What means ANSI flange pressure rating? How to select the right flange rating?
The term “flange rating” (or class) refers to the maximum pressure (in psi or bars) that a flange withstands at increasing temperatures. Flanges with a higher rating (class) are stronger than flanges with lower ratings, as they bear more pressure at increasing temperatures. Flanges made in different materials show different pressure-temperature performance at the same rating. In the article, you find the pressure rating charts for carbon, alloy, and stainless steel flanges and some guidance about selecting the proper rating for your piping application.
ANSI FLANGE PRESSURE RATING EXPLAINED
Pressure rating is defined as the maximum allowed pressure that a flange can withstand at increasing temperatures. According to the ANSI/ASME B16.5 specification, there are seven flange pressure ratings: 150, 300, 400, 600, 900, 1500, and 2500.
The terms “pressure rating”, “class”, “#”, “Lb” or “Lbs” are interchangeable, i.e. they all refer to the same exact concept of pressure/temperature performance of a flange (and other equipment like valves, fittings, etc).
Let’s make this clear with an example:
If two flanges have the same bore size (example 6 inches), the same material (example A105), but two different pressure ratings (one flange is class 150, the other 300), the lower rated flange (class 150) will be smaller, lighter, and less robust than the higher rated flange (class 300). This is represented in the picture:

Now, let’s look at what this means in terms of pressure rating:
- the class 150 flange withstands just 140 psi at a temperature of 600 degrees F° (as per the rating chart below)
- the class 300 flange (bigger and stronger, but with the same bore size) withstands 570 psi at the same temperature of 600 degrees F°
- finally, a class 2500 flange of the same size bears 34 times more pressure than the class 150 rated flange, reaching a whopping 4730 psi rating at 600 F°!
So, how to select the proper flange rating?
- Find the rating table that applies to your flange scrolling below (this depends on the material of the flange, as flanges with different material grades have different pressure ratings)
- Determine the max working temperature in your piping system (i.e. select one line in the table)
- Select a rating based on the maximum pressure you expect at that temperature level (i.e. select one column in that line)
- Voilà, you have the required rating!
To help you do this easily, find below the ASME B16.34 pressure rating charts for the most common flange materials (carbon, alloy, stainless).
CARBON STEEL FLANGE RATING CHART

ANSI FLANGE ASTM A105, A350 Gr. LF2/LF6 Class 1
The flange rating table shows the maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in PSI
ANSI/ASME B16.34 | ANSI PRESSURE RATING | ||||||
Temperature (in F°) | 150# | 300# | 400# | 600# | 900# | 1500# | 2500# |
< 100 | 285 | 740 | 985 | 1480 | 2220 | 3705 | 6170 |
200 | 260 | 680 | 905 | 1360 | 2035 | 3395 | 5655 |
300 | 230 | 655 | 870 | 1310 | 1965 | 3270 | 5450 |
400 | 200 | 635 | 845 | 1265 | 1900 | 3170 | 5280 |
500 | 170 | 605 | 805 | 1205 | 1810 | 3015 | 5025 |
600 | 140 | 570 | 755 | 1135 | 1705 | 2840 | 4730 |
650 | 125 | 550 | 730 | 1100 | 1650 | 2745 | 4575 |
700 | 110 | 530 | 710 | 1060 | 1590 | 2655 | 4425 |
750 | 95 | 505 | 675 | 1015 | 1520 | 2535 | 4230 |
800 | 80 | 410 | 550 | 825 | 1235 | 2055 | 3430 |
850 | 65 | 320 | 425 | 640 | 955 | 1595 | 2655 |
900 | 50 | 230 | 305 | 460 | 690 | 1150 | 1915 |
950 | 35 | 135 | 185 | 275 | 410 | 685 | 1145 |
1000 | 20 | 85 | 115 | 170 | 255 | 430 | 715 |
Hydrostatic Test Pressure (in Psig) | 450 | 1125 | 1500 | 2225 | 3350 | 5575 | 9275 |
The flange rating table shows the maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in bars
ANSI/ASME B16.34 | ANSI PRESSURE RATING | ||||||
Temperature in C° | 150# | 300# | 400# | 600# | 900# | 1500# | 2500# |
-29 / 38 | 19.6 | 51.1 | 68.1 | 102.1 | 153.2 | 255.3 | 425.5 |
50 | 19.2 | 50.1 | 66.8 | 100.2 | 150.4 | 250.6 | 417.7 |
100 | 17.7 | 46.6 | 62.1 | 93.2 | 139.8 | 233 | 388.3 |
150 | 15.8 | 45.1 | 60.1 | 90.2 | 135.2 | 225.4 | 375.6 |
200 | 13.8 | 43.8 | 58.4 | 87.6 | 131.4 | 219 | 365 |
250 | 12.1 | 41.9 | 55.9 | 83.9 | 125.8 | 209.7 | 349.5 |
300 | 10.2 | 39.8 | 53.1 | 79.6 | 119.5 | 199.1 | 331.8 |
325 | 9.3 | 38.7 | 51.6 | 77.4 | 116.1 | 193.6 | 322.6 |
350 | 8.4 | 37.6 | 50.1 | 75.1 | 112.7 | 187.8 | 313 |
375 | 7.4 | 36.4 | 48.5 | 72.7 | 109.1 | 181.8 | 303.1 |
400 | 6.5 | 34.7 | 46.3 | 69.4 | 104.2 | 173.6 | 289.3 |
425 | 5.5 | 28.8 | 38.4 | 57.5 | 86.3 | 143.8 | 239.7 |
450 | 4.6 | 23 | 30.7 | 46 | 69 | 115 | 191.7 |
475 | 3.7 | 17.4 | 23.2 | 34.9 | 52.3 | 87.2 | 145.3 |
500 | 2.8 | 11.8 | 15.7 | 23.5 | 35.3 | 58.8 | 97.9 |
Notes:
- ASTM A105: An extended exposure to temperatures above 425°C, converts the carbide phase of steel to graphite (therefore this material is not recommended for constant temperatures above this value.
- ASTM A350 LF6: shall not be used for temperatures above 260 C°
ANSI FLANGE ASTM A350 Gr. LF3, A350 LF6, Class 2
The flange rating chart shows the maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in PSI
ANSI/ASME B16.34 | ANSI PRESSURE RATING | ||||||
Temperature in °F | 150# | 300# | 400# | 600# | 900# | 1500# | 2500# |
-20 to 100 | 290 | 750 | 1000 | 1500 | 2250 | 3750 | 6250 |
200 | 260 | 750 | 1000 | 1500 | 2250 | 3750 | 6250 |
300 | 230 | 730 | 970 | 1455 | 2185 | 3640 | 6070 |
400 | 200 | 705 | 940 | 1410 | 2115 | 3530 | 5880 |
500 | 170 | 665 | 885 | 1330 | 1995 | 3325 | 5540 |
600 | 140 | 605 | 805 | 1210 | 1815 | 3025 | 5040 |
650 | 125 | 590 | 785 | 1175 | 1765 | 2940 | 4905 |
700 | 110 | 570 | 755 | 1135 | 1705 | 2840 | 4730 |
750 | 95 | 505 | 670 | 1010 | 1510 | 2520 | 4200 |
800 | 80 | 410 | 550 | 825 | 1235 | 2060 | 3430 |
850 | 65 | 270 | 355 | 535 | 805 | 1340 | 2230 |
900 | 50 | 170 | 230 | 345 | 515 | 860 | 1430 |
950 | 35 | 105 | 140 | 205 | 310 | 515 | 860 |
1000 | 20 | 50 | 70 | 105 | 155 | 260 | 430 |
ANSI FLANGE ASTM A350 Gr. LF1
The flange rating table shows the maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) — in PSI
ANSI/ASME B16.34 | ANSI PRESSURE RATING | ||||||
Temperature °F | 150# | 300# | 400# | 600# | 900# | 1500# | 2500# |
-20 to 100 | 235 | 620 | 825 | 1235 | 1850 | 3085 | 1545 |
200 | 215 | 560 | 750 | 1125 | 1685 | 2810 | 4680 |
300 | 210 | 550 | 730 | 1095 | 1640 | 2735 | 4560 |
400 | 200 | 530 | 705 | 1060 | 1585 | 2645 | 4405 |
500 | 170 | 500 | 665 | 995 | 1495 | 2490 | 4150 |
600 | 140 | 455 | 610 | 915 | 1370 | 2285 | 3805 |
650 | 125 | 450 | 600 | 895 | 1345 | 2245 | 3740 |
700 | 110 | 450 | 600 | 895 | 1345 | 2245 | 3740 |
750 | 95 | 445 | 590 | 885 | 1325 | 2210 | 3685 |
800 | 80 | 370 | 495 | 740 | 1110 | 1850 | 3085 |
850 | 65 | 270 | 355 | 535 | 805 | 1340 | 2230 |
900 | 50 | 170 | 230 | 345 | 515 | 860 | 1430 |
950 | 35 | 105 | 140 | 205 | 310 | 515 | 860 |
1000 | 20 | 50 | 70 | 105 | 155 | 260 | 430 |
ALLOY STEEL FLANGE RATING CHART

ANSI FLANGE ASTM A182 Gr. F1 (Chrome Moly)
The flange rating table shows the maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in PSI
ANSI/ASME B16.34 | ANSI PRESSURE RATING | ||||||
Temperature °F | 150# | 300# | 400# | 600# | 900# | 1500# | 2500# |
-20 to 100 | 265 | 695 | 925 | 1390 | 2085 | 3470 | 5785 |
200 | 260 | 680 | 905 | 1360 | 2035 | 3395 | 5660 |
300 | 230 | 655 | 870 | 1305 | 1955 | 3260 | 5435 |
400 | 200 | 640 | 855 | 1280 | 1920 | 3200 | 5330 |
500 | 170 | 620 | 830 | 1245 | 1865 | 3105 | 5180 |
600 | 140 | 605 | 805 | 1210 | 1815 | 3025 | 5040 |
650 | 125 | 590 | 785 | 1175 | 1765 | 2940 | 4905 |
700 | 110 | 570 | 755 | 1135 | 1705 | 2840 | 4730 |
750 | 95 | 530 | 710 | 1065 | 1595 | 2660 | 4430 |
800 | 80 | 510 | 675 | 1015 | 1525 | 2540 | 4230 |
850 | 65 | 485 | 650 | 975 | 1460 | 2435 | 4060 |
900 | 50 | 450 | 600 | 900 | 1350 | 2245 | 3745 |
950 | 35 | 280 | 375 | 560 | 845 | 1405 | 2345 |
1000 | 20 | 165 | 220 | 330 | 495 | 825 | 1370 |
STAINLESS STEEL FLANGE RATING CHART

ANSI FLANGE ASTM A182 Gr. F304, 304L
The flange rating table shows the maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in PSI
ANSI/ASME B16.34 | ANSI PRESSURE RATING | ||||||
Temperature °F | 150# | 300# | 400# | 600# | 900# | 1500# | 2500# |
-20 to 100 | 275 | 720 | 960 | 1440 | 2160 | 3600 | 6000 |
200 | 230 | 600 | 800 | 1200 | 1800 | 3000 | 5000 |
300 | 205 | 540 | 720 | 1080 | 1620 | 2700 | 4500 |
400 | 190 | 495 | 660 | 995 | 1490 | 2485 | 4140 |
500 | 170 | 465 | 620 | 930 | 1395 | 2330 | 3880 |
600 | 140 | 435 | 580 | 875 | 1310 | 2185 | 3640 |
650 | 125 | 430 | 575 | 860 | 1290 | 2150 | 3580 |
700 | 110 | 425 | 565 | 850 | 1275 | 2125 | 3540 |
750 | 95 | 415 | 555 | 830 | 1245 | 2075 | 3460 |
800 | 80 | 405 | 540 | 805 | 1210 | 2015 | 3360 |
850 | 65 | 395 | 530 | 790 | 1190 | 1980 | 3300 |
900 | 50 | 390 | 520 | 780 | 1165 | 1945 | 3240 |
950 | 35 | 380 | 510 | 765 | 1145 | 1910 | 3180 |
1000 | 20 | 320 | 430 | 640 | 965 | 1605 | 2675 |
1050 | 20 | 310 | 410 | 615 | 925 | 1545 | 2570 |
1100 | 20 | 255 | 345 | 515 | 770 | 1285 | 2145 |
1150 | 20 | 200 | 265 | 400 | 595 | 995 | 1655 |
1200 | 20 | 155 | 205 | 310 | 465 | 770 | 1285 |
1250 | 20 | 115 | 150 | 225 | 340 | 565 | 945 |
1300 | 20 | 85 | 115 | 170 | 255 | 430 | 715 |
1350 | 20 | 60 | 80 | 125 | 185 | 310 | 515 |
1400 | 20 | 50 | 65 | 95 | 145 | 240 | 400 |
1450 | 15 | 35 | 45 | 70 | 105 | 170 | 285 |
1500 | 10 | 25 | 35 | 55 | 80 | 135 | 230 |
ANSI FLANGE ASTM A182 Gr. F316, 316L
The flange rating table shows the maximum pressure for flanges of classes 150/300/400/600/900/1500/2500 at increasing temperatures (Celsius or Fahrenheit) – in PSI
ANSI/ASME B16.34 | ANSI PRESSURE RATING | ||||||
Temperature °F | 150# | 300# | 400# | 600# | 900# | 1500# | 2500# |
-20 to 100 | 275 | 720 | 960 | 1440 | 2160 | 3600 | 6000 |
200 | 235 | 620 | 825 | 1240 | 1860 | 3095 | 5160 |
300 | 215 | 560 | 745 | 1120 | 1680 | 2795 | 4660 |
400 | 195 | 515 | 685 | 1025 | 1540 | 2570 | 4280 |
500 | 170 | 480 | 635 | 955 | 1435 | 2390 | 3980 |
600 | 140 | 450 | 600 | 900 | 1355 | 2255 | 3760 |
650 | 125 | 445 | 590 | 890 | 1330 | 2220 | 3700 |
700 | 110 | 430 | 580 | 870 | 1305 | 2170 | 3620 |
750 | 95 | 425 | 570 | 855 | 1280 | 2135 | 3560 |
800 | 80 | 420 | 565 | 845 | 1265 | 2110 | 3520 |
850 | 65 | 420 | 555 | 835 | 1255 | 2090 | 3480 |
900 | 50 | 415 | 555 | 830 | 1245 | 2075 | 3460 |
950 | 35 | 385 | 515 | 775 | 1160 | 1930 | 3220 |
1000 | 20 | 350 | 465 | 700 | 1050 | 1750 | 2915 |
1050 | 20 | 345 | 460 | 685 | 1030 | 1720 | 2865 |
1100 | 20 | 305 | 405 | 610 | 915 | 1525 | 2545 |
1150 | 20 | 235 | 315 | 475 | 710 | 1185 | 1970 |
1200 | 20 | 185 | 245 | 370 | 555 | 925 | 1545 |
1250 | 20 | 145 | 195 | 295 | 440 | 735 | 1230 |
1300 | 20 | 115 | 155 | 235 | 350 | 585 | 970 |
1350 | 20 | 95 | 130 | 190 | 290 | 480 | 800 |
1400 | 20 | 75 | 100 | 150 | 225 | 380 | 630 |
1450 | 20 | 60 | 80 | 115 | 175 | 290 | 485 |
1500 | 20 | 40 | 55 | 85 | 125 | 205 | 345 |
HOW TO SELECT FLANGE RATING
If you are still in doubt about how to select the flange rating, take a look at this useful video:
10 Responses
{08/28/19 @ 15:12 EDT}
I found this site to contain much useful information but not exactly what I need. I hope you can help regarding the correct
ASME flange to use for methane service @ 1000°C and 0.2 MPa. I think 900# RF or RTJ? Please, where could I find that information?
Thanks for any help.
Ps. Information not found in “Flange Pressure Rating Explained (and Charts)” article. Charts end at 1500 F (815°C)
The bolts in flanges will relax so flange over 1500F are troublesome. Typical the connect would be internally insulated so the flange and bolts would operate at a lower temperature.
Hi,
I have a question about pressure-temperature rating. For which fittings the standard define class rating?
Specifically i want to know why “insulating joints” has class rating?
Thanks
Hi
If my pipe is SS 316L. My Backing Flange is #150 lb forged Steel, lap joint (Galvanized) should the Flange pressure rating be based on a Carbon Steel #150 Flange?
How you calc max pressure testing of flang A105 900#
in google search it was 3350psi
Good day,
I have a 200mm T/10 BS4504 galvanized carbon steel flange. I want to multi drill it to T/1600. What will the pressure rating be on the flange after drilling?
I have to flange 24 inch diameter mild steel pipes for a water pressure as low as 10 psi. I am concerned why should I use #150 flanges which are over strong for my need? I am desperately looking for some other flange standards which deal with very low pressures. I will be much obliged if some one can help.
Useful information but not complete.
You didn’t mention size. Let’s assume if I select for 10″ 300# flange will this hold the same pressure as 6″ 300# flange of the same material.
I don’t think so.
By the way great website, and well maintained to know even more from other articles.
Hi.
Please suggest flange dimension for T= 1200K and Pressure=100 bar. Also provide reference if possible.
thanks in advance
Thank you for sharing this information. I can get flange rating data quickly by using this chart. I recommend you to make a flange pressure rating calculator instead of only chart. Calculators will be more easier to use.