Flanges Pn Pressure Ratings

Reference data and engineering information about flanges pn pressure ratings for material properties applications.

Overview

Engineering reference data for Flanges Pn Pressure Ratings in material science and properties.

$\sigma = \frac{F}{A}$

Force per unit area.

$\varepsilon = \frac{\Delta L}{L_0}$

Change in length per original length.

$\sigma = E \varepsilon$

Stress proportional to strain in elastic region.

$\Delta L = \alpha L_0 \Delta T$

Length change due to temperature.

Symbol	Description	Unit
$\sigma$	Stress	Pa
$\varepsilon$	Strain	—
$E$	Young's modulus	Pa
$\alpha$	Thermal expansion coefficient	1/°C
$\Delta T$	Temperature change	°C

The following table shows the relationship between ASME B16.5 Flange Class ratings and the corresponding ISO 7005 PN (Pression Nominal) ratings.

PN (Pression Nominal): The French equivalent of "Pressure Nominal." It is a rating designator followed by a number indicating the approximate pressure rating in bars.
Unit Conversions:
- $1 \text{ bar} = 1 \times 10^5 \text{ Pa (N/m}^2\text{)} = 0.1 \text{ N/mm}^2 = 14.5038 \text{ psi}$
Important Property: PN ratings do not provide a proportional relationship between different PN numbers (e.g., PN 50 is not twice the rating of PN 20). In contrast, Class numbers do maintain a more proportional relationship. Therefore, Class numbers are recommended before PN ratings for system design.
Critical Design Rule: The pressure rating for a piping system must follow the pressure-temperature rating of the weakest pressure-containing item in the system.