Need to know. Mig/Tig vs stick

[davesl708]

I have some past experience in welding stainless steel. Mostly 304 using stick for the heavy stuff and heliarc for the sheet metal.

My question is, does Mig or Tig welding have the same tensile strength and get as good penetration as stick welding when welding mild steel? Would Mig or Tig be used on 3/8" or thicker metal that will get heavy loading?

 

[Shield Arc]

Last time I did any stainless steel Mig welding was in the 1970s. We used a tri mix gas. Far as penetration, I really don't know. If doing pretty much flat welding you can get into spray arc transfer welding.
https://www.millerwelds.com/resources/weld-setting-calculators/mig-solid-core-welding-calculator
Selecting a shielding gas for joining stainless steel - TheFabricator.com

 

[yomax4]

I guess you could say that the mig wire has a tensile strength of it's own no matter what you are sticking it to. Often 70S6 in the 60K to 70K range. Mig is the most likely to put on too cold making for dangerously low strength in the joints. Tig would be pure welding and the tensile would likely be more toward what the base metal is because you need to melt the base metal into a puddle to get the weld going. I guess stick too could easily be laid down too cold causing dangerous strength. ie: 90K tensile rod ran too cold could be only 10K tensile in the joint. Cold welds are why people need to practice and learn how to " read the bead "..

 

[nybirdman]

Tig is used almost exclusively in the nuclear industry;I would think it is strong enough.You will not see a mig machine in a nuclear plant or ship.
My experience is on pipe in nuclear plants;normaly tig the first two passes and 7018/8018/9018 out.
I have welded on pipe with as much as 3-1/2" wall thickness(low pressure side of the turbine) and 100% x-ray.
I have been told that on a nuclear ship it is TIG all the way out.

 

[Shield Arc]

I have been told that on a nuclear ship it is TIG all the way out.

I live in a county with 3 Navy ship yards. One is a Trident sub base. All the welders that I know who work in these yards tell me all pipe welding is done with Tig only.

 

[C4Ranch]

3/8" with a relatively cheap mig..

http://youtu.be/bUEIdio6uY4

 

[C4Ranch]

Bottom line, depends on your technique , machine and experience..

 

[davesl708]

Thanks guys. Good info.

 

[woodlandfarms]

So why TIG for naval nuclear pipe? Because it is slower and more precise? Something in the TIG process that makes it better?

So, how do you wel a 4" thick piece of pipe? Just layers upon layers? How long does this process take?

 

[Gary Fowler]

So why TIG for naval nuclear pipe? Because it is slower and more precise? Something in the TIG process that makes it better?

So, how do you wel a 4" thick piece of pipe? Just layers upon layers? How long does this process take?

TIG is more precise AND slower due to the weld metal deposition rate. Like all welding processes, improper technique can leave weld defects like lack of fusion between passes, porosity etc. About the only defect that you don't get with TIG is slag entrapment but you can still get impurities in the weld from dirty rods that if not cleaned will look like slag on an Xray.
As for how long it takes, it depends on the welding procedure as to the amount of filler metal (thickness) per pass that is allowed, the current available etc. As with all welding, certain processes are faster than others but may not be all position capable. It is always better to put in multiple thin passes rather than one thick pass where possibility of cold lap increases if the current is not high enough. There is also the limitation of interpass temperature which is the maximum temperature the parent metal can be between passes AND the related Joules of energy that can be introduced into each pass. You can damage the parent metal if you get it too hot by using too much voltage/current in the electrode (or with the arc from a TIG torch). This is why in order to get a good weld, a procedure for welding the material must be qualified and the procedure followed to the letter when welding. This is especially true for materials other than mild steel which is the most forgiving of all weldable materials.