Tube and Pipe Dimensions

Hello sb,

pretty good answer my friend! GA on its way...............

U.S. tube is OD fand controlled by wall thickness.

Hi John

We did this all about a year ago. Very basiclly, what you need to remember is that a PIPE is a container or vessel, so you are concerned with the INSIDE dimensions. TUBE, however, is structural and therefore you need to be concerned about the OUTSIDE dimension. The fact that tube is used as pipe AND that people have found ways to join tube together like pipe doesn't matter.

For the full details go to Forum Thread: Tubes or Pipes?

So, in other words, your rep was right although I doubt he knows why!

Dear Friend,

Its globe rule only its not only UK or US.Why because the Tube is not having scedule .So that the reason we are specified for the Tubes only OD.

Thanks

Binoi.S

Just to add my 2 cents worth. I know for aluminum, tube may be specified in either of three ways: OD x ID, OD x W or ID x W. Never as OD x ID x W. So tube is a precision product.

Pipe, on the other hand, is a commodity product. As said before, it's specified by nominal OD x schedule. The wall thickness is controlled by a wall tolerance or a weight per foot, depending on the nominal OD.

JT has it right.

Yes to the best of my knowledge it is global. Tube is OD x wall unless DOM (Drawn over Mandrel) which is technically OD & ID, DOM in SSID (Special smooth ID) is ID and Wall. Pipe is to the pipe charts as per SB's comments NPS and schedule. Pipe can be made off the "pipe charts" but the reality is the more generous tolerances vs tube and uses the NPS for the first designation. It gets a few wrinkles in welded vs seamless for tolerances but just think of how the material is made and it makes sense. Next application is important- not all pipe is pressure tested but in general pipe is made for the transmission of fluid, gas, etc. Tube is for structural or mechanical application, exception hydraulic line.

PS UK vs US - the big difference is the use of seamless versu DOM (DOM = US and Seamless = UK)

JohnDG and all,

Although I agree with the basic view that tube is OD and pipe ID, the real world is less simple. At larger sizes (around 8 or 10"), pipe switches from ID to OD dimensions. In various trades, the answer depends on the specification of the standard to which it is dimensioned. One day, in Jamaica, I went to an electrical wholesaler to buy some 1/2" conduit, and was asked to clarify, because English Thread was OD, U.S. was ID, and the Metric "equivalent" was also sold!

Best to specify intent or to clarify the method of measurement, as some have noted, by specifying type of measurement and any schedule or desired wall thickness.

--JMM

I think we all have been though this before. Pipe dimensions are generally called out by I.D and the I.D will be close but only up to 12" nominal and then it is measured by OD. If you really look at it close you will find that this is not really true. Take 2" nominal pipe for instance. If you measure a Sch. 40 or 80 pipe the OD will be the same 2.375" and the I.D will be different because of the increased wall thickness. . If you look at 14" and above in any schedule the O.D is always the same as the size and it dose not change with the Schedule either. They do this because it would be very hard to make pipe fittings with different O.D measurements Tubes are not only used for structural purposes. Anyone that tells you this has obviously never been into a boiler or heat exchanger. As far as I know all tubes structural or high pressure do go by ID and wall thickness.

"As far as I know all tubes structural or high pressure do go by ID and wall thickness."

As far as I know it is OD and wall thickness (not only structural) because in heat exchangers whether small ones (for lube units) or huge ones(for power plants) we regularly buy SS tubes - these have to have control on OD since the reamed holes are controlled and then tube expansion is done. If you control the ID, you may likely to land up in problem.

You are right and I stand corrected. Tubing does go by O.D. and this is what meant to say. I think I did to many d's (ID, OD) in my post. Thanks for pointing this out to me.

I have read posts through #12.

One more point to add.............pipe threading dies/taps are not to be used on tubing.

Unless tubing is special made to pipe OD and WALL thickness thread depth will not producer adequate seal.

One post suggests pipe is always threaded. There is a plethora of pipe weld fittings in heavy industrial use....and don't forget that cast iron pipe is a whole different ball game/fittings/joining methods...clay and plastic too.

MR. GUY

Very good point and that is another reason all piping OD stays the same for all sizes no matter what schedule. Can you imagine how difficult our lives would be if it were not? First off you would have to be very careful to choose the correct OD fitting or threading die. Also there would always be someone who wanted a welder to counterbore the outside of a heavier fitting (this would look really bad on a x-ray to say the least) to use on a thinner schedule pipe the same as we sometimes have to do on the I.D of a pipe or fitting now. Also in a bind people would be having pipe machined on ends so the threading dies they have on hand would work. I guess there is a reason it is the way it is and someone has already been through this many years ago. I think it would be easier if they would just call all sizes of pipe by its actual OD and Schedule and not use nominal measurement terms at all on the pipe sizes below 14" OD.

The only tube threaded on the OD that I remember is drill tube, the tube used for diamond core drilling. Drill pipe (oil well type drilling pipe) actually has OD and ID thread. But normally that is on the end forgings that are friction-welded onto the pipe, except on upset (forged) drill pipe.

I think I am nearly off topic.

Pipes are not always threaded but the size is suitable for threading. These standards are made as such otherwis how do you say say 12" Pipe to PVC standard or 12" to Brass Standard etc ?

So the pipes are controlled (as are tubes) to the pipe standards and it is for user to thread or weld the pipes (you get SW or BW elbows, tees etc to pipe standards (and i at least have not seen to tunbe standards) so there you have unthreaded pipes.

negative. see statement re: tube fittings.

This is especially true in process piping.

I cannot speak for everyone, but that is what I learnt when I sold tube and pipe in the UK many years ago.

As I remember, the reason was that the pipe was used for transmission of gases or liquids, and therefore the internal dimension was the critical one. One the other hand the tube was either destined for machining, or for insertion in a tube sheet, or a boiler wall, or a bicycle frame, etc etc, and therefore it was the OD that was critical.

However, that was a long time ago, but I believe the argument still holds.

What has complicated the matter now is that the customer, to reduce his price for a machined component, looks also at pipe stocks to see if there is one that he can use more economically. And perhaps from that arises the confusion.

It may also be that the method of manufacture affected the dimensioning (OD v. ID). Pipe made from plate was rolled and the bore dimension was used to define the material. Whereas tube, hollow bar or whatever was rolled or extruded or welded using an external die or roller that would determine the OD as fixed, and the ID only by inference.

Happy New Year to you all,

There are lots of good answers here today!

I just wanted to throw out there a brief explanation for the discrepancy between the I.D. rating on a pipe and it's actual I.D.

Once upon a time the actual measurements were the same... then pipe manufacturers started using better materials and were able to make pipes that could withstand the same amount of pressure using less material... Rather then throw the entire engineering and construction world into chaos by making it necessary to rip out the older pipes in order to make repairs using the newer pipes; they kept the old nomenclature and made the new pipes outer diameters match the old pipes outer diameter so they could be coupled together, thus the confusing world of pipe sizing was reborn.

I understand the ID to OD dimensioning differences to controls flows and volumes more accurately

Yes this is aglobal rule but there is an other defferent that is the BWG this is concerns to the tube

yes in america too.

pipe however changes to od only after 14" overall.

Many (belated) thanks to all respondents.