Class 150 Pressure Rating - Class 150 / 300 Flange Pressure Rating

According to ASME B16.5, the steel flange has seven pressure ratings: Class 150-300-400-600-900-1500-2500, which is very clear. The Class 300 flange can withstand more pressure than the Class 150, because the Class 300 flange needs to be made of more material to withstand greater pressure. However, the pressure capacity of the flange depends on many factors. The pressure rating of the flange is expressed in pounds, and a pressure rating has a different representation. For example, 150Lb, 150Lbs, 150# and Class 150 mean the same.

Examples of Pressure Rating

The bearing capacity of flanges varies with temperature. As the temperature increases, the bearing capacity of the flange decreases. For example, the Class 150 flange has a pressure capacity of 270 PSIG at room temperature; has a pressure capacity of 180 PSIG at 400℉; has a pressure capacity of 150 PSIG at 600℉; has a pressure capacity of 75 PSIG at 800℉.

In other words, when pressure falls, temperature rises, and vice versa. Valve Flanges can be made of a variety of materials, such as stainless steel, cast iron, ductile iron, carbon steel, and so on, each with a different pressure rating. The following figure shows an example of a flange in NPS12. As you can see, the diameter of the flange inner hole and face is the same. However, the flange outside diameter, bolt hole center circle diameter, and bolt hole diameter increase with the increase of the pressure level. The number and diameter of bolt holes are: CL150 – 12 x 25.4 CL300 – 16 x 28.6 CL400 – 16 x 34.9 CL600 – 20 x 34.9 CL900 – 20 x 38.1 CL1500 – 16 x 54 CL2500 – 12 x 73

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Examples of Pressure Temperature Rating

The pressure-temperature rating means the maximum allowable working gauge pressure (pressure in Bar) of the material and class at the rated temperature (Celsius). The linear insertion method can be used to determine the intermediate temperature, but insertion between flange levels is not allowed. Flange joints can be suitable for pressure-temperature ratings if the bolts and gaskets of the flange joints meet the relevant limitations and the alignment and assembly of the flange joints are in accordance with standards.

The rated temperature corresponding to the rated pressure is the case temperature of the pressure vessel of the flange and the flange pipe. In general, this temperature is the same as the temperature of the stored fluid. When the temperature is – 29 ℃ (- 20 ℉), the following rating, shall be no greater than – 29 ℃ (- 20 ℉) rating.

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

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

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

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

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