[Gordonlam]

Hi there, couldnt find the stainless steel page so i am just gonna post it here.

I have been struggling for my advance tig course at school for the stainless steel, hope there is someone could help me out a bit.

The task is supposed to be easy, tig welding, Stainless steel, 1G position. 1.6mm or 3mm (sorry about that coz im in Australia). Only 1.6mm filler rod was supplied (sorry i forgot the class, you weld wt u are given in school).
My instructor required it to be full penetration.

My problem (actually the whole class) was i could either get it done with a colorful weld (which i assume i did with good timing and heat) with only a little penetration (less than 50 percent) or done with black weld (which i assume is overheat) with full pen.

Is that anyone could give me some advice on that? I suggested my instructor that if i could prep a 3mm plate to no land, focus on the pen on my root run/despite the colour of the weld and then 2nd run i could focus on the colour/temp to fill up the rest, but he insisted that theres no need to prep and it is possible to do it in one run.

FYI he only passed one guy in that class and that weld i would say is a shitty weld - got full pen in the back but the whole weld is all black. He said that black colour could be wipe off by some chemical. I am not sure if i should believe that.

Of coz we all asked him to show us how to do it once but he refused. I dont mean to be a stereotype or a dick but all the instructors in school cant weld at all.

Just so you know i am not exactly new to welding. I have been a welding for 3 years. One of my previous jobs was welding aluminum toolbox so i think i know how to tig weld. Just dont have much experience for Stainless. I actually passed the task eventually did wt he wanted. Full pen but black weld. But i just dont think it is the right way to do it and i wanna be able to get a Stainless steel job in the future and i dont think that black weld could pass any trial.

Sorry for too many words and i appreciate if someone could help me for this.

Cheers

Gordon

[Artie F. Emm]

Others will respond- but i *think* the black is caused by too much weld heat.

Your instructor needs to put up or shut up.

[LtBadd]

Hello Gordon
The correct way to weld stainless and get full penetration is with a back purge. Without a purge the backside of the weld will be black as you have observed.

Think of it this way, if you need gas shielding when TIG welding, then when making a full penetration weld the back side will be molten metal as you penetrate, this also needs to be shielded.

It seems you have already figured this out, too bad your instructor hasn't.

[big gear head]

You would be very surprised at how much easier it is to get full penetration when you have a back purge, and how much cleaner the weld will be. Stainless must have some kind of backing, either purge or some other material clamped to the back, to prevent oxidation of the weld. The oxidation from the back side will contaminate the whole weld. Stainless is different from other materials, where mild steel, aluminum and others don't always need shielding on the back, stainless does.

I keep some blocks of aluminum in my weld booth to clamp on the back of stainless pieces when I weld them. Many times you can't purge the back side, but backing it up with aluminum helps quite a bit. The aluminum holds argon from the front of the weld and prevents most of the oxidation on the back side. It also draws a lot of heat from the weld, so more apms will be required.

[GFab70]

I agree with Artie. Your instructor should be able to demonstrate ANY and ALL tests he/she is requiring you to take. I instruct (not welding) on occasion and would be embarrassed to ask something of someone I couldn't do myself. If all the students feel the same approach the instructor as a whole, if that doesn't work approach the school superintendent as a whole and ask how they can help.

Sent from my SM-N910R4 using Tapatalk

[Poland308]

As others have said The black and rough surface on the back is from lack of shielding. Often called sugaring. It means you have changed the properties of the metal itself. Jody has a vid about SS properties you may want to find. Sometimes this is allowed for some applications. But the weld will be more brittle and prone to cracking. This is not allowed for most of the applications were a person would be likely to use SS for its corrosion resistance or looks. It definitely should not be a taught method of welding.

[Rick_H]

So are you currently not welding with an aluminum backer plate behind it? I assume in 1f you are, with a 3/32"-1/8" gap put, no edge prep, just brush and wip it clean use about a 1/4" long good tack at the top and bottom. Then with about 85 amps you should be able to get all the way through, breaking down the edges for complete pen. If this is true, clamp it to the bracket that piece will move easily pulling away from the backer.

Sounds like the test I took for the AWS 17.1 but had to weld vertical up. Easiest way was smash the pedal when you add filler and continue moving up.

[bruce991]

Aluminum foil can be used as well to make a purge envelope. I agree purging is essential on both sides on SS. We made food service piping at my job and inside looked as nice as outside. No black burning so clean on both sides a scotch brite wheel and done, at times we used an acid paste to remove any possible iron based metals from being attracted and rusting. Jodi explains this chemical reaction I don't recall the terminology.

[LtBadd]

at times we used an acid paste to remove any possible iron based metals from being attracted and rusting. Jodi explains this chemical reaction I don't recall the terminology.

I believe that is called passivation.

[Gordonlam]

Rick - there was no backer plate. Backer plate was never exist in our school tasks i duno why. im gonna try it your way this week. thank you for your advice.

Gfab70 - the instructors only demonstrate how to set up the machines. They showed us how to mig and stick a 1F at the beginning and thats all. i understand its not easy to tig weld when u r old and cant see properly but one of the instructor showed up how to mig weld vertical up mild steel and it was totally crap. i mean how hard can it be, if you spend some time to practice and maybe watch jody's video for a couple times it should be done easily. They just dont care at all, just sit there and get paid.

Thanks for all these replies. It is actually really pathetic to look for help here while i am in a freaking welding school.
I have learnt nothing but theory in school so far. Everything when i hv a problem i just go watch jody's video. I hope the instructors are better in the State.

[Gordonlam]

Big Gear Head - so do u mean the purging would affect the front side of the weld as well?

[Poland308]

Purging the back side will affect the front side. If you have no purge or protection then while the puddle is molten all the way through the material ( in order to get full penetration it will be) impurities will be drawn up through the molten metal to the surface. The same principal that makes refining possible.

[Boomer63]

I think the folks out here who are talking about backers and purge gasses are right on the money. I have to confess that my TIG Stainless skills are limited; I teach plate stainless in several positions, and pipe stainless - where we use carbon steel pipe with stainless filler; that can get you a 6G AWS certification for pipe greater than (I think it is something like) 2 7/8", and up to 2XT the test pipe ID. I am saying this to let you know that my experience is limited ... but I here is a story from my school here.

Keep in mind, I am NOT in charge of this program ...YET! But that is coming soon, and so are some BIG changes ...

I had my students plasma cut some 1/4" carbon steel plates which were 12" wide and 36" length: I wanted strips 6" wide, so that I could use the plas to cut a beveled edge so that all of our students could get practice working that 'V' Groove. So I had a pile of real nice donated steel 6" X 36" X 1/4". One of the night time instructors told their class to take those strips, butt the ends together length-wise, and weld them using a 7018 X 1/8" rod. This instructor told the class that they "should be able to get complete penetration", with the iron completely butt up to each other. Wasted all of the iron my crew had cut.

I was real, real pissed ...

After a couple of meetings with my 'bosses', I cooled down, somewhat. In the end, I figured that if that instructor wants a job after I take over, then I will give them a weld test which will be pass/fail, with the job depending on the test. The test will (of course) be welding 1/4" plate butted together, using a 7018, 1/8" rod, and I expect full penetration. One practice plate allowed.

What I am trying to point out with this long post, is that sometimes the instructor has their head up their rear end. Now, if someone can point out to me that they weld butt joint, 1/4" A36 with a 7018 - NO JOINT PREPARATION - and can get full penetration, then stand corrected. What doing all of the welding wrong does, is to develop the muscle memory of the wrong way to do something. Then not only does the correct way need to be learned, but the incorrect way needs to be 'unlearned'.

Sorry about the length of the post!
Gary

[big gear head]

Big Gear Head - so do u mean the purging would affect the front side of the weld as well?

If you weld stainless with no backing or no back purge then the contamination from the back side will get pulled into the whole weld.

Purging the back side makes the whole weld cleaner, and I've found that with back purge it's easier to get full penetration.

Using a backing plate is a little different. A backing plate will trap argon that passes through the gap between the plates and help shield the back side of the weld. It's not as good as back purge, but it's much better than nothing. A backing plate will also draw some heat from the weld, so you will probably need to use more amps to get full penetration. The backing plate should be aluminum, copper or something that will not get welded to the back side. If you use steel then the backing plate will end up getting welded to whatever you are welding.

[Rick_H]

Before I could take a pipe course a few years ago I had to take an intermediate class that allowed me to test to the aws 17.1. When we ran open root stainless and carbon steel we had a 1/4" alum plate behind it, with alum a steel plate was used. They used the plates instead of gas due to expense.

Funny was I did the open root steel with no backer and the teacher just laughed, he said why are you in this class...lol My response, So I can take the pipe class. Even though a lot was remidial for me I still took bits and pieces from the class, and being a booth 6-8 hours a day allowed me to concentrate or my skills, instead of having a line down where time is money. Going to the classes were worth every penny for me, I was self taught so it re enforced to me what I knew.

Shame to hear your not getting that same experience.... Any questions ask away, lots of good guys here.

[Rick_H]

Big Gear Head - so do u mean the purging would affect the front side of the weld as well?

If you weld stainless with no backing or no back purge then the contamination from the back side will get pulled into the whole weld.

Purging the back side makes the whole weld cleaner, and I've found that with back purge it's easier to get full penetration.

Using a backing plate is a little different. A backing plate will trap argon that passes through the gap between the plates and help shield the back side of the weld. It's not as good as back purge, but it's much better than nothing. A backing plate will also draw some heat from the weld, so you will probably need to use more amps to get full penetration. The backing plate should be aluminum, copper or something that will not get welded to the back side. If you use steel then the backing plate will end up getting welded to whatever you are welding.

Exactly

[Rick_H]

at times we used an acid paste to remove any possible iron based metals from being attracted and rusting. Jodi explains this chemical reaction I don't recall the terminology.

I believe that is called passivation.

It could be either pickling or passivation.... Most solutions pickle which removes all iron based material, heat tint etc cleans the metal very good. Once stainless is clean when exposed to enough oxygen it self heals (passivates) to keep the corrosion resistance layer...as long as it wasn't over heated.

I use Bradford Derustit Wonder Gel....works very good, still nitric acid but smells a lot less then other.cleaners I've used.

[bruce991]

Yes pickling paste is what we used. One annoying habit when working in maintenance is when you change out a grinding disc and set it down and one of your fellow maintenance guys grabs it and uses it on a carbon steel and you grab it and bingo contamination.

[LtBadd]

Yes pickling paste is what we used. One annoying habit when working in maintenance is when you change out a grinding disc and set it down and one of your fellow maintenance guys grabs it and uses it on a carbon steel and you grab it and bingo contamination.

Shop I used to work at does a lot of SST pipe, we won't do any carbon steel work with SSR pipe in house. It was rare that any of our jobs was carbon.

[Boomer63]

[quote="Rick_H"]Before I could take a pipe course a few years ago I had to take an intermediate class that allowed me to test to the aws 17.1. When we ran open root stainless and carbon steel we had a 1/4" alum plate behind it, with alum a steel plate was used. They used the plates instead of gas due to expense.

Funny was I did the open root steel with no backer and the teacher just laughed, he said why are you in this class...lol My response, So I can take the pipe class. Even though a lot was remidial for me I still took bits and pieces from the class, and being a booth 6-8 hours a day allowed me to concentrate or my skills, instead of having a line down where time is money. Going to the classes were worth every penny for me, I was self taught so it re enforced to me what I knew.

Shame to hear your not getting that same experience.... Any questions ask away, lots of good guys here.[/quote
After the first semester, I do a lot of open root no backer welding in several positions. It is all what I think of as 'pre-pipe'. It is true that I can teach them a bit about pipe welding, but I don't have enough time, and there is no way they could get real world experience here, to learn how to be a 'Pipe Fitter'.
Gary

[Gordonlam]

hey guys i tired it with an aluminum backer plate. Got full penatration at my first attempt. All my mates were surprised how easy it supposed to be. I wanna post up a pic here with my phone but i duno how.

Anyways thanks for all the advice.

Gordon

[big gear head]

Glad to hear that it worked for you.

[Rick_H]

Good job....how'd that go over with your instructor?