Stainless steel 304 flanges (18Cr-8Ni) may be manufactured from forgings, castings, or plates, respectively. It includes ASTM A182 Gr. F304 forgings, ASTM A351 Gr. CF8 castings, and ASTM A240 Gr. 304 plates. The flange dimensions are generally in accordance with ASME B16.5. It can be classified into 7 classes: 150, 300, 400, 600, 900, 1500, and 2500. The working pressures for which SS 304 flanges can be applied at elevated temperatures are listed in below tables (it is also known as “pressure-temperature ratings” for the material).

Pressure-Temperature Ratings for SS 304 Flanges

Temp. °F	Class 150	Class 300	Class 600
-20~100	275	720	1,440
200	230	600	1,200
300	205	540	1,075
400	190	495	995
500	170	465	930
600	140	440	885
650	125	430	865
700	110	420	845
750	95	415	825
800	80	405	810
850	65	395	790
900	50	390	780
950	35	380	765
1000	20	355	710
1050	-	325	650
1100	-	255	515
1150	-	205	410
1200	-	165	330
1250	-	135	265
1300	-	115	225
1350	-	95	185
1400	-	75	150
1450	-	60	115
1500	-	40	85

*The working pressures by classes of 150, 300, 600, unit: psig.

Temp. °F	Class 900	Class 1500	Class 2500
-20~100	2,160	3,600	6,000
200	1,800	3,000	5,000
300	1,615	2,690	4,480
400	1,490	2,485	4,140
500	1,395	2,330	3,880
600	1,325	2,210	3,680
650	1,295	2,160	3,600
700	1,265	2,110	3,520
750	1,240	2,065	3,440
800	1,215	2,030	3,380
850	1,190	1,980	3,300
900	1,165	1,945	3,240
950	1,145	1,910	3,180
1000	1,065	1,770	2,950
1050	975	1,630	2,715
1100	770	1,285	2,145
1150	615	1,030	1,715
1200	495	825	1,370
1250	400	670	1,115
1300	340	565	945
1350	280	465	770
1400	225	380	630
1450	175	290	485
1500	125	205	345

*The working pressures by classes of 900, 1500, 2500, unit: psig.

Since pipe flanges of Class 400 are rarely used in engineering practice, its data are not listed. All values in the above two tables are in US customary unit. You may contact us to get the technical specification in ISO metric unit. Pipe flanges made of A351 Gr. CF3 are not to be used over 800°F. At temperatures over 1000°F, SS 304 flanges made from forgings and plates shall be used only when the carbon content is 0.04% or higher. The listed data are also applicable for A182 Gr. F304H, A351 Gr. CF3, A240 Gr. 304H.