ANSI FLANGES PRESSURE RATING

According to ASME / ANSI, flanges are manufactured in seven different pressure ratings (alternatively defined "pressure class"): 150, 300, 400, 600, 900, 1500 and 2500. Flanges with higher rating can withstand higher pressures than flanges with lower pressure ratings. The pressure rating defines the maximum pressure that a flange of a given class can withstand for any given temperature: as the temperature increases, the pressure rating of a given class flange decreases (the table below, for instance, shows that a carbon steel ANSI flange class 150 withstands up to 285 psi at <100 F°, 200 psi at 400 F° down to 20 psi at 1.000 F°).

Of course, flanges in different materials have different performance in terms of rating / temperature by class. The stronger the material, the higher the allowed pressure at a given temperature.

Given a certain NPS, as the flange pressure rating increases the weight and the size of the flange also increases (fact that translates into more metal, more holes, more bolts). The picture below represents the size increase of a flange, at incremental steps of its class (at same nps):

Class of flanges

 
Calculation of flanges pressure rating: click here
 

ANSI FLANGE PRESSURE RATING

CARBON STEEL FLANGES

Maximum flange pressure class in psi by tempearture and ANSI flange rating, for ASTM A105 / A350 flanges (flange pressure rating ASME B16.5):

Temperature (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 (psig) 450 1125 1500 2225 3350 5575 9275

Flanges pressure rating in bars for common carbon steel ANSI flanges (ASTM A105 / ASTM A350 LF2 / ASTM A350 LF3 / ASTM A350 LF6)

TEMP 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
538 1.4 5.9 7.9 11.8 17.7 29.5 49.2

 

STAINLESS STEEL FLANGES

Flanges pressure rating in bars for common stainless steel ANSI flanges (ASTM A182 F304L / ASTM A182 F316L)

TEMP C° 150# 300# 400# 600# 900# 1500# 2500#
-29 TO 38 15.9 41.4 55.2 82.7 124.1 206.8 344.7
50 15.3 40 53.4 80 120.1 200.1 333.5
100 13.3 34.8 46.4 69.6 104.4 173.9 289.9
150 12 31.4 41.9 62.8 94.2 157 261.6
200 11.2 29.2 38.9 58.3 87.5 145.8 243
250 10.5 27.5 36.6 54.9 82.4 137.3 228.9
300 10 26.1 34.8 52.1 78.2 130.3 217.2
325 9.3 25.5 34 51 76.4 127.4 212.3
350 8.4 25.1 33.4 50.1 75.2 125.4 208.9
375 7.4 24.8 33 49.5 74.3 123.8 206.3
400 6.5 24.3 32.4 48.6 72.9 121.5 202.5
425 5.5 23.9 31.8 47.7 71.6 119.3 198.8
450 4.6 23.4 31.2 46.8 70.2 117.1 195.1

 

 

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