Pipe vs Tube strength.

[Bob Korves]

The methods in how it's produced limits seamless pipe or tube for pressure applications. In most cases I think we expect to pay more for seamless product in any material category. The seam isn't as visible in welded structural pipe or tube as you find in steel or stainless steel but it's there, and the extrusion process cleans it up really nice.

Pipe is sized as nominal and the OD doesn't change and the wall thickness changes with the schedule of the pipe, with sch. 40 being called standard. If you want to be close on size when you begin then you might want to choose tubing. Price on pipe will be more expensive when you move from standard schedule 40. For the most part pipe in all the different materials which it's available is the same OD size.

From the hobby standpoint, if cost is a factor then practice or build your projects with what ever you have. Structurally the materials are the same in whatever the alloy you choose for both pipe and tube. I usually go with what I was taught when $$$ is a factor; "Don't trade labor for material." Seldom do the labor costs for producing a product weigh less than the material cost.

Correct, Russ. There is nothing about a 1/2" pipe that is 1/2". That is why they call it "nominal". As Russ says, there is an oddball O.D. and then the I.D. changes with the series. There are many "schedules" which are related to wall thickness and pressure rating.
http://www.engineersedge.com/pipe_schedules.htm
The nominal size has nothing to do with the actual size of the pipe. Get used to looking at a chart like the one above if you need the dimensions of pipe.
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Nominal: (of a quantity or dimension, especially of manufactured articles) stated or expressed but not necessarily corresponding exactly to the real value:
"legislation allowed variation around the nominal weight (that printed on each packet)"
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Pipe is WAY off...

 

[RJSakowski]

Interesting trivia.

Initially, pipe refereed to the actual inside diameter. Since materials were not as strong then, the walls were thicker, giving rise to the o.d.'s that we have today. As materials improved, the thicker walls weren't required but since all fittings were geared to the o.d., they increased the i.d. instead to be compatible with legacy pipe works. Since pipe is used for moving fluids, often at a specified pressure rating, this produced a less expensive product with better flow characteristics. A win-win.

Now you know the rest of the story.