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Introduction
Whether you’re manufacturing or installing flanges, you need to understand flange ratings and pressures. The flange ratings and pressures mentioned in this article indicate the pressure ratings that flanges can withstand according to certain standards. These are typically expressed as Class 150, Class 300, Class 900, etc. This article will explain flange pressure ratings.
What is Flange Pressure Rating?
A flange’s pressure rating indicates the pressure and temperature that a flange can withstand within a certain pressure rating, as defined by international standards such as the American Standard or the Japanese Standard.
For example:
- ASME B16.5 class 150 flange: This indicates that the flange can withstand a maximum pressure of 285 psi at 100°F.
- ASME B16.5 class 300 flange: This indicates that the flange can withstand a maximum pressure of 740 psi at 100°F.
What are Flange Rating Classes?
Flanges don’t have a single strength rating; different production standards may also indicate different pressure ratings. However, the ASME standards are generally used.
- Class 150
- Class 300
- Class 400 (less common today)
- Class 600
- Class 900
- Class 1500
- Class 2500
The higher the number, the higher the pressure rating. The thicker the flange, the greater its strength.
How Does Temperature Affect Flange Rating?
As temperature increases, the pressure rating of a flange decreases. The reason is: metal softens when heated.
A flange that can withstand 19 bar pressure at room temperature may only be able to withstand 10 bar pressure at 400°C. This is why flange specifications include both pressure and temperature.
The pressure ratings of flanges of different pressure classes are as follows:
- Class 150 carbon steel flange: at 100°F (~38°C): ~285 psi (~19 bar).
- Class 150 carbon steel flange: at 500°F (~260°C): ~170 psi (~11.7 bar).
Therefore, when selecting a flange, it’s important to choose a pressure rating based on actual use.
Common Flange Pressure Ratings by Class
The following are the actual pressures corresponding to the pressure ratings of carbon steel flanges at room temperature.
| Flange Class | Pressure Rating (psi) |
| Class 150 | 285 psi (19 bar) |
| Class 300 | 740 psi (51 bar) |
| Class 600 | 1480 psi (102 bar) |
| Class 900 | 2220 psi (153 bar) |
| Class 1500 | 3705 psi (255 bar) |
| Class 2500 | 6170 psi (425 bar) |
Why Flange Ratings Matter
In addition to affecting the safety of piping systems, flange ratings are important for the following reasons:
- Safety: Selecting the appropriate flange can reduce the risk of leaks and other risks in the piping system.
- Efficiency: Selecting a flange with the appropriate pressure rating can extend its service life, reducing the frequency of replacement.
- Compliance: When selecting a flange, adhere to the flange’s manufacturing standards.
What is Class 150 Pressure Rating in Bar?
You may not understand what bar or kilograms per cubic centimeter (kg/cm³) in the Class 150 pressure rating specifically represent. Specifically, a Class 150 carbon steel flange has a pressure rating of 19 bar at room temperature. This can be expressed in kg/cm², meaning 19.3 kg/cm².
What is a Class 300 Pressure Rating in Bar?
- Class 300 = approximately 51 bar at 100°F (38°C).
- Equivalent to 52 kg/cm².
- Mostly used in chemical plants and refineries.
What is a Class 600 Pressure Rating in Bar?
- Class 600 = approximately 102 bar at 100°F.
- That’s roughly 104 kg/cm².
- Mostly used in high-pressure oil and gas industries or steam piping systems.
How to Read a Flange Rating Chart
Flange rating charts typically display the pressure rating, temperature, and maximum allowable pressure range.
Using them specifically is to find the flange rating, its applicable temperature, and maximum pressure range. This can effectively mitigate certain safety risks.
Tools: Flange Rating Calculators
To calculate flange ratings, find online calculators. Simply enter the flange rating, temperature, and material type, and the flange’s allowable pressure value will be automatically calculated.
Summary
The flange pressure rating is a standard that specifies the flange’s rated pressure range and actual pressure at elevated temperatures.
The above information details the room temperature and elevated temperature pressures for flanges of different ratings. If you have any further questions, please contact our engineers.
