In carbon steel piping, "standard weight" is 0.375" wall for all sizes 12" and above.
In smaller pipe sizes, Sch. 40 and standard weight are the same. But in sizes 12" and above, Sch. 40 keeps getting heavier with increasing pipe size. So, for example, 24" Sch. 40 pipe is 0.687" wall.
"Schedule 40", if I remember right, is nomenclature from ASTM A53, which only covers pipe up through 24" size. So I'm not sure if there is such a thing as 28" Sch. 40 pipe.
The "s" normally refers to a separate, lighter schedule for stainless steel pipe. I don't remember what specification it is in (maybe A312?), but that specification may not extend past 24" either. (You can download these specs from ASTM for a fee.)
Anyway, the link above shows that 3/8" wall thickness for "standard" weight. That may be different from stainless, and doesn't correspond to a Sch. 40- so make sure what it is that you're needing.
You can also have pipe custom fabbed from plate, and when you get into 28" stainless steel pipe, it may be just as economical to do that. And in that case, you could make it whatever wall thickness and OD/ID you wanted.
Perhaps someone with these specs in hand can correct the above if needed?
Dimension of steel pipe is covered in ASME B36.10M "Welded and Seamless Wrought Steel Pipe". This standard covers pipe sizes from 1/8" to 80".
Dimension of stainless steel pipe is covered in ASME B36.19 "Stainless Steel Pipe". This standard covers pipe sizes from 1/8" to 30", however, 28" is not covered.
Both these specs have same OD, the only difference is in Schedule number (B36.19 schedules have an "S", e.g. Sch 10S, and is thinner - if different from that of B36.19M).
As noted, there is no Schedule 40 for 28" pipe, according to B36.10. Standard wall is .375", so your ID for a 28" pipe would be 27.25.
In truth, a 28" pipe is not commonly found in nature. 24", 30" and 36" seem to be more common and readily available. Unless you're planning to use a large quantity that would justify a run of this size, you may be better served by jumping up to 30".
Edward L. Klein
Pipe Stress Engineer
Houston, Texas
"All the world is a Spring"
All opinions expressed here are my own and not my company's.
