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TOPIC: Rule or standard which applies to minimum nipple?

6 years 7 months ago #8268

  • josefelixtovar
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Hello, I would like to know the rule or standard that applies to the definition of the distance that must be allowed between the nipple minimum of two fittings based solders, this based on the pipe diameter.

Re: Rule or standard which applies to minimum nipple? 6 years 7 months ago #6757

  • Jop
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This part of your posting "two fittings based solders" suggests to me that you are talking about Copper Tubing and socket fittings joined by soldering often called "Sweat" joints.
Now if that is true then the distance between two sweat fittings can be almost zero. The short piece of copper tubing between the two fittings does not need to show, it can be completely covered with the overflow of solder.

Of interest to myself and I am sure others is, why are you so concerned about this that you are asking this question?
Do it once and Do it Right

Re: Rule or standard which applies to minimum nipple? 6 years 7 months ago #6758

  • josefelixtovar
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I apologize for not expressing myself well, but I meant carbon steel pipes, with a sch. 80

Re: Rule or standard which applies to minimum nipple? 6 years 7 months ago #6759

  • Jop
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You wrote: "I apologize for not expressing myself well, but I meant carbon steel pipes, with a sch. 80".
This tells me you you might be using either "Screwed" make-up or "Socket-Weld" make up.

For "Screwed" (Threaded) assembly the minimum distance between the two fitting shoulders would be based on wrench dimensions. To do the assembly the fitter needs to thread the nipple into the first fitting or valve, then make it wrench tight. Then the next fitting (or Valve) can be threaded on, made wrench tight and aligned.

For "Socket-weld" assembly the minimum distance between the shoulders of two fittings (or valves, or a fitting and a valve) would be based on the dimensions of the Fillet Weld and a gap between the two Fillet Welds so there is no over lap of the head affected zones (HAZ).

Unless you have a very special situation you should not try to customize the length of Pipe Nipples. It is cheaper to buy them in bulk (large quantities) based on what is available from your supplier and use them "As-Is".

Pipe Nipples: A Nipple is a name given to a short length of pipe. It is not really a fitting in the same context as an elbow or a Tee. Nipples are cut from pipe and can be purchased in 4", 6" and 12" standard lengths. Pipe Nipples can also be made (at an added cost) any length by the piping crew in the field.

Look here for some commercial data on Pipe Nipples: Pipe Nipples
Do it once and Do it Right

Re: Rule or standard which applies to minimum nipple? 6 years 7 months ago #6760

  • 11echo
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“Store bought” threaded nipples start at about 12” long, and decrease in length at increments of ½”, down to what is called a “close nipple” …almost back to back threaded ends:

http://www.thefind.com/search?query=close+nipple+steel

Normal threaded pipe systems are threaded in the field during fabrication. However when the pipe to be threaded is 12” or shorter the normal field tooling doesn’t have the length to hold the pipe ridged enough and try to cut threads with a die, and the pipe will start twisting in the holder, hence the reason to purchase the prefab threaded nipples.

Socket welded piping can get as short as a welder can get a welding rod in (at the proper angle) to run a bead. Depending on whether the fittings are 3000#, 6000#, or larger (the shoulder on the fittings gets thicker the higher the rating) …I’ve seen socket welded fittings with about 1” between weld beads on 1” piping. What I have listed here is what “could be done” …the real trick is “should it be done”! As JOP pointed out when you have weld beads closer then 3” you get a over lapping heat effected zone, this can cause the steel to become brittle and fail at this location on high pressure/high stress piping. This can be over come with the use of PWHT (post weld heat treat) procedure, where this area is heated back up to approximately 1750 Deg.s F and slowly brought down to ambient temperature. Now the other side of this do you need too? If this is not high pressure/high stress piping then you probably would NOT need to do the PWHT and the piping system would function correctly as-is. IF you have questions about this then address them to your stress dept. for clarification.
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