Sciencemadness Discussion Board - Welding and Chemistry, Can you teach me?

Welding and Chemistry, Can you teach me?

Sedit - 14-6-2010 at 16:01

I started a job as a welders assistant today and im going to undergo long hours and on the job welding traning leading to certification. I know this is abit like spoon bending at the moment and infact it sort of is but I will indeed be doing my own research in the process no doubt. Sadly long hour and long commute will leave me alot less time then I wish to study up on it.

So what is the chemistry behind welding? Oxidation reactions to be expected, mineral content of dross, techniques ect....?

Anyhelp would be greatly appreciated because im pretty much going into this as a complete greenhorn with alot riding on my sholders since the tanks we are welding are large Stainless steal(I assume) tanks for use a containment vessles in Nuclear reactors. Needless to say if they fail inspection which will be very complete it will be a major setback and we must complete by october.

At the moment my main dutys will more then likely be grinding the welds in preperation for polishing. If I go to deep the failed inspection rest on my head.

So I know we have more then a few people with welding experiance and being the chemist you are im sure you could not resist figuring whats going on deep inside as the two, sometimes disimular metas combine.

gregxy - 14-6-2010 at 16:46

If its welding, hopefully there won't be much chemistry going on

.

For metals like stainless steel, aluminum or titanium a TIG setup is used (tungsten electrode and argon or helium shield gass). You draw an arc between the tungsten electrode to melt the metal and the inert gas keeps the oxygen away. The metal just melts and reflows. Sometimes welders play tricks with the voltage polarity to strip of as much of the oxide as possible while the weld is being made.
Critical welds may be done entirely in an inert atmosphere.

Dissimilar metals are usually soldered or braized instead
of welded. (but never for high strength work).

Properties of metals (coefficient of thermal expansion, thermal conductivity, melting point, reactivity ) are important to know. For example aluminum is an excellent thermal conductor so it requires a much higher current to weld than steel or titanium. Titanium is a poor thermal conductor so
not much heat is needed but N2 from the air can diffuse
into the weld and react forming brittle zones. Therfore you
must maintain an argon flow during the cooling of the weld.

Preheating the metal to reduce stress due to expasion
when welding is a big deal and the rate of cooling after
welding can be too.

A materials science book would be a good place to start.
The way that metals respond to heat treatment is quite interseting and very important if you are a welder. The strength of alloy steels can vary by 5:1 depending on
how it was heat treated.

Good luck!

Sedit - 14-6-2010 at 16:56

"If its welding, hopefully there won't be much chemistry going on"

Well, your explination of needed sheild gas on Ti and the likes is exactly what I was talking about as far as thats concerned. There is a complex chemistry going

Im a fast learner on things and I want to go in if nothing else seeming to know WTF im talking about or atlest have a head start on what there talking about. If it is indeed Ti we will be welding which I would not rule out due to the nature of the tanks I will need to know how to identify and potentially handle these brittle areas that might arise from the other welders mistakes since I will be grinding there work in the early stages on the job.

The more I learn now the more my pay rises when my review arives in 90days and that leap could indeed be a life changing amount if I play my cards right and gather the material I need to learn in the process.

Keepem comming folks I can use any little tidbit you toss in no matter how small it seems to be.

Thanks for your help greatly

[Edited on 15-6-2010 by Sedit]

densest - 14-6-2010 at 16:57

There are a lot of books about the practical aspects of welding. The "Machinists Handbook" (now in its 27th edition!) has a long chapter with a lot of detail.

More or less: welding is joining pieces of metal by adding more molten metal and making a solid solution of the work piece and the added metal. Usually the added metal melts near the melting point of the work.

That part's easy - melt a little iron and pour it on the joint. The hard part is, as always, in the details.

Thermal physical effects, like changing the crystal structure of the work, annealing or hardening the work, expanding or contracting it to introduce stresses, buckling, crazing, cracking, etc..., and resulting shape of the weld.
Thermal chemical effects between work parts and/or added metal - evaporating alloying ingredients, metal-metal reactions, metal-impurity reactions, etc.
Thermal chemical effects between air and metal or shielding gas and metal.
Electrical effects on plasma and metal if using electric welding (almost always).

All this turns into:
choice of welding method (TIG, etc.)
choice of shielding gas & rate of gas flow
choice of voltage/current/polarity/AC/DC
how fast to move electrodes
distance between work and electrode
gap between work pieces to be filled
choice of flux (if used)
choice of rod/wire alloy
depth of weld
amount of excess metal to add

For most applications, there are tables of recommended ranges of values for all these parameters. For any particular job, someone with experience can narrow that down to specific settings.

Manual skills include striking the initial arc, steady control of the hand-held electrode, careful adjustment of work pieces before starting, proper fixturing to hold the work during welding & cool-down, preparation, removal of spatter & flux & oxide.

The chemistry part is mostly about avoiding bad effects. Most industrial alloys (especially ones like stainless steel) are proprietary mixtures with as many as ten elements in controlled proportions. When you melt this in an electric arc, it's very easy to add or subtract enough through oxidation, evaporation, added metal, etc. to make the metal unusable. Oxides must be removed before metal-to-metal joining can happen. This can be done mechanically (grinding, filing), chemically beforehand (acids, etc.), or with flux during the operation (acid halides, borates, or reducing agents). Flux chemistry can be interesting but often not terribly relevant to the welding operation. Flux often is also used to protect the molten metal from air.

A very important part of steel chemistry is the quantity and state of carbon: is it dissolved, precipitated as graphite, combined with iron as a carbide? If there are significant alloying elements, does the carbon react with them? This is all dependent on the temperature history of the metal - how long has it been at what temperature in what order. Controlling this while welding is very important.

The metallurgical physical/chemical effects of crystal structure and pure physical effects of heat can be even more important. Some alloys can't be welded easily because their properties change too easily, the necessary conditions (temperature, pressures, etc.) can't be made with normal equipment, the rod/wire alloy is expensive or exotic, or elaborate pre- or post- annealing, normalizing (strain relief), or hardening must be done.

Most welding uses a flux and/or a shielding gas to keep oxidation minimal. The rod or wire may contain added alloying elements to replace those lost during the welding operation. Quick processing is also important!

Preparatory grinding removes scale, oxides, etc. leaving bare metal shaped to the proper form to accept the weld metal. Afterwards, grinding removes excess metal & waste to shape the result to the proper form.

That's the 15km/50,000ft version.

Sedit - 14-6-2010 at 17:16

I was already told most welding will be MIG or TIG.

""This can be done mechanically (grinding, filing), chemically beforehand (acids, etc.),"""

I am pretty sure this will be done, by me, mechanically using a grinder but I would note rule out pickling of the steal.
I am really concerned of spoting the carbides since I know they will no matter the material reduce the quality of the weld.

densest - 14-6-2010 at 17:31

I'd really recommend looking in your local library for DIY welding books. They'll introduce you to a lot of the simplest parts. Machinery's Handbook has a lot on the physics & physical/chemical aspects. If you're starting out doing the post-welding grinding to clean up the work, you should ask for a bunch of failed or test pieces to learn on. The DIY books will have pictures of good and bad welds.

The chemistry part is mostly "don't mess up whatever state the metal is in now".

The metallurgical aspects of crystal sizes & shapes, etc. is interesting, but what you need to know is what the good and bad states look like macroscopically (sheen, surface texture, color, etc.). Most (but not all) of the metal state can be seen if you know what you're looking at. That takes experience and either a bunch of pictures to look at or an experienced teacher showing you good and bad pieces (or both).

Sedit - 14-6-2010 at 18:28

I have heard oxides aka high dross areas, appear black where as those on the verge have signs of discoloration such as the blusish colors ect... that is seen when heating metals. With Ti the Nitride formation that leads to a weaker brittler weld has a yellowish appearence to them is this all correct?

I have assumed that the weld should appear relatively like the starting metal and that the melt seams should be as uniform as possible but I dont know exactly what impact this will have.

Quote:

I'd really recommend looking in your local library for DIY welding books. They'll introduce you to a lot of the simplest parts. Machinery's Handbook has a lot on the physics & physical/chemical aspects. If you're starting out doing the post-welding grinding to clean up the work, you should ask for a bunch of failed or test pieces to learn on. The DIY books will have pictures of good and bad welds.

I have a freind that desires to teach me welding and there is also my neighbor, the one that got me the job, is a certified welding instructor which is going to help me along at en excellerated rate and where I want togo to the library its going to be sometime before I have the time to get there hence the reason for asking here and doing my research on the internet.

Contrabasso - 14-6-2010 at 23:01

Ask your welding instructor what books they suggest for the metalurgy of welding.

watson.fawkes - 15-6-2010 at 07:09

Quote: Originally posted by densest

A very important part of steel chemistry is the quantity and state of carbon: is it dissolved, precipitated as graphite, combined with iron as a carbide? If there are significant alloying elements, does the carbon react with them?

I'm going to second this recommendation in particular. Pretty much everything in the chemistry of steel involves a iron-carbon phase diagram in some way. (They look like this example, taken semi-randomly from a web search.) You'll learn about the major crystal forms from these diagrams. As a rule, alloying agents don't change the overall crystal structure. As an example, 300- and 400-series stainless steels have different basic structures.

The next thing to learn about for welding is the effect of temperature history on crystal structure. The way that steels are cooled determines the resulting microstructure. Supercooling in steel is completely ordinary, locking in a "non-equilibrium" crystal structure. The relaxation time of that crystal, though, is so long (longer than the age of the earth, at least) that it's permanent for every practical purpose. Since the goal of a weld is to match the base metal as closely as possible, you'll want to understand both the original microstructure as well as how heat changes that structure. The acronym HAZ (heat-affected zone) is all over welding literature for this reason. It takes a bit of perspective shift to understand solid-solid reactions within a material, which include crystal rearrangements, but it's worthwhile. (Hint: they're often essentially two-dimensional wavefronts.)

One other chemistry-related topic that's significant: go look up a table of gas solubilities in molten metals. One source of weld porosity, similar to that for casting, is a result of gas coming out of solution as the metal cools. For example, since everything happens so fast, oxygen in solution leads to buried oxides, not desirable as you will surmise.

I'll recommend the ASM Handbook for a good scientific overview of the field. Volume 3 is nothing but phase diagrams. Volume 4 is heat treatment. Volume 6 is welding, brazing, and soldering. They're written at the level of a graduate school textbook.

The WiZard is In - 15-6-2010 at 08:56

Quote: Originally posted by Sedit

I started a job as a welders assistant today ....

So what is the chemistry behind welding?

The most chemistry in welding is thermite welding. For a
good example of thermite welding see (I don't remember
which channel it is on) "Build It Bigger" the episode
on the St. Louis Cardinals baseball stadium, where they
weld RR track using thermite. Note - they preheat the
track before welding. (Sorry to disappoint the 9/11 bombing
conspiracy nuts.)

Cadweld® - Copper oxide welding is widely used to weld Cu
ground (earthed for those in Europe) wire to ground bars.

The WiZard is In - 15-6-2010 at 08:58

Quote: Originally posted by Sedit

I started a job as a welders assistant today ........

So what is the chemistry behind welding?

You could look into the chemistry of welding gases —

oxygen
hydrogen
nitrous oxide
acetylene
MAPP
&c., &c., &c.

gregxy - 15-6-2010 at 09:46

Nitridation in titanium welding will cause yellow - purple colors of the metal due to the formation of nitride films on the surface. Welding is more art than science (of course science is at the base of it all but is more often used after the fact to figure out what went wrong or right).

If this is critical welding they will X-ray or magna-flux the welds to look for cracks voids etc.

I took a metals class in the evening at the local high school.
There wasn't much science but hands on experience and advice from someone that knows how to do it is very valuable. Maybe you could do that to get extra practice and impress your boss.

Sedit - 15-6-2010 at 15:24

Sorry all haven't had time to read all the replys Ill get around to it when I can....

There is something that highly bugs me about this job. You spend 10 hours a day grinding.... grinding stainless steel which you are breathing dust of all day and which you are completely covered in appearing like the tin man in a matter of minutes with no way around it. WTF am I going to do about the large amounts of Chrome entering my system on an extended period of time in pretty large amounts?

After the first day I can honestly say im not 100% sure im going to stick with it because they appear to not be holding up on there original offer for pay rate and if they don't there is no way I can work for the peanuts they want me to right now.

This is HIGHLY CRITICAL weldin and X-ray is just one of a number of test they will run on these since they are used in the storage of nuclear waste. Thats about as critical as it gets for storage containers since after it comes out of the reactor it sits in here fo years until its no longer hot and can be disposed of.

densest - 15-6-2010 at 20:16

@sedit - I don't know where you are, but I believe in the US and EU your employer must give you adequate dust protection = a real breathing mask (not just a nuisance dust mask!).

Of course, what the law requires and what really happens is different. Still, a major contractor for something as heavily monitored as those tanks should be responsible. If you are ready to chuck the job, ask for the mask, and if they give you one, be sure it fits and the filters are appropriate and not past their expiry date.

Sedit - 16-6-2010 at 15:43

We have a couple of different mask that I checked thru toda ranging from full resperators to "dust mask"

I chose a "dusk mask" that has another ventilators filter in the front if it for comfort since 10 hours in a full facial respirator would be hell, these mask are much higher ranger for the lowend dustmask that most jobs offer. I find this to help a bit but I still have metallic snot at the end of the day and my skin is still coated in grey dust. If it wasn't so hot out I would no doubt be using coveralls but the temperature prohibits that right now.

The long hours are what are turning me off along with a roughly 1 hr 10-30 min commute each way along with 10 hour days 6 days a week. I have enough time to comehome, wash the shit off of me, and go to bed and since they don't appear to as though they are going to honor there 15-20$ an hour original offer then they can shove it. They seem to have forgoten they contacted me asking me to apply not me begging for a job. If there not willing to hold up there end then... well... I might have to leave them with a few not so kind parting words, but we will see.

tentacles - 17-6-2010 at 13:19

There are some fantastic stainless welding primers online from the major welding equipment vendors, check esab and miller etc. I expect in a critical application like yours that the welding would be mostly preheated material using MIG with that fancy flux cored SS wire + argon(blend, probably).

Here's one of them: http://content.lincolnelectric.com/pdfs/products/literature/...

I remember reading some good stuff on esab's site a while back too... Did a lot of research before I started welding up my go kart frame a couple years ago.

Sedit - 17-6-2010 at 14:02

Im going to have alot more time then I thought on focusing on learning to weld... without saying to much, since one of the dozens of heavily lawyered up documents I had to sign before working may prohibit me from doing so(I had to sign away my Intellectual property for christ sake LMAO), a couple days into the job and the plant has been shut down for god knows how long due to some QC issues there having or someshit. All in all its the last straw on a rapidly built haybail and I placed a couple applications in closer places on my way home.

Think im going to get my first instructions on welding this weekend though if I can make time for it. I love the idea of learning to weld because it will open a whole new door to my tinkering that iv been doing for years. As of now all I have ever had a chance to work with is spot welders but not its a whole new ball game.

Quote:

Very nice chart watson I am going to see if I can dig up a simular one for stainless steal since job aside im sure most of what I want to weld will infact be SS. I see alot of remarks of there being no chemistry or little chemistry in welding but many must understand that crystal structure, dissolution, temperature effects, the way one metal bleeds in or perhaps comes out will liquid or cooling ect...ect..ect.. is infact just high temperature chemisty even if its not the kind of stuff you normally consider chemistry. I worked with ceramics for quite sometime to understand the amount of things that can take place while extremely heated like that. One of my favorite things to do with a kiln is trying to grow Zinc oxide crystals. Take a metal that is comprised of a Zn alloy and imagine if I liquified it. Some oxides are going to form faster on the surface then others and so forth. Proper control or atlest consideration of these factors would make anyone a better welder.

Magpie - 17-6-2010 at 14:07

Quote: Originally posted by Sedit

The long hours are what are turning me off along with a roughly 1 hr 10-30 min commute each way along with 10 hour days 6 days a week. I have enough time to comehome, wash the shit off of me, and go to bed and since they don't appear to as though they are going to honor there 15-20$ an hour original offer then they can shove it. They seem to have forgoten they contacted me asking me to apply not me begging for a job. If there not willing to hold up there end then... well... I might have to leave them with a few not so kind parting words, but we will see.

Becoming a certified welder is a worthy goal. If you are just coming in off the street with no prior experience or training in welding, like a course at a junior college or a trade school, but are going to get all your training gratis from your new employer, then I think you can expect some tough times until you prove yourself. What do the certified welders say? Do they think you are getting screwed, or is it worth sticking it out? Of course, I'm sure they are glad to have someone else doing all the grinding.

watson.fawkes - 17-6-2010 at 14:56

Quote: Originally posted by Sedit

I see alot of remarks of there being no chemistry or little chemistry in welding but many must understand that crystal structure, dissolution, temperature effects, the way one metal bleeds in or perhaps comes out will liquid or cooling ect...ect..ect.. is infact just high temperature chemisty even if its not the kind of stuff you normally consider chemistry. [...] Proper control or atlest consideration of these factors would make anyone a better welder.

I'm not sure how much a better welder as such it will make you, since so much of that is developing a good feel for the material and acquiring new somatic skills (much like athletics). What it will make you, eventually, is a competent weld process engineer. I was reading a fair bit about this subject a couple of years ago, and I can attest with no hesitation that there's plenty of room for intellectual and creative people. The number of ways of varying process parameters is truly enormous, and only someone who cares about the metallurgy etc. is going to do a first-rate job consistently.

quicksilver - 20-6-2010 at 08:32

Just as an aside, I did this thing almost exactly about 15yrs back. I needed a welding certification for a job (contracted to Motorola) and rec3ived same via a community college quite a ways from my home. I was very interesting & fun. The metallurgy was taught by someone who should not have been a teacher and that was a fucking chore. I simply read the book & passed the exams. Metallurgy could have been a damn good part of the cert. (It's a AWS cert) but instead it was tedium.

Not in usa

ou8e2 - 7-7-2010 at 17:42

Sedit,Great news wonder what got u working//?Hope u'r still there?Swip thought u welded at the Brass Plant...well don't worry about how u sound or what they say as we agree with above high post's ,mainly Greg'g'y's Listen,learn,look ya.Hands on is best as they will watch you n see how straight your lines,=beads are,neat or not.like stop at con's site and b sure some b,ill'let you do there work/?Don't worry,just wing it like ...u know ,your brass work's not too shabby'??!Right ,could b wrong but life's short,b safe,were the real mask eh?so u don't die younger,toxic shit ya no,worse then under the f.me hood.Hair short or tyed back,no loose boot's ,shirt.ie .keep your fly up!serious.had a bud burn his bag.hot metal liquid ouch.Don't want any Rhodium!down u pants.Good Luck!good job!p me anytime SAFETY #uno