threading directly in PVC pipe fitting

[levesq01]

Quick question here. Is there any regulation (ASTM/ANSI) or documentation that confirm that you can tap threads directly into a PVC sch 80 PVC pipe fitting. In my case it's a 1/4" NPT into a 1 1/2" sch 80 elbow and "T".
Thanks.

 

[BigInch]

Very unlikely you will find such a statement.

We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer

 

[rconner]

I think you would find at least a good bit of discussion on threaded joint topics on this (with "Advanced...") and other forums with a good web search. A hole or for that matter tap cut in any pipe is of course a point of weakening stress concentration. While there of course is a long history of threaded piping application, and generally good degree of success particularly with strong and machinable metal pipes, there is also some history of problems involving threaded connections(and wet tapping etc. involving same). It appears the latter is particularly true with lesser strength materials such as plastics. Notice in the concluding answer at

http://www.homebuyerstalk.com/showthread.php?t=56552

that this poster mentions high leakage percentages of 30-50% and notes quite correctly and in maybe at least partial explanation for same that the NPT thread seal was designed, came first with "iron pipe" (not much weaker plastics etc., and of course most field/labor experience out there as well is with same). While the plastics industry claims success with plastic threaded stuff, and who knows perhaps even some level of same is on record, there appear to be greater incidence I have seen online of problems with particularly connections involving plastic threaded items, so installation is at the very least likely much more sensitive, and problems likely increase with threaded tap size.

In this regard I have also not seen a great deal of detailed supportive research involving various modal testing readily available concerning capabilities of directly threaded taps/joints involving plastic components or piping material mixes involving plastics; however, I am aware of the quite detailed comparative testing published by the Ductile Iron Pipe Research Association at

http://www.dipra.org/pdf/DIPvsPVCTapping.pdf

(note however these taps are a little larger than those with which you are reportedly dealing). Some other reports appear some less flattering, e.g. that of “Big Gus”, OP on the thread I’ve noticed at

http://www.sprinklertalk.com/wbb/index.php?page=Thread&threadID=1436

(don’t know if he is related to our “BigInch”!)

Everyone have a good weekend :>)

 

[BigInch]

Oh.. I think you can do it, provided the replacement material is considered and provided, but I think the code objection would be to cutting the threads into the main as too much of a stress concentrator and it would not have any reinforcement. Why not do it like a normal "welded" hot tap using a reinforcing split tee.

We will design everything from now on using only S.I. units ... except for the pipe diameter. Unk. British engineer

 

[europipe]

or make a threaded boss.