Gasket , Stud Bolt & Nut Buyer’s Guide: Matching ASME B16.5 Non-Metallic, Semi-Metallic and Metallic Gaskets to A193 / A194 Bolting for Petrochemical, Power and Marine Service

Buyer's Guide 2026

A flanged pressure-boundary joint is only as good as the three components that seal it: the gasket, the stud bolt, and the nut. Pick any one wrong, and the joint drifts. This buyer's guide walks EPC piping leads, refinery TA coordinators and procurement engineers through the gasket , stud bolt & nut decision tree by service environment — from low-pressure FF (flat face) water lines up through ASME B16.5 Class 2500 RTJ (ring-type joint) reactor loops — and shows how a mill-direct supplier bundles the matching pipe flanges, pipe fittings and industrial valves into one BOM line.

A flanged pressure-boundary joint is a stress loop. The gasket , stud bolt & nut group lives together on that loop: the bolt load has to seat the gasket to its target gasket stress, hold it through pressure and thermal cycles, and release cleanly at the next turnaround without seizing the stud or brinelling the flange face. Industry failure-data studies repeatedly place gasket selection and bolt-up errors at the top of the leak-cause distribution. That is why most refinery and EPC procurement specs now call out a single "bolting kit" line item — gaskets, studs, and nuts that share the same MTC traceability chain — rather than three unrelated part numbers ordered from three different vendors.

For B2B buyers, the practical consequence is that the gasket , stud bolt & nut trio, the pipe flanges they sit in, and the matching pipe fittings downstream should be sourced together. A flange with an RF (raised face) groove that ships with a spiral-wound gasket, two A193 B7 studs, and four A194 2H nuts from one mill-direct supplier saves the buyer the geometry-mismatch, MTC-fragmentation, and freight-split problem that a multi-source BOM creates. EZ Steel Industrial ships this exact package out of one mill-direct program with EN 10204 3.1 mill test certificates bundled per joint.

ASME B16.21 (non-metallic), B16.20 (semi-metallic and metallic), and EN 1514 (European) collectively cover the gasket world. For practical procurement, every gasket falls into one of three families, and the family alone tells you which flange face and pressure class it will live in.

The three families scale with temperature and pressure because their material hardness has to keep up with the unit load the bolt can deliver. A soft compressed-fiber sheet that seals perfectly on a Class 150 water line will extrude and blow out at 40 bar steam service. A spiral-wound gasket that is forgiving on a Class 300 RF face will not seat at all on a Class 900 RTJ groove because the geometry is wrong. The job of this buyer's guide is to make that mapping explicit so a procurement engineer never has to back-track after a hydrotest failure.

The face geometry on the flange is the first thing a buyer must match. Six face types cover 99% of refinery, petrochemical facilities and power plants & aerospace flanges.

A field-engineer rule of thumb: a flat-face (FF) flange must never be mated with a raised-face (RF) flange in the same joint — the geometry of the gasket seat is different, and forcing the issue creates a leak path the moment the line is pressurised. When you source the gasket , stud bolt & nut kit together with the matching pipe flanges from one mill-direct supplier, the face-type compatibility is built into the BOM line and you do not have to remember the rule at the warehouse.

The stud bolt is the load-bearing member. ASME B18.31.2 and ASME B16.5 define the dimensions; ASTM A193, A320, and A453 define the material grades. The grade is selected by temperature and by whether the service is "high-temp" (above 0 °C) or "low-temp" (below 0 °C).

Three practical rules for buyers:

• Match the stud to the temperature envelope, not to the room-temperature strength. A B7 stud at 480 °C will creep; a B16 stud at 200 °C is over-specified and harder to procure.
• In sour (H₂S) service, use B7M or L7M. The restricted hardness (HB 235 max) avoids sulphide stress cracking. NACE MR0175 / ISO 15156 must be cited on the PO.
• Stainless B8 / B8M studs are not interchangeable with B7 studs in a carbon-steel flange. The galvanic mismatch at the thread interface will gall the stud the first time it is removed.

The nut must be one grade harder (or at least equal in hardness) to the stud it pairs with. ASTM A194 lists the matching nut grades. The pairing rule is codified in ASME B16.5 and mirrored in the B16.5 stud-bolt length tables.

Buyers that source the gasket , stud bolt & nut kit as one BOM line avoid the most common pairing mistake: a 2H nut on a B7M stud in sour service. The hardness of the 2H exceeds the B7M stud and creates a stress-riser that can crack the stud under cyclic loading.

The fastest way for a procurement engineer to choose the right gasket , stud bolt & nut combination is to start from the service, not from the flange size. The five most common service envelopes cover most industrial pipework.

Gasket: CAF (compressed asbestos-free), EPDM, or Nitrile rubber with cloth ｉｎｓｅｒｔ. Stud bolt: A307 Grade B carbon steel or B7. Nut: 2H. The line operates at low pressure and ambient temperature, so the bolt load is modest. If the flange is cast iron, use FF + full-face gasket. If the flange is ductile iron or carbon steel, use RF + ring-type gasket.

Gasket: spiral-wound with graphite filler, 304/316L winding + inner/outer rings. Stud bolt: A193 B7 (up to 450 °C) or B16 (up to 595 °C). Nut: 2H or 7. For the superheater outlet above 540 °C, switch to a metallic RTJ (R or BX profile) on a Class 900 RTJ flange. The transition from semi-metallic spiral-wound to metallic ring joint is the single biggest material upgrade in any boiler pipe rack.

Gasket: spiral-wound with graphite or PTFE filler for RF; metallic ring joint (R, RX, BX) for RTJ. Stud bolt: A193 B7 (carbon / alloy) or B8M (stainless). Nut: 2H or 8M. In sour service (NACE MR0175), restrict to B7M / L7M studs with 2HM nuts. The exact gasket thickness and winding material will depend on whether the line is clean hydrocarbon (use thinner gasket for better recovery) or fouling hydrocarbon (use thicker gasket to absorb differential thermal growth).

Gasket: PTFE envelope, flexible graphite, or filled PTFE for highly corrosive chemicals. Stud bolt: B8M (316) or B8 (304) for chemical compatibility. Nut: 8M. For VOC or toxic service, use TG (tongue & groove) or MFM (male & female) so the gasket cannot blow out. For sulphuric acid and hydrochloric acid, use a flexible graphite gasket with a 316L ｉｎｓｅｒｔ ring to prevent media attack on the winding.

Gasket: spiral-wound with PTFE filler, or metal-jacketed graphite for LNG auxiliaries. Stud bolt: A320 L7 (down to −101 °C) or A320 L43 (down to −101 °C, high strength). Nut: L7. For seawater service, use B8M (316) studs and 8M nuts to resist chloride pitting; back them with a flexible graphite gasket with a 316L ｉｎｓｅｒｔ ring. For LNG and ethylene service at −165 °C, the L7 / L7 pairing is mandatory; a B7 stud will brittle-fracture.

Once the gasket and stud grades are picked, three mechanical parameters finish the job. Get any one of them wrong and the joint will pass hydrotest but fail at the first thermal cycle.

ASME B16.5 Table 4.3.1 gives the standard stud-bolt length for each flange class and size. The length is calculated so that, after the nut is tightened, two to three threads protrude beyond the top of the nut. The buyer simply cites the ASME class and the nominal pipe size; the supplier cuts the stud to the listed length. Non-standard lengths are an exception and must be approved by the project piping lead.

For standard ASME B16.5 studs, the thread engagement is built into the standard length. For non-standard or machined studs, the rule is that the engagement length (the length of stud thread inside the nut) must be at least equal to the stud nominal diameter. A 1-inch stud needs at least 1 inch of thread in the nut. Less engagement and the nut will strip before the gasket reaches its target stress.

PCC-1 is the ASME Post-Construction Committee guideline for controlled bolt-up. It defines a four-step pattern: (1) hand-snug all studs, (2) tighten to 30% of target torque in a star pattern, (3) tighten to 60% in a star pattern, (4) tighten to 100% in a star pattern, then a final pass at 100% to equalise. The target torque is calculated from the desired gasket stress, the bolt cross-section, and the lubrication K-factor. A Molykote 1000 or equivalent anti-seize gives a K-factor of about 0.16; a plain dry stud gives 0.20–0.30. The buyer should always specify the lubricant and the K-factor on the PO so the field crew is not guessing at torque.

These are the five field failures that come back to procurement. Each one is preventable at the RFQ stage.

• Wrong face type on the gasket. An RF gasket will not seat on an FF flange, and an RTJ ring will fall out of an RF groove. Confirm the flange face on the isometric, not the spool drawing, before cutting the PO.
• Missing inner ring on the spiral-wound gasket. For Class 600 and above, or for any service with a flow-change / thermal cycling, the inner ring is mandatory to prevent the winding from being eroded by the media. If the PO says "spiral-wound with outer ring only," the inner ring is missing.
• Mismatched nut grade. A 2H nut on a B7M stud, or a 7 nut on a B16 stud, is non-standard. Either the stud or the nut will fail at the first thermal cycle. Cross-check the stud-and-nut pair against the ASTM A194 / A193 table above.
• Stud-bolt length off by one thread pitch. A stud that is 5 mm too long will bottom out before the gasket reaches target stress. A stud that is 5 mm too short will not engage the nut by the required diameter. ASME B16.5 stud-bolt length tables are non-negotiable for standard flanges.
• No MTC traceability per joint. A B7 stud without a 3.1 certificate, or a spiral-wound gasket with no lot number, will be rejected at hydrotest by most owner inspectors. The MTC chain is part of the procurement spec, not optional.

Each of these five failures translates to a hydrotest rework, a turnaround extension, or a weld rework on the pipe fittings the joint was feeding. Catching them at the RFQ stage is the single biggest cost-saver in any piping-package procurement.

The following seven items are the minimum data a buyer should put on the RFQ. A mill-direct supplier that has to ask for any of these items by return email is not really mill-direct.

1. ASME B16.5 / B16.47 flange class and nominal pipe size (NPS) for each joint.
2. Flange face type: FF, RF, TG, MFM, RTJ. With the profile for RTJ (R, RX, BX).
3. Service fluid, design pressure, design temperature, and minimum / maximum operating temperature.
4. Sour / NACE requirement: NACE MR0175 / ISO 15156 yes or no.
5. Stud-bolt material grade (A193 B7 / B7M / B8 / B8M / B8M2 / B16 / A320 L7 / L43).
6. Nut grade (A194 2H / 2HM / 7 / 8 / 8M / 8M2 / L7).
7. Gasket type and filler (non-metallic CAF / PTFE / graphite; semi-metallic spiral-wound with inner & outer ring; metallic RTJ R / RX / BX).

Five questions buyers ask most often:

EZ Steel Industrial is a mill-direct manufacturer of gasket , stud bolt & nut hardware for refinery, petrochemical facilities, marine & ship-building, power plants & aerospace and general industrial pipework. The bolting kit is bundled with the matching pipe flanges, pipe fittings and downstream industrial valves so the joint arrives at site as a single BOM line with EN 10204 3.1 traceability, a written bolt-up procedure, and a torque table.

Standard stock includes A193 B7 / B7M / B16 / B8 / B8M / B8M2 / B8M3 / A320 L7 / L43 stud bolts with A194 2H / 2HM / 7 / 8 / 8M / 8M2 / L7 heavy hex nuts; spiral-wound gaskets in 304 / 316L with graphite, PTFE or mica filler and inner / outer rings; ring-type joint gaskets in R / RX / BX profiles; camprofile gaskets; flexible graphite and PTFE sheet gaskets. ASME B16.5 / B16.47 / B16.20 / B18.2.1 / B18.2.2 / ASTM A193 / A194 / A320 / F104 / F37 / EN 1514-1 to -4 / EN 12560-1 to -7 conformance on every shipment.

Send your RFQ with the seven items above and we will return a quote within 24 hours, including the matching flange drawing, the MTC chain layout, and the bolt-up torque table for the chosen lubricant. For NACE MR0175 sour service, RCC-M nuclear service, or cryogenic (down to −196 °C) service, please flag the requirement on the inquiry and we will return the material certificate schedule together with the quote.