What Is Flange Rating and How to Choose the Right Pressure Class?

If you choose the wrong flange pressure rating, your system may leak or even fail. It can stop production and cost you money. Here’s how to fix that.

A flange rating shows how much pressure and temperature a flange can handle safely. Ratings are grouped in classes like 150, 300, or 600. You can check limits using a flange rating chart or flange pressure rating chart before you choose your flange.

Let’s look at what flange ratings mean and how you can choose the right one.

What Is Flange Rating?

A flange rating tells you the safe limits of pressure and temperature a flange can handle. It helps you avoid leaks and damage. The higher the flange rating pressure, the stronger the flange. You will often see ratings such as 150, 300, or 600. Each number means how much load your flange can take. You can find these values in a flange rating chart or use a flange rating calculator to check them.

Flange Class Explained

Each flange class shows how much pressure it can hold. The most common classes are 150, 300, 600, 900, 1500, and 2500.
Here’s a simple table to show the flange class pressure rating at about 100°F (ASME B16.5, carbon steel):

Matching your actuator to the right flange class matters as much as matching the flange itself — an undersized actuator on a Class 600 line won’t seal reliably under load. Talk to our engineering team for torque and pressure specs across our pneumatic and electric actuator series.

Always confirm with a flange pressure rating chart before you buy or install.

Relationship Between Class Number and Working Pressure

The higher the class number, the more pressure the flange can take. Thicker flanges, stronger bolts, and heavier parts are used for higher classes. For example, a flange class 150 pressure rating is much lower than Class 300. The table below shows how temperature affects the pressure limit:

You can use a flange rating table or flange rating calculator to check the right value for your case.

Flange Rating Standards

You will often hear about the ANSI flange rating, which is part of ASME B16.5. This standard sets the rules for flange sizes, materials, and flange pressure rating. Other global standards include ISO, DIN, and JIS. Following these makes sure your parts fit and work together, no matter where they come from. You can compare values between these standards using a flange rating pressure chart.

Rating Tables

A flange rating chart or flange rating table lists how much pressure each flange class can take at different temperatures. For example, a stainless steel flange may keep higher pressure than carbon steel at the same heat.

Checking these tables helps you avoid mismatched parts and system failures.

Sourcing actuators for multiple flange standards on the same order? Request our full actuator specification catalog — torque curves, connection dimensions, and certification data for every series, sorted by ASME, ISO, and DIN compatibility.

Why Standard Flange Pressure Ratings Are Crucial

Standard ratings make your system safe and easy to maintain. A correct flange rating prevents leaks, downtime, and costly repairs. It also helps you meet inspection rules and pass audits. With standard sizes, you can replace parts from different brands without problems.

Common Issues Caused by Incorrect Rating Selection

If you pick the wrong flange pressure rating, you can face leaks, gasket failures, or pipe cracks. A flange that is too weak may break under load. A flange that is too strong adds extra cost and weight. Always double-check your choice with a flange rating pressure chart before installation.

How to Choose the Right Flange Rating?

To choose the right rating, start with your system’s pressure and temperature. Then, check the flange rating chart or use a flange rating calculator. Look at the material you are using and the standard that applies, such as ASME B16.5. Choose the smallest rating that safely fits your needs.

Step-by-Step Guide for Selecting a Suitable Pressure Class

1. Know your system’s pressure and temperature.
2. Choose the correct standard (ANSI flange rating or ASME B16.5).
3. Identify the material (carbon steel, stainless, alloy).
4. Check the flange rating pressure chart for each class.
5. Compare flange class 150 pressure rating with higher ones.
6. Use a flange rating calculator for final confirmation.
7. Keep records for maintenance and safety checks.

FAQ

What are the ASME B16.5 Flange Ratings?

They are standard pressure classes for flanges. Common ones are 150, 300, 600, 900, 1500, and 2500. Each shows how much flange pressure rating it can handle. You can find details in a flange rating table or flange pressure rating chart.

What is the Difference Between 150 and 300 Flange Rating?

The main difference is pressure. A flange class 150 pressure rating can take about 270 psi at 100°F. Class 300 can take around 740 psi. Class 300 flanges are thicker and heavier. Always check your flange rating chart to confirm before you buy.