Spiral wound gaskets, ring joint gaskets, sheet gaskets, stud bolts and nuts for ASME B16.5 and B16.47 flanged joints, in standard and NACE compliant grades.
- Standard: ASME B16.20, ASME B16.21, ASME B18.2.1, ASTM A193, ASTM A194, ASTM A320
- Grades: A193 B7, A193 B7M, A193 B8, A193 B8M, A194 2H, A194 2HM, A194 8, A194 8M, 304 graphite, 316 PTFE
Specifications
| Outer diameter | For 1/2" - 60" flanges |
|---|---|
| Length | Gasket thickness 1.5 - 4.5 mm, stud bolt per ASME B18.2.1 |
| Ends | Ring joint, spiral wound, sheet, or jacketed |
| Surface treatment | Zinc or Xylan coated studs, or plain |
| Manufacturing process | Wound, machined, and forged |
| Pressure rating | Class 150 to 2500 |
| Connection type | For raised face, flat face, or ring joint flanges |
Gasket Selection by Flange Face
The gasket must match the flange face. A raised face flange, which is the most common, uses a spiral wound gasket with a centering ring, a sheet gasket, or a jacketed gasket. A flat face flange, typically used where the flange is cast iron or where the joint is against a valve or vessel with a flat face, uses a full face gasket so that the bolts pass through the gasket. A ring joint flange has a grooved face and uses a solid metal ring joint gasket, which seals by the wedging action of the ring into the groove and is the choice for high pressure and high temperature service above class 900 and for critical gas tight applications. The wrong gasket type for the face will not seal regardless of bolt torque, so confirm the face type before ordering.
Bolting Grades and B7 versus B7M
The most common flange bolting for high temperature and high pressure service is ASTM A193 grade B7 studs with ASTM A194 grade 2H nuts. B7 is a chromium-molybdenum alloy steel, quenched and tempered, with a minimum tensile strength of 860 MPa at sizes up to 2-1/2 inch. For sour service, B7M is used instead. B7M has the same chemistry and strength as B7 but a lower maximum hardness limit, 235 HB or 22 HRC, and is supplied with 2HM nuts, so that the bolting satisfies NACE MR0175. For low temperature and cryogenic service, ASTM A320 grades L7 and L7M are used. Stainless bolting, B8 and B8M, is used for corrosion resistance or where non-magnetic properties are needed, but note that stainless bolting has lower tensile strength and a much higher risk of galling during tightening than alloy steel bolting.
What is the difference between B7 and B7M stud bolts?
Both are ASTM A193 chromium-molybdenum alloy steel studs with the same chemistry and the same minimum tensile strength. The difference is the hardness limit: B7 has no maximum hardness restriction beyond the standard, while B7M is limited to 235 HB or 22 HRC so that it satisfies NACE MR0175 for sour service. B7M is supplied with A194 2HM nuts, which have the same hardness control. Use B7 for normal service and B7M for wet H2S service.
Which gasket should I use for a class 1500 flanged joint?
For class 900 and above, a ring joint gasket is normally specified, because it seals by a metal to metal wedging action into the groove and withstands the high bolt loads and thermal cycling better than a spiral wound gasket. If the flange face is raised face rather than ring joint, a spiral wound gasket with a suitable filler can be used, but confirm this against the specification. Ring joint gaskets are available in soft iron, low carbon steel, stainless steel and various alloy grades; the gasket grade should be matched to the flange material to avoid galvanic or hardness mismatch.
Materials
- Alloy steel
- Stainless steel
- Graphite
- PTFE
- Non-asbestos fibre
Typical applications
- ASME B16.5 and B16.47 flanged joints
- Refinery and petrochemical piping
- High temperature and high pressure joints
- Sour service flanged connections
- Cryogenic service with A320 bolts
Inspection & testing
- Dimensional inspection per ASME B16.20
- Material certification per ASTM
- Hardness testing of bolts and nuts
- PMI on alloy and stainless steel
- Mechanical testing of bolts
- Third-party inspection on request
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