ASME B16.21
ASME B16.21-2011
NONMETALLIC FLAT GASKETS FOR PIPE FLANGES
1 SCOPE
This Standard covers types, sizes, materials, dimensions, tolerances, and markings for nonmetallic flat gaskets. These gaskets are dimensionally suitable for use with flanges described in the referenced flange standards.
2 GENERAL
2.1 Relevant Units
This Standard states values both in SI (metric) and U.S. Customary units. As an exception, the diameter of bolts and flange bolt holes is expressed in inch units only. These systems of units are to be regarded separately as standard. Within the text, U.S. Customary units are shown in parentheses or in separate tables. The values stated in each system are not exact equivalents; therefore, each system of units shall be used independently of the other. Combining values from the two systems—except for bolt diameters and flange bolt holes—constitutes nonconformance with this Standard.
2.2 Quality Systems
Requirements relating to the product manufacturer’s quality system programs are described in Nonmandatory Appendix A.
2.3 References
Standards and specifications adopted by reference in this Standard are listed in Mandatory Appendix II.
2.4 Flanged Joints
A flanged joint consists of separate and independent, though interrelated, components: the flanges, gasket, and bolting, assembled under the influence of the installer. Proper control must be exercised in the selection and application of all these elements to achieve a joint with acceptable leak tightness. Additional guidance for flange assembly can be found in ASME PCC-1 (see Nonmandatory Appendix B).
2.5 Types
Dimensions are provided for the following gasket types, which are suitable for use with the indicated flange facings:
| Gasket Type | Flange Facing |
|---|---|
| Full face | Flat face |
| Flat ring | Raised face |
2.6 Size
NPS (Nominal Pipe Size), followed by a dimensionless number, is the designation for nominal pipe size as described in ASME B36.10M and relates to the reference nominal diameter (DN) used in international standards. The relationship is as follows:
| NPS | DN |
|---|---|
| ½ | 15 |
| ¾ | 20 |
| 1 | 25 |
| 1¼ | 32 |
| 1½ | 40 |
| 2 | 50 |
| 2½ | 65 |
| 3 | 80 |
| 3½ | 90 |
| 4 | 100 |
General Note: For NPS ≥ 4, the corresponding DN = 25 × NPS.
2.7 Pressure Class Designation
Class, followed by a dimensionless number, designates common flange pressure-temperature ratings as provided in the referenced flange standards.
3 MATERIALS
3.1 Composition
Gaskets shall be made of resilient or pliable materials. Metal or nonmetal composites may be incorporated as reinforcement or filler material.
3.2 Service Requirements
Selection of a material suitable for a given service application is the responsibility of the user, subject to applicable code or government regulations. The selected material shall be compatible with the fluid and suitable for the pressure-temperature conditions of the service.
4 DIMENSIONS AND TOLERANCES
4.1 Dimensions
Gasket dimensions shall be in accordance with Tables 1 through 9 (Tables I-1 through I-9 of Mandatory Appendix I) for the specified flange standards, sizes, and classes. Selection of gasket thickness is the responsibility of the user, taking into account the properties of the gasket material and the intended service application.
4.2 Tolerances
(a) Outside Diameter
- For NPS 12 and smaller: +0.0, −1.5 mm (+0.0, −0.06 in.)
- For NPS 14 and larger: +0.0, −3.0 mm (+0.0, −0.12 in.)
(b) Inside Diameter
- For NPS 12 and smaller: ±1.5 mm (±0.06 in.)
- For NPS 14 and larger: ±3.0 mm (±0.12 in.)
- Bolt circle diameter: ±1.5 mm (±0.06 in.)
- Center-to-center of adjacent bolt holes: ±1.0 mm (±0.03 in.)
5 MARKINGS
5.1 Material Marking
Unless otherwise specified by the purchaser, gasket material shall be marked with the material manufacturer’s name or trademark and material designation.
5.2 Gasket Marking
Gaskets shall be packaged with the following information marked or tagged on the package or gasket: NPS, class, gasket manufacturer’s name, material designation, thickness, and ASME B16.21. The DN designation may be included at the manufacturer’s option.
RF Gasket Dimensions for ASME B16.1
| NOMINAL SIZE | Gasket I.D. | Gasket O.D. 150# | Gasket O.D. 300# |
|---|---|---|---|
| 1/2″ | 27/32″ (21 mm) | 1-7/8″ (48 mm) | 2-1/8″ (54 mm) |
| 3/4″ | 1-1/16″ (27 mm) | 2-1/4″ (57 mm) | 2-5/8″ (67 mm) |
| 1″ | 1-5/16″ (33 mm) | 2-5/8″ (67 mm) | 2-7/8″ (73 mm) |
| 1‑1/4″ | 1‑21/32″ (42 mm) | 3″ (76 mm) | 3‑1/4″ (83 mm) |
| 1‑1/2″ | 1‑29/32″ (48 mm) | 3‑3/8″ (86 mm) | 3‑3/4″ (95 mm) |
| 2″ | 2‑3/8″ (60 mm) | 4‑1/8″ (105 mm) | 4‑3/8″ (111 mm) |
| 2‑1/2″ | 2‑7/8″ (73 mm) | 4‑7/8″ (124 mm) | 5‑1/8″ (130 mm) |
| 3″ | 3‑1/2″ (89 mm) | 5‑3/8″ (137 mm) | 5‑7/8″ (149 mm) |
| 3‑1/2″ | 4″ (102 mm) | 6‑3/8″ (162 mm) | 6‑1/2″ (165 mm) |
| 4″ | 4‑1/2″ (114 mm) | 6‑7/8″ (175 mm) | 7‑1/8″ (181 mm) |
| 4‑1/2″ | 5″ (127 mm) | 7″ (178 mm) | 7‑5/8″ (194 mm) |
| 5″ | 5‑9/16″ (141 mm) | 7‑3/4″ (197 mm) | 8‑1/2″ (216 mm) |
| 6″ | 6‑5/8″ (168 mm) | 8‑3/4″ (222 mm) | 9‑7/8″ (251 mm) |
| 7″ | 7‑5/8″ (194 mm) | 10″ (254 mm) | 10‑7/8″ (276 mm) |
| 8″ | 8‑5/8″ (219 mm) | 11″ (279 mm) | 12‑1/8″ (308 mm) |
| 10″ | 10‑3/4″ (273 mm) | 13‑3/8″ (340 mm) | 14‑1/4″ (362 mm) |
| 12″ | 12‑3/4″ (324 mm) | 16‑1/8″ (410 mm) | 16‑5/8″ (422 mm) |
| 14″ | 14″ (356 mm) | 17‑3/4″ (451 mm) | 19‑1/8″ (486 mm) |
| 15″ | 15″ (381 mm) | — | 20‑1/8″ (511 mm) |
| 16″ | 16″ (406 mm) | 20‑1/4″ (514 mm) | 21‑1/4″ (540 mm) |
| 18″ | 18″ (457 mm) | 21‑5/8″ (549 mm) | 23‑1/2″ (597 mm) |
| 20″ | 20″ (508 mm) | 23‑7/8″ (606 mm) | 25‑3/4″ (654 mm) |
| 22″ | 22″ (559 mm) | 26″ (660 mm) | 27‑5/8″ (702 mm) |
| 24″ | 24″ (610 mm) | 28‑1/4″ (718 mm) | 30‑1/2″ (775 mm) |
RF Gasket Dimensions for ASME
(Classes 150, 300, 400, 600, 900)
All dimensions in mm
| NPS | Gasket I.D. | Gasket O.D. | ||||
| Class 150 | Class 300 | Class 400 | Class 600 | Class 900 | ||
| 1/2″ | 21 | 48 | 54 | 54 | 54 | 64 |
| 3/4″ | 27 | 57 | 67 | 67 | 67 | 70 |
| 1″ | 33 | 67 | 73 | 73 | 73 | 79 |
| 1-1/4″ | 42 | 76 | 83 | 83 | 83 | 89 |
| 1-1/2″ | 48 | 86 | 95 | 95 | 95 | 98 |
| 2″ | 60 | 105 | 111 | 111 | 111 | 143 |
| 2-1/2″ | 73 | 124 | 130 | 130 | 130 | 165 |
| 3″ | 89 | 137 | 149 | 149 | 149 | 168 |
| 3-1/2″ | 102 | 162 | 165 | 162 | 162 | — |
| 4″ | 114 | 175 | 181 | 178 | 194 | 206 |
| 4-1/2″ | 127 | 178 | — | — | — | — |
| 5″ | 141 | 197 | 216 | 213 | 241 | 248 |
| 6″ | 168 | 222 | 251 | 248 | 267 | 289 |
| 7″ | 194 | 254 | — | — | — | — |
| 8″ | 219 | 279 | 308 | 305 | 321 | 359 |
| 10″ | 273 | 340 | 362 | 359 | 400 | 435 |
| 12″ | 324 | 410 | 422 | 419 | 457 | 498 |
| 14″ | 356 | 451 | 486 | 483 | 492 | 521 |
| 15″ | 381 | 511 | — | — | — | — |
| 16″ | 406 | 514 | 540 | 537 | 565 | 575 |
| 18″ | 457 | 549 | 597 | 594 | 613 | 638 |
| 20″ | 508 | 606 | 654 | 648 | 683 | 699 |
| 22″ | 559 | 660 | — | — | — | — |
| 24″ | 610 | 718 | 775 | 768 | 791 | 838 |
Notes:
- All values are in millimeters (mm).
- “—” indicates dimension not specified for this class and size combination.
- Gasket dimensions are suitable for ASME B16.5 standard flanges.
Full Face Gasket Dimensions for ASME B16.1
CLASS 150
| NOMINAL SIZE | ID (in/mm) | OD (in/mm) | NO. OF HOLES | HOLE DIA (in) | BOLT CIRCLE (in/mm) |
|---|---|---|---|---|---|
| 1/2″ | 13/16″ (21) | 3‑1/2″ (89) | 4 | 5/8″ | 2‑3/8″ (60.3) |
| 3/4″ | 1‑1/16″ (27) | 3‑7/8″ (98) | 4 | 5/8″ | 2‑3/4″ (69.9) |
| 1″ | 1‑5/16″ (33) | 4‑1/4″ (108) | 4 | 5/8″ | 3‑1/8″ (79.4) |
| 1‑1/4″ | 1‑5/8″ (41) | 4‑5/8″ (117) | 4 | 5/8″ | 3‑1/2″ (88.9) |
| 1‑1/2″ | 1‑7/8″ (48) | 5″ (127) | 4 | 5/8″ | 3‑7/8″ (98.4) |
| 2″ | 2‑3/8″ (60) | 6″ (152) | 4 | 3/4″ | 4‑3/4″ (120.7) |
| 2‑1/2″ | 2‑7/8″ (73) | 7″ (178) | 4 | 3/4″ | 5‑1/2″ (139.7) |
| 3″ | 3‑1/2″ (89) | 7‑1/2″ (191) | 4 | 3/4″ | 6″ (152.4) |
| 3‑1/2″ | 4″ (102) | 8‑1/2″ (216) | 8 | 3/4″ | 7″ (177.8) |
| 4″ | 4‑1/2″ (114) | 9″ (229) | 8 | 3/4″ | 7‑1/2″ (190.5) |
| 5″ | 5‑9/16″ (141) | 10″ (254) | 8 | 7/8″ | 8‑1/2″ (215.9) |
| 6″ | 6‑5/8″ (168) | 11″ (279) | 8 | 7/8″ | 9‑1/2″ (241.3) |
| 8″ | 8‑5/8″ (219) | 13‑1/2″ (343) | 8 | 7/8″ | 11‑3/4″ (298.5) |
| 10″ | 10‑3/4″ (273) | 16″ (406) | 12 | 1″ | 14‑1/4″ (362) |
| 12″ | 13‑3/4″ (324) | 19″ (483) | 12 | 1″ | 17″ (431.8) |
| 14″ | 14″ (356) | 21″ (533) | 12 | 1‑1/8″ | 18‑3/4″ (476.3) |
| 16″ | 16″ (406) | 23‑1/2″ (597) | 16 | 1‑1/8″ | 21‑1/4″ (539.8) |
| 18″ | 18″ (457) | 25″ (635) | 16 | 1‑1/4″ | 22‑3/4″ (577.9) |
| 20″ | 20″ (508) | 27‑1/2″ (699) | 20 | 1‑1/4″ | 25″ (635) |
| 22″ | 22″ (559) | 29‑1/2″ (749) | 20 | 1‑3/8″ | 27‑1/4″ (692.2) |
| 24″ | 24″ (610) | 32″ (813) | 20 | 1‑3/8″ | 29‑1/2″ (749.3) |
CLASS 300
| NOMINAL SIZE | ID (in/mm) | OD (in/mm) | NO. OF HOLES | HOLE DIA (in) | BOLT CIRCLE (in/mm) |
|---|---|---|---|---|---|
| 1″ | 1‑5/16″ (33) | 4‑7/8″ (124) | 4 | 3/4″ | 3‑1/2″ (88.9) |
| 1‑1/4″ | 1‑21/32″ (42) | 5‑1/4″ (133) | 4 | 3/4″ | 3‑7/8″ (98.4) |
| 1‑1/2″ | 1‑7/8″ (48) | 6‑1/8″ (156) | 4 | 7/8″ | 4‑1/2″ (114.3) |
| 2″ | 2‑3/8″ (60) | 6‑1/2″ (165) | 8 | 3/4″ | 5″ (127) |
| 2‑1/2″ | 2‑7/8″ (73) | 7‑1/2″ (191) | 8 | 7/8″ | 5‑7/8″ (149.2) |
| 3″ | 3‑1/2″ (89) | 8‑1/4″ (210) | 8 | 7/8″ | 6‑5/8″ (168.3) |
| 3‑1/2″ | 4″ (102) | 9″ (229) | 8 | 7/8″ | 7‑1/4″ (184.2) |
| 4″ | 4‑1/2″ (114) | 10″ (254) | 8 | 7/8″ | 7‑7/8″ (200) |
| 5″ | 5‑9/16″ (141) | 11″ (279) | 8 | 7/8″ | 9‑1/4″ (235) |
| 6″ | 6‑5/8″ (168) | 12‑1/2″ (318) | 12 | 7/8″ | 10‑5/8″ (269.9) |
| 8″ | 8‑5/8″ (219) | 15″ (381) | 12 | 1″ | 13″ (330.2) |
| 10″ | 10‑3/4″ (273) | 17‑1/2″ (445) | 16 | 1‑1/8″ | 15‑1/4″ (387.4) |
| 12″ | 13‑3/4″ (324) | 20‑1/2″ (521) | 16 | 1‑1/4″ | 17‑3/4″ (450.9) |
| 14″ | 14″ (356) | 23″ (584) | 20 | 1‑1/4″ | 20‑1/4″ (514.4) |
| 16″ | 16″ (406) | 25‑1/2″ (678) | 20 | 1‑3/8″ | 22‑1/2″ (571.5) |
| 18″ | 18″ (457) | 28″ (711) | 24 | 1‑3/8″ | 24‑3/4″ (628.7) |
| 20″ | 20″ (508) | 30‑1/2″ (775) | 24 | 1‑3/8″ | 27″ (685.8) |
| 22″ | 22″ (559) | 33″ (838) | 24 | 1‑5/8″ | 29‑1/4″ (743) |
| 24″ | 24″ (610) | 36″ (914) | 24 | 1‑5/8″ | 32″ (812.8) |