leak free pipe welding

[PoorOwner]

How do you MIG weld a pipe (like an exhaust pipe) all around and leak free?
assuming mild steel, no coating, **** joint and good fit. Tacked 2 or 3 points.

The leak point is usually where the weld ended and restarted (e.g. turning around the pipe, seems the initial weld is not hot enough.

It has always puzzled me how to do it. I once welded a pipe to a plate just to test, pour some water in it and it leaked out pretty quick

 

[Lwel9226]

Practice... a lot.. and then some more.... You will figure it out after a while...

LynnW

 

[1953mercury]

Like Lynn said, practice. I generally use .023 wire when welding up exhaust systems. not absolutely necessary, but easier to control your bead, and makes for a neater, cleaner job overall. On amperage, you want to be just shy of burning through for good penetration, and keep moving. Mike

 

[sberry]

Backstep too, run in to the starts.

 

[gofastwclass]

Fit up is everything. Bad fit will weld bad plain and simple. but it sounds like you have that bit sorted.

As mentioned earlier practice a LOT. For me I go past my starts .25" or so and make sure to burn in the start / restart. If you've seen a pipeline welder or watched any welding videos with Bob Moffatt, he uses this technique on restarts and edges.

Another help is a video from our good friend Jody at Welding Tips and Tricks even though it's a lap joint, the technique is the same.

 

[bad_idea]

Your start-stops should overlap. Tack it in 4 places. Weld from tack to tack. 12 o'clock to 3 o'clock. 6 o'clock to 9 o'clock. 3 - 6. 9-12. You should have 4 overlaps (bulges. high spots) that you need to grind down some to make the weld consistent.

 

[BD1]

You could set a sleeve inside to help line up and have some backing for welding.

 

[PoorOwner]

I have used a pipe expander to fit the pipes and that is the time my pipes are easily leak free with heat cranked up. My MIG has tab power so it was hard to find a sweet spot between one and two tabs. The starting off a bit seems like a good idea.

I think i may also practice TIG welding you can get a puddle nice and hot first at the starting location.

 

[sberry]

The power is the wire feed adjustment. The voltage is the intensity or arc length, have to turn it up to run more wire. In reality it's not much increase in power. If you are in between use the wire feed to get it right.

 

[bad_idea]

You could set a sleeve inside to help line up and have some backing for welding.

A backing ring. In pipe fitting they manufacture backing rings for **** joined piping. For exhaust you can cut a 1" or 2" long piece of the tubing you are using, cut a slit out of it (length wise), squeeze it and slide it into the pipes.

 

[BD1]

A backing ring. In pipe fitting they manufacture backing rings for **** joined piping. For exhaust you can cut a 1" or 2" long piece of the tubing you are using, cut a slit out of it (length wise), squeeze it and slide it into the pipes.

Old days we used a tin can.


Sent from my iPhone using Tapatalk

 

[sberry]

Nothing wrong with a backing ring but I don't use them most of the time. I fit tight and even noodle it on if needed. I bought a generic muffler the other day, too short to be exact replacement but I cut the other one out, skinned the splice back and **** weld the new one in. Almost made up an extension to add length but the easy button was hold it up, weld on and one end was even crooked. So much easier than fittin it all perfect or making it all clamp up and a side benefit or 2 is,,, no leaky and doesn't twist or come loose.

 

[sberry]

Some simple repairs.

 

[rpcraft]

One key is having a welder that is versatile enough to have lower heat and not blow through. Some of your 120 welders are going to have a hard time, especially if they have a wire speed controller that is not independent of your heat range.

 

[sberry]

Wire speed is heat.

 

[rpcraft]

Wire speed is heat.

What I meant if it was not clear is make sure you have a setup that has seperate Voltage and wire speed, not combined in one knob (like some of the cheap **** Lincoln/Century 120 welders

 

[danielbuck]

I've had no problems stacking quick and hot mig tack welds on exhaust **** joints. I like to put them in pretty hot so they flatten out.

You can usually see leaks (on diesel) after it's been run for a while, and rarely do I have a pin hole.

Helps ALOT if you can bring the exhaust piece to your workbench and get good access all the way around the weld.

Here's one with **** welds, overlaps, and flanges all in one. Flex pipe was an overlap joint, and I was able to run a fairly hot bead almost 1/4 the way around before it starts getting too hot:

On flanges and overlap joints I do actual beads, instead of tacks.