Welded Pipe Question

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I have installed a compressor and small piping system in my shop for use with a plasma cutter. To help dry the air I have used 3/4" pipe from the compressor shown entering the left side of the photo. Note that the vibration isolation does not appear in the photo but is located between the compressor and the rack.  I then have a 2" section of pipe for an expansion chamber. The piping then reduces to 1/2" pipe to the upper right of the rack where my regulator/filter and quick disconnects are located. Everything fitted up nicely except for the top reducer to 2" pipe connection where no matter how hard I try, I can't get the threads to seal. I've used (and redone) dope, tape and lots of muscle.My question: If I remove the section of of 2" piping and seal weld the leaky connection, will it be a safety concern with the compressed air? My compressor tops out at 175 PSI so the system should never see any higher pressures. I do know how to protect myself form the zinc oxide fumes if I perform this weld. Attached Images
Reply:I wouldn't recommend welding on the 2" fitting for a couple of reasons. The base metal of the fitting is not suitable for welding  and you would need to remove all the teflon tape, pipe dope, etc prior to welding.I'd change out the fitting, chase the threads on the end of the 2" nipple and use a good grade of thread lube / sealant. If your threads and fitting are good there is really no need for any type of sealant.On another note:Your using the 2" as a "knock out pot" to remove moisture. Gravity will move the liquid to the lower part of the 2" pipe.  Your out flow from the 2" nipple should be located closer to the top of your 2" nipple. With the outflow located at the bottom, the flow is going to pick up the moisture at the bottom of the nipple and carry it down stream.Thanks,HoboLincoln SA200's... at least 15 - 20. They come and go. Growing partial to the "Short Hoods" in my old age. Last count on Short Hoods was 13 in possession.
Reply:Originally Posted by TimmerEverything fitted up nicely except for the top reducer to 2" pipe connection where no matter how hard I try, I can't get the threads to seal. I've used (and redone) dope, tape and lots of muscle..
Reply:I'm glad I asked the question. Tonight I'll disassemble the 2" section and replace it with an exact duplicate which means......New Threads! I use quality dope and we will see if I can stop the leak. I just didn't feel right about welding on threaded pipe. I'm just guessing but where its the only leak I had I assume I may have some bad threads in the 2" or the fittings. As far as the outflow goes, I will incorporate a couple of 90 degree elbows in prior to the drain valve to act as a "baffle". I'm not dealing with a lot of moisture as it is.Thanks your your input!!It pays to be safe!
Reply:If the flex between comp and piping is long enough it doesn't look too complicated to swap ends on 2" and add a tee to bring the air in and retain the drain as it is. Also have the leaking end of the 2" cut and rethreaded and a new bell reducer. Maybe that would take care of the leak.                                                               MikeOl' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:Loctite makes a sealant for pneumatic service. Goes on as a liquid and sets up after assembly. Would probably work well for what you're doing.
Reply:Update: I was going to reuse the old pieces and make the system operate with the pieces I had at hand. Then I decided I was going to have this system for a very long time and I wanted it correct. soooo..... With the help of a pipe fitting friend I built a new 2" section and I did install the outlet near the top of the 2" pipe section. This one screwed together without any resistance like the last one had. That makes me think the older threads were somehow not quite right. I ran out of daylight so I didn't get it inserted into the system. That will be tonight's project I'll put a photo on when I get it all operational. Then the only thing left will be to learn how to operate the plasma cutter!!!!Thanks everyone for your suggestions..............this is the place to come for good help and to learn a thing or two.
Reply:Blue Block, the only way to go on everything but potable water threaded joints. http://www.accentshopping.com/product.asp?P_ID=148706Use USA pipe and fittings and that will cure alot of head aches as well.Disclaimer; "I am just an a$$hole welder, don't take it personally ."
Reply:Okay....here is the updated configuration. It seems to work well. Now to hook up the plasma cutter..............Thanks again for all the help! Attached Images
Reply:unless you special-ordered the material for this project  to be suitable for the175 psi,with a safety factor,  none of that stuff is rated above 125 psi...
Reply:Now you've got it. Looks like it's good to go.Lincoln SA200's... at least 15 - 20. They come and go. Growing partial to the "Short Hoods" in my old age. Last count on Short Hoods was 13 in possession.
Reply:Weldbead,It all safely exceeds the 175psi (except for the regulator--rated for 175psi--Its getting changed out this weekend because it feels cheap).....I checked it all. Thanks for the concern.Last edited by Timmer; 10-13-2012 at 02:13 AM.