A refinery, a chemical plant, a power station and a desalination train all share one vulnerable component: the bolted flanged joint. Walk through any of those sites after a hydrostatic test and the pattern is the same — the joints that leaked were not the joints that used the most expensive flange or the highest-grade pipe. They were the joints where the gasket, the studs, the nuts, the flange facing, and the torque procedure were not designed to work together. One supplier shipped a spiral-wound gasket to ASME B16.20. A different supplier shipped a stud bolt set to ASTM A193 B7. A third supplied a Class 300 raised-face weld neck flange. The inspector found that the gasket was 0.8 mm thinner than the flange called for, the bolt lengths were short by two threads, and the lubrication on the nuts was wrong. The joint leaked at 30 bar before the line was ever put into service.

This article is built around how a 30-year integrated mill — EZ STEEL INDUSTRIAL in Changsha, China — packages the gasket, stud bolt and nut set, the pipe flanges and the bolting so they ship together, trace together, and torque up the way the designer expected.

Why the Joint, Not the Pipe, Is Where the Project Wins or Loses

Pipe, fittings and industrial valves get the most attention in a process line RFQ, but the bolted joint is the part of the system that is held together by friction. The pipe sees internal pressure. The flange sees bending. The gasket sees compression creep, thermal cycling, and chemical attack. The stud bolt sees sustained tensile load and torque-down stress. If any one of those four is mis-specified, the joint will find the weakest link — usually on a Sunday night, six weeks after commissioning.

A coordinated bundle of gasket stud bolt nut sets and matching pipe flanges changes that equation. Material certificates share a single heat-number scheme. Gasket thickness matches the flange facing within the standard's tolerance. Bolt length and thread pitch match the flange drilling, not the catalog guess of the distributor. And the entire bundle arrives with one quality dossier, so the inspector signs off one set of papers, not five.

Step 1 — Pin the Service Envelope, Then Pick the Gasket

The right gasket is decided by the service envelope, not the catalog. The four numbers that matter most are the design temperature, the design pressure, the media (hydrocarbon, steam, seawater, acid, caustics), and the expected number of thermal cycles. Once those are fixed, the gasket shortlist collapses to a small set of constructions. EZ STEEL INDUSTRIAL supplies the three families that cover the bulk of industrial service.

Spiral-wound gaskets for the bulk of oil, gas, steam and chemical service

Spiral-wound gaskets to ASME B16.20 are the workhorse of the industry. They are built by winding a metal strip (usually 304, 316L, Monel 400 or Inconel) with a non-metallic filler (graphite, PTFE, or non-asbestos fiber) around a metal centering ring. The construction gives the gasket enough resilience to seat against minor flange imperfections while still holding a tight seal at elevated temperature. For a Class 300 hydrocarbon line at 400 °C, a graphite-filled spiral wound with an outer guide ring is the default. For a 90/10 copper nickel alloy seawater line, a non-asbestos filler is preferred so the graphite does not promote galvanic attack on the flange face.

Ring-type joint (RTJ) gaskets for high-pressure hydrocarbon

Above Class 600, the standard shifts to ring-type joint gaskets in soft iron, low-carbon steel, 304, 316, or Monel. RTJ gaskets sit in machined grooves on the flange face and seal by plastic deformation of the ring itself. They are reliable, but they are unforgiving. The groove depth and angle have to match the ring style — R, RX, or BX — exactly. A Class 900 BX gasket installed in an R groove is a guaranteed leak path.

Flexible graphite and non-asbestos sheet for low-pressure utility

For utility water, low-pressure air, and general service below Class 150, reinforced graphite sheet or compressed non-asbestos sheet gaskets are typically the most cost-effective choice. They cut easily to non-standard flange sizes and are forgiving on flat-face cast iron flanges. The cost saving only works if the temperature stays inside the sheet's rated envelope — typically 200 °C for non-asbestos, 450 °C for graphite with stainless ｉｎｓｅｒｔ.

Step 2 — Match the Stud Bolt and Nut Set to the Gasket and the Flange

A common mis-spec is to order the stud bolt and nut from one supplier and the gasket from another, with the flange from a third, and then to assume that the bolt length in the catalog will be correct. It rarely is. The correct bolt length depends on the flange thickness, the gasket thickness, the nut thickness, and the number of thread pitches that must protrude beyond the nut after torque-up. EZ STEEL INDUSTRIAL sizes the gasket stud bolt nut set against the actual flange drawing, not against a generic class table.

The governing standards for the stud bolt and nut are ASTM A193 for the bolt material and ASTM A194 for the nut. The grade is set by service temperature.

For stainless bolts on stainless flanges, two extra details matter. First, the correct lubricant must be specified — a high-temperature anti-seize that does not contain copper (copper-containing compounds can promote stress corrosion cracking on austenitic stainless at elevated temperature). Second, the bolt and nut are usually ordered as a matched set from the same heat lot so the thread engagement and hardness are consistent.

Step 3 — Lock the Gasket to the Flange Facing and the Flange to the Pipe Schedule

A gasket cannot be specified in isolation. The flange facing dictates which gasket geometry is acceptable. An RF (raised face) flange with serrated finish accepts a spiral-wound or a flexible graphite sheet gasket. A flat-face (FF) flange — usually on cast iron or FRP equipment — needs a full-face gasket that extends to the bolt holes. An RTJ flange needs a ring-type joint gasket that matches the groove profile exactly. A tongue-and-groove pair needs a gasket that fits the groove width with adequate compression margin.

Once the facing and gasket are pinned, the pipe flanges have to match the pipe schedule. A Class 150 weld neck flange rated for use with a Sch 40 pipe is not automatically rated for a Sch 80 pipe of the same nominal size. The hub bore, the welding bevel, and the pressure-temperature rating are tied to the pipe wall. EZ STEEL INDUSTRIAL ships steel flanges in carbon (ASTM A105, A350 LF2), stainless (A182 F304L, F316L), and alloy (A182 F11, F22, F91) families, with hub bores pre-machined to the pipe schedule on the RFQ. This avoids the on-site reaming that extends shutdowns.

Step 4 — Torque Procedure: Where 80% of Field Leaks Are Born

Even a perfectly specified bundle will leak if the torque-up procedure is wrong. The two recurring mistakes on site are uneven torque and over-torque. ASME PCC-1 (Guidelines for Pressure Boundary Bolted Flange Joint Assembly) is the governing reference, and it points to three practical rules.

First, the recommended torque must be calculated from the actual gasket seating stress, the bolt area, and the lubricant's measured friction coefficient — not from a generic "torque table" borrowed from another project. Second, the torque must be applied in a star (4-pass) sequence with at least three passes: 30%, 60%, and 100% of the final value, so the gasket seats evenly and the flange face stays parallel. Third, after the line reaches operating temperature for the first time, a re-torque pass is recommended for spiral-wound gaskets on a Class 300 or higher service, because graphite filler relaxes during the first heat-up.

A bundled supply makes the torque procedure easier to enforce. The mill ships the gasket, bolt, nut, and lubricant as one package, with one set of installation instructions written for that specific combination. The field crew does not have to reconcile data from three different suppliers to figure out which torque value is correct.

Step 5 — Documentation That Survives an Inspector's Audit

A clean pressure-boundary bundle ships with a documentation dossier that includes the following: material test certificates (MTCs) for the flange to EN 10204 3.1, traceability for the stud bolt and nut (A193/A194 grade, heat number, lot number), a certificate of conformance for the gasket to ASME B16.20, the cure date and shelf life for non-asbestos and graphite sheet gaskets, and a torque table derived from the actual lubricant on the bolt. For nuclear or offshore service, additional documentation — such as RCC-M, NACE MR0175, or specific EN 10204 3.2 witnessing — is added.

When the bundle comes from a single integrated mill, the inspector receives one dossier with one file structure. When the same parts arrive from three or four different suppliers, the inspector is left to reconcile documents that may not even be in the same language or use the same data fields. The first scenario passes an audit in a day. The second scenario can stall a project for weeks.