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Technical Library > GASKETS > GASKETS TYPES AND DIMENSIONS > Non Asbestos Gaskets
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SOFT GASKETS (NON-ASBESTOS)


This article defines soft gaskets for flanges per ASME B16.21, illustrates the most common materials used in the petrochemical industry and, shows the dimensions of soft (flat cut) gaskets for ASME B16.5 and ASME B16.47 RF flanges.


 

WHAT ARE SOFT GASKETS?

Soft gaskets are economical products to seal flanges, used for low-pressure/low-temperature non-critical applications in the petrochemical and process industries. Other types of gaskets, metallic and non-metallic (ring joint gaskets, spiral wound, Camprofile and metal jacketed) are used for more demanding temperatures/pressures, applications and, corrosion rates.

The sizes, types, materials, dimensions, dimensional tolerances, and markings for soft gaskets for petrochemical applications are set by ASME B16.21. The two main types are the “full face” (FF) for FF flanges and the “flat ring” type for raised face flanges.

Non-metallic gaskets are produced out of fiber’s sheets which are cut with water pressure machines. The dimensional range for these types of gaskets is between 5 and 5.000 mm, and bigger (in this case, which is rare, the is not uncommon that multiple fiber sheets are joined together to achieve the required dimension).

 

Soft gaskets non asbestos
The terms, “flat-cut gaskets”, “die-cut gaskets”, “compressed sheet gaskets” and “asbestos-free gaskets” are synonyms to define soft gaskets.

 These cheap types of gaskets can match flanges of any dimensional norm, the most typical are:

  • DIN flanges
  • ANSI B 16.5 flanges
  • ASME/ANSI B 16.47 series A
  • ASME/ANSI B 16.47 series B
  • DIN 2632 – 2638 flanges

 


MATERIALS FOR SOFT GASKETS (NON-ASBESTOS FIBRES)

The most common materials used to manufacture soft gaskets are aramid fibers (Kevlar), glass fibers, elastomers, Teflon (PTFE), graphite, neoprene and various binder materials:

  • Aramid NBR binder
  • carbon graphite reinforced
  • glass reinforced (steam service gasket)
  • PTFE bi-axially oriented (silica filler)
  • SBR (styrene-butadiene)
  • CR-chloroprene (Neoprene)
  • EPDM gasket (ethylene propylene)
  • fluorocarbon (Viton)
  • graphite
  • BUNA-n-rubber (nitrile, NBR gasket)
  • chlorosulfonated polyethylene (Hypalon gasket)
  • aramid + SBR binder (premium type gasket)
  • graphite + ss316/316l insert
  • PTFE biaxially oriented (with hollow glass microsphere) blue
  • PTFE biaxially oriented (pigment-free)-gray
  • expanded PTFE gasket
  • PTFE joint sealant
  • PTFE envelope slit type
  • PTFE envelope milled type
  • PTFE envelope formed type
  • MICA sheet
  • ceramic fiber

The materials used for soft gaskets are a mix of Aramid (Kevlar) and non-organic fibers, blended with different polymers that are chosen depending on the required mechanical and chemical properties of the application (nitrile rubber, i.e. NBR, is the usual binder).

Non-asbestos gaskets can also be coated with graphite, for non-stick and steam resistance, mixed with PTFE for excellent chemical resistance, or with EPDM for potable water applications.

WHY NON-ASBESTOS FIBERS?

Non-Asbestos fibers have fully replaced asbestos for decades. In the past, asbestos was used for multiple applications (including the production of flat-cut gaskets) as it has excellent resistance to high temperatures. However, it became apparent that asbestos damaged human health, inducing lung cancer and other types of incurable illnesses. As a consequence, asbestos was outlawed and the industry had to turn to different types of materials to manufacture gaskets (soft fibers).

 


SOFT GASKETS DIMENSIONS (ASME B16.21)

SOFT GASKETS DIMENSIONS (ASME B16.5 RF FLANGES)

Soft gaskets sizes

NPS d1
(ID)
d2 (GASKET OUTSIDE DIAMETER)
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
42 76 83 83 83 89
48 86 95 95 95 98
2 60 105 111 111 111 143
73 124 130 130 130.2 165
3 89 137 149 149 149 168
102 162 165 162 162
4 114 175 181 178 194 206
5 141 197 216 213 241 248
6 168 222 251 248 267 289
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
16 406 514 540 537 565 575
18 457 549 597 594 613 638
20 508 606 654 648 683 699
24 610 718 775 768 791 838

All values in millimeters

 

SOFT GASKETS DIMENSIONS FOR ASME B16.47-SERIES A

Soft gaskets sizes

NPS d1 (ID) d2 (GASKET OUTSIDE DIAMETER)
Class 150 Class 300 Class 400 Class 600
26 660 775 835 832 867
28 711 832 899 892 914
30 762 883 953 946 972
32 813 940 1006 1003 1022
34 864 991 1057 1054 1073
36 914 1048 1118 1118 1130
38 965 1111 1054 1073 1105
40 1016 1162 1114 1127 1156
42 1067 1219 1165 1178 1219
44 1118 1276 1219 1232 1270
46 1168 1327 1273 1289 1327
48 1219 1384 1324 1346 1391
50 1270 1435 1378 1403 1448
52 1321 1492 1429 1454 1499
54 1372 1549 1492 1518 1556
56 1422 1607 1543 1568 1613
58 1473 1664 1594 1619 1664
60 1524 1715 1645 1683 1721

All values in millimeters

 

SOFT GASKETS DIMENSIONS FOR ASME B16.47-SERIES B

Soft gaskets sizes

NPS d1 (ID) d2 (GASKET OUTSIDE DIAMETER)
Class 150 Class 300 Class 400 Class 600
26 660 725 772 746 765
28 711 776 826 800 819
30 762 827 886 857 879
32 813 881 940 911 933
34 864 935 994 962 997
36 914 987 1048 1022 1048
38 965 1045 1099
40 1016 1095 1149
42 1067 1146 1200
44 1118 1197 1251
46 1168 1256 1318
48 1219 1307 1368
50 1270 1357 1419
52 1321 1408 1470
54 1372 1464 1530
56 1422 1514 1594
58 1473 1580 1656
60 1524 1630 1705

All values in millimeters. Dimensional tolerances:

  • For outside diameter NPS 12 and smaller: +0 / -1.5 mm.; NPS 14 and larger: +0 / -3.0 mm.
  • For inside diameter NPS 12 and smaller: ± 1.5 mm; NPS 14 and larger: ± 3.0 mm

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