This article provides a rigorous, authoritative reference to C276 Alloy Blind Flange Dimensions under the ASME B16.5 standard. All dimensions presented are identical to those for any material compliant with B16.5; however, the superior mechanical properties and corrosion resistance of forged ASTM B564 UNS N10276 elevate performance far beyond generic flanges.
The minimum specified yield strength of C276 is 41 ksi (283 MPa) in the annealed condition, with typical values reaching 50–60 ksi, enabling higher pressure-temperature ratings and exceptional resistance to crevice corrosion, pitting, and stress-corrosion cracking.
Hastelloy C276 Blind Flanges
Blind flanges, also called blanking flanges, are solid disks used to isolate piping sections, terminate lines, or provide future expansion capability. In high-corrosion service, the blind flange becomes the weakest link if not manufactured from a truly universal alloy.
Our factory forges every C276 blind flange from certified billet stock, ensuring a uniform microstructure free of segregation. Each piece undergoes 100% ultrasonic examination, positive material identification (PMI), and hydrostatic testing where required. Surface finishes meet or exceed ASME B16.5 requirements: standard raised face (RF) with 125–250 µin Ra serrated finish, or optional RTJ, flat face, or machined to customer drawing.
ASME B16.5 Standard Overview
ASME B16.5 governs dimensions, tolerances, materials, and pressure-temperature ratings for flanges NPS ½ through NPS 24. For nickel alloy flanges, the standard reference is ASTM B564 for forging. Pressure classes range from Class 150 to Class 2500. All C276 blind flanges we supply are fully traceable to heat and lot, with mill test reports (MTRs) including chemical analysis, tensile properties, and hardness.
Key dimensional parameters include:
O – Outside diameter of flange
T – Minimum thickness of flange (excluding raised face)
R – Outside diameter of raised face (1/16 in height standard for Classes 150–2500)
C – Bolt circle diameter
n – Number of bolt holes
d – Bolt hole diameter
Tolerances are tight: OD ±0.06 in for NPS ≤ 24, thickness +0.12 in / –0.00 in (Class 150–600), bolt hole location ±0.03 in.
Class 150 C276 Blind Flange Dimensions (ASME B16.5)
Class 150 is the most widely specified for low-to-moderate pressure systems. Below are the complete dimensions in inches.
|
NPS |
O (in) |
T (in) |
R (in) |
C (in) |
n |
d (in) |
Approx. Weight (lb) |
|
½ |
3.50 |
0.44 |
1.38 |
2.38 |
4 |
0.63 |
1 |
|
¾ |
3.88 |
0.50 |
1.69 |
2.75 |
4 |
0.63 |
2 |
|
1 |
4.25 |
0.56 |
2.00 |
3.13 |
4 |
0.63 |
2 |
|
1¼ |
4.63 |
0.63 |
2.50 |
3.50 |
4 |
0.63 |
3 |
|
1½ |
5.00 |
0.69 |
2.88 |
3.88 |
4 |
0.63 |
4 |
|
2 |
6.00 |
0.75 |
3.63 |
4.75 |
4 |
0.75 |
5 |
|
2½ |
7.00 |
0.88 |
4.13 |
5.50 |
4 |
0.75 |
7 |
|
3 |
7.50 |
0.94 |
5.00 |
6.00 |
4 |
0.75 |
9 |
|
3½ |
8.50 |
0.94 |
5.50 |
7.00 |
8 |
0.75 |
13 |
|
4 |
9.00 |
0.94 |
6.19 |
7.50 |
8 |
0.75 |
17 |
|
5 |
10.00 |
0.94 |
7.31 |
8.50 |
8 |
0.88 |
20 |
|
6 |
11.00 |
1.00 |
8.50 |
9.50 |
8 |
0.88 |
26 |
|
8 |
13.50 |
1.13 |
10.63 |
11.75 |
8 |
0.88 |
45 |
|
10 |
16.00 |
1.19 |
12.75 |
14.25 |
12 |
1.00 |
70 |
|
12 |
19.00 |
1.25 |
15.00 |
17.00 |
12 |
1.00 |
110 |
|
14 |
21.00 |
1.38 |
16.25 |
18.75 |
12 |
1.13 |
140 |
|
16 |
23.50 |
1.44 |
18.50 |
21.25 |
16 |
1.13 |
180 |
|
18 |
25.00 |
1.56 |
21.00 |
22.75 |
16 |
1.25 |
220 |
|
20 |
27.50 |
1.69 |
23.00 |
25.00 |
20 |
1.25 |
285 |
|
22 |
29.50 |
1.81 |
25.25 |
27.25 |
20 |
1.38 |
355 |
|
24 |
32.00 |
1.88 |
27.25 |
29.50 |
20 |
1.38 |
430 |
Class 300 C276 Blind Flange Dimensions (ASME B16.5)
Class 300 provides approximately double the pressure rating of Class 150 at ambient temperature. Dimensions:
|
NPS |
O (in) |
T (in) |
R (in) |
C (in) |
n |
d (in) |
Approx. Weight (lb) |
|
½ |
3.75 |
0.56 |
1.38 |
2.63 |
4 |
0.63 |
2 |
|
¾ |
4.63 |
0.63 |
1.69 |
3.25 |
4 |
0.75 |
3 |
|
1 |
4.88 |
0.69 |
2.00 |
3.50 |
4 |
0.75 |
3 |
|
1¼ |
5.25 |
0.75 |
2.50 |
3.88 |
4 |
0.75 |
4 |
|
1½ |
6.13 |
0.81 |
2.88 |
4.50 |
4 |
0.88 |
6 |
|
2 |
6.50 |
0.88 |
3.63 |
5.00 |
8 |
0.75 |
8 |
|
2½ |
7.50 |
1.00 |
4.13 |
5.88 |
8 |
0.88 |
12 |
|
3 |
8.25 |
1.13 |
5.00 |
6.63 |
8 |
0.88 |
16 |
|
3½ |
9.00 |
1.19 |
5.50 |
7.25 |
8 |
0.88 |
21 |
|
4 |
10.00 |
1.25 |
6.19 |
7.88 |
8 |
0.88 |
27 |
|
5 |
11.00 |
1.38 |
7.31 |
9.25 |
8 |
0.88 |
35 |
|
6 |
12.50 |
1.44 |
8.50 |
10.63 |
12 |
0.88 |
50 |
|
8 |
15.00 |
1.63 |
10.63 |
13.00 |
12 |
1.00 |
81 |
|
10 |
17.50 |
1.88 |
12.75 |
15.25 |
16 |
1.13 |
124 |
|
12 |
20.50 |
2.00 |
15.00 |
17.75 |
16 |
1.25 |
185 |
|
14 |
23.00 |
2.13 |
16.25 |
20.25 |
20 |
1.25 |
250 |
|
16 |
25.50 |
2.25 |
18.50 |
22.50 |
20 |
1.38 |
295 |
|
18 |
28.00 |
2.38 |
21.00 |
24.75 |
24 |
1.38 |
395 |
|
20 |
30.50 |
2.50 |
23.00 |
27.00 |
24 |
1.38 |
505 |
|
22 |
33.00 |
2.63 |
25.25 |
29.25 |
24 |
1.63 |
640 |
|
24 |
36.00 |
2.75 |
27.25 |
32.00 |
24 |
1.63 |
790 |
C276 Blind Flange Pressure Class and Temperature Derating
While ASME B16.5 standardizes dimensions, it is imperative to understand that C276 allows for higher pressure retention at elevated temperatures compared to standard austenitic stainless steels. However, the physical dimensions of a Class 150 C276 blind flange are identical to a Class 150 carbon steel blind flange. The difference lies in the pressure-temperature rating.
For example, at 500°F, a Class 150 carbon steel flange may have a maximum non-shock working pressure of roughly 140 psi. In contrast, a C276 flange of the same dimensions can often withstand significantly higher pressures due to the alloy's superior yield strength retention at temperature.
Engineers must not upsize the flange dimensions unnecessarily if the material grade provides the required safety margin. Conversely, downsizing the class to save cost on expensive C276 material is a dangerous practice that violates design safety factors.
Manufacturing Tolerances and Quality Assurance
In our factory, the production of C276 blind flanges involves precision forging and CNC machining. The "rigor" in our process comes from adhering to tight tolerances that exceed standard commercial requirements.
Face Finish: The raised face surface finish must be between 125 and 250 AARH to ensure proper gasket seating. A surface that is too smooth may cause gasket slippage; one that is too rough may cause leakage.
Concentricity: The bolt circle must be concentric with the flange OD. Eccentricity can lead to uneven bolt loading, causing stress corrosion cracking in the bolts or the flange hub.
Thickness Tolerance: ASME B16.5 allows a slight negative tolerance on thickness, but for C276 applications, we maintain a positive tolerance to ensure the pressure rating is never compromised by material removal during machining.
Every C276 blind flange undergoes Positive Material Identification (PMI) to verify the nickel, molybdenum, and chromium content. Furthermore, dimensional verification is conducted using calibrated coordinate measuring machines (CMM) to ensure every bolt hole and diameter matches the ASME B16.5 blueprint.
By adhering strictly to ASME B16.5 dimensional standards, we ensure that these components integrate seamlessly into existing infrastructure while delivering the superior corrosion resistance expected of Hastelloy C276.
