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Parent - By Tommyjoking (****) Date 05-10-2007 08:36 Edited 05-10-2007 10:32
Jeez....

I Knew it all along subconciously...all welders are just a bunch a freaks that like to play with atoms and absorb punishment from light speed particles.   LOL

Dang guys this is pretty interesting stuff ....I did not know all the shit I was causing/doing all these years.

I wonder if i can use this "experiment " to prove the need for a rod oven at work for our mild steel tig rods???  I guess rust aint the same as humidified flux?
Parent - By Tommyjoking (****) Date 05-10-2007 08:37 Edited 05-11-2007 06:07
Jeez....

I Knew it all along subconciously...all welders are just a bunch a freaks that like to play with atoms and absorb punishment from light speed particles.   LOL

Dang guys this is pretty interesting stuff ....I did not know all the stuff I was causing/doing all these years.

I wonder if i can use this "experiment " to prove the need for a rod oven at work for our mild steel tig rods???  I guess rust aint the same as humidified flux?

GREAT THREAD
Parent - - By DaveBoyer (*****) Date 04-26-2007 02:44
Now this thread has got Me thinking... What happens if the same test is done on a FCAW weld done with wire that has been casually stored in the shop for a while V/S fresh wire. Could this be something to look into with regard to the "Worm Holes & Chicken Tracks" ?
Parent - - By 803056 (*****) Date 04-26-2007 03:41
Now your are starting to think!

Self shielded flux cored electrode will absorb more moisture over time than a gas shielded FCAW electrode simply because the self-shielded electrode typically have a greater volume of flux. Some of the earlier FCAW electrode produced nearly as much diffusible hydrogen as the non-low hydrogen SMAW electrodes.

There are FCAW that will produce low levels of hydrogen, but they do have to be protected. The new seizmic requirements address some of those concerns.

Al
Parent - By jwright650 (*****) Date 04-26-2007 12:48
Al,
As for showing this test to the guys in my shop, I have to make this a real life case for them to see this test as valid in their mind's eye. So storing rods over a pie plate that is full of water, or quenching the weld sample in water(to make the most bubbles possible)....just isn't gonna cut here with my guys. For them to buy into this, they need to see a rod that was laying out of the oven on top of on of their machines for a day or two, I need to show them something that could happen in our shop and the importance of storing the rods properly...or more importantly not picking up any old rod just to make a few tacks or to finish welding the last few inches of weld on a piece because of convenience of a rod laying in close proximity vs walking over to the oven to get one rod to finish.
Parent - - By CWI555 (*****) Date 04-26-2007 03:44
Could be onto something there.
Parent - - By bellaru (*) Date 04-26-2007 07:17
my test worked great,,,,,,,,,,,thanks again Al...........
Parent - - By Gunther Date 04-26-2007 08:34
Al and rest.

I only "stumbled" upon this thread relatively late into it.
Great method to illustrate to the ignorant welder the basics of the problem without getting the issue all confused and to technical.  Again great!  I will also give this experiment a bash.

Just a quick question, one of the last posts were regarding FCAW, I would like to chime in there and ask the same question regarding SAW fluxes not baked/dried properly.
Would it be safe to assume the same results would be achieved?
Parent - - By welderwv (*) Date 04-26-2007 12:08
OK I am trying this experiment today with my advanced welding class.  I went to walmart last night and I bought of case of beer and two of the biggest bottles of baby oil they had.  The check out lady, I am sure, thinks I am a pervert now!!!

After reading the post of SAW flux I was thinking about the fab shop I worked in.  We did a lot SAW.  Most not critical work but build up of highly worn pulverizing yokes for coal and power plants.  But we started to use it on UT work on thick sections.  We would pulse mig the roots and one or two more layers and then fill the grooves with SAW.  These were hand held SAW units with the compressed air forced flux hoppers.  I am thinking now that the flux left in these hoppers over night with the compressed air most definitely was exposed to moisture.  We had some filters on the air supply but you all know that moisure builds up in these air lines.  We had to store the unused flux from the bags in the oven but we never emptied the hoppers. 

The only time we had problems with the UT though was a batch of laminated steel.  Now I did most of the roots for the job with GMAW-P but did not participate in the SAW.  We used, if I remember correctly, lincoln 780 & 980 flux. Just curious to see what you guys think of the flux in these hoppers absorbing moisture from the compressed air.  I know from watching the welders that they always topped off the hopper at the end of the shift so the next day they could pick right up so most of the day they were welding with flux that had been in the hopper for 10 or 12 hours. 
Parent - By darren (***) Date 04-28-2007 06:22
this is the best thread yet
darren
Parent - - By JA (**) Date 04-26-2007 12:57
i'm a welder too,,,,,,,,,,,,does that make me "ignorant" also.....?
Parent - - By new tito (***) Date 04-26-2007 14:27
I've got my wheels turning now.

Most of this subject is over my head, but I'm wondering if there is any signifigance to the microscopic surface of the welded specimen that was welded with the improperly stored electrode.  I've been keeping up with this thread and it seems very interesting, but like I said, it seems most of it is over my head.  Well just this morning it clicked!!  I'm sure everyone is aware of the whole mentos in diet coke experiments.  You know, where the two guys on Youtube.com made facinating shows with the spray produced by dropping mentos candies into diet coke bottles?  I'm also sure alot, if not most of you are familiar with the show Mythbusters?  They had an episode dealing with experimentation of the mentos thing.  They tried mentos in different types of liquids as well as tried different types of candies in varios liquids including diet coke. 

To get to my point, basically, if I can remember right, the extreme fizzing really only worked with mentos due to some reaction with the diet coke and maybe the CO2 in it (please forgive me if I'm not recalling correctly, it was quite a few months ago that the program aired).  Anyway, the reason why mentos was the only candy that did this was because it was determined the surface of the mentos when viewed under magnification has little tiny indentations on it, similar to a golf ball.  For some reason that I can't recall, the gasses in the diet coke along with a few other factors had a very extreme reaction do to these indentations.  See if you can find the episode on discovery.com, it will explain it better and give the true outcome of the results.

Back to how this may be tied together - As aevald mentioned in his experiment above, a weld sample welded with improperly stored electrodes when polished and viewed under magnification looked like swiss cheese.  I wonder if the as welded surface of these same types of specimens would show any types of indentations similar to the mentos candies, and if this could and does have any reaction with the baby oil?  It seems that if gasses are escaping from the surface of a cooling weld, that there is a possibility that some type of indentation would be left.

I wonder how these weld samples would perform in diet coke??

Like I said though, this subject is over my head, but it seems there could be some coincedence.
Parent - - By Lawrence (*****) Date 04-26-2007 18:55
Well,

Broke out the beekers and mineral oil

Results in the first 1/2 hour are that both samples appear to be degassing at about the same rate.

Lots of fine bubbles at the centerline.... Both the properly stored E7018 HR4 and the stuff that has been sitting on my desk since Al posted that picture are pretty much doing the same thing.

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

After 30 minutes it is clear that the oven treated electrode is actually producing more gas.

Students theorize that the controls are bad.

We quinched to save time and the oven rod was hottest when quenched. 

Next week we air cool both samples and see what happens.

Stay tuned.
Parent - - By 803056 (*****) Date 04-27-2007 01:52
I have to say this thread is taking on some interesting twists and it seems to be making a lot of us think about what is actually happening. Isn't that the purpose of any demonstration?

I have never had a properly stored Lo-Hi or a fresh Lo-Hi electrode taken from a sealed can produce more gas than either the damp Lo-Hi or the E6010. Some bubbles, yes, but of very limited quantity and duration. Again, it depends on the electrode flux formulation, i.e., E7018 versus E7018-H4R. There is a significant difference. Don't forget, low hydrogen electrodes purchased on non-hemetically sealed containers are required to be baked at elevated temperatures (600 to 800 degrees) before being placed in the holding oven (at 250 or higher). So, if you purchase electrodes in cardboard containers, I don't believe I would consider them to be hemetically sealed in all cases.

The reason for quenching the welded sample is to trap the maximum amount of hydrogen to show the potential for introducing hydrogen in to the weld. Most of us know that heating a weldment to 450 degrees F and holding it at temperature for several hours allows the hydrogen to escape without damaging the weldment, i.e., that's why its call a hydrogen bake-out. If you don't quench the sample, you allow much of the hydrogen to escape. (another reason to preheat)

The sample in the demonstration is a single pass weld. A weld that is an inch or more in thickness is going to take a lot longer to off-gas than the single pass weld. It stands to reason that it will take longer for the atomic hydrogen to diffuse through thicker material. I find it fascinating that the hydrogen atom is passing through solid steel! The most critical time is the first 48 hours because that is the period of time that the most hydrogen is still present in the solidified metal. The hydrogen atom is so small that it is mobile, it moves from one location to another, it takes time to move and the thicker the weldment, the longer the hydrogen takes to find its way to the surface and escape into the air. One of the primary reasons AWS D1.1 has the 48 hour waiting period for the inspection of A514, A517, and other high strength steels is to allow the hydrogen to diffuse out of the weldment.If the hydrogen is going to do damage, there is a high probability it will occur during that 48 hour period. Does that mean all the hydrogen will have diffused out into the air during that 48 hour period and there is no chance of further cracking? Hell no, as was said, the cracking can manifest itself after a considerable lapse of time. There is still some hydrogen within the atomic lattice.

It is a good observation to note that thick sections will have multiple microstructures. Those areas that see the highest cooling rates are more prone to martensite and bainite, with ferrite and pearlite in those regions that experience slower cooling rate. Also consider that the residual stresses and applied stresses are not uniform throughout the weldment.

The E6010, by far, should off-gas longer than the Lo-Hi, damp or dry. The E6010 weld bead should off gas for several hours. The damp Lo-Hi will off gas for some time depending on just how damp the ambient environment is. The idea of using the pie plate full of water is to speed things up a bit. The idea of the demonstration is to show the potential for introducing hydrogen into the weld via the type of flux, i.e., cellulose or moisture, the damp E7018 electrode flux covering. Again, if you are using E7018-R or E7018-H4R, the results will not be as impressive because the flux is specifically formulated to resist moisture pick up. Wasn't that the original guestion asked in this thread?

If you look closely, the entire surface of the weld bead turns white with little bubbles until they start to coalesce and form the streamers rising up from the weld bead. The atomic hydrogen is much too small to see with the human eye or even a microscope. You only see the bubbles that consist of many thousands (maybe hundreds of thousands) of hydrogen atoms. When enough of the hydrogen atoms congregate and the bubble gets large enough, it floats to the surface of the baby oil (which slows the rise of the bubble so we can see it).

I don't claim to have all the answers. I met a past president of AWS that started working on this problem in 1941 and we still don't know all the particulars of what or how the hydrogen does its dirty deed.

As for the SAW flux, different fluxes have the potential for absorbing more or less moisture. The bonded fluxes are typically hygroscopic and they are usually stored in a manner similar to Lo-Hi electrodes to ensure or at least minimize moisture pick-up. Fused fluxes are not hygroscopic and do not require the stringent storage conditions as the bonded fluxes.

This is a great subject. While we may not know the exact mechanism that causes the cracks to occur, we do know how to prevent the hydrogen induced cracks. That what we have to teach our welders. And if this demonstration gets them to thinking, it has served its purpose.

Best regards - Al
Parent - - By bellaru (*) Date 04-27-2007 02:46
Al , i've been doing this for the last 2 days,,,,,,,,,,,,i even sliced the weld nugget in half and watched it pour out,,,,but like what was mentioned before , nothing in the HAZ,,,,,,,,,,,what about the underbead cracks.......it seems that most of the gas is excaping from everywhere except where you would find an underbead crack.........

i understand that rapid cooling will lock in as much gas as possible (for the demonstration),,,,,,but will that not harden things up a bit and sort of entrap it in a way that medium carbon and high carbon steels would do.....?

how about a 11018 electrode,,,,is it more difficult for the gas to excape from that type of weld......?
Parent - By 803056 (*****) Date 04-27-2007 03:28
Now remember, we are limiting our discussion to carbon steel and you're going way past my level of expertise, but think about where the metal will cool the fastest. In the HAZ next to the base metal where it is relatively cool compared to the molten weld puddle. The thermal conductivity of the steel base metal is much higher than that of the air above the weld bead, so the weld puddle is going to solidify along the edges of the weld bead first and the last location to solidify is the top surface along weld centerline. The region that has the highest cooling rate is that area most likely to have the hardest microstructure, again in the HAZ. However, the hydrogen is in the molten weld puddle. As the weld solidifies, the hydrogen is supersaturating the solidified weld and is trying to escape, i.e., diffuse into the atmosphere. Some of the atomic hydrogen is, perhaps by happenstance, over time, going to diffuse into the HAZ. Remember, the atomic hydrogen is very small and will move about within the atomic lattice, but there is a time element involved. It is there, in the HAZ, that there will be a higher concentration of carbon (base metals usually have more carbon and other elements that increase the carbon equivalency than the weld metal) and it is there that we will see cracking due to the higher hardness of the microstructure.

We can control the hardness by controlling the cooling rate by preheating and controlling the heat input, or we can control the chemistry, i.e., low carbon, or perform a post weld heat treatment to temper the hard microstructure or perform a stress relief or normalize it or anneal it (each with a higher temperature or slower cooling rates).

In this demonstration I used plain carbon steel which does not have enough alloying elements to get "really" hard by quenching it in water. Plus the fact that the steel has to be fully austenized when you quench it to produce the maximum hardness, i.e., maximum amount of martensite (or other hard microstructures). The welded sample is most likely not at "red" heat when you quench it for this demonstration. If you were to use a piece of hardenable steel you might be able to produce some quench cracks if you are quick enough with the quench.

Even the E11018 contains insufficient carbon to become "real" hard. They use elements other than carbon to produce the high strength associated with 9018, 10018, etc. If you are interested in producing underbead cracks, you can do so by welding a quench and tempered steel in a cruciform cross section with a fit-up that is tight (zero root opening) with a cellulose covered electrode (E6010 or E7010). It will produce underbead cracks after a short period of time. You will have to section, polish, and etch the sample to see them when they first start to form. Over time they should propagate to the surface where you can see them.

As for the hydrogen diffusing from the E11018 weld, it should happen just as it does with the E7018 if the rods are exposed to humid conditions and they absorb the moisture. Check out D1.1 and look at the allowable exposure times for the high strength welding electrodes. As the strength level goes up, the exposure limits are reduced because the steels that require the high strength electrodes are more highly alloyed and form hard microstructures more easily than plain carbon steel. Thus they are more prone to hydrogen induced cracking.

Again, this is just my take on the subject and I'm no expert on the subject. Some of these other gentlemen have more knowledge about this than I do.

Best regards - Al
Parent - By TimGary (****) Date 04-27-2007 10:48
Perhaps a reason why folks are not seeing the bubbles escape from the areas that are known to be susceptible to hyd cracking is because the hyd has difficulty escaping from those areas, thus cracking results?
Parent - - By DaveBoyer (*****) Date 04-27-2007 03:59
Is it possible that the hydrogen passes through the weld bead more easily than the parent metal, and that might explane why the bubbles seem to NOT come from the HAZ? Does hydrogen pass through steel tanks and pipes at ordinary temperatures, or does this only occur when hydrogen is incorporated at welding temperatures?  OR could the hydrogen atoms be clinging to the surface and not be visible untill they coaless at a change in surface texture [the weld bead]?
Parent - By js55 (*****) Date 04-27-2007 20:34
Dave,
It is possible that the mulitaxial orientation of BM grains would provide a more tortuous path for H2 to move along (especially in fine grained materials), as opposed to weld metal grains that are aligned with the isotherm and often much larger, depending upon heat input and BM grain practice. This may serve to trap H2.
But this would need to be combined I think with Al's coelescence idea. That H2 is diffusing from the HAZ and BM, its just that it is not coelescing in order to see it.
Talk about speculation!!
Parent - - By 803056 (*****) Date 04-28-2007 16:50
Wow, some of the questions this thread has generated would keep three or four PhDs busy for a lifetime.

First of all, its atomic hydrogen that is diffusing through the atomic lattice. The monatomic hydrogen wants to combine with something, anything, even another atomic hydrogen atom to form a larger molecule.

I've read many articles on the subject, so I'm not trying to pass any of this off as original thought on my part. There are several different explanations of how the atoms behave in the atomic lattice. One I like is that the atoms are like balloons full of air that are rubbing up against each other. They kind of "mush" together, but still there are small voids between the balloons, opps, I meant to say atoms. The atomic hydrogen, the smallest of all atoms, is small enough to pass through these voids and in time, after many dead ends and missteps, it bumps into something it finds appealing. Another atomic hydrogen atom, or perhaps as the studies at the University of Tennessee suggest, an free carbon atom, poof, you have a hydrogen molecule or a much larger methane molecule that exerts stress on the surrounding atomic lattice and with a little bad luck, a crack is initiated.

The demonstration I depicted in the photograph several days ago shows the hydrogen evolving from the surface of the weld bead. The atomic hydrogen must follow a torturous route to find its way to the surface of the weld bead where if combines with other hydrogen atoms to form the bubbles that float to the surface of the baby oil. We don't see the hydrogen atoms trapped within the atomic lattice. They are still in the process of moving or diffusing within the atomic lattice. It is only those hydrogen atoms that find their way to a microstructure that is hard and brittle that cracks will develop. That type of microstructure is often found in the HAZ and thus, underbead cracking occurs. As you can imagine, it takes time for the atomic hydrogen to stumble into the HAZ, after all, which is the shortest path, sideways into the HAZ or toward the surface of the weld bead and into the air? I can only assume there is a mathematician out there that can predict how many hydrogen atoms will diffuse into the adjacent HAZ (and play their dirty little tricks) versus the number of atoms that find their way to the surface of the weld bead. I can further imagine that the ratio of those finding their way to the HAZ compared to those that escape is rather small.

Based on the thought process I have outlined, I have to believe that if sufficient time was allotted and if there was sufficient atomic hydrogen present, you would eventually see some hydrogen bubbles rising from the HAZ assuming they didn't combine with other hydrogen atoms and get "locked" in or they don't combine with a carbon atom and get "locked" in to the atomic lattice. There will be no cracking unless there is a hard brittle atomic lattice structure surrounding the hydrogen molecule or methane molecule.

The critical temperature range for hydrogen induced cracking is reported to be between the temperatures of -50 degrees F and 450 degrees F. Below -50, the atomic lattice is too confining and the hydrogen atoms are immobile. Above 450 degrees, the atomic lattice is expanded and "loose" enough that the hydrogen atoms are free to escape. Thus, you hear of folks talking about welding on the North Slope of Alaska without preheat and they don't experience cracking problems. And we have the "hydrogen bake-out" that is performed at temperature in excess of 450 for several hours to allow the hydrogen to escape without causing cracking problems.

If hydrogen molecules could easily pass through the atomic lattice structure of steel, we would be hard pressed to contain hydrogen gas in high pressure flasks. Hum, isn't that one of the problems we're having with hydrogen propelled vehicles, the containment of the hydrogen in a safe manner? So, the selection of materials used to store the gas and the pressures involved must be considered. That being said, I don't believe the hydrogen molecules do pass through the lattice easily, it was just another related distraction to think about.

Best regards - Al
Parent - By jwright650 (*****) Date 04-29-2007 14:24
Hey Al,
Speaking of how do you contain hydrogen?.......Remember the Hindenberg?
Parent - By js55 (*****) Date 04-27-2007 13:44
"I have to say this thread is taking on some interesting twists and it seems to be making a lot of us think about what is actually happening. Isn't that the purpose of any demonstration?"

It is EXACTLY the purpose of a demonstration. This is a good one. Somehow I think we are not going to solve this one here, but we will all know more than we did before. Thats for sure.
Parent - By 803056 (*****) Date 04-27-2007 19:05
OK fellas, I've heard from several of you that the results were less than expected.

Well, I tried the demonstration this morning and it fell flat on its face and me with mud on mine.

I was going to a contractor's facility this morning to do some inspection, so I stopped at Walgrens and picked up some baby oil. When I got to the shop I grabbed a couple of pieces of 3/32 E7018-H4R from an open can in the heated warehouse. Who knows how long it's been open, at least a couple of days and it's been raining since midnight.

I had the welder cut three pieces of backing bar about 2 inches long and we ground them to bright metal.

He welded the first sample with some cellulose pipe rod and dropped it into the bucket of water. While he welded the second sample with a piece of 3/32 E7018-H4R from the oven, I dried and cleaned off the first sample and immersed it in the baby oil. He slid the second sample into the water and started to weld a third sample with the E7018-H4R I took from the warehouse. I snatched the second sample from the water, dried and cleaned it, and submerged it in the baby oil beside the first sample. He finished the third and last sample and slid it into the water. I fished it out and dried and cleaned it. Finally, I slipped it beneath the surface of the baby oil, tucked neatly beside the first two samples.

The cellulose covered electrode reacted within 30 seconds, the surface of the weld was hidden from view by the multitude of tiny bubbles, finally after a minute or so, a curtain of small bubbles worked their way up though the baby oil. Not as many in my photo, but they were there in all their glory. Unfortunately, instead of off gassing for several hours, the show was over in about an hour with just a few bubbles left over after two hours. It was a real disappointing show!

The "exposed" E7018-H4R; nothing. After five minutes, not a damn bubble to be seen. The dry and exposed E7018-H4R produced exactly the same result. Not a bubble to be seen! The moisture resistant covering must really work!

I usually use E7018. Just the garden variety stuff, no moisture resistant coverings, no H8 or H4, and the results are as you saw in my photograph.

The photograph I sent in the other day was taken about ten years ago. I've done the demonstration many times since then and never had the dismal results I had this morning. All I can say is that this is the first time I have tried the demonstration with pipe rod (with the brown covering) or moisture resistant covered E7018. The results were less than impressive. So, my conclusion is to try this with the E6010 that has the white covering (not the brown pipe rod) and use "Plain Jane" E7018. The results should be more impressive.

Best regards - Al
Parent - - By js55 (*****) Date 04-27-2007 20:24
Al,
The emotional impact of the demonstration speaks for itself. And your mention of oneof our colleagues working on this problem since 1941 speaks for itself as well, as we pompously struggle for a solution.
There is a mystery here. The outgassing is clearly related to the low hydrogen (or something related) condition. I cannot come up with any other variable. But it isn't acting the way it should, based upon current thinking. I'm hoping this thread doesn't stop here, that the experiments and demos continue, and perhaps we'll come to some conclusion even if its inadequate.

PS: I too am astonished at the idea of H2 moving through (clearly not so) solid metal.
Helium too, as some of the Aluminum guys I'm sure are frustratingly aware of.
Parent - - By darren (***) Date 04-28-2007 20:35 Edited 04-28-2007 20:42
and ladies and gentlemen we are only talking on the atomic/molecular level.

we are only beginning our scientific model development and have come no where near to any hard and re provable results. our children and their children will be speaking of the SUB ATOMIC aspect of the same dilemma. i can only imagine all the candid banter about bozons and gluons and all the rest. think of this threads development if we tried also to entertain quantum theory and the myriad of other  esoteric meta/quasi/unified theories that abound

on a very basic level there is 'stuff' and 'space' how much stuff is in a given space or how much space is in a given stuff is our basic understanding of density. science is only beginning to understand how little stuff ( in fact it might not even be stuff) there actually is and the incredible amount of  space (it might not even be space)there is. 
i realize that this is all tongue in cheek drivel, it is just to add some humor about how little we really know and how absolutely marvelous we are doing with that little knowledge.
to further exacerbate the funny bone. electrons are only tendencies, and in theory there could be only one electron and it is very very very busy. and we all think we are over worked and need a raise.

on a serious note in response to the thread. two questions that come to mind are if the weld was done on the bottom of a bowl shape and inverted in the oil after the weld had cooled would there be a small bubble in the top of the underside of the dome or would the gases rise and be trapped on the underside of the weld between the weld and the parent metal.(now topside of weld because the bowl has been inverted to a dome configuration) essentially are the gases being "squeezed" out or are they succumbing to gravity and rising out of the weld in the pictures we saw earlier in the thread. also what is occupying the space that the hydrogen used to occupy within the metal. if it is nothing then is the weld still shrinking by the amount of the volume of escaping hydrogen?

please keep the posts on this topic coming as it is real science and one of the best possible examples as to why these forums and indeed the internet are the greatest hope for our future
darren
Parent - - By 803056 (*****) Date 04-29-2007 17:40 Edited 04-29-2007 17:57
There's a whole lot of truth to your comments. We know very little about the world around us and how everything really works.

As I mentioned once before, I met a fellow that worked on the problem of why armor plate cracked when it was welded with regular steel electrodes. He spoke with me at length about this. His Doctorate degree was based on research on the solubility of gases in metals.  He came to the conclusion that the problems weren't the oxygen or nitrogen from the atmosphere. Those gases could be either "pushed out of the way" by proper shielding or counteracted by adding deoxidizers to the mix. Hydrogen was the culprit. He was able to minimize the amount of hydrogen introduced into the weld via the flux by changing the constitution of the fluxing elements.

He was working on the welding of armor plate in WWII. He found that if he welded the samples using what we would consider to be an E6010 electrode (cellulose flux covering) or an E6013 (rutile based covering) there would be cracks in the HAZ. Not a desirable thing if you are one of the crew members of that tank. If he welded the sample with a "fresh" austenitic stainless steel electrode (that used limestone based coverings) the samples didn't crack. However, if the ASS electrodes were left out on the bench over the weekend, the welds made with the exposed electrodes cracked in the same manner as the carbon steel electrodes. Hence he surmised that the secret was in the flux covering. He had some carbon steel filler metal coated with the limestone flux and the results were as expected. If the were made using freshly produced electrodes were fresh from the oven (so to speak) the welds and HAZ were crack free. If the electrodes were left on the bench and exposed to the atmosphere for a period time, the results were less rewarding with increased exposure times.

He said he was very happy to announce to the US Army that he solved the problem of welding armor plate and they thanked him for his efforts. Then they reminded him that the US was still at war with Germany and Japan and so he was still sworn to secrecy and was not to tell anyone of his findings. He asked why, after all, now it was possible to weld armor plate with carbon steel instead of austenitic stainless steel, a much more economical means of fabrication.

They told him that the Germans were welding tank hulls the same way the US was, with stainless steel electrodes. That required chrome and nickel. The Germans had limited amounts of each and it had to be imported. The US could limit the availability of the metals by sinking ships and blowing up railroad lines. The Germans had to make hard decisions on how best to use the strategic metals available. They could build tanks, rocket engines, and later, jet engines, all of which required chrome and nickel. The limited quantities of chrome and nickel limited their manufacturing capabilities. Meanwhile, the US essentially had unlimited chrome and nickel available and we didn't face the dilemma the Germans did.

Last spring I made a trip to the tank museum at Aberdeen, Maryland. I checked out some of the German tanks and sure enough, they were welded using stainless steel filler metals. They were shiny silver!

It was a great story to listen to and it seems to be confirmed by some of the reading I've done.

As to your last question, it sounds like a great experiment. I would expect the atomic hydrogen would take the shortest path of least resistance to the surface of the metal, what ever direction it should be. That being the case, the hydrogen would collect on the surface of the weld, on the bottom of the assembly in the case you describe. That is not to say there would be no hydrogen bumping along within the atomic lattice of the base metal substrate (now on the top). However, the path to "freedom" through the base metal substrate would be much long, more torturous, and it would take much longer for the hydrogen to see the light of day. I expect the laws of probability would dictate the bulk of the atomic hydrogen would appear on the surface of the weld due to the shorter distance traveled and the shorter time needed to escape the confines of the atomic lattice.

Now, let's get back to the real question of, "How many angles can dance on the head of a pin?"

I reread all the replies to this post from the begining. It was worth the time it took to reread all the comments. There are some questions raised that could keep us busy for many, many years to come. Now, who's buying the beer?

Best regards - Al
Parent - - By Stephan (***) Date 04-29-2007 20:38
Al,

I am so impressed about your way and ability to communicate and to demonstrate a way for making something visible, what is invisible under normal conditions. And thus to show also all those great people who are welding the future (who one else if not the welders?!) a combination of making something easily understandable which is - in its origin - extraordinary intricate. It has surely its reasons that a former AWS-President has begun to work on the problem already in 1941 and 66 years later we yet don't know all the peculiarities being responsible for that what we can observe. Therefore my truly congratulations!

I have been very busy over the last days and when I have opened up the AWS-Forum now after this longer period I have been captured immediately by this thread (is it a wonder?) or better by the way it took since the very first question has been asked and founded its origin.

I have (under the consideration that so many greatly appreciated fellows have already made their wonderful contributions) thought if it would even make sense to put up the thread for giving my - as you name it (I like the expression) $ 0.2 response.

But I am honest, the topic and its course over the time wouldn't certainly let me sleep calm in the future when not talking to you all about what has been discussed. I request your understanding...

I honestly hope to have interpreted the content of the high-level discussions correctly but when I read what has been discussed until today, there are three main but different questions meanwhile to be discussed:

1.  How can we know it's hydrogen escaping when the Bead on Plate-Welds being submerged underneath the test-agent (Baby-Oil) and not other gases or gaseous constituents?
2.  Why does the - let's suppose it is - hydrogen escape only from the weld-metal-deposit and not from the Heat Affected Zone?
3.  Does it make sense to use your experiment for visualizing the degassing of hydrogen from the weld metal deposit under the consideration of Hydrogen Induced Cracking and its mechanisms?

As you can imagine the topic itself and furthermore the outstanding good questions (as far as I have seen correctly) coming mainly from Jeff who has thus surely the main fraction for the (fortunately) thread's continuation, have busied my tiny brain to think about them.

Here is my humble attempt to express how I have dealt with the different stated queries.

Ad 1: "How can we know it's hydrogen escaping when the Bead on Plate-Welds being submerged underneath the test-agent (Baby-Oil) and not other gases or gaseous constituents?"

I have tried to find a way to an answer by having a closer look onto the physical properties of the different gases been named in one post. Additionally I have tried to consider what you have already mentioned in one of your replies to not repeat what already has been said and certainly understood. Therefore I have focused my interest on the differences in the atomic structures of different gases like nitrogen, oxygen, or e.g. Helium as that element, following in regard to its size directly behind the hydrogen. Before talking about the ability of these different gases to diffuse through solid matter or to have a closer look how much the atomic distinctions between the named gases are, I would have a short sidestep to the answer:

"What is diffusion, actually?"

My intention is - as meanwhile should already been known in the forum - to try to understand the natural (physical) sense of everything we experience and are confronted with in welding and to use terms not only because it sounds good when they are used, but wanting to know, what kind of function is hidden behind the term. And as always, the mechanisms of what "Diffusion" really stands for, are once again too complicated to be treated here. When I have considered about finding nonetheless an "easy" explanation for "Diffusion" I had the idea to fall back on a man surely everybody may know in the forum: Albert Einstein! Einstein was namely one of the famous wizards who have already long time before I was born, a closer look onto what the inner mechanisms in metallic materials are. He researched in particular on theories to explain the inner torsion within metals and sequences where properties like "Relaxation" can be explained with. Thereby he created a model whereupon those observations could be described with. Within these theoretical structures he defined also what "Diffusion" can be treated as. In simple words Einstein said:

"The act of elementary diffusion is to be seen as a stress-induced transfer of a resolved atom from one to another (adjacent) position within a defined period of time."

Truly simple, isn't it?

O.K. He has presumably used lots of mathematic formulae to prove what has been stated in this simple sentence above, but this should be of no more interest here. The crucial point further is, that he has also found out something interesting with regard to what has been discussed or posted, respectively, by you. Namely the fact that the extent of diffusion has to do with the metals microstructure the diffusion is occurring in. This can be expressed by the coherence of how many adjacent atoms the resolved and diffusing atom can take in and I do not want to treat this deeper here. Simply expressed does this mean, that the higher the package-density of the base metals microstructure is, the lower is the likelihood that an atom can change its position. Therefore diffusion in body-face-centred cubic microstructure metals is hindered more than in body-centred cubic microstructure (strongly simplified). What should be noted at all until here is the fact that diffusion is an expression for how induced ENERGY can improve the movement of atoms or molecules within solid or gaseous matter mostly to create a balance of all different elements being contained within the matter. How ever the energy looks like, it doesn't matter at all, since energy is and stays - of course - energy and exists only in different states.

Under considering the hitherto stated, I would like to come to the specific atomic differences between the gases been named within the thread. Subsequently I have collected only one single interesting value for the gases Hydrogen, Helium, Nitrogen and Oxygen which are from my point of view certainly the most interesting gases in welding and in coherence to the original topic here, to be focused on. The "relative mass" of their atoms. These are for:

Hydrogen: 1.0078
Helium:  4.0026
Nitrogen:  14.007
Oxygen:  15.999

What is so interesting at these values? Well, as you have also already stated, it is an evidence for their atomic size. As Bill has described, atomic hydrogen consists of 1 Proton and 1 Electron, nothing more. Other states of matter are the Hydrogen-isotopes "Deuterium" consisting of 1 Proton + 1 Neutron + 1 Electron and "Tritium" consisting of 1 Proton + 2 Neutrons + 1 Electron. By the way, Deuterium is being used for nuclear reactors by being the moderator-liquid (heavy water = D2O).

The - for me personally - interesting on hydrogen, in regard to what has to be discussed (is it hydrogen what we can observe in the Baby-Oil) is the fact, that hydrogen exists under normal circumstances only molecular (as H2) but not atomic.
What has been proved is the fact, that hydrogen is being resolved in weld-deposits in its atomic state of matter and thus having the highest ability to move through the solid matter, or the metal's lattice, respectively. Due to the extremely low size and mass of its atoms the hydrogen's ability to move within solid matter is a few decimal powers higher than for any other element!
But however, there must be hydrogen, at least in its molecular state of matter, since this element does its dirty deeds in Hydrogen Induced Cracking, where I would like to come to later on. This means basically that the hydrogen which is contained within the moisture (water = H2O) and this again being attached to the electrode covering or SAW-flux must be separated while welding. And it does so - of course, otherwise we would not need to talk about herein. How does it work..? Just comparable to any other reaction within the beloved tool we are working with day by day - the arc! By "providing" energy to the water-molecule coming from the electrode-covering or SAW-flux when the arc is being ignited and the plasma is being formed, the water-molecule is being "broken up" (nice term Al!) or dissociated first. This needs an energy of 572 K Joule/molecule and can be expressed simply by: 2 molecules of water (2 H2O) + Energy = 2 molecules of molecular hydrogen (2 H2) + 1 molecule of Oxygen (1 O2).

Or clearer: 2 H2O + 572 kJ = 2 H2 + O2. 

What we have now is molecular hydrogen H2 which is relatively stable in its state of matter. The next step - and also this occurs - is the splitting (dissociation) of the Hydrogen molecule within the arc's atmosphere. Therefore once again energy has to be induced to separate the molecule into its atoms. This specific energy is 428 K Joule/molecule hydrogen. Not less, isn't it? But there is enough energy within the arc plasma to perform this. After that we have atomic hydrogen within the arc atmosphere which is subsequently resolved by the liquefied weld-metal. A liquid iron-melt can resolve remarkable amounts of hydrogen whereas solidified iron can only resolve very low amounts of it.  By the way, under normal conditions, e.g. when an H2-molecule is separated by electrolysis, the atomic state of hydrogen is only extremely short termed, since atomic hydrogen exists only a time of < 1 second(!) before it recombines to molecular hydrogen again (the chemists speak of a "statu nascendi" which means that the element is atomic and thus reactive in a high amount only in the moment it is generated - at least as far as I have heard that a long time ago from a very good colleague who was a chemist and due to I liked it I have noticed it at that time).

O.K. so far so good. What about the question if it is hydrogen or - perhaps - other gases which we can observe gassing out into the test-agent Baby-Oil. Well, as far as I interpret correctly what I have learned, it must - at least in the very largest fraction - be hydrogen. And this has - from my point of view - amongst many others the following main reason. Of course the arc's energy is used for dissociating and ionising different fractions of gases - otherwise we would not achieve an arc plasma. But - please remember the data stated above - these gases have (also Helium) much higher atomic weights or masses, respectively. And thus their molecules have a multiple mass or size compared that of hydrogen. Even Helium, which is an atomic inert gas, thereby non reactive like hydrogen and thus absolutely not comparable with that, has ~ 4 times the mass of atomic or twice the mass of molecular hydrogen. I do not treat further on Helium here, because - as mentioned above - it's non reactive, used mainly as a shielding gas and only in negligible values in the surrounding atmosphere. It should be treated only due to it is the next larger atom after hydrogen. Coming to the next important gas - Nitrogen. As can be seen, nitrogen has a mass of ~ 14 times the mass of hydrogen(!) and next higher oxygen which has a relative atomic mass of ~ 16 times that of hydrogen. Due to both elements form molecules one can see that their masses are twice the values I have mentioned. Namely approx. 28 times that of hydrogen in case of Nitrogen and approx. 32 times that of a hydrogen atom in case of oxygen. Thereof one can derivate approximately the size of the gas-atom or molecule. This again leads finally also to higher levels of energy necessary for their diffusion. Furthermore, and I guess this is a crucial point at all, these mentioned gases (Nitrogen and Oxygen) are strongly disposed to create compounds with different elements the base- or the filler-material is alloyed with (e.g. Manganese, Silicon, Aluminum, Titan...). This is well known as these elements are deoxidising and denitrifying. The named gases are thus strongly bound and - as far as I interpret it - only to be separated from these compounds by inducing high levels of energy into the material to split the gaseous molecules from them and to enable them to effuse out of the material by diffusion caused processes. Therefore it is my interpretation that the very main fraction of what can be observed in the Baby-Oil is hydrogen and not other gases been dealt with above. Finally "Diffusion" is - in terms of its technical definition - a statistical process by coincidental particle motion, but not a process being caused by mechanical forces. This atomic particle movement - within the solid matter - enables the low sized hydrogen to diffuse through this matter and to escape through the surface into - in case of your experiment - into the Baby-Oil and thus to be visualized. Not for nothing your method has been comparably standardized on different national levels, only using defined test-conditions, e.g. using Glycerine (Japan) or Quicksilver (Germany) instead of Baby-Oil, to achieve repeatable results in determining the hydrogen-contents of the weld-deposit. Much more accurate however is the method of using gas-chromatography for determining the diffusible hydrogen-content of a weld-deposit. Finally I would like to compare the already mentioned low resistance the hydrogen meets on its way through the solid matter with electron-beam-welding conditions (although it is a bit ventured). Why is it possible to achieve the deep-fusion-effect when using EBW? Simply expressed, because the elementary particle "electron" can move through the vapour-capillary which has a lower density compared with the solid state of the to be welded base material. This again reduces the amount of resistance the electron meets on its way through the material by decreasing the probability of collision with other particles. Hydrogen - farthermost comparable to this - meets only small resistance on its way through the lattice and thus is escaping through the materials surface.
There is, by the way, a direct relationship between the concentration of the resolved hydrogen, its balance-constancy and the surrounding hydrogen's partial pressure. This has been expressed by SIEVERT and proves that the coherences between the molecular hydrogen's pressure (e.g. in the area of fisheyes) and the atomic pressure do stand in a stringent relation to each other. 

Ad 2. "Why does the - let us suppose it is - hydrogen escape only from the weld-metal-deposit and not from the Heat Affected Zone?"

First of all in regard to this question - as far as it is allowed to ask it so - I don't know if the hydrogen, as we assume, is only coming from the weld-deposit and not from the adjacent Heat Affected Zone - at least from small areas of that. But by having a closer look onto what kinds of factors have to be fulfilled that hydrogen can escape from the weld-deposit may clarify a small part of this question. Firstly it should be allowed to ask: "When do we recognize Hydrogen Induced Cracking?" I guess - but I request you to correct me if I am wrong - only when we have to weld "critical" steel-base-materials (High Strength Low Alloyed and others). What I would like to do is first, to have a closer look onto the conditions being existent when the base-material is welded by using SMAW. I fully agree with Jeff who has mentioned that "...box cars of unheated cellulose coated weld materials..." are welded every day, without a threat to weld metal strength. Now I have tried to find out - although I have already known that cellulose electrode weld-deposits have much higher hydrogen contents compared with properly treated basic electrode weld-deposits - accurate data to be able to compare both values to each other. What I could find were mean values for the weld-deposit's hydrogen-contents:

Cellulose covered stick-electrode:      ~ 40 cm^3/100g weld metal
Basic covered stick-electrode:      ~ 10 cm^3/100g weld metal
Low-Hydrogen basic covered stick-electrode:  <  4...5 cm^3/100g weld metal

It was impressive for me to see, that the cellulose electrode's weld-deposit contains such a high value of hydrogen, but on the other hand it was not dramatically surprising, since - as Jeff already told us - these kinds of sticks need a definite amount of bounded water or moisture, respectively, to work properly. Under the consideration of what has been discussed on a high level within this thread and in particular to the attempt to reply the question "2" one should have a view on the possibilities the hydrogen can be resolved within the material. Therefore one should firstly clarify where the hydrogen has its sources to be resolved subsequently. These, or better some of these, are:

-  Electrode coverings (or SAW fluxes) being afflicted with moisture. Here one has to consider, that there are two different mechanisms to be observed. Crystal-Water which has "only" a kind of surface adhesion to the cover or flux and chemical absorbed water, being deposited into some covering compounds structure on a molecular level. Whereas the first "Crystal-Water" can be removed e.g. by re-drying the electrodes, it is nearly impossible to remove the chemical absorbed water and thus hydrogen from the substances mentioned above. This - as far as I know - is also the reason for the impossibility to re-dry cellulose electrodes since they consist of organic substances - even cellulose - being used for generating high amounts of shielding gas constituents while welding, thus protecting the weld bead by that and to compensate the lack of slag constituents. If one would try to remove the hydrogen by re-drying cellulose electrodes he would destroy the covering and the electrode would be unusable subsequently.

-  Hydrogen containing substances and pollutions on the work-piece's surface having no been removed by cleaning and e.g. preheating.

-  In case of SMAW the actual humidity the welding process is being performed.

O.K. now we have the sources the hydrogen can come from. What is significant here - from my point of view - all these sources were activated by the welding-process by itself. For winning the hydrogen from the source its being "built-in" we have to start the welding process - of course. What happens next..? Yes, strongly simplified by my way of treating the problem, it is being mainly resolved within the weld-deposit, since this is the place which has the state of a liquid phase and as already described by you in a great and understandable way, this phase is able to resolve it, as long it is simply liquid. First with increasing solidification of the melt its solubility for hydrogen decreases significantly. Is there an imbalance between the speed the melting-bead solidifies and the speed the hydrogen tries to escape from the melt - while its solubility is decreasing - exactly this what you have already explained - occurs, the hydrogen is being resolved forcedly within the weld-deposit. So - please correct me when I see it wrong - the likelihood to find high amounts of hydrogen is greater for the volume of the deposited weld-metal than for those areas of the component where hydrogen has not been resolved since these have a strongly reduced solubility by their solid state of matter. Now we have a problem. We have - depending to the surrounding conditions - high amounts of hydrogen contained within the weld-deposit. But help is on the way... And this, dear Al, at least as far I interpreted what you have proved, you have shown it. By using your brilliantly head, your ability to weld(!) and a filling of Baby-Oil!

Please let me resume...

From my point of view we have two entirely different problems to discuss, the first - of course - is the fact of hydrogen being attached to substances within the electrode coverings or to SAW-fluxes and the second is the hydrogen being responsible for what Jeff has mentioned several times, Hydrogen Induced Cracking - truly a hard stuff!

I would like to give you an insight why I think that these are actually different but however, inseparable problems. What happens when you are going to quench the weld directly after welding? Yes, I fully agree with you, you take care for capturing the hydrogen within the weld-deposit before it can escape. But... on the other hand, what happens then? Well, it was great to read from different results many of the greatly appreciated fellows have achieved when repeating your experiment. This speaks for the hard calculability of some natural - or better - physical processes. And by the way, I guess this is also of the reasons for using gas-chromatography for determining the hydrogen-content of weld-deposits meanwhile. To understand what I mean. We have - although we are talking about hydrogen being responsible for both, the bubbles in Baby-Oil as also for Hydrogen Induced Cracking - two different sequences of how this hydrogen can work within the weld. Therefore one can distinguish:

-  Diffusible Hydrogen and
-  Residual Hydrogen

Now it is going to become a bit tricky. What is diffusible? We have yet heard that the resolved hydrogen is so small in its size that it is no problem for it to move through solid matter - otherwise we would see no bubbles in Baby-Oil. But now we are talking of hydrogen which should reside within the metal? Sounds ridiculous, but it truly isn't. Everything what has been said until today - at least in my humble opinion - within this thread is showing in the right direction and deals with lots of single parts of the complex puzzle.

Hydrogen can only diffuse when it's in its atomic state and the short times it exists under "normal" conditions (< 1 s) indicate its endeavour to react with any kind of other atoms. My interpretation (you know I am no chemist) is that by having now both, the lowest size of all atoms at all + an extremely effort to react with any similar (to recombine to molecular hydrogen) or other atoms, the kinetic energy of the hydrogen atom and thus its partial pressure is higher that of the surrounding metal structure. This means, it must "find a way" to reduce its own free energy and escapes through the solid state of matter (weld-deposit) to eliminate the energy-imbalance between the inner weld-deposit and the outer atmosphere. So far my interpretation of an explanation why the main fraction of diffusible hydrogen is escaping from the weld-metal. Additional to that here one can find a relative inhomogeneous cast-metal-structure and not a rolled one as mostly to be found at the sheet-metal-base-material, just as mentioned by Allen. The rules of diffusion again say that the compensation of any atomic imbalance has a negative algebraic sign which means that - comparably to thermodynamical processes where the heat is always moving from the hotter to the colder region - the direction of compensation is always from the higher atomic concentration (within the weld-deposit) to the lower atomic concentration (outside the workpiece' surface. Or as you have already described it in your post, it will take always the easiest way to move or the way of lowest resistance - as everything in nature! What should that mean now..? Well in my interpretation the nature itself takes a wonderful care for the main fraction of hydrogen been resolved within the weld-deposit, by sending this main fraction of atoms out to find an easy way through the solid state of matter to effuse through its surface. By the way, I have read once an article dealing with the mathematical calculation of hydrogen-distribution within a weld-seam. As far as I remember well, there could be a kind of a "GAUSSIAN-Distribution" (hump-curve?) be observed over the cross-section of the seam. This means, there could experimentally be found a relatively homogenous increase in hydrogen content with the increasing volume of weld-metal. The peak could be detected in the centre of the seam, where the depth of fusion was at its maximum.

O.K. but what about the Hydrogen Induced Cracking? When everything would work perfectly and the natural processes would completely take care for removing the hydrogen from the metal, we would not need to talk about this problem. But however, we have to. And here I would like to come to even this amount of hydrogen which does not remove from the weld-metal and which will however reside in the material although no more bubbles can be observed in the Baby-Oil. And even this fraction of hydrogen - in Germany we use the term "Residualer Wasserstoff" - is trapped within the material and takes - unfortunately - care for a delayed, or hydrogen induced (cold)-cracking. Of course the imbedded hydrogen has a statistical motion within the material (with a tendency to escape from the material). This means, so far my interpretation, there is a finite likelihood for the atom to move in any direction it is possible to move to. But also here, the driving force of any activity of the atom is the effort to minimize its own energy-level by reacting with other atoms or by finding places within the material where a reaction can lead to even this energy-level reduction. And there are even these places within every metallic material being used by all of us... Yes, all the microscopical and sub-microscopical "faults" like grain-boundaries, dislocations (in particular!) etc. etc. or - restraint created microstructures like Martensite and other high-energy-level microstructure standing under strong tension-forces. 

I have set "faults" in quotation marks since without - particularly - the dislocations we would not achieve those material properties we are able to achieve today. But I am sure that this is more than well known, therefore I do not treat this further herein. Nevertheless, it is important to have a view exactly to these regions in every practical metallic base material. Since these are the regions showing likewise imbalances on the energy-level. Normally these "distorted" microstructure areas of the material have higher energy-levels compared with the rest of the crystal and also - comparable to the hydrogen as mentioned above - trying to achieve a reduction of their free energy. And how can this reduction can be achieved (amongst others)? Right.. e.g. by bonding hydrogen atoms to their boundary areas! By doing so both occurs, on the one hand the free surface-energy of the distorted phase-boundaries is being reduced by bonding atomic hydrogen and on the other hand the atomic hydrogen can recombine to its molecular state - and... looses its ability to diffusible move through the material! The areas within the material are called "Hydrogen-Traps", probably basing on their strong endeavour to catch atomic hydrogen to minimize their free energy-level.

Now one could ask, due to there are of course different "traps" being able to capture the atomic hydrogen: "Are there also differences in their strength to bound the molecular hydrogen?" Yes! Basically the kind of energy attaching the hydrogen and let him recombine to its molecular state is called: "Bond-Energy". In order to give a better understanding I have tried to find out the levels of these specific energies for different hydrogen traps, please see also the attachment "Kind_of_trap_pdf".

I do not want to treat the kinds of traps to keep it furthermore simple. But what can be seen from the different bond-energy-levels cohering to the different kinds of hydrogen traps, the hydrogen is being strongly attached to a lot of traps.

To shorten the post - what about the lots of theories of Hydrogen Induced Cracking when welding higher strength steels and the attempt to reply the question why the hydrogen is degassing mainly from the weld-deposit? From my point of view a bit of my interpretation should show the most bubbles may be observable and escape from the weld-deposit. Due to the bubbles show the amount of hydrogen, not been trapped within traps as mentioned above. And these bubbles stand mainly for the diffusible hydrogen. Let us assume that an amount of hydrogen is being trapped in a particular region of the Heat Affected Zone, either the coarse grain zone or e.g. the zone of Martensite. Both regions show strong distortions in the free energy level and are thus preferred to be targets for the atomic hydrogen. Here it is captured and it would take high levels of energy again to resolve it again from these regions and much higher amounts of energy to gas them off from the material due to they have now the molecular state of matter - it becomes residual hydrogen. Therefore - but this is my very own interpretation and once again, I request to be corrected if I should be wrong - I guess no bubbles from especially these regions can be observed escaping into the Baby-oil.

Hydrogen Induced Cracking whereas takes its beginning when those amounts of hydrogen been diffusible first, were trapped, recombine to their molecular state and are concentrated in the regions of the traps. SIEVERT again has shown, that the height of molecular hydrogen's partial pressure can increase extremely within hollow spaces. There should exist an interesting theory for the explanation of Hydrogen Induced Cracking, coming from TROJANO.

As Jeff already explained, to induce a cold-crack three different requirements must be met. Hydrogen, Tensions and a sensitive microstructure. All these three are dependent to each other, i.e. the increase of one of them leads to a decrease for the others. Shortly concluded the TROJANO theory says, that due to the higher solubility for hydrogen in e.g. Martensite, the total amount of hydrogen is increased. Thereby the amount of necessary tensions can be decreased. Stands the material under continuously critical stresses and an increasing concentration of hydrogen in a specific critical trap-region, after a so called "Incubation"-time a small material's fissuring can be induced due to the increasing hydrogen's partial pressure in this region. Through this fissuring the pressure is being decreased again and the crack continuation stops. As heard hydrogen is being concentrated preferably in regions of highest amounts of 3-axial tensions. These regions are proven to exist directly before the crack-tip. Hereby once again the concentration of hydrogen is increased, the pressure increases and a micro-crack evolves. By "melting" both, micro-crack and the already existing crack-tip, the crack continuation is enabled...

Only one of different theories and I agree with you, stuff for many future years.

Finally I personally suppose due to the relatively high amounts of bond-energy and due to recombination to its molecular state the hydrogen can hardly escape from the specific regions of the Heat Affected Zone. But if I am right by this interpretation I am not able to say...

Ad 3: "Does it make sense to use your experiment for visualizing the degassing of hydrogen from the weld metal deposit under the consideration of Hydrogen Induced Cracking and its mechanisms?"

From my personal standpoint I am - to repeat myself - greatly impressed of what you have shown and explained through this thread. When I interpret it right, the experiment has been dedicated to visualize something what is invisible under normal conditions and to show in an easy way what works within the weld. By this, one can receive an impression of an element having the smallest atom at all and its endeavour to react what ever it takes. Finally every other atom of the periodic table is being founded on and built of hydrogen.

I have been remembered on another most famous physical experiment, while reading your posts. The "Bubble-Chamber". As you perhaps may know a famous US-American born in Cleveland, Donald Glaser, who has received the Nobel Prize for inventing this "tool", had the idea after having had a few glases of beer together with his colleagues. While they have sat around one of his colleagues should have said, that Nuclear Physics should as be so easy as the tracks of the bubbles in the beer can be observed. That was the birth for Glaser's idea to think about making gamma-rays (purely energy) observable! 

In how far your experiment is usable to predict the exact amount of diffusible and residual hydrogen being trapped within the weld-deposit is certainly another question. But from my point of view this question should not being asked - and probably was not planned to be asked - in the coherence with the posts been stated in this thread. I - just as all the other appreciated fellows - am and have been astonished by your outstanding expertise and your ability to explain complex technical issues in a very understandable way.

Therefore my honest thank you and - if I would meet you personally - I would buy the beer!
You have deserved it!

Regards from Germany,
Stephan
Attachment: Kind_of_trap.pdf (14k)
Parent - By 803056 (*****) Date 04-29-2007 23:16
Hello Stephan;

You certainly tied up some loose ends and you answered a lot of question I've had bouncing around in my head.

I wouldn't know where to start the search to find the detailed information you presented. I truly enjoy hearing how the mechanism works. When you know the details, it usually is pretty simple.

Thanks for the compliments and thank you for the information you provided. I'm sure many of us enjoyed your response. It is amazing how a little atom can instigate so many problems and yet it could possibly be the answer to many of the energy problems we face today. It is a crazy world out there and there is just so much to learn.

If I ever have the opportunity to travel to Germany, I will let you buy the beer because you will know which beer is the best one to drink.

Bellaru, I can't remember a question on this forum that has generated the interest or the transfer of information your question has. An apparent simple question of "what is it about low hydrogen electrodes that enables you to use a much lower pre-heat.....?" has led us on a merry quest for more and more information. You have managed to spark the interest and response of an international audience.

Yet, did we actually answer your question?

Best regards - Al
Parent - - By ssbn727 (*****) Date 04-30-2007 20:38
Hi Stephan!

Should'nt the person that wrote the kind_of_trap.pdf have also included oxygen with the interstitionals?

Just curious.
Great response btw... As usual you're not one that's conservative in your interpretations... In other words meticulous as usual!!! This is a compliment in case you're wondering!!!

Respectfully,
Henry
Parent - - By Stephan (***) Date 05-01-2007 18:55 Edited 05-01-2007 21:09
Henry!

Once again I would like to thank the American Welding Society for enabling the Forum!

To quote yourself, Henry,: "You hit (once again) the nail right on the head..", by asking this interesting question.

The person who has prepared the (simple) pdf is no one else than the person who is currently typing these characters into the keyboard of his notebook. I hope you may agree with me when I say, to create a simple pdf, containing data which others have collected by using their specific Know-how and specific equipment or hardware to finally find what they are looking for, is certainly no problem. I have found these data by searching  lots of lots of hand written notices (hard job!) I have scrawled down on an infinite number of sheets and pieces of paper over the past years. Do you know the peculiar feeling to be sure that you have something special written down anytime ago and to know that you haven't thrown it away (since you have never thrown, and will never throw something away) but to not knowing where to find it?

With regard to the bond-energy of hydrogen traps I have found these data some years ago by having read an article in the German Welding Society's Journal "Schweißen und Schneiden". Besides the data, I unfortunately have only noted the names of the scientists who have conducted specific investigations with the target to find a mathematical way for calculating the amount and distribution of hydrogen within the weld-deposits of basic and rutile covered electrodes under additional consideration of a Weldment deformation. The project at that time was a cooperation between the very famous "Institut für Schweißtechnik und Fügetechnik (ISF)" of the German University of Aachen under the management of the venerable and famous Prof. Dr.-Ing. Ulrich Dilthey and the Ukrainian PATON Welding Institute under the management of Prof. Dr.-Ing. Konstantinowitsch Pokhodnya. In particular the German ISF has carried out - as far as I know - lots of cooperative projects together with the Russians since - please correct me if I should see it wrong - there is certainly no other institute in the world being comparable with them in regard to the explicit mathematical treatment of welding and all arc-welding sequences. The US-American (MIT,...) institutes excepted - of course.

O.K. the longer the speech the short sense.

You are right Henry, the element Oxygen is missing under the interstitials and I could not find data on this element in a coherence to the topic we have discussed (Hydrogen-Traps).

Only with view on the atomic properties of oxygen (recognizable from the periodic table of elements) it should have the ability to be resolved interstitially. And yes, at least as I know, some (quite low) amount of oxygen is soluble interstitially within the metal's lattice. And further, following the rules of thermodynamical balance, above this interstitial soluble amount, other constituents being formed (Oxides etc.). Here again specific elements - having a high affinity to the oxygen - are used to deoxidise the metal. But I would like to come to this specific issue later on.

I have hardly thought about your question (I willingly admit... I always do). I am sure that one who would have studied chemistry would friendly smile and would be able to reply immediately.

But (fortunately?) I am no scientist at all, I am happy to be a welder.

Therefore please find subsequently my humble ideas of what I think about...

The first I have thought about: "Why is oxygen not mentioned under the interstitials?"

Well from my point of view, the easiest way to reply may be, they simply have forgotten it, or they have presumed that also other elements having the ability to be resolved interstitially within the lattice, were commonly well known and thus, the listed elements would represent only a reduced "collection" of interstitials.
Due to I suppose that these outstanding experts as named above would surely not forget any important item or aspect with regard to a complete view on the subjects treatment, I would like to prefer the latter - of course not being sure if I am right at all by supposing that.

O.K. under presuming the mentioned above I have then thought about the element oxygen and if this element should be contained within the row of interstitials. Therefore I have tried to put on where a clear physical differentiation of the interstitial - including oxygen - would be able to conduct. First I had a view on their chemical characters. There we have three solids (Carbon, Silicon and Titanium) and two gases (Nitrogen and Oxygen). Next step was a closer look onto their chemical characterisation (valences, possible chemical compounds,...) - but always under the consideration that hydrogen is playing the major role in all considerable sequences the elements could be treated by.

I could find out what surely you and every other appreciated fellow in the forum would likewise have found out. There can different compounds being formed by all mentioned interstitials in combination with (atomic) hydrogen. I interpret this by the fact that atomic hydrogen is one of the most reactive elements and thus probably comparable to some elements of the 7th main group of the periodic table of the elements - the group of halogens.

O.K. with regard to the list of the mentioned interstitials we have thus

-  Hydrogen contaminated Titan(-Carbide?)-Compounds (solid)
-  Silicon-Hydrogen Compounds (e.g. Silanes = solid)
-  Carbon-Hydrogen-Compounds (e.g. CH4 = Methane = gaseous)
-  Nitrogen-Hydrogen-Compounds (e.g. NH3 = Ammonia = gaseous) and... a well known
-  Oxygen-Hydrogen-Compound (H2O = Water = liquid!)

Can you read my thoughts?

I am honest. I have tried to find out by having a deep look into my literature of chemistry (complex stuff) to clarify firstly for me personally the sequences and mechanisms for the formation of metal-oxides. I had the feeling - at least as far I can estimate this for myself - to have understood a significant portion of how specific sequences work and what the fundamentals for these procedures are. But I have learned a invaluable lesson a time ago which I will certainly never forget in my lifetime (you have been my teachers). It would make absolutely no sense to put some tricky formulae into a post although it would be helpful for treating the subject of matter but no one wants to read that and is willing to study the details further on. Just like Steven Hawking once should have said: "One mathematical formulae within the book, reduces the number of buyers of the book by the half!"

Therefore I have considered about the mentioned mechanisms, to find a way to express what I personally think and what my problems at the inclusion of oxygen into the list of interstitials are.

I truly hope that there might be one of you who could give me a hint for letting me sleep calm again, because you, Henry, stroke something what I have not considered before my participation in this great thread.

Cohering to what Christine said, the physical-chemical forces holding the molecules (themselves) being formed together are quite strong ones. But the forces holding together the molecules to each other again are relative weak ones (see the water-molecule). Now I have a few problems - truly! What I would be interested in, are the subsequent questions.

In particular considering "Oxygen". Pure Iron has the ability to resolve a specific amount of oxygen which is - as usual - strongly depending on thermodynamical influences. When changing the composition of the base-metal (Iron) by e.g. alloying different elements to it or by having - unwillingly - trace elements within the iron, the solubility for oxygen is drastically decreased. Now my obstacle in thinking about the "interstitial" element Oxygen. What means interstitial solution with regard to the formation of Oxides? Does it mean the interstitial locations have to be "filled up" up to a specific thermodynamical limited threshold value, and first after that compounds like the known (Iron-)Oxides are formed by an imbalance or supersaturation, respectively?

Or, is Oxide formation to be seen as only an interstitial solution of oxygen within the lattice of the metal? This means, when considering the latter, the Oxides were a result of the interstitial solution.

This question could of course also be asked for the other "interstitial" Hydrogen-Traps.

What furthermore is interesting from my point of view. What about the state of the oxygen when it is resolved by the lattice (ideal solution?)? Is it - comparable to hydrogen - diffusing in its atomic state to, and forming Oxygen-molecules after finding, its place on the interstitial locations?

Only then - as far as I interpret it - the atomic hydrogen would have the "chance" to couple onto the Oxygen molecule (being interstitially resolved into the metals lattice) and to form... WATER! Even the liquid state of a Oxygen-Hydrogen-Molecule! And this is - compared with the other interstitial traps - a unique behaviour. We would have to find water within the Weldment - at least in these submicroscopical regions where the Oxygen is being interstitially stored in the lattice -  and I really do not know if we would when we would start to search for...

Whereas, when the Oxygen is forming Oxides by supersaturation and thus being in its molecular state, its valences were saturated and the hydrogen again would not have the chance to be coupled onto these already existing compounds. Since it is proven that different elements have a strong affinity to oxygen (deoxidisers) these compounds would not be split up by the hydrogen on its path through the metal.

Oh Dear, my head is spinning around.

Finally... basically Oxygen should have the chance to be listed under the interstitial elements. But due to Oxygen plays such a very unique and special role in coherence to hydrogen by forming water with it, I am not sure if it would not have been the reason for the Professors who have investigated the hydrogen-trap bond energy to not integrate it into the row of interstitials. Only my very own speculation!

Perhaps one of you great ladies or gentlemen may take my hand and show me the way to where the knowledge is..!

Therefore my hearty "Thanks" in advance...

Best regards,
Stephan

P.S. Thank you Henry... You know what for!
Parent - By js55 (*****) Date 05-02-2007 17:10
I didn't read all of Stephens post but I will. I wanted to comment on something at this point which ties into a comment by AL.
I'm not sure the BCC/FCC point matters. The H2 diffusion will not rely on movement through these matrices, it will diffuse predominantly through grain bondaries. These grain boundararies formed as the growing BCC/FCC/HCP matrices meet each other can create large linear (linear though quite torturous) voids (quite large in relation to the size of a hydrogen atom, in fact, large enough that many other things can move through them as well, like low melt eutectics (as the backfilling phenomena of nickel alloys testifies), carbon, etc). These are essentially integranular Interstate Highways.
The other thing is, the hydrogen would know no preferrable direction. Its inertia would take it up, down, left, right, wherever. At least until entropy began to spend its energy and the influence of gravity began to have an effect. Gravity effects most everything eventually, as testified by my aging appearance.
And though the hydrogen would find itself in the BM much like a rat in maze huntin for cheese (some getting trapped-the dangerous some) much would find its way out.
Parent - - By jwright650 (*****) Date 05-10-2007 10:34
Lawrence,
Have you retried your experiment yet? Just wondering.....
Parent - By Lawrence (*****) Date 05-10-2007 11:58 Edited 05-10-2007 12:02
John,

I have suddenly found myself very busy. (the good kind of busy) A grant proposal we have been working on appears to be approved, which means I may have a full time faculty partner next fall and credit classes going in the evenings to help support local industry who need welders so badly (more on that later)

Since classes last week were focused on GTAW aluminum and I had wondered aloud if we might see similar results in overheated, poorly prepped aluminum, I was able to do one more test.

I took a piece of 6061 1/8  no surface prep and ran a very slow fillet with ER4043 filler. The result was the expected "grainy" surface on the weld face, especially at the weld termination.  This sample I plopped into the mineral oil with no results whatever.

My Guess is that either the Hydrogen degasses very very quickly and simply leaves the grainy surface or it is held within and cannot migrate interstitally in aluminum.  Not being a mettelurgist I don't really know anything.

Edit:
Now you have me wondering about a comparison between poorly stored E7018 welded to gague metal compared to GTAW.......We shall see
Parent - - By Gunther Date 05-05-2007 08:20
JA

No har intended.
But I am sure you know the type I am talking about here.
Parent - By JA (**) Date 05-06-2007 03:11
no problem Gunther , no problem at all..........and "yes" , i do know the type........
Parent - By bellaru (*) Date 04-30-2007 02:57
i even did it with E71-T-8,,,,,,,,,,,it has been sitting outside in the LN25 for days........only a few bubbles then nothing.........

it seems the FCAW wire held up real good..........
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