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wrote:
wrote:

The OD for 3/4" schedule 10 pipe is 1.050".
The OD for 3/4" schedule 40 pipe is 1.050".
The OD for 3/4" schedule 80 pipe is 1.050".

The ID's are different for each.

Why did you not say that the OD for *1.050* schedule 10 (or 40 or 80)
pipe is 1.050" ? Because to most of the plumbing world (and
yourself),
it's known as 3/4" nominal ID pipe, not 1.050 OD.

No, not to me. Further, I have never heard anyone else refer to pipe
that way either. It is referred to as I did above, by nominal size and
schedule. '3/4" nominal ID pipe' is an oxymoron. Nobody calls it
'3/4" nominal ID pipe. They call it '3/4" pipe', or '3/4" schedule 40
pipe', or whatever schedule they are using.

They are all 3/4" pipe. I've never heard anyone refer
to pipe as 'nominal pipe', 'nominal ID pipe', or 'ID' pipe.

The nominal size for pipe does NOT corresond to a specific ID,
it corresponds to a range of IDs. Without knowing the schedule
you cannot determine the ID for pipe from the nominal size.
However if you know the nominal size you do know the OD, that
is unambiguous. Therefor to say that pipe is 'sized by ID' is
wrong.

? Are we arguing over
how a pipe is "measured" or "sized" vs. how it is "named" or
"called"?
How are we to reconcile that 3/4" pipe is named for its nominal ID,
yet
it is hardly ever called 1.050" pipe, unless it is called by
something
for which it is "measured"?

Again, pipe is not mesured by ID and it is never called 'nominal ID'
or even 'nominal' either. 3/4" pipe is called 3/4" pipe,
understood to be schedule 40 unless otherwise specified and also
understood to have no dimensions equal to 3/4" unless the speaker
or the listener does not understand pipe.

Because the ID was the most important characteristic in terms of
determining the pipes resistance to flow, water pipe was named for
its
ID. The 3/4" pipe size was thus established by some 'primordial 3/4"
ID
pipe' whose OD turned out to be 1.050". When they made pipe with
other
wall thickneses, for the sake of compatibility with existing fittings
(and dies) which thread onto the OD, they varied the ID slightly to
be
able to keep the OD constant. Nevertheless, they persisted in calling
it by its nominal ID.

I suspect, though I cannot verify this, that nominal pipe sizes were
established by taking the actual ID and subtracting an allowance
for accumulated scale (corrosion allowance). Since I haven't verified
that, I didn't suggest it befor now. I think my GUESS is as good as
yours. The fact is that for any given nominal size AND schedule
the standard SPECIFIES the OD and the wall thickness, from which
the ID may be calculated. Without knowing the scedule you do not
know the ID. Pipe is not sized by ID.

Further, if you are doing a flow calculation, as I have, you
will use the ID appropriate to the schedule and not a 'nominal'
ID.

The actual ID for schedule 40 pipe is ALWAYS larger than the nominal
size so calling it nominal ID makes no more sense than calling it
nominal OD etymology notwithstanding. Adding 'ID' or 'OD' to the
word 'nominal' does not convey any additional information and may,
in fact, mislead people as to the dimensions of the pipe.

However, some types of tubing were always named for their OD, thereby
avoiding this whole mess.

And I have not, as someone suggested, confused tubing with pipe.

--

FF