Table of content
Introduction
Flange class is usually used in the ASME standard to refer to the pressure that a flange can withstand. Usually there are class 150, class 300, class 600, etc. Its different numbers represent different pressures. The larger the number, the higher the pressure it can withstand. This article will take a closer look at flange classes and working principles.
What Is the Class of Flanges?
Flange class is mainly a standard for a system of flanges established by ASME (American Society of Mechanical Engineers). Flange class is the pressure level that can be withstood at a given temperature. There are mainly the following classes.
- class 150
- class 300
- class 400
- class 600
- class 900
- class 1500
- class 2500
What Is Class 150 and Class 300 Flanges?
Class 150 and class 300 are one of the flange standards.
class 150: Suitable for low-pressure piping systems. The maximum pressure that can be borne at the rated ambient temperature is 270 psi.
class 300: is also commonly used in low-pressure piping systems, but its pressure resistance is higher than 150. The maximum pressure that can be borne at the rated ambient temperature is 570 psi.
How Do Temperature and Pressure Affect Flange Classes?
The pressure that the flange can withstand decreases as the temperature increases. For example, the pressure resistance of class 600d at the rated temperature is 1500 psi, but the ability to withstand pressure decreases as the temperature increases.
At the same time, the pressure resistance of flanges made of different materials is also different. The pressure resistance of stainless steel is higher than that of carbon steel at the same level.
What Does Class 250 Flange Mean?
Class 250 flanges are a pressure rating of flanges. They are usually used in ductile iron piping systems and are mostly used in water treatment systems.
Are Class 900 and Class 1500 Flanges the Same?
The two are different. But both are used in high-pressure piping systems.
class 900: The pressure resistance level is lower than 1500, but it is also mostly used for high pressure. Such as steam and oil pipelines.
Class 1500: Withstands pressure higher than 900, mostly used in factories such as oil refineries with higher pressures.
For ½ to 2½ pipes, class 900 and class 1500 flanges may have the same size, but their wall thickness and pressure rating are different.
Flange Class vs. pipe Schedule: What’s the Difference?
Different flange grades are suitable for different pipe specifications. For example, flange specifications include class 150, class 300, etc., but pipe specifications only include sch 40, sch 60, etc. It is very necessary to choose the appropriate flange grade and pipe specification in pipeline installation.
Flange Pressure Rating Chart
| Flange Class | Pressure Rating (psi) at Ambient Temp |
| Class 150 | 270 psi |
| Class 300 | 570 psi |
| Class 400 | 740 psi |
| Class 600 | 1,150 psi |
| Class 900 | 2,250 psi |
| Class 1500 | 3,750 psi |
| Class 2500 | 6,250 psi |
For more specific reference, please refer to the asme b16.5 chart.
Summary
Different flange grades withstand different pressures, and as the ambient temperature increases, the pressure they withstand decreases. Therefore, when selecting flange grades, the temperature changes in the actual construction environment can also be considered. So that a more suitable flange can be selected.
Flanges play a vital role in the pipeline system, so flange selection must refer to the flange grade table and the actual environment. It is safer to choose a higher grade flange within the controllable range.
