Satish Lele
lelepiping@gmail.com

Flange Class / Rating
ASME and ANSI: Most flanges are supplied with flanges conforming to dimensional standards developed by the American Society of Mechanical Engineers (ASME) and accredited by the American National Standards Institute (ANSI). Various committees within ASME are charged with developing, issuing and maintaining individual standards. The ASME B16 committees have this responsibility for valves, flanges and flanged fittings. Standardized dimensions for
  • Cast iron flanges and flanged fittings are provided in ANSI/ASME B16.1 standard
  • Steel and stainless steel in the ANSI/ASME B16.5 standard
  • Ductile iron in the ANSI/ASME B16.42 standard.

Compliance with the applicable standardized flange and flanged fitting dimensions is voluntary but ensures uniformity so that flanged valves from one manufacturer will bolt to flanges from another.
Flange Classes: There are four common pressure classes within the ANSI/ASME standards listed above. Class 125 and Class 250 are cast iron flanges and flanged fittings while Class 150 and Class 300 are ductile iron, steel or stainless steel. Hence, ANSI/ASME B16.1 Class 125 flanges are made from cast iron, ANSI/ASME B16.5 Class 150 can be made from steel or stainless and ANSI/ASME B16.42 Class 150 is made from ductile iron.
However, the bolting pattern is the same for both Class 125 and 150 so, regardless of material, they will bolt together. This is also the case for Class 250 and 300. Cast iron flanges are usually flat faced, while ductile iron and steel are usually raised face. When bolting a cast iron flange to a steel or ductile iron flange, the raised face of the mating flange should be removed to avoid breaking the cast iron flange when tightening the bolts.
Pressure and Temperature: The ANSI/ASME standards also provide pressure ratings for various classes of flanges and flanged fittings. The pressure ratings change based on the material from which it is made and/or the temperature at which it operates. The nominal flange Class (e.g., Class 125) generally represents the maximum working pressure at the temperature of saturated steam at that pressure. For example, an ANSI/ASME B16.1 Class 125 flange is rated for 125 PSI at 353oF.
But when used at colder temperatures, such as that of water, the ANSI/ASME maximum working pressure is higher than the nominal class. ANSI/ASME B16.1 rates Class 125 flanges and flanged fittings made from high strength cast iron for 200 PSI at temperatures up to 150o F. ANSI/ASME B16.42 rates Class 150 ductile iron flanges and fittings for 250 PSI at temperatures up to 100oF. Complete flange and flanged fitting pressure-temperature ratings can be found in tables within the applicable ANSI/ASME B16.x standard.
AWWA: The American Water Works Association (AWWA) also has committees charged with addressing the needs of the water works industry. The AWWA C110 committee considered the ANSI/ASME pressure ratings too conservative when used on water. Through burst testing they determined flanges and fittings made from high strength cast iron and with dimensions conforming to ANSI/ASME B16.1 Class 125 could be rated for a working pressure of 250 PSI with at least a 3.0 safety factor. This allows Class 125 cast iron flanges and flanged fittings to have the same pressure rating as Pressure Class 250 ductile iron pipe. AWWA C110 does not address ANSI/ASME B16.1 Class 250 cast iron flanges or flanged fittings that have a 300 to 500 PSI or higher pressure rating and a totally different bolt pattern than Class 125. Mistakes sometimes occur because cast iron or ductile iron flanged fittings have 250 cast in them (indicating a 250 PSI pressure rating) but the flange dimensions and bolt pattern conform to ANSI/ASME B16.1 Class 125 (or ANSI/ASME B16.42 Class 150). These will not bolt to an ANSI/ASME B16.1 Class 250 flange.
AWWA Valve Pressure Ratings: ANSI/ASME B16 and AWWA C110 pressure ratings are based on flanges and flanged fittings conforming to standardized geometry and dimensions, including wall thickness. By comparison, valves are available in countless types, shapes, configurations and geometries that vary from one manufacturer to the other. While the valve’s connecting flanges may conform to ANSI/ASME B16.x dimensions, there are many reasons why its pressure rating may not be the same as a flange or flanged fitting made from identical material as the valve. It is the responsibility of the valve manufacturer to establish the pressure ratings for their products. The design professional should consult the manufacturer’s published information and not assume it is the same as the flange or fitting being bolted to it. However, the pressure ratings of many ANSI/ASME B16.x flanged valves used in waterworks service are defined in AWWA standards applicable to that type of valve. The pressure rating (or Pressure Class) listed in the AWWA valve standard may or may not conform to the ANSI/ASME B16.x or the AWWA C110 pressure rating, leading to even more confusion.
The AWWA valve standards which define a Pressure Class or pressure rating are too numerous to detail, but include C500 gate valves, C504 butterfly valves, C507 ball valves, C508 check valves and C517 eccentric plug valves. The design professional should become familiar with the applicable AWWA valve standard and select the pressure class that is adequate for the working pressure and be aware that the valve’s pressure class and connection flange class may not correspond.
Every component of a piping system should be able to withstand the highest pressure that could be realized at the location where it is installed. It’s hoped the above sheds some light on the pressure ratings for flanges and flanged valves.


Pressure - Temperature Ratings
For Steel Pipe Flanges and Flanged Fittings
American National Standard ANSI B16.5 - 1988
Class 150 lb. 300 lb. 400 lb. 600 lb. 900 lb. 1500 lb. 2500 lb.
Pres
psig
450 1125 1500 2225 3350 5575 9275
Temp oF Maximum Allowable Pres psig
-20 to 100 285 740 990 1480 2220 3705 6170
200 260 675 900 1350 2025 3375 5625
300 230 655 875 1315 1970 3280 5470
400 200 635 845 1270 1900 3170 5280
500 170 600 800 1200 1795 2995 4990
600 140 550 730 1095 1640 2735 4560
650 125 535 715 1075 1610 2685 4475
700 110 535 710 1065 1600 2665 4440
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
Ratings apply to materials.
SA-1051.2 SA-515-702 SA-516-702 SA-181-701.2 SA-350-LF2 SA-537-C1.13 SA-216-WCB2
NOTES:
1.  For service temperatures above 850 F it is recommended that killed steels containing not less than 0.10% residual silicon be used.
2.  Upon prolonged exposure to temperatures above 800 F, the carbide phase of carbon steel may be converted to graphite.
3.  The material shall not be used in thickness above 2-1/2 in.
Flanges of ANSI B16.5 shall not be used for higher ratings except where it is justified by the design methods of the Code. Ratings are maximum allowable non-shock working pressures expressed as gauge pressure, at the tabulated temperatures and may be interpolated between temperatures shown. Temperatures are those on the inside of the pressure-containing shell of the flange. In general, it is the same as that of the contained material.
Working Pressure by Classes, bar
Class150 lb.300 lb.400 lb.600 lb.900 lb.1500 lb.2500 lb.
Temp oCMaximum Allowable Pressure, bar
-29 to 381949.666.299.3148.9248.2 413.7
 5018.448.164.296.2144.3240.6400.9
10016.242.256.384.4126.6211.0351.6
15014.838.551.377.0115.5192.5320.8
20013.735.747.671.3107.0178.3297.2
25012.133.444.566.8100.1166.9278.1
30010.231.642.263.2 94.9158.1263.5
325 9.330.941.261.8 92.7154.4257.4
350 8.430.340.460.7 91.0151.6252.7
375 7.429.939.859.8 89.6149.4249.0
400 6.529.439.358.9 88.3147.2245.3
425 5.529.138.958.3 87.4145.7242.9
450 4.628.838.557.7 86.5144.2240.4
475 3.728.738.257.3 86.0143.4238.9
500 2.828.237.656.5 84.7140.9235.0
538 1.425.233.450.0 75.2125.5208.9
Material for Flanges
Carbon Steel Flange
ASTM A105, ASTM A350 LF1, LF2 CL1/CL2, LF3 CL1/CL2
ASTM A694 F42, F46, F48, F50, F52, F56, F60, F65, F70

Stainless Steel Flange
ASTM A182 F304/304L, F316/316L, F316H, F310, F321
F44 (UNS S31254)

Alloy Steel Flange
ASTM A182 F1, F5a, F9, F11, F12, F22, F91
Chemical Requirements (Composition, %, max)
Material Symbol C Mn P S Si Ni Cr Mo Cu N V Co
ASTM A105 0.35 0.60-1.05 0.035 0.040 0.10-0.35 0.40 0.30 0.12 0.40   0.08  
ASTM A350 LF2 0.30 0.60-1.35 0.035 0.040 0.15-0.30 0.40 0.30 0.12 0.40   0.08 0.02
ASTM A182 F304 0.08 2.00 0.045 0.030 1.00 8.0-11.0 18.0-20.0          
ASTM A182 F304L 0.03 2.00 0.045 0.030 1.00 8.0-13.0 18.0-20.0          
ASTM A182 F316 0.08 2.00 0.045 0.030 1.00 10.0-14.0 16.0-18.0 2.00-3.00        
ASTM A182 F316L 0.03 2.00 0.045 0.030 1.00 10.0-15.0 16.0-18.0 2.00-3.00        
ASTM A182 F321 0.08 2.00 0.045 0.030 1.00 9.0-12.0 17.0-19.0          
EN 10025 S235JR 0.20 1.40 0.045 0.045           0.009    
20Mn 0.17-0.23 0.70-1.00 0.035 0.035 0.17-0.37 0.30 0.25   0.25      
20 0.17-0.23 0.60-1.00 0.030 0.020 0.17-0.37 0.25 0.25   0.25      
16Mn 0.13-0.19 1.20-1.60 0.030 0.020 0.20-0.60 0.30 0.30   0.25      

Mechanical Requirements
Material Symbol Tensile Strength, min, MPa Yield point, min, Mpa Elongation, min, % Reduction of area, min, % Hardness, max, HB Min. Impact
Average, J
Test Temp, °C
ASTM A105 485 250 22 30 187    
ASTM A350 LF2 485-655 250 22 30   20 -46
ASTM A182 F304 515 205 30 50      
ASTM A182 F304L 485 170 30 50      
ASTM A182 F316 515 205 30 50      
ASTM A182 F316L 485 170 30 50      
ASTM A182 F321 515 205 30 50      
20Mn 450 275 24 50 197    
20 410 245 25 55 156    

A ASTM cross reference material specification of fittings, flanges, unions and cast and forged valves can be found in the table below:
Material Forgings Castings Wrought Fittings
Carbon Steel
Cold Temperature Service
A105
A350-LF2
A216-WCB A234-WPB
A420-WPL6
Carbon-1/2 Molybdenum Alloy Steel
High Temperature Service

A182-F1

A217-WC1
A352-LC1

A234-WP1
3-1/2 Nickel Alloy Steel
Low Temperature Service

A350-LF3

A352-LC3

A420-WPL3
1/2 Cr-1/2 Mo Alloy Steel
1/2 Cr-1/2 Mo-1 Ni Alloy
3/4 Cr-1 Mo-3/4 Ni Alloy Steel
1 Cr-1/2 Mo Alloy Steel
A182-F2


A182-F12 CL2

A217-WC4
A217-WC5



A234-WP12 CL2
1-1/4 Cr-1/2 Mo Alloy Steel
2-1/4 Cr-1 Mo Alloy Steel
5 Cr-1/2 Mo Alloy Steel
5 Cr-1/2 Mo Alloy Steel
9 Cr-1 Mo Alloy Steel
13 Cr Alloy Steel
A182-F11 CL2
A182-F22 CL3
A182-F5
A182-F5a
A182-F9
A182-F6
A217-WC6
A217-WC9

A217-C5
A217-C12
A743-CA15
A234-WP11 CL2
A234-WP22 CL3
A234-WP5

A234-WP9
Type 304 Stainless Steel (18 Cr-8 Ni)
Standard
Low Carbon
High Temperature Service

A182-F304
A182-F304L
A182-F304H

A351-CF3

A351-CF8

A403-WP304
A403-WP304L
A403-WP304H
Type 310 Stainless Steel (25 Cr-20 Ni)
Type 316 Stainless Steel (16 Cr-12 Ni-2 Mo)
Standard
Low Carbon
High Temperature
A182-F310H

A182-F316
A182-F316L
A182-F316H
A351-CK20



A351-CF3M
A351-CF8M
A403-WP310

A403-WP316
A403-WP316L
A403-WP316H
Type 317 Stainless Steel (18 Cr-13 Ni-3 Mo)
Type 321 Stainless Steel (18 Cr-10 Ni-Ti)
Standard
High Temperature Service


A182-F321
A182-F321H

A403-WP317

A403-WP321
A403-WP321H
Type 347 Stainless Steel (18 Cr-10 Ni-Cb)
Standard
High Temperature Service

A182-F347
A182-F347H

A351-CF8C

A403-WP347
A403-WP347H
Type 348 Stainless Steel (18 Cr-10 Ni-Cb)
Standard
High Temperature Service

A182-F348
A182-F348H
 
A403-WP348
A403-WP438H
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