ISO 228 Pipe Threads

Overview

Engineering reference data for ISO 228 Pipe Threads 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

Symbol	Description	Unit
$Re$	Reynolds number	—
$\rho$	Fluid density	kg/m³
$v$	Flow velocity	m/s
$D$	Characteristic dimension	m
$\mu$	Dynamic viscosity	Pa·s
$P$	Pressure	Pa
$f$	Darcy friction factor	—

Thread Dimensions Table

Key Properties and Standards

Thread Terminology

• TPI (Threads Per Inch): A count of the number of threads per inch, primarily used for American fastener systems.
• Thread Pitch: The distance between successive threads, measured in millimeters, standard for metric systems.
• G-Threads: These are parallel (non-tapering) pipe threads conforming to the DIN-EN-ISO 228-1 standard, featuring a $55^{\circ}$ flank angle.

Related Standards & Designation

• *ISO 228-1:2000: Specifies dimensions, tolerances, and designation for non-pressure-tight pipe threads.
• *ISO 228-2:1987: Covers verification of these threads using limit gauges.
• Whitworth Thread Family: G, R, and Rp threads are part of the Whitworth pipe thread system (also known as BSPP and BSPT).
• Pressure-Tight Joints: ISO 228 threads are specifically designed for applications where the pressure seal is not made on the threads themselves. For threads where pressure tightness is achieved on the thread form, refer to ISO 7-1.
• Designation Example: A thread is designated by the standard number followed by the thread size, e.g., ISO 228 G 3 1/4".

Interactive Charts

References

• Original Source