Internal pipethreads NPT & BSP

You can use either sch 40 or sch 80 - depending on the pressure involved and the application. So.....................

What are your pressures and application?

I am not sure that i explained myself well enogh; if i make 2" NPT internal threads in a 2" sch 40 pipe, will there be a problem with the wall thickness? And the same for 2" BSP internal threads??

Ahhhhh - I see .............

YES - it is a big problem trying to make a 2" FNPT (female NPT) out of 2" pipe - for all practical purposes it will not work.

Have a look at these dimensions and try to visualize why -

http://www.webfootcustomcalls.com/temp/NPTThreadSpecstable3.pdf

Can you just mount a standard 2" pipe coupling to whatever you are doing?

You can get them threaded both ends, or one side socket welded.

Or how about a threadolet?

I would suggest that you go to the next thicker schedule pipe size on anything schedule 40 and below. Although threaded schedule 40 may be thick enough for low pressures I would not take that chance. This is just a general rule I have always followed in my industrial pipe fitting career and I am not sure there is a code or standard that states this to the point. I don't know why you would want to thread the inside of a pipe because it is very uncommon to do this. Most people thread the outside of the pipe and the couplings are other fittings have internal threads. As far as wall thickness and pressure rating strength of pipe that has been threaded goes it doesn't really matter which side the threads are on. IMO.

pipewelder

Use a coupling.

Think about it - the OD of 2" sch 40 pipe is 2 3/8". If you put male threads on the piece of pipe the OD will still be 2 3/8" (not exactly - yes, the thread is tapered and is a bit smaller than the OD of the pipe, but not by much). Now, if you are going to screw that male pipe thread (MNPT) into a set of mating threads. the ID of the coupling will match the OD of the pipe.

You may be able to use a piece of sch 80 pipe and turn it into a coupling, but (without checking the wall thickness and ID of the sch 80 pipe, you may have to bore it out before you can thread it, or (worse yet) may not have enough material to get proper threads.

In short - make it simple and use a coupling.

Travis

If you put male threads on the piece of pipe the OD will still be 2 3/8" (not exactly - yes, the thread is tapered and is a bit smaller than the OD of the pipe, but not by much)

I have to disagree with this statement. The problem is not the threaded part that screws inside of a coupling or fitting but the small area of threads that the coupling or fitting dose not cover. (The depth of threads is cut nearly half way through the wall thickness on Sch. 40 pipe) The pipe will be weaker in this area. This why allot of specs. (especially steam and condensate and highly corrosive materials) will require Sch.. 80 nipples in areas that are to be threaded so that the min. wall is still achieved. If you are running schedule 20 or schedule 10 pipe you will have very little wall after threading and I have seen this thinner pipe distort when threading and/or tightening in these cases. It is common practice at least in my area to use the next thicker schedule for any threaded areas on most piping other than water or air lines to maintain the desired min wall thickness.

pipewelder