What is a pipe schedule?
Pipes are designed to carry fluid, therefore their internal diameter is their critical dimension. This critical dimension is referred to as the nominal bore, commonly abbreviated as NB. Obviously, for pipes containing pressurised fluids the wall thickness, and by implication the pipe's strength, is important. Wall thickness is expressed in "schedules", referred to as pipe schedules.
What Standards Govern Pipe Sizes?
In the oil and gas and related down stream industries the most common standards are
- ASME/ANSI B 36.10 Welded and Seamless Wrought Steel Pipe, and
- ASME/ANSI B36.19 Stainless Steel Pipe
Does Pipe Schedule Change With Pipe Size?
For all pipes with the same NB (nominal bore) the outside diameter remains relatively constant. Therefore any variation in schedule i.e. wall thickness, affects only the inside diameter. As the schedule number increases, the wall thickness increases, and the actual bore is reduced.
Pipe Schedule Charts
The wall thickness associated with a particular schedule depends on the pipe size as can be seen from the charts below for some of the more common sized carbon steel pipes encountered.
Abbreviations used: NB - nominal bore, STD - Standard, EH - Extra Heavy, DBL EH - Double Extra Heavy.