Is 24" Sch 40 wall 0.687" or 0.688"? 2

[JStephen]

Yeah, I know, stupid question that doesn't make any practical difference. But I find the wall thickness of 24" Sch. 40 listed as 0.688" in some sources, as 0.687" in other sources. Did it change at some point? Or is it different in different standards? Or is this a conversion from millimeters that gets rounded differently? I'm thinking there are some smaller sizes that have similar minor discrepancies also. Any ideas or history on this?

 

[EdStainless]

Historically there were differences between the steel and stainless specs, and sometimes just a couple of thousandths.
Check ANSI B36.10 or the applicable spec to be sure.

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P.E. Metallurgy, Plymouth Tube

 

[CADCAMTech]

This is just a guess but it may just be a difference in how it was rounded, 11/16 of an inch is 0.6875. So one source may have rounded up and the other rounded down. Either way 0.001 inches is pretty small and I would assume that both 0.688 and 0.687 inches fall within the manufacturer/mill tolerance range for the wall thickness.

 

[JStephen]

CAD, I suspect that's correct. One of the other discrepancies I have marked in my table is 8" Sch. 120 at either 0.718 or 0.719". And that is 23/32" either rounded or truncated. It hadn't occurred to me that the 0.688 was a fractional number. But looking at the chart, I see the Sch. 60 to Sch. 160 are all either 16th or 32nd fractions as well.

 

[CADCAMTech]

JStephen,
It is my understanding that those piping standards Schedule 40, 80, etc were defined using the imperial system, so it is likely that many if not all of the sizes and wall thicknesses work out to some fraction of an inch (1/2, 1/4, 1/8, 1/16, 1/32, 1/64).

 

[racookpe1978]

Yes, rounded with that 1/32th +/- 0.0005 left over.

But the round-up or round-down should depends on which way the person who wrote the table "feels" is conservative.

If the thickness is to be used to calculate strength, then the lower value assumes a smaller thickness, so the final calc is a (little bit) more conservative.

If the table is used for weight (as to figure out pipe support requirements) then a thicker wall will be a (little bit) more conservative since the weight/foot of pipe will be a little bit higher. Heat transfer, flexibility, heat loss, weight-per-foot, purchase price estimate (thousands of pounds of steel needed for shipping, each would imply a different effect. Tolerances are far greater. And, many tables repeat the pipe weight, strength, wall thickness, S, inertia, etc. independently from other sources. Few references re-calculate them in the table itself.

In real life, it should not matter. Less than the thickness (and weight) of a paint layer.