Checking and improving fit of NPT female pipe threads

[oceanobob]

Dimension the problem? Since a lot of pipe installation is to make almost all the male pipe threads (except for nipples) and purchase the fittings, would like to know if a short involvement with a new HSS pipe tap would improve the subsequent fitment? While gaging may also be the answer, not sure if that will detect the possibility the threads, being mass produced, allow for some extra space - which then challenges the pipe sealant's ability to prevent leaks.

The basic process would be to insert the tap in the fitting and maybe turn it a quarter to a half turn, not so much it alters the fitting greatly but more or less would be analagous to a the nickname 'ghost pass'.
If a small amount of hand tapping would refine the shape and the details of the thread form and this helps to improve the fitment, the process could also be gaged before and after to validate the operation.

Seems that since we make the male threads (up to four inches using sched 40 and sched 80 steel pipe A53 and A106), the focus of the issues/comments is the male thread yet the fitting is somehow never mentioned....thus the musing how would we know if the fitting is the contributor.

 

[Gordon Heaton]

If your fittings are chinese, you've already lost the battle. They are almost always too deep to begin with so turning a tap 'quarter to half' turn will make them completely unusable. You should be pretty safe with the males if threading your own, but the chinese version of those are also always loose too.

 

[rons]

After the 1/2 turn tap operation the hole will be larger and whatever screws into it will go deeper.
If you are using Teflon tape/paste what difference is there? No Se.

 

[gbent]

If you must use chinee fittings, use twice as many turns of good quality teflon tape, then coat liberally with pipe dope.

 

[oceanobob]

There is a possibility the fitting will be import but purportedly will be "better" if we invoke the fire sprinkler FM stamp. This will require ordering in advance and shipping in, no jumping in the shop truck to get some fittings from local supply house.
As it is, we see the fittings are import but from various sources on the other side of the Pacific.

 

[gbent]

Order your fittings from McMaster Carr. The ones I get from them are Anvil brand, made in USA.

 

[GregSY]

Your writing style reminds of those Chinese-to-American article that are popping up all over the internet these days. WTF...

 

[john.k]

Use a system called NPTF Dryseal.

 

[Milland]

Unless the fittings are greatly off-spec, anything you do with a tap will make things worse due to the fresh edge discontinuity generated by taper threads and flute count of the tap (straight threads obviously don't have this issue).

If you want to improve the fit up, CLEAN the fittings and male threads well, then apply a proper amount of quality sealant in a consistent manner to the male threads (as close to the nose as possible without intruding onto the face or bore), then assemble to suit. Allow sufficient drying time before exposing the joint to fluids.

The only way to really get good female taper threads is to single-point them or threadmill with a proper leadout to "feather" the discontinuity. Taps only work because of sealant and good assembly practice.

I don't use tape on anything critical as it can cause issues with loose strands or insecure joints.

 

[rons]

Use BSP threads and you won't have any issues. If I could cut them I would convert. Wot.

Have also converted NPT to NPS and seated a squared nut edge to the flat side of a second fitting. No sealant needed.

One last thing about imports. When they get the alignment off the connection looks like a POS.
That is the time I would think about a jig to align the hole straight with a tap. Never did it yet.

 

[oceanobob]

For whatever reason, I cleaned the extra Korean flange of the paint at the f threads applied a thin coat of red Dykem, and allowed it to dry.
The tap, a new Cleveland, was inserted clean yet dry and by hand it went all the way (ergo about 10 threads).
Noticed the tap appeared to contact the flange (only) at the thread root, especially at the larger diameter of the taper.
Added a small amount of tapping oil and very lightly turned the tap about a couple turns which definitely showed the tapping action was at the larger diameter of the flange; the thread crest was untouched throughout.
Conclusion: the flange thread is a little less taper than spec'd, assuming the tap is correct.

The pic of the tap uncleaned - shows the very little material that was removed.




Now, if only I had a plug and a ring gage.

 

[RC Mech]

“Dimension the problem?” “Challenges the pipe’s sealant ability”, “Ghost pass”, “refine shape and details of the thread form”?

With all due respect, learn how to write in English before participating in predominantly English speaking forum.

With less due respect, stick to working in whatever the fuck field you’re from before delving into manufacturing. We have to compete with these smooth-brains? JFC.

 

[henrya]

That’s a pretty rough response.

 

[reggie_obe]

If fit matters, buy Ward pipe fittings: https://www.wardmfg.com/

 

[henrya]

Would any of you NPT experts have a program set up to make me a couple of 1/2" NPT plugs? Start with 1" square bar stock and turn the male 1/2" NPT to standard dimension, leaving a 1" long square section on top. No holes, no nothing else. I will take care of the rest. 304 or 316 stainless, please.

 

[Richard King]

I have has issues in the past on K&T Hydraulic pumps on Horz. Milling machines and the threaded pipe threads leaked even with Teflon Tape and it sucked air. I had a Loc-Tite rep tell me about the sealant that takes 24 hours to dry and you get 100% seal. It has worked on other pipe thread leak applications and I swear by it. You have to let it dry. https://www.zoro.com/loctite-loctite-567-thread-sealant-pipe-thread-sealant-6ml-tube-low-white-2087068/i/G5770926/?gclid=d9a9080649e31c525ec66b42cca345b7&gclsrc=3p.ds&msclkid=d9a9080649e31c525ec66b42cca345b7&utm_source=bing&utm_medium=cpc&utm_campaign=ml_all_na_na_ssc_Bing Smart Shopping&utm_term=4586131722563170&utm_content=All Products

 

[cyanidekid]

Order your fittings from McMaster Carr. The ones I get from them are Anvil brand, made in USA.

no, its NOT that easy.

you can't count on McMaster for quality anything without checking on the brand and or origin,( this really pisses me off). the single worst piece of stainless ive ever come across was a stainless nipple from them made in India. total garbage ( client ordered it).

I usually prefer to order from somewhere that tells me up front the brand and origin without having to ask. ya'll can hate on MSC, but at least they tell ya up front. they sell Anvil made in USA also.

 

[rons]

The pic of the tap uncleaned - shows the very little material that was removed.


View attachment 376776View attachment 376777View attachment 376778

Now, if only I had a plug and a ring gage.

There is an intersection of the two mates. Right in the middle. It will work by design and not be perfect.
What you will do with a clean up tap would make it better assuming that you tap matches your male threaded part.
You will still use tape and you will know it's better. That angle of about 2.5 degrees is what it comes out to.

 

[RC Mech]

Would any of you NPT experts have a program set up to make me a couple of 1/2" NPT plugs? Start with 1" square bar stock and turn the male 1/2" NPT to standard dimension, leaving a 1" long square section on top. No holes, no nothing else. I will take care of the rest. 304 or 316 stainless, please.

If you’re serious, yes I can do this. Depending on the total quantities, I’m not sure it’s worth starting with square stock and plowing through that interrupted cut in 316. Turn/mill may be easier.

If no one closer to TN offers to do this, hit me up.

As far as the post above, I’ve already got my hand slapped by PM’s mods. The OP comes off as a 1st year Eng student applying vague principles out-of-context. Same as the countless number of CO-OP students I’ve dismissed and never re-hired who were infatuated with “delrin”. No technical reason for loving POM, just a word they’ve heard and parrot incessantly.

I’m not an “old” guy but with each passing day I have to admit I further understand where the old codgers get their sass from. WE (the royal WE) who live and breath this stuff have learned it through rigorous study both in and out of the classroom. You’d be hard-pressed to come up with a trade that is MORE technical than machining and tool making.