Thread a short pipe coming out of a wall?

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I have a short piece of 1-1/2 inch underground pipe coming out of an exterior wall and into my basement. It is a gas supply line. Here is a photo:
http://i56.tinypic.com/qx9kl1.jpg
The part coming out of the wall and before the first silver fitting is about 5 inches long to that point.
My question is, if I take all of the fittings off, and I cut the pipe to make it shorter, is there any way to thread the remaining piece of pipe in place while it is still in the wall?
And, if so, what is approximately the shortest length I can make that pipe and still thread it while in place in the wall?
It's a long story why I am asking this question -- most of which is explained in a thread I started here on 11/08/2010 with the subject "ID this gas pipe fitting?"
Thanks.
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You can thread it with the appropriate pipe die and tool. There would certainly be enough left to easily thread, You might be able to rent one at a tool rental shop. Sounds like you need to shorten it for some reason? The threading tool can be run right up to the wall and should cut threads to within 1/4 to 1/2" of the wall, so you could cut it off about 1 3/4 from the wall.
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On 11/20/2010 12:07 PM, snipped-for-privacy@optonline.net wrote:

The only thing I'd worry about is turning the next thread on the other side of the wall. It looks like, but I can't really tell from the pic, that the pipe is going through a sleeve pipe in the concrete. If it's not a sleeve and is threaded into it, then you can remove it and put in a new shorter nipple. But my guess is that it is just a sleeve.
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wrote:

It is just a sleeve in the block wall that it goes through. On the other side of the wall, it is all underground all the way out to the shutoff at the street. So there is no access to the pipe on the outside without digging the whole thing up.
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snipped-for-privacy@optonline.net wrote: ...

Not w/ a standard threader, no....the leading end of a pipe threader is inches long to align the die with the length of pipe to ensure start threading evenly. Otherwise, there's no hope of getting started straight w/ a plain die, particularly on this large a pipe (iirc, this is 1-1/2 or maybe larger, even; I recall it's a supply to a 3-unit building not just a single residence).
OP is getting too fine here, imo. Build around it and make do.
I suppose one alternative would be to thread on past the existing as far as can, then cut the remaining off leaving the proper thread length.
Remember that NPT threads are tapered and require that taper for proper leakproof tightening.
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wrote:

Chances are good that I will just end up building around what is there rather than actually trying to shorten the pipe and thread the end. But, I thought I'd check here to see what the options may be for threading it. If I were going to try to thread the pipe, assuming that I figured a way to do that, I like the idea of continuing the existing threads and then cutting off the pipe. However, you pointed out an important issue about the need for tapered threads. I am not sure how I would be able to achieve that.
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Is there some important reason those pipes need to be covered up or built into something ?
That big of a gas service it is better to leave it exposed so that if you ever start smelling gas you won't need to be digging into walls to have the pipes sniffed with the leak detector meter...
Since this is a multi-unit dwelling IF you wanted to mess with this pipe at all, it would behoove you to hire a licensed and qualified gasfitter so that you won't be liable for anything if you mess with it yourself and it leaked for whatever reason down the road...
~~ Evan
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On Sat, 20 Nov 2010 19:49:43 -0800 (PST), Evan

Best advice right there. You don't to want mess with that nipple. Probably gas company property. No way for you to ensure the joint outside isn't leaking after you fool around with it. I wouldn't touch anything from the street el to the wall. Too much chance of creating a leak outside.
--Vic
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RogerT wrote: ...

Don't leave excessive thread length on the stub end--NPT dies are tapered; the thickness of the die provides the proper taper from start to end of a full cut.
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dpb wrote:

...
BTW, FYI...
Following is picture of my threader for 1-2" pipe; a single die-head ratchet handle and head would be somewhat smaller but not by a tremendous amount...
<http://www.ridgid.com/Tools/65RC-Receding-Threader/EN/index.htm
Sample single head/die -- good up to 1-1/4" and I think you have 1-1/2" iirc????
<http://www.ridgid.com/Tools/Enclosed-Ratchet-Threader-Sets/EN/index.htm
Answer remains it'll take a sizable extra length and as somebody else noted, you'd be wise to have a backstop wrench to resist the torque that would take another couple inches besides...
--
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Thanks. I doubt that I'm even going to attempt this, but it's good to know how the taper works.
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RogerT wrote:

Not likely. Threading takes a lot of torque, the pipe may break or spin out or strip at the other end in the ground unless the cement has a good hold on it.
--
LSMFT

Simple job, assist the assistant of the physicist.
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If the pipe can't withstand the torque of threading, which isn't all that great, then it shouldn't be carrying gas to begin with.
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Likely that is the only logical choice. The odd fitting is a gas union and should easily unscrew allowing a shorter nipple to be installed. Confirm the fitting purpose with your gas company since it is an unusual type not used in many areas.
Joe
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Roger-
Hold on there for a bit....... I re-read the entire previous thread & looked at all the photos.
It's raining here & I've been waiting for a break to walk out to the garage to measure my pipe dies. The largest one I have is 1". It's meant to go on the Rigid 00-R handle.
I think to thread 1-1/2" pipe you'll need a 12-R and those dies are a bit larger.
With my smaller set, from back side to front edge of pipe, you need I'm wet but I have hard numbers
With the 1" die in my handle set you need at least 3"" from the wall and that would not give you any finger space to wrap around the handle, you'd be "clawing" at the with your fingers.
I'm figuring the with a big boy like 1-1/2" you'll need even more clearance.
I would suggest not cutting anything until you have the exact dimensions of your re-threading solution.
Hex style dies for "threading" pipe are available but they are more for thread chasing / thread repair. Getting one to starting squarely on a pipe stub would be quite a trick. :(
The overall length of the thread; good thread (~3/4) and imperfect threads (~1/4") is just a bit over 1".
McMaster Carr has one but its huge, 3.5" across the flats.
2573A93 Thread Repair Hex Dies Right Hand, 1-1/2"-11-1/2 NPT, 3-1/2" W Across Flats In stock at $159.35 Each
Back on your original thread, having taken another look at all the photos & the current ones as well, I think the fitting in question is some sort of union, with the rusty part threading over the shiny part.
Did you ever determine if the shiny part was magnetic? (steel vs aluminum)
cheers Bob
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wrote:

Roger-
Hold on there for a bit....... I re-read the entire previous thread & looked at all the photos.
It's raining here & I've been waiting for a break to walk out to the garage to measure my pipe dies. The largest one I have is 1". It's meant to go on the Rigid 00-R handle.
I think to thread 1-1/2" pipe you'll need a 12-R and those dies are a bit larger.
With my smaller set, from back side to front edge of pipe, you need I'm wet but I have hard numbers
With the 1" die in my handle set you need at least 3"" from the wall and that would not give you any finger space to wrap around the handle, you'd be "clawing" at the with your fingers.
I'm figuring the with a big boy like 1-1/2" you'll need even more clearance.
I would suggest not cutting anything until you have the exact dimensions of your re-threading solution.
Hex style dies for "threading" pipe are available but they are more for thread chasing / thread repair. Getting one to starting squarely on a pipe stub would be quite a trick. :(
The overall length of the thread; good thread (~3/4) and imperfect threads (~1/4") is just a bit over 1".
McMaster Carr has one but its huge, 3.5" across the flats.
2573A93 Thread Repair Hex Dies Right Hand, 1-1/2"-11-1/2 NPT, 3-1/2" W Across Flats In stock at $159.35 Each
Back on your original thread, having taken another look at all the photos & the current ones as well, I think the fitting in question is some sort of union, with the rusty part threading over the shiny part.
Did you ever determine if the shiny part was magnetic? (steel vs aluminum)
cheers Bob
+++++++++++
I didn't check the silver fitting with a magnet yet, but I will.
I also found this link about threading pipe: http://www.extremehowto.com/xh/article.asp?article_id `299 .
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Good points. It's been decades since I threaded any pipe and I sold the set of dies I had. Along with your comments on cutting, I'd add it's critical how it's cut too. It should be cut with a pipe cutter, so the end is prefectly clean. You can't just cut it with a reciprocating saw, etc.
I also agree with those that expressed concern for what might be on the other side that we don't know about, ie another fitting, etc. Without holding the pipe to keep it from moving, it's possible the torque could tighten another nearby fitting on the other side and cause it to start leaking. With gas, especially, you want to be able to check all fittings that have been moved to make sure there is no leak.
All factored in, sounds like the most he could shorten it would be a couple inches and most likely not worth it.

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On Sun, 21 Nov 2010 05:24:27 -0800 (PST), snipped-for-privacy@optonline.net wrote:

This fitting could well be a dielectric union- provides electrical interruption to protect the main gas lines from unwanted current flow which causes corrosion. Removing this union may be in violation of gas vendor rules. Check with them first! Second, as has been mentioned, you may cause a leak in the fittings out under the fill by all the vibration and torqueing.
--
Mr.E

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DD_BobK wrote:

The long distance is so the die starts straight on the pipe (as at least one person said). Once the thread is started, in the die sets I have used you can reverse the cutting edges and use the die backwards so the die face is about at the edge of the cut threads.
I am leery (as other are) that torquing the pipe could produce leaks at joints on the other side of the wall. The pipe runs through the wall in a sleeve, which could allow gas leaking on the other side into the basement.
You would gain some space if you could eliminate the mystery fitting plus the next one and just put an elbow on the supply pipe. I wouldn't remove them without knowing why they are there. If the mystery fitting is a dielectric separation it could be on the other side the elbow.
I have a moderately high level of paranoia about gas pipes. Advice from the gas utility would be nice.
--
bud--

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bud-- wrote: ...

...
That eliminates the design taper entirely by doing so, though...

Which is _a_good_thing_ (tm) and certainly a reason to not do the above to ensure good fitting threads...for water I'd worry less; for gas I'd not consider it.
--
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