Piping systems are limited by their weakest components, which are often the flanged joints. Flange pressure ratings are standardized by (up to 24 inches) and ASME B16.47 (above 24 inches). Pressure Classes
Once the minimum required thickness is calculated, the next step is to select a commercially available pipe from standard "schedules" (e.g., Schedule 40, Schedule 80). The pipe's nominal wall thickness must equal or exceed t_min . These standard thicknesses are directly linked to a pipe's pressure rating at a given temperature.
The behavior of a fluid inside a pipe depends heavily on its velocity, density, viscosity, and the pipe diameter. This behavior is characterized by the dimensionless :
) , which determines whether the flow is laminar, transitional, or turbulent:
Where:
Commonly used in water distribution and fire protection systems due to its simplicity, though limited to water at ambient temperatures:
Once the hydraulic sizing confirms the inside pipe diameter, the pipe wall thickness must be determined to safely contain the internal operating pressure. Codes and Standards
= Darcy friction factor (derived from the Colebrook-White equation or Moody Chart) = Length of the pipe ( = Inside diameter of the pipe ( = Fluid velocity ( = Acceleration due to gravity ( Minor Losses ( -Factor and Equivalent Length)
), a dimensionless value representing the ratio of inertial forces to viscous forces: Piping systems are limited by their weakest components,
In turbulent flow, the friction between the fluid and the pipe wall depends on the relative roughness of the pipe. The Darcy Friction Factor (
0.2 to 1.0 bar per 100 meters (0.1 to 0.5 psi/100 ft)
= Weld joint strength reduction factor (for elevated temperatures) = Coefficient valid for valid (depends on material and temperature) To find the , mechanical and structural allowances must be added:
Pipeline Transportation Systems for Liquids and Slurries The pipe's nominal wall thickness must equal or exceed t_min
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= Mill manufacturing tolerance (typically 12.5% or 0.125 for seamless pipe) 5. Pipe Material Selection and Flange Pressure Classes
): Fluid flows in parallel layers with minimal mixing. High-viscosity fluids typically exhibit laminar flow. Transitional Flow (