On most piping projects, the gaskets, stud bolts and nuts together cost less than 3% of the total pipework value — yet they are responsible for almost every flanged joint leak that triggers an unplanned shutdown. The reason is not that the parts are low quality. The reason is that they are usually purchased as an afterthought, one item at a time, against a price-per-kilogram benchmark, with no engineering connection to the pipe flanges they are supposed to seal.

This guide is written for procurement engineers, EPC piping leads, refinery maintenance planners, shipyard piping supervisors, and OEM skid builders who need to source gasket stud bolt nut sets that actually match the pressure class, the media and the operating temperature of the joint. We will walk through gasket type selection, stud bolt material grades, nut pairing, and the four most common flange facings, then close with a bundled-sourcing model that lets you place one PO and receive a matched set from a single mill.

1. The Three Elements Work as a System

A flanged joint is a mechanical assembly, not a collection of parts. The gasket seals because the stud bolts preload it to a controlled surface pressure. The nut holds the stud bolt at that preload. The flange transmits the load to the pipe. If you change any one of these — for example, you upgrade from a flexible graphite gasket to a spiral wound gasket, or you swap a B7 stud bolt for a B8 stainless stud — the bolt load, the gasket stress and the flange face deformation all change together.

That is why the four variables below must be locked down before you choose a part number:

• Pressure class — ASME B16.5 Class 150, 300, 400, 600, 900, 1500, 2500 (or the PN equivalent). Higher class means higher bolt preload, which means stronger stud bolt material and a gasket that survives the load.
• Operating temperature — from cryogenic LNG (-196 °C) to refinery hydrocracker outlet (above 500 °C). Material selection changes with temperature, especially for bolting.
• Media — hydrocarbons, steam, seawater, sour H₂S service (NACE MR0175), strong acids, potable water (WRAS / NSF). Each of these restricts the gasket filler, the metal winding strip and the stud bolt coating.
• Flange facing type — RF, FF, RTJ, tongue & groove, male & female. The facing geometry dictates which gasket shape is even mechanically possible.

2. Gasket Types and Selection

Gasket selection is where the joint either starts to hold or starts to leak. Below is the practical decision tree we use with our customers who buy gasket stud bolt nut sets as a bundle.

2.1 Soft (non-metallic) gaskets

Compressed non-asbestos fiber, flexible graphite, PTFE envelope. Used for Class 150 / PN16 utility service — water, air, low-pressure hydrocarbons, food and pharmaceutical lines. Cheap, conformable, but limited in temperature (graphite ≈ 450 °C in steam, PTFE ≈ 250 °C) and pressure (typically ≤ Class 300 with adequate bolting).

2.2 Spiral wound gaskets (ASME B16.20)

The workhorse of the refinery, petrochemical and power-plant world. A V-shaped metal strip (usually 304, 316L, 321 or alloy 825) is wound alternately with a non-metallic filler (graphite, PTFE, mica) to form a gasket that is mechanically resilient, semi-metallic and capable of recovering from thermal cycling. Standard for Class 150–600 in hydrocarbon service; common up to Class 900 with inner and outer rings.

2.3 Ring-type joint gaskets (RTJ)

Solid metal rings, oval or octagonal cross-section, machined to fit the RTJ groove of the flange. Used from Class 600 upward, and almost universal in high-pressure refinery, wellhead and high-temperature hydrocarbon service. Sealing depends on plastic deformation of the ring under bolt load — the ring is soft relative to the flange groove. Materials follow ASME B16.20: soft iron, low-carbon steel, 304, 316, 321, 347, alloy 625 / 825, Monel.

2.4 Kammprofile and metal-jacketed gaskets

A solid metal core with a soft sealing layer bonded to both faces. Excellent recovery, low seating stress, often used in heat exchangers and vessel nozzles. More expensive than spiral wound, but with better performance on cyclic and low-bolting-load situations.

3. Stud Bolt Material Standards (ASTM A193)

The stud bolt carries the entire preload of the joint. Material grade selection is driven by temperature, corrosion and any NACE / sour-service requirement. The four grades that cover roughly 90% of industrial projects are listed below.

A common mistake is using a generic Grade 8.8 (ISO 898) stud bolt on a refinery flange because it is cheap and on the shelf. Grade 8.8 is a carbon-steel bolt with no formal ASME / ASTM pedigree, no EN 10204 3.1 certification, and no traceability. On a B16.5 Class 300 hydrocracker flange at 420 °C it will creep and relax within months. Always specify ASTM A193 — it is a small price difference for a documented pressure-boundary part.

4. Nut Standards (ASTM A194)

The nut must be matched to the stud bolt. Pairing the wrong nut with the right stud bolt is one of the most common audit findings on a piping QA walk-down. The table below is the pairing we recommend on every shipped bolting set.

Heavy hex (2H) is used on ASME B16.5 flanges because the wrench clearance on a standard hex nut is too tight at Class 300 and above. For Class 150, a standard hex is acceptable, but the cost saving is marginal and many EPC specifications call for heavy hex uniformly to simplify inventory.

5. Matching the Gasket to the Flange Facing

The facing type on the pipe flanges determines which gasket geometry can physically be installed. This is the simplest decision in the joint, but it is also the most often miscoded in a purchase order.

• Raised Face (RF): The default facing for ASME B16.5 carbon and stainless steel flanges. Accepts soft gaskets, spiral wound gaskets (with or without inner/outer rings) and ring-type joint gaskets when the RF is also grooved.
• Flat Face (FF): Used on cast iron, glass-lined or non-metallic flanges. Must be paired with a soft gasket only — full-face gaskets that extend to the bolt holes. A spiral wound on a flat face will not seal.
• Ring-Type Joint (RTJ): The flange has a machined groove. The only valid gasket is an RTJ ring matched to the groove number (R, RX, BX). Mixing an RTJ gasket on an RF flange — or vice versa — is one of the most common fabrication errors.
• Tongue & Groove / Male & Female: Used for self-aligning joints in heat exchangers and vessels. Soft gaskets, cut to the tongue or male face profile.

6. Common Procurement Mistakes to Avoid

After supplying bundled gasket stud bolt nut sets to refineries, EPC contractors and shipyards for over thirty years, we see the same five errors come up again and again on incoming RFQs. Avoid them and your joint will hold.

• Reusing a gasket after torque release. Spiral wound gaskets are designed to seal once. A re-used SW has taken a permanent set, lost recovery, and will not meet the same tightness class the second time around.
• Mixing stud bolt grades on the same joint. Half B7 and half B8 will load unevenly. The joint will not seat flat, and the B7 side will carry the entire service load.
• Wrong facing × gasket combination. Spiral wound on FF, RTJ on RF, soft on RTJ — all physically possible to install, all certain to leak at the first pressure test.
• Skipping EN 10204 3.1 / 3.2 traceability. Bolting that sits inside a pressure boundary needs an MTR that proves chemistry, mechanical properties and heat treatment. A "mill test certificate" without the EN 10204 type on it is a commercial document, not a pressure-boundary document.
• Ordering to a price per kilogram. A correct bolting set is purchased per qualified joint, with the stud bolt length, the nut grade, the washer count and the gasket part number all locked. A kg-based price comparison almost always substitutes material.

7. Bundled Sourcing from EZ Steel Industrial

EZ Steel Industrial is a mill-direct manufacturer of carbon, stainless, copper-nickel and alloy pipe flanges, with a parallel product line for the gasket stud bolt nut sets that go with them. Founded in 1994 and operating under an ISO 9001 quality system, we hold dimensional and metallurgical QC for the flanges, the gaskets, the stud bolts and the nuts on the same production system, and we ship them on a single commercial invoice with a single set of EN 10204 3.1 MTRs.

A bundled supply order looks like this in practice: a project sends us the line list with pipe spec, flange class, facing and media. We return one datasheet per item, one MTR bundle, one shipment. No more matching a flange from supplier A with a gasket from supplier B and a stud bolt from a fastener distributor. No more cross-checking heat numbers at receiving. No more "out of stock, partial shipment" follow-ups.

Our eight product lines — carbon and carbon alloy steel, stainless steel, copper-nickel alloy, heat efficiency tubes, pipe fittings, pipe flanges, gaskets / stud bolts / nuts, and industrial valves — are all in-house. That is the practical reason we can package a flange together with its complete bolting and sealing set without subcontracting any element to a third party.