View Full Version : Seeking wisdom on repairing thin Tubing

02-03-2005, 02:44 PM
I managed to screw up one of the emission lines from the exhaust pipe to a check valve on my '85 Jeep. I broke it almost through trying to unthread the check valve, which had corroded to a large nut on the end of the tube. I have the new check valve to install, but the old one virtually came apart when I used a monkey wrench & some frustration on it. I am soliciting advise/humor on how to get it right again. My thought is to hacksaw off the corroded tread on the old check valve & just Tig weld the new one on; threads on a hot exhaust part are an exersize in sadism/humor. It's all steel & the check valve appears to be basically a 1/2" pipe nipple welded to the bottom of the checkvalve body. I have basic Tig skills. The Tube is somewhat of a challange to me. It is thin, about .040" thick& 3/4 Dia. & I tore it half way though trying to get the checkvalve off. Also the tube wore a small hole rubbing against the block. I propose to put a patch over both areas & Tig weld those on. While I could probably do but joints in .040" steel, I intend to do lap joints so the material will be a thickness I can easily deal with (just slap on the patch & weld). I have a large amount of .032" steel sheet that will serve I think. The tubing is only very corrooded near the checkvalve, so I should be able to get the joints clean & bright, and not blow holes with the Tig. Have I missed something?

02-03-2005, 03:23 PM
Hi! If the metal is clean enough you should be able to tig the tear together the way it is, providing you can get the torn edges to line up ok. Get an .040 tungsten and use mig wire for filler. I use .023 or .030 for these repairs. The best is the wire that isn't copper coated. I have to use a 2X cheater to see that stuff now. Good Luck!

[This message has been edited by torker (edited 02-03-2005).]

02-03-2005, 04:05 PM
That had not occured to me Torker. I don't have Mig mire handy but I do have some .035 308L (stainless) filler rod. If I can get the edges together as you said, I'll try it. Thank you for your insight.

02-03-2005, 04:18 PM
Silicon Bronze, anybody,and maybe a sleeve to slip over your broken/torn spot?

02-03-2005, 07:47 PM
dont use too much amperage (its about 20-40 for tig 'in thin wall cromoly tubing)

02-03-2005, 09:29 PM
Okay gurls..here's some really thinwall welding for you...I didn't feel like taping my 2X in my helmet so it's a bit shaky..lol The very top part that comes over the top is done with .023 filler @ 16.5 amps, 8cf of argon...would have been better with .030 because of the gap that needed filling. The bottom part of the weld is with 1/16" tig rod...hammered flat and ground down as much as I could get it. This took 23.5 amps...this was just to melt the filler! You can see a big difference...had to put so much heat into the filler that it melts the base as soon as the arc gets near it. Once you get the puddle flowing and astablished you can ride back on the puddle a bit and it won't slump. If there was no gap the 1/16" filler does a little better job. Actually if there is no gap and it's clean, many times you can just fuse these little welds...you don't need filler unless you need the reenforcement.BTW...tube is .030 thick.

[This message has been edited by torker (edited 02-03-2005).]

02-03-2005, 09:50 PM

Just a walk in the park. 1/16" tungsten, sharpened. 1/16" tig filler wire, silicon-bronze. Set max amps to 25 or so.

Secret is the silicon-bronze filler. Good strength (about 50,000 tensile) and a melting point just above butter. Start the arc, warm weldment area gently, but don't melt the base metal yet. Bring the filler rod in and put a drop where you need it. Move the arc over on top of the drop and increase pedal until the drop flows out. Once it flows, back off the pedal slightly and continue until finished. Nothing beats silicon-bronze for sheet metal, and that's essentially what you have.

Barry Milton

02-03-2005, 11:04 PM
Well I'm not "SuperWelder" I guess. I used patches of .032" mild steel over the bad parts (thank God I didn't saw out the bad parts like I had intended originally). I had no problem running a bead on the mild steel, but I blew holes in the tubing like I had a plasma cutter instead of a Tig torch. I sort of got a bead to run for small stretches by just running on the mild steel. Not at all like Torker's pretty bead, but I didn't work up that good a fit-up. I finally gave up & used JB Weld. I still need to Tig the checkvalve on but it's like 3/32 wall thinkness & I know it's steel. I tried a magnet on tubing & it stuck so it must be steel also. It did get paper thin from wear & bending where it broke, maybe that was my problem, plus poor fit-up. I used maybe 40-50 amps & .040 tungsten on DC-. I will definely pick up some silicon bronze to try out; & some suitable tuning I can identify, & a tubing bender, either Harbor Freight or build the one in Vincent Gingery's book. At this point I'll be very glad to get it past the smog check so I can catch up with my registration. Thank you for your valuable advise.

02-04-2005, 12:09 AM
Ha...that bead wasn't very pretty! I'm out of practice on this small stuff. Did a few more and for this time of the night and 4 pots of coffee today...lol..they're getting better again...wish I could see better. The one on the left is .023 filler again..was going really good til I gooojed the tungnsten in the puddle! Middle is 1/16" filler and rod @ 24 amps. Right is 3/32 tung with 1/16" filler.
The next pic is the reason I like the little filler...you can see a progressive amount of filler droop...the rear is the .023...note it is nearly flat on the id. Don't forget...this is .030 wall tubing and the gap is a hacksaw blade width. Any heavy filler is going to droop in there if you are off even a bit. I used to build all my own headers for my hotrods and kind of wanted the insides to be really smooth. This was the best way I could find to do it.
Crossthread..I'm wondering if that tubing you where trying to weld was alumanized? That stuff can give you fits trying to tig it.
Barry..I've never tried that silicon bronze filler. Any idea how it would hold up using it on engine headers? Thanks!

02-04-2005, 01:36 AM
Russ you was drinking when you welded that - I can tell - looks like birdpoop http://bbs.homeshopmachinist.net//biggrin.gif

02-04-2005, 07:16 AM
Hahahaha...Naw Thrud...I just can't see them little boogers any more. Lose the sight line and having trouble watching that little puddle. Sometime if you're down here, I have an old Camaro I'll show you...I tigged all the body panels in it...can hardly see the welds.

02-04-2005, 09:36 AM
I regularly TIG steel tubing down to 0.51mm (0.021") for bicycle frames. The key is having a pulser unit.

I run 100 Amps on the SyncroWave 250
70% for peak current
20% for background current
25% on-time
1 pulse / second

Get everything as clean as you can and use the foot pedal to slowly ease off as you work along the weld because the heat spreads fast in the thin stuff.

Good luck.

02-04-2005, 09:58 AM
Glenj has a good point, pulsing is great way to go.

I use it when something needs to be really nice appearing. For me it's slower than non-pulse. But as Glenj notes, it's great on thin stuff, 0.040" and under.

02-04-2005, 12:01 PM
could someone elaborate on the tig pulser? i've heard of them, but i'm not sure i've ever seen one, nor can i find any substantial information on the 'net...

02-05-2005, 09:27 AM
A pulse unit for a TIG welder allows you to created a square wave output current. The power coming out the tip will be "pulsed" between an upper and lower current setting at a specific rate and for a specific amount of time. It's like you were pushing up and down on the foot pedal say once a second between flat out and 1/2 way down. You have control over the high current lever (peak), the low current level (background), how often the change between currents occurs (frequency) and the percentage of one cycle that the high current is on (on time).

The advantage when welding thin material is that you can have a short high current pulse to melt the puddle as you add filler then a lower current pulse as you move the torch. This keeps the overall heat going into the material down and allows welding of very thin stuff. For example on thin (.02") 4130 tubing I'll use the following settings.

70 amp peak current
20 amp background current
1 pulse per second
25% on time


02-05-2005, 10:02 AM
I can further elaborate on a pulser unit. It is a $1200 option on my welder. That's why I don't have one! This just may be out of the price range for a home shop. One of the pulp mills I used to work at just brought in a new state of the art Miller with all the bells and whistles...$12,000. That thing was wicked to weld with in pulse mode. It was too big to fit in my lunchbox http://bbs.homeshopmachinist.net//biggrin.gif

02-05-2005, 11:46 AM
Glenj described it well. His pulser is more adjustable than mine...my HTP Invertig 200 pulse specs are:

DC Pulsing Frequency 0.4 to 300 Hz
AC Pulsing Frequency 0.4 to 2 Hz
Pulsing Base Current 25%

So on DC welding (mild steel, stainless, cast iron) the on-off cycle is adjustable from 300 times/second, down to .4 times/second. Like Glenj, usually set mine for 1 or 2 pulses/second. Depends on material thickness, size (thermal mass) of part, phase-of-the-moon, etc.

On aluminum, pulsed-arc tig looks like robotic welding. If the job has to look "just perfect", I'll pulse. Works as well on .250" material as on .025" thickness.

Barry Milton

02-06-2005, 06:47 PM
If I ever find the elusive sack of cash beside the road I'd spend $3000 of it on one of these for sure. All the bells and whistles and especially good control in the low amp range, built in pulsing, pre and post flow etc.

The 200 DX model is 45lbs, my Syncrowave 250 is about 400lbs.


02-06-2005, 07:43 PM
this pulser unit sounds interesting. i understand the newer model machines have one, but i'm pretty sure my syncrowave 180 (older style) don't got one.

is it possible to get one for that machine. if so, where and how much?

02-07-2005, 05:12 AM
I know where there is a used Miller synchro wave Aero for only $5k here in Edmonton...(600A)

02-07-2005, 06:22 AM
Thrud...If I remember correctly that is the machine that the pulpmill bought (for $12K) that I liked so much. I just don't have the power output to run one of them in my shop. Too bad...I've got about $6K in my Rinkin and it's only half the machine.
Glen...have you actually talked to someone who owns a Dynasty? I was going to buy one before I got my present machine. I tried one at a trade show. Was pretty neat..sharp tungsten on the edge of 1/16" alu, you could run a bead along the edge so easy it was sick. I was impressed but our local college bought one and they had nothing but grief with it. I went up there numerous times to try it some more before I bought one and it was always broke down. Hope they got the bugs out.
psomero...Did you ask your Miller dealer about a pulse unit?

02-07-2005, 09:32 AM
I know someone who had a Dynasty 200DX on loan for a few months. Other than a bit of noise from the automagic power supply he loved it. It didn't have ebough juice for his purpose though. I have not looked into a unit seriously enough to hear of any failures so thanks for the reliability info.

Not sure if Miller still makes the pulse unit I have. I'll check for a model number tonight.