Strength of 3/4" iron pipe threads.

Thanks,

Boyntonstu

In article ,
says...
Strength of 3/4" iron pipe threads.

Thanks,

I think this was posted recently a few times, if you check google it
should turn up the answer for you.

--
Duncan Munro
http://metal.duncanamps.com

Yeah it was Stu himself a week ago. Maybe time for you to get a book, eh
Stu?

Todd L

"Duncan Munro" wrote in message
.. .
In article ,
says...
Strength of 3/4" iron pipe threads.

Thanks,

I think this was posted recently a few times, if you check google it
should turn up the answer for you.

--
Duncan Munro
http://metal.duncanamps.com

"Stu" wrote in message
om...
Strength of 3/4" iron pipe threads.

Thanks,

Boyntonstu

Here ya' go, Stu:

3/4" iron pipe threads produce 32,450 ksi inverted shear strength. That is,
assuming you've torqued the joint to a value between 86.5 and 86.6 ft-lb,
backed off a half-turn, and re-tightened by 11/16 of a turn.

Enjoy!

Ed Huntress

In article , Ed Huntress
says...

3/4" iron pipe threads produce 32,450 ksi inverted shear strength.

Hmm. That sounds like a lot. Is this for the
special 'nobendium' alloy?

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

Ed Huntress wrote: 3/4" iron pipe threads produce 32,450 ksi inverted shear
strength. That is, assuming you've torqued the joint to a value between 86.5
and 86.6 ft-lb, backed off a half-turn, and re-tightened by 11/16 of a turn.
^^^^^^^^^^^^^^^
Ed, I looked in the index of Machinery's Handbook, and couldn't find this.
So I turned all the pages, and STILL couldn't find it. I KNOW this will
come up again, so I'd love to know to look for it. Please hurry. I'm
holding my breath.

Ed Huntress wrote:

"Stu" wrote in message
om...
Strength of 3/4" iron pipe threads.

Thanks,

Boyntonstu

Here ya' go, Stu:

3/4" iron pipe threads produce 32,450 ksi inverted shear strength. That is,
assuming you've torqued the joint to a value between 86.5 and 86.6 ft-lb,
backed off a half-turn, and re-tightened by 11/16 of a turn.

Enjoy!

Ed Huntress

You can get at least 23.76% more than that if you use unobtanium pipe.

Jeff
--

Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can smile when things are going wrong, you've thought of someone to
blame it on."

Stu wrote:

Strength of 3/4" iron pipe threads.

Thanks,

Boyntonstu

You just don't give up, do you Stu?

Jeff

--

Jeff Wisnia (W1BSV + Brass Rat '57 EE)

"If you can smile when things are going wrong, you've thought of someone
to blame it on."

Jeff Wisnia wrote:

Ed Huntress wrote:


"Stu" wrote in message
.com...

Strength of 3/4" iron pipe threads.

Thanks,

Boyntonstu

Here ya' go, Stu:

3/4" iron pipe threads produce 32,450 ksi inverted shear strength. That is,
assuming you've torqued the joint to a value between 86.5 and 86.6 ft-lb,
backed off a half-turn, and re-tightened by 11/16 of a turn.

Enjoy!

Ed Huntress


You can get at least 23.76% more than that if you use unobtanium pipe.

Jeff



Even Better than that, if you fill the pipe with heavy water, its extra
gravitational attraction will lessen the "pull" of the earths gravity by
about .000258758 g/M/L. Note that if you put a resivoir above it, the
larger you make it, the more you can hang from the pipe. To acheive
the ultimate suspensive force, you must couple your resivoir to an
ocean,... or at least one of the great salty lakes. You must use PVC
pipe for this coupling though, or else the free gravitrons will adhere
to a metal coupling pipe and you wont get anywhere.

mark

"jim rozen" wrote in message
...
In article , Ed Huntress
says...

3/4" iron pipe threads produce 32,450 ksi inverted shear strength.

Hmm. That sounds like a lot. Is this for the
special 'nobendium' alloy?

Yes, except that nobendium loses strength when you bend it.

Ed Huntress

"Leo Lichtman" wrote in message
...

Ed Huntress wrote: 3/4" iron pipe threads produce 32,450 ksi inverted
shear
strength. That is, assuming you've torqued the joint to a value between
86.5
and 86.6 ft-lb, backed off a half-turn, and re-tightened by 11/16 of a
turn.
^^^^^^^^^^^^^^^
Ed, I looked in the index of Machinery's Handbook, and couldn't find this.
So I turned all the pages, and STILL couldn't find it. I KNOW this will
come up again, so I'd love to know to look for it. Please hurry. I'm
holding my breath.

It's written in secret code, right after the index.

Ed Huntress

In article , Ed Huntress
says...

Yes, except that nobendium loses strength when you bend it.

Oh, well. That's no problem.

I'm not strong enought to do *that*.

:^)

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

Ed Huntress wrote:

It's written in secret code, right after the index.


In my 12th edition, it's written on the edge of the page, in green ink,
where it can only read by those having a high moral tone and heroic
studliness.

Kevin Gallimore




-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Group,

First let me apologize for posting my question more than one time.
The problem was the Google was 'hiding' my posts and I repeated them
because I believed that they were not posted. I asked Google to
'splain.

Why did I ask this questiion?

See my homebuilt elevator that 'hangs' on the threads of a single 3/4"
black iron pipe.


http://www.imagestation.com/album/?id=4288894713 Homebuilt Elevator

Thanks again,

BoyntonStu


Jeff Wisnia wrote in message ...
Ed Huntress wrote:

"Stu" wrote in message
om...
Strength of 3/4" iron pipe threads.

Thanks,

Boyntonstu

Here ya' go, Stu:

3/4" iron pipe threads produce 32,450 ksi inverted shear strength. That is,
assuming you've torqued the joint to a value between 86.5 and 86.6 ft-lb,
backed off a half-turn, and re-tightened by 11/16 of a turn.

Enjoy!

Ed Huntress

You can get at least 23.76% more than that if you use unobtanium pipe.

Jeff

In article , Stu says...

Group,

First let me apologize for posting my question more than one time.
The problem was the Google was 'hiding' my posts and I repeated them
because I believed that they were not posted. I asked Google to
'splain.

They do that, down in the fine print they often say
that 'some similar search results were omitted, click
here if you want to see them' or something like that.

BTW if the machine is already built and works fine,
why investigate the tensile strength issue now?

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

In article , axolotl says...

In my 12th edition, it's written on the edge of the page, in green ink,
where it can only read by those having a high moral tone and heroic
studliness.

Hmm. Could I see it, if the studliness were
'amazingly excessive,' and not merely heroic?

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

And he wants us to register so we can watch 15 minutes of his dirty
movies. I don't want any spam so I'm not gonna register.

Nor am I gonna register my gun


On Sat, 11 Oct 2003 04:24:33 GMT, Jeff Wisnia
wrote:



Stu wrote:

Strength of 3/4" iron pipe threads.

Thanks,

Boyntonstu

You just don't give up, do you Stu?

Jeff

See my homebuilt elevator that 'hangs' on the threads of a single 3/4"
black iron pipe.


http://www.imagestation.com/album/?id=4288894713 Homebuilt Elevator


It looks very nice, Stu. About the strength issue: Pipe threads are made to
seal against fluid leaks, and are nowhere near as strong as a straight
thread, because first one wall (say, the pipe) and then the other wall (the
fitting) tapers to a thin section. So you only have real thread strength
over a short section near the middle of the thread.

Secondly, black iron pipe isn't spec'd for tensile or compression strength.
It's spec'd on wall thickness, and, if you want to get fussy about it, it's
the hoop strength (the strength against expansion of fluids inside) that's
implicit in its specification. That, and allowance for corrosion, uneven
construction, and ham-fisted plumbers.

Thirdly, even a straight thread on a hollow tube is a complicated strength
issue. Thread strengths and standards are based on threading solid bar or
rod. When you thread a tube, the standard strength calculations go out the
window. Your minor diameter now is based on effective wall thickness as well
as the depth of thread. There also is an issue concerning the tendency of
the inner threaded piece to collapse from the angular forces imposed on it
by the 60-degree thread angles. That's not an issue with bar or rod.

If you have to deal with calculated strengths, the first thing you want to
do is to go to a mechanical tubing, rather than plumbing pipe. Then you'll
have to consult someone who knows his stuff on the thread-strength issue for
tubing. Either that, or use another method of assembly. You may actually
have plenty of strength for the application with pipe-threaded plumbing
pipe. But you won't be able to prove it, and, if liability is an issue,
you'd be dead meat.

Good luck.

Ed Huntress

In article , Ed Huntress
says...

It looks very nice, Stu. About the strength issue: Pipe threads are made to
seal against fluid leaks, and are nowhere near as strong as a straight
thread, because first one wall (say, the pipe) and then the other wall (the
fitting) tapers to a thin section. So you only have real thread strength
over a short section near the middle of the thread.

NPT threads are pretty much always sharp V form threads at
the root of the male threads. This, along with the generally
rough surface finish in black iron pipe, will cause failures
to occur at the distinct stress concentration at the root
of the threads.

I would suggest that the joints in question be static
tested for, say, five or so times the static load they
are expected to bear in use, to account for any dynamic
loading they might see.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

In article ,
Stu wrote:
Group,

First let me apologize for posting my question more than one time.
The problem was the Google was 'hiding' my posts and I repeated them
because I believed that they were not posted. I asked Google to
'splain.

Google is not the best way to post to usenet newsgroups. I do
know that it can be very slow to go from the posting to showing up in
the database. There are many other ways to post which don't involve
requiring a web browser to do it. It's strength is that it is a path to
access things posted to usenet a long time ago, long after normal
news servers have expired it.

Why did I ask this questiion?

See my homebuilt elevator that 'hangs' on the threads of a single 3/4"
black iron pipe.

Does this mean that you also haven't seen the various responses
to your (several) postings? In short, the answer seems to be that steel
pipe is not rated for structural use, and as a result, you won't find
the information in any handbook. Steel pipe is too variable in multiple
ways -- and the flanges into which you want to screw it are probably the
weakest link of the entire setup.


http://www.imagestation.com/album/?id=4288894713 Homebuilt Elevator

Hmm ... I encounter the following message:

"Before you view images from Homebuilt One Person Elevator,
you'll need to sign-in. If you're not already a member, now's
the time to join. Why join? Because ImageStation is all about
sharing. It's where you can store, edit, and share digital
images, and it's all FREE."

Well ... I don't believe in giving some random imaging service
my e-mail account (and perhaps other information), so they can spam me,
so all I will see is the first image.

However -- I don't think that *I* would want to trust that
assembly, from what I see of it in the one photo. Perhaps with machined
threaded pieces from a known steel in place of the cast or forged floor
flanges, and a thicker-walled pipe -- perhaps with straight threads,
instead of the usual tapered pipe threads, it *might* be a bit safer.

If it is only you who is going to ride it, you know how it is
made, and you can't sue yourself it if fails. If someone else is on it
when it fails, you really have no protection from a lawsuit, without an
engineering assessment of it from licensed professional structural
engineers.

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

In article x_0ib.78702$Ri4.27008470
@news4.srv.hcvlny.cv.net, says...

Secondly, black iron pipe isn't spec'd for tensile or compression strength.
It's spec'd on wall thickness, and, if you want to get fussy about it, it's
the hoop strength (the strength against expansion of fluids inside) that's
implicit in its specification. That, and allowance for corrosion, uneven
construction, and ham-fisted plumbers.

ASTM A53 (plain old black pipe) does specify yield and
tensile strength. The AISC allows its use, the most common
use is naturally as columns. According to my 1973 Steel
Construction Manual Fy = 36ksi, the same as A36 structural
steel.


Thirdly, even a straight thread on a hollow tube is a complicated strength
issue. Thread strengths and standards are based on threading solid bar or
rod. When you thread a tube, the standard strength calculations go out the
window. Your minor diameter now is based on effective wall thickness as well
as the depth of thread.

Yup, this was my response to one of Stu's earlier posts,

"Assuming a stout flange, my SWAG is that failure would
occur at the root of the threads near the fitting, where
the wall of the pipe is thin due to the threads."

Ned Simmons

In article , Ned Simmons
says...

"Assuming a stout flange, my SWAG is that failure would
occur at the root of the threads near the fitting, where
the wall of the pipe is thin due to the threads."

No SWAG needed, this is the point of highest stress
concentration - threaded fasteners invariably fail
at the root of the thread, exactly even with the
surface of the female threaded part.

The only question would be, how badly would the stress
concentration reduce the apparent ultimate strength
of the material? For a sharp-V NPT thread, done
with a die head in black iron, my own SWAG would
be nearly a factor of three.

That is, to figure out the strength of the pipe
under tension, simply look at the cross section
area of the pipe, calculate based on the ultimate
psi strength for black iron, and then divide by
three. Ed's comments about the joint failing
by collapsing under hoop stress not withstanding.

My guess is the pipe will break before it collapses
inwards. Another SWAG.

Jim

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

What are you talking about?

Stu

FuhhKyu wrote in message . ..
And he wants us to register so we can watch 15 minutes of his dirty
movies. I don't want any spam so I'm not gonna register.

Nor am I gonna register my gun


On Sat, 11 Oct 2003 04:24:33 GMT, Jeff Wisnia
wrote:



Stu wrote:

Strength of 3/4" iron pipe threads.

Thanks,

Boyntonstu

You just don't give up, do you Stu?

Jeff

Stu wrote:

Strength of 3/4" iron pipe threads.


Why not just make the same setup with a short piece of pipe and test in in a
press to see what it will break at?

jim rozen

No SWAG needed, this is the point of highest stress
concentration - threaded fasteners invariably fail
at the root of the thread, exactly even with the
surface of the female threaded part.

The only question would be, how badly would the stress
concentration reduce the apparent ultimate strength
of the material? For a sharp-V NPT thread, done
with a die head in black iron, my own SWAG would
be nearly a factor of three.

That is, to figure out the strength of the pipe
under tension, simply look at the cross section
area of the pipe, calculate based on the ultimate
psi strength for black iron, and then divide by
three. Ed's comments about the joint failing
by collapsing under hoop stress not withstanding.

My guess is the pipe will break before it collapses
inwards. Another SWAG.

I'm no engineer, and only an amateur machinist.
My problem with this is, if there is a taper-thread-induced concern with "pipe"
thread, why not disclaim its use for vertical holding whatsoever, rather than
go into guesses as to the possibilities?
FM

In article , Fdmorrison says...

I'm no engineer, and only an amateur machinist.

Often amateur machinists a) have a better intuitive grasp
on the issues than 'real' engineers, b) know enough to
look stuff up when they know they *don't* know the answer,
and c) have open minds.

My problem with this is, if there is a taper-thread-induced concern with "pipe"
thread, why not disclaim its use for vertical holding whatsoever, rather than
go into guesses as to the possibilities?

That is pretty much what others have said on this thread
before. Pipe threads are not spec'd for tensile strength
but facts are this widget is already built. My two suggestions
(calculate based on the minimum wall thickness, then divide
by three to account for stress concentration, and the other
was to simply make up a joint like that, and stress to
failure) are only to encourage the fabricator to think a
bit more about his machine.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

In article ,
says...
In article , Fdmorrison says...

I'm no engineer, and only an amateur machinist.

Often amateur machinists a) have a better intuitive grasp
on the issues than 'real' engineers, b) know enough to
look stuff up when they know they *don't* know the answer,
and c) have open minds.

My problem with this is, if there is a taper-thread-induced concern with "pipe"
thread, why not disclaim its use for vertical holding whatsoever, rather than
go into guesses as to the possibilities?

That is pretty much what others have said on this thread
before. Pipe threads are not spec'd for tensile strength
but facts are this widget is already built.

The argument that tapered pipe threads are not intended to
carry a tension or compression load is nonsense. (I don't
mean to imply you said this, Jim.) If there is pressure in
the pipe, then there is an axial force on the joint equal
to the pressure x area of the pipe ID.

Ned Simmons

"Ned Simmons" wrote in message
...

The argument that tapered pipe threads are not intended to
carry a tension or compression load is nonsense. (I don't
mean to imply you said this, Jim.) If there is pressure in
the pipe, then there is an axial force on the joint equal
to the pressure x area of the pipe ID.

Ned Simmons

And that may run a couple of hundred psi. Those loads on plumbing pipe from
internal pressure are nowhere near the strength expected of mechanical
tubing in tension or compression, Ned.

Ed Huntress

In article LIzib.6306$Eh3.2408645
@news4.srv.hcvlny.cv.net, says...
"Ned Simmons" wrote in message
...

The argument that tapered pipe threads are not intended to
carry a tension or compression load is nonsense. (I don't
mean to imply you said this, Jim.) If there is pressure in
the pipe, then there is an axial force on the joint equal
to the pressure x area of the pipe ID.

Ned Simmons

And that may run a couple of hundred psi.

Which gives us the lower bound on the axial strength of the
threads, but says nothing about the upper bound. Much
higher pressures are acceptable with forged fittings and
heavy wall pipe. 3000 psi fittings are readily available up
to 4" NPT(F), 6000 psi up to at least 2".

Those loads on plumbing pipe from
internal pressure are nowhere near the strength expected of mechanical
tubing in tension or compression, Ned.

I don't see how that's relevant. The question is not what
the optimum solution is, but rather, can pipe threads carry
significant axial loads. Clearly they can.

Ned Simmons

In article , Ned Simmons
says...

I don't see how that's relevant. The question is not what
the optimum solution is, but rather, can pipe threads carry
significant axial loads. Clearly they can.

I will again interject that the real question is, how
close to the line is this widget? Black iron hardware
store pipe with sharp-V NPT threads, 3/4 inch IIRC.

Best way to figure that is to a) use the minimum minor
diameter for that NPT thread and calculate the X-section
area, then divide the ultimate number by about three.

Or b) purchase the same fittings from home desperate
and load to failure.

Jim

==================================================
please reply to:
JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com
==================================================

"Ned Simmons" wrote in message
...
In article LIzib.6306$Eh3.2408645
@news4.srv.hcvlny.cv.net, says...
"Ned Simmons" wrote in message
...

The argument that tapered pipe threads are not intended to
carry a tension or compression load is nonsense. (I don't
mean to imply you said this, Jim.) If there is pressure in
the pipe, then there is an axial force on the joint equal
to the pressure x area of the pipe ID.

Ned Simmons

And that may run a couple of hundred psi.

Which gives us the lower bound on the axial strength of the
threads, but says nothing about the upper bound. Much
higher pressures are acceptable with forged fittings and
heavy wall pipe. 3000 psi fittings are readily available up
to 4" NPT(F), 6000 psi up to at least 2".

Those loads on plumbing pipe from
internal pressure are nowhere near the strength expected of mechanical
tubing in tension or compression, Ned.

I don't see how that's relevant. The question is not what
the optimum solution is, but rather, can pipe threads carry
significant axial loads. Clearly they can.

Ned Simmons

Then the job is to quantify strength of a joint that was never designed for
much strength. Pipe threads are designed to seal, not to exploit the
strength of the material. Straight threads are.

As I said, it may well do the job here. But don't expect it to perform like
a straight thread, for the reasons given by several people here. And don't
expect to find a spec on it. There may be such a thing, but it's largely
incidental if it is.

Ed Huntress

In article zoGib.8878$Eh3.4447339
@news4.srv.hcvlny.cv.net, says...
"Ned Simmons" wrote in message
...
In article LIzib.6306$Eh3.2408645
@news4.srv.hcvlny.cv.net, says...
"Ned Simmons" wrote in message
...

The argument that tapered pipe threads are not intended to
carry a tension or compression load is nonsense. (I don't
mean to imply you said this, Jim.) If there is pressure in
the pipe, then there is an axial force on the joint equal
to the pressure x area of the pipe ID.

Ned Simmons

And that may run a couple of hundred psi.

Which gives us the lower bound on the axial strength of the
threads, but says nothing about the upper bound. Much
higher pressures are acceptable with forged fittings and
heavy wall pipe. 3000 psi fittings are readily available up
to 4" NPT(F), 6000 psi up to at least 2".

Those loads on plumbing pipe from
internal pressure are nowhere near the strength expected of mechanical
tubing in tension or compression, Ned.

I don't see how that's relevant. The question is not what
the optimum solution is, but rather, can pipe threads carry
significant axial loads. Clearly they can.

Ned Simmons

Then the job is to quantify strength of a joint that was never designed for
much strength. Pipe threads are designed to seal, not to exploit the
strength of the material. Straight threads are.

Oh, come on, Ed. What's so different about pipe threads
that they don't "exploit the strength of the material"? The
sharp thread form likely causes some stress concentrations,
but other than that, I don't see much difference.

Sure, they have to seal, but there's gonna be no seal if
the pipe is ejected from the fitting with 6000 psi behind
it. That doesn't happen in a properly made up joint.


As I said, it may well do the job here. But don't expect it to perform like
a straight thread, for the reasons given by several people here. And don't
expect to find a spec on it. There may be such a thing, but it's largely
incidental if it is.

Of course it's not going to behave *exactly* like a
straight thread. Why is that a problem? Perhaps the
analysis is a bit more involved than for a straight thread
on a solid member(though other than taking into account the
thin wall at the root of the thread, and the effects of the
sharp vee, I'm not convinced of that), but if all the
components of every new design had to be used in a mannner
that was anticipated and pre-calculated we wouldn't see
much progress, would we?

As far as finding a spec, I expect you're right, and I said
as much in a post to the OP back on 10/2. My objection is
to the several (unsubstantiated IMO) assertions that pipe
threads are unsuitable for carrying axial loads.

Ned Simmons

In article ,
says...
In article , Ned Simmons
says...

I don't see how that's relevant. The question is not what
the optimum solution is, but rather, can pipe threads carry
significant axial loads. Clearly they can.

I will again interject that the real question is, how
close to the line is this widget? Black iron hardware
store pipe with sharp-V NPT threads, 3/4 inch IIRC.

Best way to figure that is to a) use the minimum minor
diameter for that NPT thread and calculate the X-section
area, then divide the ultimate number by about three.


Not knowing all the details of the device, I was reluctant
to make a calculation before. Since it's now built, they
can't blame us for any mishaps, can they? g

I get about .925 dia at the root of the thread at the gage
line of a 3/4 NPT fitting. ID is .824 . Yield on A53B pipe
is 35 ksi min. Ultimate tensile is 60 ksi min.

..138 in^2 x 35000 lb/in^2 = 4830 lb to yield
..138 in^2 x 60000 lb/in^2 = 8280 lb to ultimate tensile

I assume your 3X multiplier is a stress concentration
factor, which sounds reasonable to me, so there will be
some yielding at the root above 4830/3 = 1610 lb., and
failure will occur at 8280/3 = 2760 lb. There's likely a
pretty high uncertainty in the second number depending on
exactly what happens at the root as it yields.

Ned Simmons

In article , Ned Simmons
says...

I get about .925 dia at the root of the thread at the gage
line of a 3/4 NPT fitting. ID is .824 . Yield on A53B pipe
is 35 ksi min. Ultimate tensile is 60 ksi min.

.138 in^2 x 35000 lb/in^2 = 4830 lb to yield
.138 in^2 x 60000 lb/in^2 = 8280 lb to ultimate tensile

I assume your 3X multiplier is a stress concentration
factor, which sounds reasonable to me, so there will be
some yielding at the root above 4830/3 = 1610 lb., and
failure will occur at 8280/3 = 2760 lb. There's likely a
pretty high uncertainty in the second number depending on
exactly what happens at the root as it yields.

I have not run those numbers but they look good to me.

One point is, my 3X is a stress concentration factor,
for sharp V threads that are die cut. I made that up
off the top of my head.

Another consideration is, the ultimate 2700 that you
suggest is for a purely *static* load. It might be
possible to get shock loads that produce what,
five or ten Gs?

Jim

==================================================
please reply to:
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==================================================

In article , Ed Huntress says...

Then the job is to quantify strength of a joint that was never designed for
much strength. Pipe threads are designed to seal, not to exploit the
strength of the material. Straight threads are.

And therein lies one problem. NPT threads want to get as close
to a zero clearance fit-up as possible, so the roots of the
male threads are machined sharp V. This provides a stress
concentration that would be atrocious in a fastener. Bolts
typically have rolled, not cut threads, and in the higher
strength grades have radii at the roots.

Still Ned's analysis shows it will probably hold up, as
long as nobody jumps on it or anything.

Jim

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In article , Ned Simmons
says...

As far as finding a spec, I expect you're right, and I said
as much in a post to the OP back on 10/2. My objection is
to the several (unsubstantiated IMO) assertions that pipe
threads are unsuitable for carrying axial loads.

Not that they can't, but rather they are supremely
unsuited to it. The sharp V thread form provides
on problem, and the fact that NPT threads are
invariably die-cut is another.

Die cut threads are rougher and this roughness
translates into microscopic tears in the
thread - surface defects that provide stress
concentrations. That and the sharp V form can
weaken the thread by large factors compared
with properly rolled threads.

This is why no pipe manufacturer would ever suggest
his fittings be used for axial loads, and would never
supply a spec for that purpose.

Sure for a railing or something it would work fine,
and your own numbers suggest that his lift will
not fail unless subjected to a shock loading of
five or ten gs.

Jim

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"Ned Simmons" wrote in message
...
In article zoGib.8878$Eh3.4447339
@news4.srv.hcvlny.cv.net, says...
"Ned Simmons" wrote in message
...
In article LIzib.6306$Eh3.2408645
@news4.srv.hcvlny.cv.net, says...
"Ned Simmons" wrote in message
...

The argument that tapered pipe threads are not intended to
carry a tension or compression load is nonsense. (I don't
mean to imply you said this, Jim.) If there is pressure in
the pipe, then there is an axial force on the joint equal
to the pressure x area of the pipe ID.

Ned Simmons

And that may run a couple of hundred psi.

Which gives us the lower bound on the axial strength of the
threads, but says nothing about the upper bound. Much
higher pressures are acceptable with forged fittings and
heavy wall pipe. 3000 psi fittings are readily available up
to 4" NPT(F), 6000 psi up to at least 2".

Those loads on plumbing pipe from
internal pressure are nowhere near the strength expected of
mechanical
tubing in tension or compression, Ned.

I don't see how that's relevant. The question is not what
the optimum solution is, but rather, can pipe threads carry
significant axial loads. Clearly they can.

Ned Simmons

Then the job is to quantify strength of a joint that was never designed
for
much strength. Pipe threads are designed to seal, not to exploit the
strength of the material. Straight threads are.

Oh, come on, Ed. What's so different about pipe threads
that they don't "exploit the strength of the material"? The
sharp thread form likely causes some stress concentrations,
but other than that, I don't see much difference.

It isn't the sharp threads, Ned. It's the fact that the walls are weak at
each end of the taper, because one side or the other is thin at either end.
Only a couple of threads in the middle of the joint can produce the full
strength you would get with straight threads, and that isn't enough to
exploit the strength of the material. There aren't enough threads where the
material on *both* elements is equally thick.

You probably could approximate the strength if you calculated the strength
of three straight threads, more or less, of the same size in the same
material.

Ed Huntress

Ed Huntress wrote:
"Ned Simmons" wrote in message
...

In article zoGib.8878$Eh3.4447339
, says...

"Ned Simmons" wrote in message
...

In article LIzib.6306$Eh3.2408645
, says...

"Ned Simmons" wrote in message
...

The argument that tapered pipe threads are not intended to
carry a tension or compression load is nonsense. (I don't
mean to imply you said this, Jim.) If there is pressure in
the pipe, then there is an axial force on the joint equal
to the pressure x area of the pipe ID.

Ned Simmons

And that may run a couple of hundred psi.

Which gives us the lower bound on the axial strength of the
threads, but says nothing about the upper bound. Much
higher pressures are acceptable with forged fittings and
heavy wall pipe. 3000 psi fittings are readily available up
to 4" NPT(F), 6000 psi up to at least 2".


Those loads on plumbing pipe from
internal pressure are nowhere near the strength expected of

mechanical

tubing in tension or compression, Ned.

I don't see how that's relevant. The question is not what
the optimum solution is, but rather, can pipe threads carry
significant axial loads. Clearly they can.

Ned Simmons

Then the job is to quantify strength of a joint that was never designed

for

much strength. Pipe threads are designed to seal, not to exploit the
strength of the material. Straight threads are.

Oh, come on, Ed. What's so different about pipe threads
that they don't "exploit the strength of the material"? The
sharp thread form likely causes some stress concentrations,
but other than that, I don't see much difference.


It isn't the sharp threads, Ned. It's the fact that the walls are weak at
each end of the taper, because one side or the other is thin at either end.
Only a couple of threads in the middle of the joint can produce the full
strength you would get with straight threads, and that isn't enough to
exploit the strength of the material. There aren't enough threads where the
material on *both* elements is equally thick.

You probably could approximate the strength if you calculated the strength
of three straight threads, more or less, of the same size in the same
material.

Just a minor nit... Wouldn't the strength be somewhat
dependent on how tightly the joint was made up? It seems
to me that the tighter you made the joint, the more load
you'd put on the material and that would have to come
out of your strength budget somehow. Not that I have
a clue how.

I still maintain that it's a bad application. I think
that any flexing could seriously weaken the joint over
time.

In article , Ed Huntress
says...

You probably could approximate the strength if you calculated the strength
of three straight threads, more or less, of the same size in the same
material.

Why three? The best way would be to use the smallest
wall section. And the sharp threads do indeed reduce
the strength.

Jim

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==================================================

On Mon, 13 Oct 2003 20:22:56 -0400, Ned Simmons wrote:
Oh, come on, Ed. What's so different about pipe threads
that they don't "exploit the strength of the material"? The
sharp thread form likely causes some stress concentrations,
but other than that, I don't see much difference.

They're *tapered*. That means you don't have full depth threads
engaging full depth threads at any point in the joint. Machinery's
Handbook says that only NPS threads should be used for axial
loading.

Gary