I've been asked numerous times to do this and finally went ahead and did it. The following (2) welds are made via a tig welder on 16g (.065" wall) 304 stainless steel. The question is, should you purge the ID of the tubing with Argon while welding? It takes a little bit more time for the set up and it costs more since the welder is using more Argon to purge. Note: The area around the tig arc is always purged or else the weld couldn't be made.

Here are the pictures

Outside of non purged weld, sorry about the poor weld but you'll get the idea.


Outside of the purged weld


Inside of both welds, non purged to the right


Non purged inside


Purged Inside


Inside Vertical View, non purged to the right

 

Obviously from the pics I'd like to have a purged weld, but is it as strong?

 

Purged looks alot better, especially if we are talking exhaust components.

The inside pic looks alot better purged, because there is very little of the weld to interfere w/exhaust flow.

Is strength a consideration at all? I may not be that important but just something to consider, It seems as though the no purged would be a better *bond*

....but Im no welder, and Exhaust components don't see alot of physical stress...so to speak.

D, who is very impressed that SMS takes ALL the details into account.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bbasso &raquo;</TD></TR><TR><TD CLASS="quote">Obviously from the pics I'd like to have a purged weld, but is it as strong?</TD></TR></TABLE>

amen.

jeez...The R forum moves fast...even @1am.

 

I know nothing about welding but the purge welds look better.

 

I would say yes. Since you are getting 100% penetration, the weld puddle is being exposed to the atmosphere on the inside of the tube. Ideally, every part of the puddle should be shielded.

Sonny

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B2FiNiTY &raquo;</TD></TR><TR><TD CLASS="quote">I know nothing about welding but the purge welds look better. </TD></TR></TABLE>

 

so you're saying that you don't have to purge SS material? I"ve always been taught to purge or else the weld will get contaminated and not be as strong

the non-purged does look like it has more penetration though

 

purged is stronger. most people who know what's up say back purging is the correct way to do it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bbasso &raquo;</TD></TR><TR><TD CLASS="quote">Obviously from the pics I'd like to have a purged weld, but is it as strong?</TD></TR></TABLE>

Purging is stronger. Purging, when done properly, prevents oxides from forming in the weld area since oxygen is not present during the weldi process. Strength is very important since there is a cat and an exhaust sytem attached to the end of the header which moves around during driving and stresses all the tubes and welds.

While the "larger" weld may look stronger, the weld actually has a lot of porosity and is weaker. Remember, with any weld, the strongest part of the joint is the thinnest material.

 

I hope your purging your headers?

 

Dave can you explain purging? I'm a stick welder 95% of the time so i'm trying to pick up all the info I can on tig.

 

S/S should always be purged for butt welds.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by B2FiNiTY &raquo;</TD></TR><TR><TD CLASS="quote">I know nothing about welding but the purge welds look better. </TD></TR></TABLE>

 

yes purge...... looks like you are trying to weld with 60 amps, to much,

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TREVER &raquo;</TD></TR><TR><TD CLASS="quote">Dave can you explain purging? I'm a stick welder 95% of the time so i'm trying to pick up all the info I can on tig.</TD></TR></TABLE>

For stainless and mild steel you would use 100% Argon for the purge. Argon is an inert gas. You seal the tube inlet and outlet and have a small exit hole. Argon is introduced into the tubing to displace all the air. The air contains O2, which at high temperatures will react with the molten metal and then oxidation takes place, and this causes a weak weld.

So there's really 2 purges taking place, a pre purge to displace the air and a continuous purge to keep it out while welding is taking place.

If you introduce more Argon then can be past through the exit hole you can cause the weld beed to bulge due to a higher internal pressure.

OT: When I worked for Corning and did a redesign on one of the induction furnaces used in making fiber optics. An induction furnace uses a coil wrapped (not touching) around a graphite cylinder and the glass is hung in the cylinder for the drawing process. It was pretty cool to see the graphite cylinder glowing at 1800+ degrees C! The furnace had a continuous purge because if any Air/O2 got in the furnace the graphite would react with the O2 and generate CO. So we monitored the CO levels to determine the effectiveness of the purge. Sorry to get off on a tangent but it was my best engineering job, a lot better the the BS one had to go through at a nuclear plant.

Trever, if you plan to weld 18g tubing with a stick welder you are a better man than I.

 

So basically you need to let the argon flow before striking the arc, to purge the oxygen from the line. I'm not sure I'm getting it? I tried to weld exhaust piping with stick for a couple hours. Not sure of the gauge but it was thin to me. At work I'm used to anything betweem 1/4'' and 2'' steel so you get the idea. After that I decided it was time to learn how to tig I took a welding class but the instructor was geared toward the type of welding I do at work so he was minimal help. I spent about 16 hours figuring it out myself.

 

purge that sucka...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ian &raquo;</TD></TR><TR><TD CLASS="quote">purge that sucka...</TD></TR></TABLE>
that helps

 

It's probably better if Dave explains it with proper vocab, but I'mma take a stab at it.

You fill the inside of the exhaust tubing with an inert gas as a means of removing any oxidizable components (mainly oxygen from what I understand). By doing this, you contain the burn of the weld to only the wall of the exhaust tubing.

The welder itself must already be purged before welding anything, so any purging there is already a given.

Does that help? Or, am I only kicking myself into redundancy?

BTW, good info. You make it easy to follow even if I have no welding experience.

 

hey guys...im still in the learning process of welding...i hope to soon get a MIG (lincoln 135 is what im looking at) so i can practice first and then learn how to do some intercooling and exahust piping...but back to my question...what kinda of amp do you use for welding a 16g pipe like the one above...bc i want to get the best size for the job and i dunno if a 230V would be better...but just trying to get some tips/opinions..thanks guy good thread

 

My Licoln 135 can handle pipes like that and even thicker just fine, yeah they don't look as pretty, but they are damn strong welds. Make sure you get a welder that can be upgraded for gas because the innershield wire makes messy welds, although it is fast and easy to weld with.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">It's probably better if Dave explains it with proper vocab, but I'mma take a stab at it.

You fill the inside of the exhaust tubing with an inert gas as a means of removing any oxidizable components (mainly oxygen from what I understand). By doing this, you contain the burn of the weld to only the wall of the exhaust tubing.

The welder itself must already be purged before welding anything, so any purging there is already a given.

Does that help? Or, am I only kicking myself into redundancy?

BTW, good info. You make it easy to follow even if I have no welding experience.</TD></TR></TABLE>

I see so you need to set something up so only argon is contained in the tubing.

I saw a converted sand blaster that was being sold as a ss tig welding booth. Same idea I guess

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">It's probably better if Dave explains it with proper vocab</TD></TR></TABLE>

I guess I'm getting rusty with my vocab

 

Nice post, Dave!!

You guys can now see the difference. The purged side is smooth. You could drag a cotton ball over it and not snag it. Some jobs I've been on, they'd check for roughness of the root this way, if they could get in to it.

On the non-purged side, you can see how rough it is. This is often called "sugar." Small particles of this can even break loose... and you guys know what those chunks could do to your turbine wheel!!