Understanding 316 Stainless Steel Flange Standards
316 stainless steel flanges are manufactured to ASTM A182 F316/F316L material specifications and dimensioned according to ASME B16.5 for sizes from 1/2 inch to 24 inches. The "L" grade (316L) features lower carbon content (0.03% max) to prevent carbide precipitation during welding, making it the preferred choice for as-welded applications requiring maximum corrosion resistance.
In ASME B16.5, 316 stainless steel belongs to Material Group No. 1.7, while 316L is classified under Group No. 1.10. This distinction affects pressure ratings at elevated temperatures.
Pressure-Temperature Ratings for 316 Flanges
The pressure rating of a 316 flange is not a fixed number-it decreases as temperature increases. This derating occurs because steel's yield and tensile strength decline at higher temperatures . Below 100°F, the ambient temperature rating applies for all lower temperatures, including cryogenic service (provided the material is suitable for low-temperature conditions).
Class 150, 300 and 600 Ratings
The table below shows maximum allowable working pressure for 316 stainless steel flanges at key temperatures:
|
Temperature (°F) |
Class 150 |
Class 300 |
Class 600 |
|
-20 to 100 |
275 |
720 |
1,440 |
|
200 |
235 |
620 |
1,240 |
|
300 |
215 |
560 |
1,120 |
|
400 |
195 |
515 |
1,025 |
|
500 |
170 |
480 |
955 |
|
600 |
140 |
450 |
900 |
|
650 |
125 |
440 |
885 |
|
700 |
110 |
435 |
870 |
|
750 |
95 |
425 |
855 |
|
800 |
80 |
420 |
845 |
Class 900, 1500 and 2500 Ratings
|
Temperature (°F) |
Class 900 |
Class 1500 |
Class 2500 |
|
-20 to 100 |
2,160 |
3,600 |
6,000 |
|
200 |
1,860 |
3,095 |
5,160 |
|
300 |
1,680 |
2,795 |
4,660 |
|
400 |
1,540 |
2,570 |
4,280 |
|
500 |
1,435 |
2,390 |
3,980 |
|
600 |
1,355 |
2,255 |
3,760 |
|
650 |
1,325 |
2,210 |
3,680 |
|
700 |
1,305 |
2,170 |
3,620 |
|
750 |
1,280 |
2,135 |
3,560 |
|
800 |
1,265 |
2,110 |
3,520 |
Note: Class 400 flanges follow the same pattern as Class 600 but are less common. For temperatures above 1000°F, use 316 with carbon content 0.04% or higher. Cast versions are limited to 850°F. Always add a safety margin and check your system's maximum pressure and temperature.
316 Stainless Steel Flange Dimensions
Below are full tables for the most popular classes (Class 150 and Class 300). All measurements are in inches. Raised-face flanges are standard unless you request ring-type joint or flat face.
Class 150 Flange Dimensions (NPS ½" to 24")
|
NPS |
Outside Diameter (O) |
Thickness (tf) |
Bolt Circle Diameter |
No. of Bolts |
Bolt Diameter |
Hole Diameter |
|
½ |
3.50 |
0.44 |
2.38 |
4 |
0.50 |
0.62 |
|
¾ |
3.88 |
0.50 |
2.75 |
4 |
0.50 |
0.62 |
|
1 |
4.25 |
0.56 |
3.12 |
4 |
0.50 |
0.62 |
|
1¼ |
4.62 |
0.62 |
3.50 |
4 |
0.50 |
0.62 |
|
1½ |
5.00 |
0.69 |
3.88 |
4 |
0.50 |
0.62 |
|
2 |
6.00 |
0.75 |
4.75 |
4 |
0.62 |
0.75 |
|
2½ |
7.00 |
0.88 |
5.50 |
4 |
0.62 |
0.75 |
|
3 |
7.50 |
0.94 |
6.00 |
4 |
0.62 |
0.75 |
|
3½ |
8.50 |
0.94 |
7.00 |
8 |
0.62 |
0.75 |
|
4 |
9.00 |
0.94 |
7.50 |
8 |
0.62 |
0.75 |
|
5 |
10.00 |
0.94 |
8.50 |
8 |
0.75 |
0.88 |
|
6 |
11.00 |
1.00 |
9.50 |
8 |
0.75 |
0.88 |
|
8 |
13.50 |
1.12 |
11.75 |
8 |
0.75 |
0.88 |
|
10 |
16.00 |
1.19 |
14.25 |
12 |
0.88 |
1.00 |
|
12 |
19.00 |
1.25 |
17.00 |
12 |
0.88 |
1.00 |
|
14 |
21.00 |
1.38 |
18.75 |
12 |
1.00 |
1.12 |
|
16 |
23.50 |
1.44 |
21.25 |
16 |
1.00 |
1.12 |
|
18 |
25.00 |
1.56 |
22.75 |
16 |
1.12 |
1.25 |
|
20 |
27.50 |
1.69 |
25.00 |
20 |
1.12 |
1.25 |
|
24 |
32.00 |
1.88 |
29.50 |
20 |
1.25 |
1.38 |
Class 300 Flange Dimensions (NPS ½" to 24")
|
NPS |
Outside Diameter (O) |
Thickness (tf) |
Bolt Circle Diameter |
No. of Bolts |
Bolt Diameter |
Hole Diameter |
|
½ |
3.75 |
0.56 |
2.62 |
4 |
0.50 |
0.62 |
|
¾ |
4.62 |
0.62 |
3.25 |
4 |
0.62 |
0.75 |
|
1 |
4.88 |
0.69 |
3.50 |
4 |
0.62 |
0.75 |
|
1¼ |
5.25 |
0.75 |
3.88 |
4 |
0.62 |
0.75 |
|
1½ |
6.12 |
0.81 |
4.50 |
4 |
0.75 |
0.88 |
|
2 |
6.50 |
0.88 |
5.00 |
8 |
0.62 |
0.75 |
|
2½ |
7.50 |
1.00 |
5.88 |
8 |
0.75 |
0.88 |
|
3 |
8.25 |
1.12 |
6.62 |
8 |
0.75 |
0.88 |
|
3½ |
9.00 |
1.19 |
7.25 |
8 |
0.75 |
0.88 |
|
4 |
10.00 |
1.25 |
7.88 |
8 |
0.75 |
0.88 |
|
5 |
11.00 |
1.38 |
9.25 |
8 |
0.75 |
0.88 |
|
6 |
12.50 |
1.44 |
10.62 |
12 |
0.75 |
0.88 |
|
8 |
15.00 |
1.62 |
13.00 |
12 |
0.88 |
1.00 |
|
10 |
17.50 |
1.88 |
15.25 |
16 |
1.00 |
1.12 |
|
12 |
20.50 |
2.00 |
17.75 |
16 |
1.12 |
1.25 |
|
14 |
23.00 |
2.12 |
20.25 |
20 |
1.12 |
1.25 |
|
16 |
25.50 |
2.25 |
22.50 |
20 |
1.25 |
1.38 |
|
18 |
28.00 |
2.38 |
24.75 |
24 |
1.25 |
1.38 |
|
20 |
30.50 |
2.50 |
27.00 |
24 |
1.25 |
1.38 |
|
24 |
36.00 |
2.75 |
32.00 |
24 |
1.50 |
1.62 |
We also supply Class 400, 600, 900, 1500, and 2500 with matching dimensions. Weld-neck, slip-on, socket-weld, threaded, lap-joint, and blind types are all available in these sizes.
Custom large-diameter or special-face flanges are produced in our company with the same precision.
Critical Factors in 316 Flange Selection
1. Flange Facing (The Seal Area)
The "facing" is the surface where the gasket is placed. For 316 stainless steel flanges, the most common is the Raised Face (RF). The raised face concentrates more pressure on a smaller gasket area, creating a superior seal. However, in applications involving glass-lined pipes or cast iron equipment, a Flat Face (FF) is used to prevent the high bolting torque from cracking the fragile flange it connects to.
2. Bore Diameter (For Weld Neck Flanges)
A Weld Neck flange must have a bore that matches the inside diameter of the pipe. If you are using Schedule 40 pipe, your 316 WN flange must be bored to Schedule 40 specs. If the bore is mismatched, you create a "step" in the flow, which leads to turbulence and accelerated erosion-corrosion.
3. Low Carbon Variant: 316L
In many cases, our factory recommends 316L (the low-carbon version). While the pressure ratings for 316 and 316L are often identical at lower temperatures, 316L is superior for components that require heavy welding. The low carbon content prevents "carbide precipitation" during the welding process, ensuring the flange remains corrosion-resistant at the weld joint.
How to Install 316 Flange?
A high-quality 316 flange is only as good as its installation. To ensure the pressure ratings listed above are met, follow these industrial standards:
Bolt Tightening: Always use a calibrated torque wrench and follow a "star pattern" or "cross-over" sequence. This ensures the gasket is compressed evenly.
Gasket Compatibility: Ensure the gasket material is compatible with both the 316 stainless steel and the fluid being transported. For 316 flanges, spiral wound gaskets with 316L filler are the industry standard for high-reliability applications.
Alignment: Flange faces must be parallel. Forcing a flange into alignment using bolt torque introduces "piping stress," which can lead to premature failure or cracking at the hub.
