Module 3 Process Piping Hydraulics Sizing And Pressure Rating Pdf Jun 2026
ASME B31.3 is the governing code for determining wall thickness, ensuring the pipe can withstand design pressure safely.
The behavior of a fluid in a pipe is dictated by three foundational equations:
Where f is the friction factor (derived from the Moody Chart), L is length, D is diameter, and g is gravity.
Based on the law of conservation of mass, the mass flow rate entering a steady-state system must equal the mass flow rate exiting. For an incompressible fluid with a constant density, this simplifies to the volumetric continuity equation:
To determine the rating, you must look up the ASME B16.5 chart for the specific material class. ASME B31
Ensure net positive suction head available ( NPSHacap N cap P cap S cap H sub a ) exceeds required head ( NPSHrcap N cap P cap S cap H sub r
hf=10.67⋅L⋅Q1.852C1.852⋅D4.87h sub f equals the fraction with numerator 10.67 center dot cap L center dot cap Q to the 1.852 power and denominator cap C to the 1.852 power center dot cap D to the 4.87 power end-fraction = Volumetric flow rate
tm=t1−Tol+ct sub m equals the fraction with numerator t and denominator 1 minus cap T o l end-fraction plus c
The actual ordered thickness must account for mechanical allowances, environmental degradation, and manufacturing tolerances: For an incompressible fluid with a constant density,
An increase in operating temperature lowers the allowable yield and tensile strength of metals. Consequently, as temperature goes up, the maximum allowable pressure for a specific flange class goes down. Designers use ASME B16.5 P-T rating tables to verify that a selected flange class can safely handle the design pressure at the maximum coincident temperature. 5. Engineering Best Practices and Safety Considerations
As the chart shows, the hydraulic analysis and pipe sizing are iterative processes. Once a feasible size is found, the pressure design phase uses the chosen diameter to calculate the required wall thickness, culminating in the final pipe specification.
Where P is the internal pressure (psig) and S is the allowable stress (psi) for the material at the operating temperature.
): Fluid flows in parallel layers with minimal mixing. High-viscosity fluids typically exhibit laminar flow. Transitional Flow ( Designers use ASME B16
: Managing the relationship between pressure, velocity, and elevation. Flow Regimes : Using the Reynolds Number
): The pressure at which a liquid turns into a vapor. This is critical for avoiding cavitation in liquid systems. Flow Regimes
t_min = (P * D) / (2 * (S * E + P * Y)) + CA