Open root gaps.

[coalsmoke]

Ok, I've noticed lately a few people posting pictures of some open root pipe work, and the gaps they are using seem to be really large, like 3/16 - 1/4" gap. Is this common practice when tig welding pipe? I sort of thought the gap would be more down in the 1/8" range to maintain a tighter internal bead profile

[enlpck]

The 'ideal' prep is the gap the same size as the land, with both being about the same as the filler size for the root. In practice, there is a lot of leeway, and some people have preference for a different fit, and many real situations end up with a fit much different. If it isn't dead tight, pretty much anything can be handled. Even dead tight is doable, but more difficult. I have run many roots where the fitup was poor enough that I had to run several passes to build into the gap before it could be bridged.

[flange jockey]

i have posted a few tig root gaps earlier,perhaps some of the work you mention coal.with these pipes a 3.25 gap was sufficient, this is light pipe.as the pipe gets larger in sch and od, it is common practice to open out the root gap to around 4mm,i think this is 5/32.its amazing just how much a root gap can close.it is possible to get a root in with a tighter gap,but its all work.although i personally go for a landing, i work with lads who go for a feathered edge and the 4mm gap.this is 8inch,not very good pics flange

[coalsmoke]

Flange, yep you are one of them guys I was referring too, nice work by the way

Thanks guys for the clarification. I am a novice still at tig, and am so used to welding things with open roots with 6010 that when I was those big roots it had me scratching my noggin. Flange, do you have to back purge or does the shielding gas from the torch give you sufficient coverage? I was just thinking about porosity on the backside / inside of the root pass.

[flange jockey]

coal there is no need for a back purge on mild steel with these larger gaps,porosity never seems to be an issue.im sorry i only had these couple of pics but if i get the chance i,ll try to get better ones in the future. thanks for your comments. flange

[SundownIII]

Flange,

That was one nice weld.

Photos were great and a very clear explanation.

Thanks

[flange jockey]

thanks sundown 111,i wont post on anything unless i feel i can pass on something useful.i really hate to contradict anyone but for me lately the bulls,,t meter on my threads has been in the red,its really out of character for me to behave as i have,a kneejerk reaction i suppose. flange

[slipery42]

coal there is no need for a back purge on mild steel with these larger gaps,porosity never seems to be an issue.im sorry i only had these couple of pics but if i get the chance i,ll try to get better ones in the future. thanks for your comments. flange

what amperage are you running and how thick is the wall? feather edge or land? I am trying to do stainless plate 3/16 beveled with open root for a test. Thought I could tig alright till the CWI said they want 100% penetration, have welded for years in food plants, welds always held and looked good, but now this tests adding a twist I am not used to open root welding. Eventually want to try pipe, I have aws in stick 1" plate and NYS DOT verticle 1" but again this is different animal I am trying to figure out. Any advise would be appreciated.

Slipery42

[bmfvtwin]

It might help answer some of your questions its helped me quite a bit

[Don52]

Try this place

It might help answer some of your questions its helped me quite a bit

Your hyperlink didn't work for me. Could you please re-post it?

[HT1]

Ok, I've noticed lately a few people posting pictures of some open root pipe work, and the gaps they are using seem to be really large, like 3/16 - 1/4" gap. Is this common practice when tig welding pipe? I sort of thought the gap would be more down in the 1/8" range to maintain a tighter internal bead profile

I have to do everything IAW the 22D
http://www.everyspec.com/MIL-STD/MIL...-STD-22D_5107/

3/16-1/4 is the LARGE end of the spectrum for joints that are not going to have a backing ring, a P2 calls for 0 - 1/8... I perfer a 0 if I can get it