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