1.10 Pipes and Tubes

  • Pipe

    • Pipe is specified completely, by its nominal diameter [or, Nominal Pipe Size (NPS), or Nominal Bore (NB)] and schedule number. The nominal diameters range from 1/8 to 30 inches for steel pipe.

    • The schedule number is defined by \[\text{Schedule number }= 1000 \frac{P}{f}\] where \(P\) is the internal pressure, and, \(f\) is the allowable stress of the material.

    • The commonly available schedule numbers are 10, 40, 80 and 120. Lower the schedule number lower is the thickness. The schedule 10 is mostly for stainless steel pipes; and, schedule 40 with carbon steel pipes.

    • Nominal diameter is close to the actual outside diameter. Actual outside diameter of pipe is more than the nominal diameter up to a nominal diameter of 12 inch. Above 12 inch, outer diameter is equal to the nominal diameter.

    • Regardless of wall thickness, the outside diameter of all pipe of a given nominal pipe size is the same, to ensure the interchangeability of the fittings.

    • Dimensions of pipe confirm to ASME/ ANSI B31 standard.

  • Tube is specified completely, by its actual outside diameter and wall thickness. The wall thickness of copper and brass tubing is often expressed in terms of Birmingham wire gauge (BWG). Higher the BWG lower is the thickness. BWG ranges from 24 (very light) to 7 (very heavy). The common BWG are 12, 14, 16 and 18.