References to pipe wall thickness typically mean the nominal, or average, wall thickness. Stainless steel schedules 40S and 80S are identical with carbon steel designations Std and XS, respectively, through 12-inch. XXS has no corresponding schedule number, but in sizes through 6-inch, XXS has a wall thickness twice as thick as XS. STD and SCH 40 are the same in sizes through 10-inch in sizes above 10-inch, STD has a wall of 3/8-inch. The addition of the letter “S” after the schedule number identified it as pertaining to stainless steel.Ĭertain relationships exist among the traditional designations of STD, XS, and XXS, the ANSI schedule numbers, and the actual wall thicknesses. Stainless steel schedule numbers from Schedule 5S through schedule 80S were added by ANSI B36.19 for sizes through 12-inch. These schedule numbers indicate approximate values for 1000 times pressure-stress ratios. That standard broadened the range of wall thicknesses, schedule numbers from schedule 10 (SCH10) through schedule 160 (SCH160). Three long standing traditional designations are used to indicate wall thickness:Įxtra Strong wall (XS), sometimes referred to as Extra Heavy wall (XH)ĭouble Extra Strong wall (XXS), sometimes referred to as Double Extra Heavy wall (XXH)įor the purpose of standardizing pipe dimensions, the American National Standards Institute (ANSI) published ANSI B36.10. Once again, pipe wall thickness is a bit more complicated. The typical value, which is not half way between, is used for calculation of section properties. You can see by the chart at the right, not all 12 Gauge allows a thickness between 0.101 to 0.111. The wall thickness of tubing is measured in inches (.0035″), or by standard gauge from 7 (heaviest) to 22 (lightest) which correspond to a range of wall thicknesses. The chart on the right, shows the relationship between NPS and the diameter. For each nominal pipe size, the outside diameter (O.D.) remains relatively constant the variations in wall thickness affect only the inside diameter (I.D.). Early pipe manufacturers made the walls in the smaller sizes much too thick, and in correcting this error in design, they took the excess from the inside to avoid changing the sizes of the companion fittings.įor sizes larger than 12-inch, NPS corresponds to the actual outside diameter. The table below cross-references the nominal dimension of a PIPE with its actual outside diameter.įor sizes from 1/8-inch through 12-inch, the NPS corresponds to the nominal inside diameter, but differs somewhat from its actual inside diameter. For example, a 1-1/2″ pipe size actually has an outside diameter of 1.9″ NOT 1.5″. Although it is related to the outside diameter, it is significantly different. Pipe is usually measured by NOMINAL PIPE SIZE (NPS). Tubing is measured by the OUTSIDE DIAMETER (O.D.), specified in inches (e.g., 1.250) or fraction of an inch (eg.
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