4

A close pipe nipple is designed so that when it is installed there is very little or no gap between the two fittings which attach to either end.

What is the proper method to install one of these? Could be black iron, brass, etc.

Here are the issues I wonder about:

  • When attaching the nipple to the first fitting, it seems you would have to grip the nipple by the threads with a pipe wrench. This may cause damage. Perhaps a protective padding is used?

  • When attaching the second fitting, how to ensure the nipple is inserted more or less evenly? The insertion torque may continue to tighten it into the first fitting which would be hard to prevent or even observe.

  • Should you just tighten both fittings simultaneously?

Example of a close nipple:

enter image description here

  • If this is US-specific terminology I'd be happy to update to add alternatives, eg British usage – UuDdLrLrSs Mar 20 '18 at 0:33
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Installing the close nipple is done by starting the nipple into the first fitting by hand. Then start the second fitting. Make sure that the suitable teflon pipe thread tape is installed on both ends of the close nipple. Then use an appropriate wrench on the second fitting to tighten the joints.

Note that the threads on a nipple like this should have a diameter taper on each end. This causes the fitting to get progressively tighter as each end is screwed into its mating part. When tightening the two joints simultaneously the two tapered joints will turn till one gets tighter than the other. At that point the looser one will then tighten up till it catches up and becomes similar tight to the other joint. Eventually you will achieve the necessary thread engagement with each end of the nipple.

  • So it seems then that the nipple is designed so that once all the threads are out of sight, it should produce a correct joint... is that right? – UuDdLrLrSs Oct 28 '18 at 13:27
  • As Michael correctly points out close nipples are tapered on each end. With this said the Pop's photo appear's to be a running thread there is usually a mismatch on the center thread for a close nipple.+ – Ed Beal Oct 28 '18 at 14:43
  • Having done several of these since my original post, this description is definitely correct, and I had no problems with any of them. That said, I did prefer to use longer ones where possible since that provided an addition surface to wrench on. So I wouldn't use a close one unless really needed. – UuDdLrLrSs Jul 11 '19 at 19:22
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All the negative thoughts are why "all thread nipples" or "close nipples" as they are sometimes called are banned by certain industries. since there is no actual plain, not threaded pipe in the center of the fitting, you do not know how much pipe material is inserted into either fitting making it a potential danger. Natural gas suppliers in my area of the country will not approve a gas supply if an "all thread nipple" is used. Due to their make up they will be the first fitting to cause a leak. So, to answer yiur question, I never used them and neither should you. There is always an alternative.

  • This doesn't answer the question, which is about installation technique. Not all applications have safety as a concern, and obviously they exist for a reason. – isherwood Mar 20 '18 at 13:41
  • My answer is good enough for my way of thinking. Any time I got these in a nipple kit I would throw them away and use the next size larger usually referred to as a shoulder nipple, unless of course I were using them for electrical work. – d.george Mar 20 '18 at 15:37
  • A close nipple is tapered on both ends. A running thread nipple as you are trying to explain it the thread that is not legal in most places. – Ed Beal Oct 28 '18 at 14:39
  • Dear ED; I do know the difference between tapered and running thread nipples. I worked as a boiler installer and service tech for 40+ years and installed boilers that used both type threads. So "NO" i am not talking about a running thread nipple. And "YES" all thread nipples are a bad idea unless you are not worried about a leaking fluid. I do use them for conduit and other applications. As I previously stated, they were not allowed on gas lines in my area and I would never use them on any pressure piping since you do not know if 1 side would always tighten correctly. – d.george Oct 29 '18 at 10:08
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The correct installation technique for a close nipple is to apply thread sealant and then thread the nipple into both fittings by hand by 2 or more turn before tightening using wrenches on the fittings, never on the nipple. The question does seem to understand that using a wrench on a nipple could be wrong, which is an understatement.

in re: "nipples with no plain pipe segment are bad/prohibited" etc. This nonsense is for the convenience of know-nothing inspectors, and doesn't actually prevent the danger it seeks to ameliorate. All nipples, pipe, and fittings except for the type called "rigid conduit" which is for electrical use only, are threaded with a "tapered" thread. The threads are conically tapered for a cone-in-cone wedge fit that becomes progressively tighter. There is no danger of one side sinking into the fitting and the other side remaining with just a couple of turns of engagement. It requires only minimal competence to distinguish between a connection make with a tapered thread and a connection made with a non-tapered aka "running" thread. The expectation that inspectors and workmen are unable to distinguish between the says as much as needs to be said.

[NB: rigid electrical conduit look like schedule 40 galvanized iron (actually its been steel for more than a century) pipe and fittings may be made using a non-tapered thread. electrical conduit joints aren't required to seal against pressure, and generally don't.]

Thread sealant generally mean using a good "pipe dope" e.g. Rectorseal No 5. Teflon tape is less messy to use but much more likely to produce a leaky joint. The tape must remain in place well enough to undergo "plastic flow" deforming itself to fill the non-conforming parts of the joint. It always shreds and stays at the leading edge of the pipe to some extent. Never use Teflon tape for fuel oil lines, the shredicles can (will) plug up the fuel oil pump and nozzle strainer. Specialty thread sealant products for specific fluids like liquid fuels and refrigerants often also seal water and natural gas, (see product labeling) . Their use is uncommon because of their high cost. Be certain the product is safety agency listed for the intended use when applicable.

  • RMC/GRC uses tapered (NPT) threads as well, except for certain fittings, which use straight threads (don't ask me why precisely this is so); this is so that they can seal against contaminant ingress (which is extremely important, especially in classified/hazardous location work, but also in wet/... locations) as well as providing an "electrically tight" grounding path despite corrosive factors. – ThreePhaseEel Aug 24 '19 at 0:02
  • "shredicles" 😀 – UuDdLrLrSs Aug 24 '19 at 11:03

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