Pipes Tubes

Overview

Engineering reference data for Pipes Tubes in fluid mechanics.

Key Formulas

Reynolds Number

$Re = \frac{\rho v D}{\mu}$

Ratio of inertial to viscous forces — determines flow regime.

Bernoulli's Equation

$P + \frac{1}{2}\rho v^2 + \rho g h = \text{const}$

Conservation of energy for steady, inviscid, incompressible flow.

Continuity Equation

$A_1 v_1 = A_2 v_2$

Conservation of mass for incompressible flow.

Darcy-Weisbach

$\Delta P = f \frac{L}{D} \frac{\rho v^2}{2}$

Pressure drop due to friction in a pipe.

Variables

Pipes vs. Tubes: Key Differences

This section outlines the fundamental distinctions between pipes and tubes in terms of sizing, tolerances, cost, and standards.

Sizing Standards

• Pipes are sized by Nominal Pipe Size (NPS), based on the approximate inside diameter. The metric equivalent is DN (diametre nominel), conforming to ISO standards, and British standards use Nominal Bore (NB). The outside diameter (OD) is constant for a given nominal size, while the inside diameter (ID) varies with the schedule (wall thickness).

  Example: For NPS 2", OD = 2.375".
  Schedule 40: ID = 2.067", thickness = 0.154".
  Schedule 80: ID = 1.939".

• Tubes are sized by the outside diameter (OD). Nominal dimensions are based on OD, and wall thickness is often specified by gauge.

  Example: For a 2" copper tube (ASTM B88), OD = 2.125", wall thickness = 0.083" for gauge 14.

Tolerances and Cost

• Pipes have looser tolerances and are generally less expensive to produce.
• Tubes have higher tolerances and are more expensive to produce.

Key Formulas

For both pipes and tubes, the inside diameter can be calculated using:

$ID = OD - 2 \times t$

where:

• $ID$ = Inside Diameter
• $OD$ = Outside Diameter
• $t$ = Wall Thickness

For pipes, $t$ is defined by the schedule for a given nominal size. For tubes, $t$ is specified by gauge or directly.

Definitions

• NPS (Nominal Pipe Size): North American standard for pipe sizing based on approximate inside diameter.
• DN (Diametre Nominel): Metric equivalent of NPS, conforming to ISO standards.
• NB (Nominal Bore): Used in British standards, similar to NPS.
• Gauge: A measure of wall thickness for tubes; higher gauge numbers indicate thinner walls.

Note on Conformity

The use of NPS in the context of pipes does not conform to American Standard pipe thread designations, where NPS means "National Pipe Thread Straight".

References

• Original Source