ID or OD

When referring to poly tube piping sizes such as 1 1/4" or 1" is this measurement ID or OD?

thanks,

It is IPS (iron pipe size) so the ID in maintained at 1" or 1.25" etc. and the OD is not.

For water lines, CTS (copper tubing size) maintains the the OD but we call it by ID; which isn't accurate for 1/2", 3/4", 1" etc., they are actually 5/8", 7/8" and 1 1/8" tubing.

I could be wrong, but I would suspect "poly tube piping" or "poly tubing pipe" are misnomers.

Gary Slusser said:

... pipe ... the ID in maintained ...

... tubing ... maintains the OD ...

Click to expand...

I have the flexible black tubing that comes in big coils and is a little over 1 inch in diameter. Is squeezes over a bayonet fitting. Is this poly?

Yes that is PE pipe (referred to by some as tubing but it is pipe) and it's IPS; the ID is maintained. Yours may be 3/4" ID. It is marked every 18-24" as all water line material is.

Steel pipe (IPS) inside diameters varies all over the place depending on wall thickness while the outside diameter remains constant. Pipe sizes are weird and confusing. As a rule of thumb, hose uses ID, tubing uses OD, and pipe, while the OD is constant, has 'nominal' measurements. A 1" IPS (NPS) pipe has approx 1-3/8" OD. Copper tube/pipe (type L, M, K, DWV) used in plumbing doesn't follow rules for standard tubing in that the size called-out isn't the actual OD.

Often, the term IPS (iron pipe size) and NPS (nominal pipe size) are used to describe the same thing. There are a couple schemes used to call out the wall thickness. Primarly a "schedule" number is used to specify wall thickness. The thinnest being sch 5, and I know it goes higher than as sch 80 (that is the thickess I have used). Steel workers may still use STD, XS, XSS to specify wall thickness (not to be confused with cast iron which I know very little about)

CTS (copper tube size) is used for copper plumbing pipes. It is also used to designate CPVC (I don't know much about cpvc because it isn't allowed in my area).

Tubing size is usually specified by OD. When ordering tubing, the actual OD and the wall thickness is given.

Hose size is specified by ID.

There is also an SDR (standard dimension ratio) scheme used for pipe.I only used SDR pipe once and I really don't know much about it; it was specified by an engineer. Technically the cpvc in CTS uses an SDR scheme. PEX also is sized by a SDR scheme.

tubing

It will be the nominal i.d., (which can have little relationship to the actual i.d.), but the o.d. could either be IPS or CTS. If it is CTS then the o.d. is usually 1/8" larger than the nominal size. If your tubing measures 1 1 /8" o.d. then it is 1" copper tube size.

I imagine a this has a lot to do with the fittings that are used with this pipe. In the case of PVC where the fittings go over the pipe, the outside diameter would be constant regardless of the ID. I think that makes sense.

bob...

pipe

ALL pipes conform to an o.d. standard. When you use insert fittings you have to use the ones for that particular particular pipe, because the i.d. will change according to the wall thickness.

Is that why I had such a hard time getting Poly 160 psi. pipe over barb fittings 30 or so years ago? You had to heat it to almost a liquid to get it to go over the barbs they sold back then. I haven't used it in that many years, so I'm not familiar with todays Poly.

bob...

Poly is still that same pain in the butt - and by heating it a bit too high, it fractures later. Thats why I propose PEX be used - better fittings and engineering.

PE is very easy to use if you plan ahead and decide how you will warm it up. I've laid it in the sun for a few minutes or used a propane torch which takes less than a minute. You can use a heat gun or bucket of hot water. Put two hose clamps on it and push it on a fitting is less than 10 seconds and properly tightening the two hose clamps with the tee handled ratchet torque wrench made for the hose clamps takes less than 2 minutes. You put them on with the screws opposite from each other.

I've never had a leak except with a suction leak on a replacement deep well jet pump installation where I had to use two short 8" pieces onto existing elbows due to the pump being in a small pit in the corner of a garage. I had overheated the 1.25" piece.

OK, thanks. Now I got it. The last few posts about heating it up made the most sense, considering how much trouble I had working with this stuff in the cold.