Production of steel pipe is generally grouped into two categories:

(1) Welded and Seamless

There are many methods of producing steel pipe in current use, however, most of the pipe produced in the worldwild is made either by the seamless, electric resistance weld (ERW) or spiral weld methods.

Continuous weld and double submerged arc weld are other common methods of manufacture.

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Ronsco provides a pipe chart for sizes of steel pipe 1/8” nominal to 48” Outside Diameter that illustrates nominal Pipe Size and Scheduled Walls as compared to actual outside diameter, wall thickness and weight/ft.

The left side of the pipe chart indicates the difference between the nominal and actual size.

Nominal sizes 1/8” through 12” are different from the actual outside diameter sizes (much like a 2 x 4 is not really 2 inches by 4inches).

In sizes greater than 14”, the nominal size is the same as the measured O.D. size.

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While many other wall thickness can be manufactured by a mill somewhere in the world, any thickness that is not on the pipe chart is considered an “Unscheduled Wall” and would normally be available by special order.
We have extensive experience in providing machining services to achieve exact wall thickness tolerances or to meet minimum ID/OD requirements.
As the engineering designs become more involved and the end use more critical the demand has increased for material with a guaranteed “minimum wall thickness”.
Generally on 24” O.D. pipe and under, manufacturer tolerances are stated as -12.5% the nominal wall thickness.
Therefore, minimum wall thickness can usually be calculated as 12.5% under the average or nominal wall thickness.
For example, 2.500” nominal wall would approximate 2.188” min wall.
Depending on the application, Tubing specifications normally have much tighter wall tolerances then Pipe specifications.

Pipe can also be machined to achieve more exact wall thicknesses or minimum ID requirements.