flange size chart

ANSI / ASME B16.5 Class 300 Pressure rating

What is pressure – temperature rating ?

The most popular pressure rating are class 150 and class 300. Both ratings refer to ASME B16.5. In this articles, we will discuss about Class 300. According ASME B16.5 – 2009, Pressure – temperature ratings are maximum allowable working gage pressures in bar units at the temperatures in degrees Celsius shown in Tables 2-1.1 through 2-3.17 for the applicable material and class designation. If you want to use psi units for pressure at the temperature in degrees Fahrenheit, then you can see Tables II-2-1.1 through II-2-3.17 of Mandatory Appendix II. The temperature gradients in the Tables increase every 25 or 50 degrees Celsius. If you want to know maximum allowable working pressure at intermediate temperatures ( for example 120 degrees Celsius) , you can do linear interpolation. However, interpolation between class designations is not permitted.

in addition of the pressure – temperature rating, there are some consideration if you use the flange at high temperature or low temperature. Here some advices from ASME :

high temperature consideration

it is necessary to anticipate decreasing bolt loads as relaxation of flanges, bolts, and gaskets takes place when we operate the flange at temperatures in the creep range. Flanged joints subjected to thermal gradients may likewise be subject to decreasing bolt loads. Decreased bolt loads diminish the capacity of the flanged joint to sustain loads effectively without leakage. At temperatures above 200°C (400°F) for Class 150 and above 400°C (750°F) for other class designations ( including class 300), flanged joints may develop leakage. Please take care to avoid imposing severe external loads, severe thermal gradients, or both.

low temperature consideration

Some of the materials listed in Tables 1A and 1B ( carbon steels materials)  may undergo a decrease in ductility when operate at low temperatures. Please note, low ductility material unable to safely resist shock loading, sudden changes of stress, or high stress concentration. The design engineer need to take some precaution since some codes or regulations may require impact testing for applications even where temperatures are higher than −29°C (−20°F).

Pressure – temperature rating for Flanged class 300

Table 1A is a guideline to select the Material Group. For example, when we use carbon steel Flanged A 105 which is C-Si material, then we will use Material Group 1.1 pressure – temperature rating ( Table 2-1.1 )

class 300 pressure rating
Table 1A Pressure-temperature rating table for selected material

Please refer to Table 2-1.1 below. Working pressure using bar unit and working temperature using Celsius unit. When we operate Flange A 105 class 300 at temperature 250 Celsius, then the maximum allowable working gage pressure will be 41.9 bar

ansi class 300 pressure rating
Table 2-1.1 pressure rating for Group 1.1 materials ( pressure unit is bar, temperature unit is Celsius)

When we operate Flange A 105 class 300 at temperature 300 Celsius, then the maximum allowable working gage pressure will be 39.8 bar. As mention earlier, we can conduct interpolation for intermediate temperature. For example, temperature 275 Celsius, then the maximum allowable working gage pressure is  40.85 bar.

For high pressure and high temperature material, such as Cr-Mo alloy F11 or F22, please refer to group 1.9 and group 1.10 material

asme ansi 300 pressure rating group 1.9
Group 1.9 material
Group 1.9 material
Temp C Pressure in bar
−29 to 38 51.7
50 51.7
100 51.5
150 49.7
200 48
250 46.3
300 42.9
325 41.4
350 40.3
375 38.9
400 36.5
425 35.2
450 33.7
475 31.7
500 25.7
538 14.9
550 12.7
575 8.8
600 6.1
625 4.3
650 2.8
asme ansi 300 pressure rating group 1.10
group 1.10 material
Group 1.10 material
Temp C Pressure in bar
−29 to 38 51.7
50 51.7
100 51.5
150 50.3
200 48.6
250 46.3
300 42.9
325 41.4
350 40.3
375 38.9
400 36.5
425 35.2
450 33.7
475 31.7
500 28.2
538 18.4
550 15.6
575 10.5
600 6.9
625 4.5
650 2.8

 

Leave a Reply

Your email address will not be published. Required fields are marked *