date 05-11-2008 23:58

Stephan as always a great reply...thank you for such an effort!

You have a great point on the mechanical induced porosity. Considering the layout of the joint, a curved edge against a flat surface...its easy to see how the weld puddle could get ahead of the escaping air deep in the joint. I think the hotter fillet helps in this respect with a bit more penetration, preventing a very narrow sharp area (on the other side) where air could get trapped. We hold a fine line on how much heat is applied vs. filler as these parts end up being showpieces inside the aircraft...we must make them look perfect as possible. We don't see the typical "blowout" of air from pressure but certainly it is possible that small amounts get trapped en-route trying to escape the molten weld. It very well could be just from the design of the joint itself that was causing a lot of the trouble. Makes sense.

Oh yea...I am feeling much better thank you!

Best regards
Tommy

By Stephan (***)

Date 05-12-2008 10:27

Thanks a lot Tommy!

Best regards,
Stephan

P.S. Good to see that you're physiologically upright again! :-)

By 803056

Date 05-14-2008 03:59

Hello Stephan;

It so nice to see you back.

I enjoyed reading your excellent explanation and differentiation between porosity related to gas reactions and/or solubility vs temperature and porosity resulting from entrapped gas (air or others) between matting surfaces. How many of us have experienced a "blow out" because of excessive internal pressure build up when welding pipe?

I completely ignored the later in my description of the potential causes of porosity, but there are so many instances of occurrence, I feel silly for not including it. It just further exemplifies the the value of have several people working on a solution to a problem.

Tommy, glad to see you are feeling better.

Best regards - Al

By Stephan (***)

Date 05-14-2008 19:29 Edited 05-14-2008 20:30

Hi Al!

It is always great to hear from you and it's twice as great when reading so kind words :-):-):-)

Thank you so much and my very best regards,
Stephan