MIG 321 grade stainless 22 gauge

By Lawrence (*****)

Date 08-04-2005 05:21

At 22 gauge your really at the outside edge for GMAW; very thin stuff you have there. Mig may raise your productivity but I fail to see it as a remedy to inert gas purge or weld quality issues.

Nonetheless, tell us more about your project. Are you looking to GMAW to join sections in a combustor or to weld in bosses?

What kind of purge problems and quality issues are you dealing with? Distortion? Misalignment? Oxidized melt thru?

Full pen groove welds? Fillets? Both?

Do you have an expanding welding fixture? Can it pre-load with consistency and remain concentric?

Probably you would select 347 filler just like you would with GTAW.

Its really hard to give input without knowing a bit more. But changing process is a pretty drastic step. If GTAW quality is low due to operator skill level, than the change to GMAW may not be a good answer either as welding on 22 gauge stainless with GMAW in a close process control situation may be equally difficult, with even greater chances for burn thru and lack of fusion issues.

By Viv

Date 08-04-2005 14:09

Thanks for the answers.

The combustor is a basically a type of pulse jet engine we have developed for large scale heating applications, combustion chamber and tail pipe is 321, inlet sections are 316L, its basically all a sheet metal fabrication job of rolled tubes and cones, one of the cones is made by metal spinning from 16 gauge all other parts are 22 gauge.

We build the engine from scratch, so flat sheet cut up to profiles then rolled and formed, sections welded up and also some bosses added for fuel lines and spark plug, a complete fabrication job if that answers your question:-)

Theres a few pictures on our web site www.glc-inc.ca we have made all the production jigs for forming parts but only as yet made a simple assembly jig to line up the major parts, no we are not using any jigs for parts weld up, but now you mention it I just had a Doh! moment:-)

Problems we are having is crappy looking welds with oxidization and some burn through problems, bigest problem is the back side of the weld that looks like the surface of the moon, thats the main issue as the gas velocity is high in certain sections of the engine.

edge preperation is just making them straight and square so they align, no beveling was required we thought on 22 gauge?

filler is 347 with argon and current range from 30 40 amps depending on the section being welded.

Changing to MIG is a big step yes but it was just an idea:-) since then and this post I discoverd the basic mistake I was making (Doh!) I did not clean off the oxide layer before welding! Ok I know in hindsight this was a big one but my welding experiance is limited and 321 is a hard one as I have found out:-(

Any suggestions on fixtures jigs would be appriciated or any other tips, purgeing seems to use a lot of gas any suggestions on that?

Viv

By - Date 08-04-2005 12:18

Lawrence makes some very good points and is correct in his statements, but let me address your questions as you have put them.
The wire type should be 347, as Lawrence said. I would recommend a mixture of 98%Argon/2% oxygen as your shielding gas. Your travel progression can be either forehand or backhand, but considering the thickness, or thinness, of your weldment, you might want to go downhand and increase your travel speed. 22ga. is rather thin, so beveling the edges is probably out of the question, but butting up the plate with about a 1/32" or 1/64" gap should allow you to break down the walls if welded properly. Most SS manufacturers, such as Avesa whom I work for, make a .023" and a .030" diameter wire, which will help you in this thin material. As Lawrence said, the only thing you can do is buy a 10# spool and try it and see what happens.

Chuck

By Viv

Date 08-04-2005 14:27

Hi Chuck, as you say Lawrence has given some good answers and summerised the real problem down to weld quality issues, maybe I was trying for the quick and easy fix rather than sort out the real problem but I am only human and not immune to the allure of a short cut:-)

I should add that I am a new welder with only a welding course and some production work for experaince, this then brings us to trying to perfect my skills with a difficult metal like 321 grade, I focused all my training on thin stainless at the college but this was on 304 and 316, 321 came as a bitter shock when we actually started here:-)

As I said to Lawrence I just found out I was making a basic error and not cleaning up the oxide layer, this led to having the current to high so as to melt the oxide layer, that then burns through the metal:-( also gives us terrible oxide round the haz and a crappy back side to the weld.

With that in mind any advice would be a godsend:-) learning to work 321 for our engine has been a steeeeep learning curve, the actual welding took a back seat to the other problems we had to solve including learning to metal spin the cones, ask a metal spinner and they will tell you it cant be done with this stuff, we did not know so did it any way:-)

I think I will get a reel of the wire you mention for a trial any way as it may be a speed solution for some of the jobs.

We may need to now focus on producing some welding fixtures and jigs to help solve some of the issues, any tips would be appriciated

Viv

By - Date 08-04-2005 15:33

Viv,
It is imperative that you protect the backside of the weld from the oxidation. That greatly compromises the corossion protection as well as the strength. If you are unable to purge the backside of the weld, at least try to use Solar Flux (brush it on the backside of the plate) or anything else that will add some protection. I'm a little surprised you are having a great deal of trouble welding the 321. The weldability of 321 is rather easy if you use proper techniques. Clean off the oxides !!! :)
Another thing is to make sure you get off all the "color" that you will see from the heat of the weld process. That is a chromium-depleted-oxide layer that prevents the steel from forming the passive layer that is necessary for maximum corossion protection. Sorry you're having so much trouble.

Chuck

By Viv

Date 08-04-2005 18:50

Yes cleaning off the oxide makes the world of differance:-) I am looking in to the whole fixtures jigs and purging issues now, we are discussing making production jigs to help sort out the none skill related issues:-)

I will get some solar flux in and give that a try as well,

From todays practice with clean metal it is looking like 80% of the problem was down to poor weld prep, must have a word with the instructor about not stressing that one:-)

Thanks for all the help

Viv

By Lawrence (*****)

Date 08-04-2005 15:45

Viv,

I think your conclusion of process control issues is right on the money. Even if you have success with GMAW and GTAW you will need great process engineering control in fixturing and welding.

Fabrication (or repair) of a combuster like your talking about here will be best accomplished with robust fixturing and really well thought out custom argon backups.

Welding 321 sheet and tube with 347 filler is not a big deal with GTAW. Distortion is similar to other 300 series stainless. Surface/edge prep is always important, but, 321 is really tough stuff and far less prone to get brittle and much easier to work with than Has-X, Waspelloy or Inco 718 or 625, which are other common choices for combusters and hot sections. I've seen some horrible looking 321/347 welds pass destructive testing.

Chuck is also 100% right in his admonishment to purge the melt-thru always. In my opinion even work that isn't expected to melt thru will benefit from a firm copper heat sink behind the weld, groove or fillet. Those heat sinks can also be argon purges or water chilled, but thats a whole other story :)

If your doing more than a couple of these things I would suggest you get input from some good specialty tool makers who focus in this field. It's an investment, but if you balence the man hours in trials and scrap you may find it an advantage in the long run.

The good news is you don't need to re-invent the wheel. This stuff is done well by many folks. Here is a link to the best help I know: http://www.pwt-online.com/

If it works its not a shortcut :) I rarely argue with success.

By Viv

Date 08-04-2005 18:58

Again thanks for all the help, now we have it nailed down as to whats going on we can fix it:-)

Becouse of all the other production problems we had to solve the welding ended up being considered as not a problem and got stuck on the back burner till it bit us hard on the bum:-)

The differance we see now is like night and day! so we will sort out the jigs and purging bars as a matter of urgency.

As useal its all the little things you do on a job that add up to success

Viv

By Viv

Date 08-04-2005 20:55

Well guys I just found another factor that was affecting our 321 welding, and if you had told me I would not have believed how much affect one little thing could have.

The Argon regulator was faulty!! it some times stuck other times gave intermitant gas, or just plain oscilated for gods sake!

I binned it and fitted a higher qaulity unit we had that came with another machine, nearly all the remaining problems disapeared.

The arc is now completly stable and the weld pool is so much more controlable, the welding beads are incomparable to what we were getting.

Its like having a new machine!

Thanks for all the tips Lawrence and Chuck we are moving forward again.

Viv

By Viv

Date 08-04-2005 21:09

For the sake of completness I should add that I did a triel tube from 321 22 gauge, rolled it and butted the edges together then tacked it about every inch and half.

Using the "what have I got in the workshop to sort this out" method without having to go and buy any thing I found a reel of three inch wide aliuminum tape, folded a peace length ways over a 3/8 tube to form a channel and then stuck it on the back of my weld area.

Fed purge gas in one end with the other end pinched down a bit to restrict the flow, apart from the fumes from the glue it worked an absolute treat!

Good back side penetration with no oxidisation problems, front side was the best I have ever done:-)

Now I need to order some copper stock in and make some proper purge bars and jigs

Viv

By - Date 08-05-2005 00:33

Viv,
Hey, with all due respect, a faulty argon regulator is not "one little thing". It might seem minor, but it can also be the root of many potential problems. :) Well, it seems you faced many problems, overcame them, and are now on your way. Lawrence and Chuck congratulate you!!! Hang in there.

Chuck

By Viv

Date 08-05-2005 02:26

Thanks Chuck, yes I have to agree with you the argon regulator in hindsight is a bit bigger than a small problem:-)

One of the interesting (and now obvious) problems was the degraded state of the tungston, overheating, contamination, crudy oxides forming behind the point.

I thought (and accused mon chum:-) that the grinding wheel reserved for sharpening the tungstons was being used for other metals and the tips were being contaminated with steel, now I know the gas was stopping and the tips were burning up, also that the welds were being oxidised.

As it was intermitant it was not an easy problem to spot, I only noticed becouse I was so focused on setting up the purge supply.

Note to self: forget pressure gauges and buy some P in a tube flow meters!

Viv
PS we wont tell mon chum he is inocent we will just keep it our little secret:-)