Most flange leaks do not start at the flange. They start with a gasket that was wrong for the fluid, a stud bolt that was under-torqued, or a nut that was ordered from a different standard than the bolt. By the time the joint is hot and pressurised on site, those small mismatches turn into a shutdown, a re-torque, or a release that nobody wants to write up. The cheap insurance is a bolted-joint specification that ties the gasket stud bolt nut assembly to the same pipe flanges and the same pipe fittings you are putting into the line.

This guide distils what EZ STEEL INDUSTRIAL has learned from shipping bolted-joint packages alongside pipe, fittings and flanges since 1994. The recommendations below match ASME B16.5, B16.47, B16.20, B18.2.1 and B18.2.2, and the assembly philosophy follows ASME PCC-1 for pressure-boundary joints.

A bolted flange joint is one engineered assembly. Treating gaskets, stud bolts and nuts as three separate procurement items is the most common way to fail that assembly. Before anyone opens a catalog page, you need four numbers locked down: design pressure, design temperature, fluid composition (including any water, chloride or H2S content), and the class rating of the flange you have already selected.

Those four numbers drive every other decision. Class 150 and Class 300 steel flanges with a raised face (RF) tolerate a much wider gasket family than Class 600 and above, which typically demand spiral-wound or ring-joint (RTJ) gaskets. Sour service, chlorine, hot oil and steam each push the stack toward a different material combination. Get those four numbers wrong and the rest of the joint is guesswork.

Gasket selection is more about chemistry and temperature than about pressure. The most common families you will see in a mill-direct gasket stud bolt nut shipment are:

• Compressed non-asbestos fibre (CNAF / CAF): for low-pressure water, air, oil and utility service, typically up to Class 300 and 200 °C. Economical, but not for high temperature or cycling service.
• Graphite with stainless or carbon steel ｉｎｓｅｒｔ: workhorse for refineries, chemical plants and steam service up to about 650 °C. Excellent thermal resistance, poor mechanical strength on its own — must be confined by a compression ring on RF faces.
• Spiral-wound (SW): metallic windings (typically 304, 316L, Monel or Inconel) with a non-metallic filler (graphite, PTFE, mica). The default choice for Class 600 and above, for high temperature, and for cyclic service. Built to ASME B16.20 dimensions.
• Ring-joint (RTJ): soft iron, low-carbon steel, 304, 316, Monel or Inconel rings machined to ASME B16.20 oval or octagonal profiles. For high-pressure Class 900 and above, refinery and high-temperature hydrocarbon service.
• PTFE / envelope gaskets: for aggressive chemicals and high-purity service, typically below 200 °C. Limited creep resistance — avoid on Class 600 RF faces unless used as an envelope over a corrugated metal core.

Flange facing is half the seal. A spiral-wound gasket on a flat face (FF) flange will crush on the first torque-up. An RTJ ring on a raised face (RF) flange has nowhere to seat. The pairing is mechanical, not optional, and it should be specified together with the pipe flanges order.

If the gasket is the seal, the stud bolt is the clamp. The two most common procurement mistakes on a gasket stud bolt nut package are mixing imperial and metric threads, and mixing B7/B7M studs with B8 or B8M nuts of the wrong class. The right answer is to pick one standard family and apply it to every joint on the line.

For most refinery, chemical and steam service, the default stud bolt is ASTM A193 B7 (medium-carbon alloy steel, quenched and tempered) with ASTM A194 2H heavy hex nuts. For higher temperature austenitic service, A193 B8 Class 2 studs with A194 8 nuts. For low-temperature or sour service, A320 L7 studs with A194 4 or L7M nuts. Threads follow ASME B1.1 (UNC) for imperial, B1.13M for metric. Bolt length is calculated as the sum of the flange thickness, gasket thickness, washer thickness if used, and one to three threads protruding past the nut — never less, and never enough to bottom out in a tapped flange.

ASME PCC-1 makes one point very clearly: the gasket must be properly seated, the flange faces must be clean, parallel and aligned, the studs must be lubricated to a known friction coefficient, and the torquing pattern must be crossed in at least four passes. Skipping any of these steps turns the torque value on a chart into fiction. The sequence looks like this:

• Clean and inspect: remove old gasket material, check flange faces for radial scratches deeper than 0.8 mm, confirm parallelism with a feeler gauge across four quadrants.
• Lubricate the threads and the nut face: machine oil alone is not enough. Use a bolt lubricant with a published friction coefficient (typical target 0.16 to 0.20) so that the torque-to-tension relationship is predictable.
• Cross-pattern torque in four passes: 30 %, 60 %, 80 %, 100 % of target torque, working in a star pattern. Move at least one bolt position between passes so the load is even.
• Verify after first thermal cycle: walk the joint again after the line has been heated to operating temperature and re-torqued to target while hot, if the gasket is graphite or flexible graphite.
• Record everything: torque value, lubricant, bolt lot number, gasket batch, MTC. This is your evidence trail if a joint is ever questioned.

The same logic that makes pipe, fittings and flanges worth sourcing from one mill applies to the bolted-joint stack. When the gasket stud bolt nut set, the pipe flanges and the matching pipe fittings arrive in one shipment with one mill test certificate, every flange face, every gasket, every stud is traceable to a single heat and a single production batch. The site QA package collapses from three documents to one. The risk of a mixed lot going into the line drops to near zero.

EZ STEEL INDUSTRIAL has been shipping that bundle since 1994. The flange program covers ASTM A105 forged steel flanges, ASTM A182 F304/F316 stainless flanges, copper-nickel flanges for marine service, and the full ASME B16.5 / B16.47 size range. The fittings program covers butt-weld, socket-weld and threaded execution in matching grades. The bolting program covers B7/2H, B8/8, B8M/8M, B16/B8M, L7/4, L7M/L7M and B16 high-temperature service, paired with spiral-wound gaskets, RTJ rings, graphite sheets and CNAF sheet stock from the same dispatch.

A few mistakes we see on most projects, even from experienced procurement teams:

• Specifying the gasket standard but not the edition. ASME B16.20 was updated in 2017 with revised ring and winding tolerances. Always pin the year of issue in the RFQ.
• Using the wrong facing for the gasket. RTJ ring on RF face, or spiral-wound on FF face, will not seal no matter how hard you torque.
• Mixing stud and nut standards. A193 B7 studs with A194 8 nuts will not develop the clamp load the chart says they will. Match them at the standard level.
• Skipping the lubricant spec. Without a known friction coefficient, target torque is meaningless. State the lubricant brand and coefficient on the installation procedure.
• Reusing gaskets. Spiral-wound and CNAF gaskets are single-use. Reuse causes seating deformation and leak paths. RTJ rings can sometimes be re-machined once; most specs still call them single-use.
• Forgetting the inner and outer rings. Spiral-wound gaskets without an inner ring can blow out under pressure; without an outer ring they lose their compression stop. Specify both unless the design specifically allows otherwise.

When a bolted-joint RFQ lands on our desk, the engineering team walks it through the same six questions:

• Step 1 — Service envelope: design pressure, design temperature, fluid, water/chloride/sour content. Sets the bolt and nut material family.
• Step 2 — Flange class and facing: 150# to 2500#, RF / FF / RTJ / M&F / T&G. Sets the gasket family and the gasket standard.
• Step 3 — Gasket choice: CNAF, graphite, spiral-wound, RTJ or PTFE. Sets the dimensions, the facing finish and the compression stop requirement.
• Step 4 — Bolt and nut choice: B7/2H, B8/8, B8M/8M, L7/4, L7M/L7M, B16 or B8 Class 2. Sets the thread series, length and quantity per joint.
• Step 5 — Documentation depth: EN 10204 3.1, 3.2, PMI, traceability per ASME PCC-1. Sets the MTC stack.
• Step 6 — Bundle scope: gasket and bolts only, or full pipe + fittings + flanges + gaskets + bolting + valves. Sets the supply model.

Running an enquiry through this filter before issuing it saves weeks of back-and-forth and produces a bolted-joint package that installs cleanly the first time.

We are a full-cycle manufacturer, not a trading desk. Our 500+ staff and 480,000-ton annual capacity run from raw-material inspection to finished goods packaging. For a bolted-joint package that means the stud bolt, the nut, the gasket and the flange all share the same metallurgical story and the same documentation batch.

Our gasket stud bolt nut program ships spiral-wound and RTJ gaskets, graphite and CNAF sheet stock, B7/2H and B8/8 stud-and-nut sets, and matched PTFE and flexible graphite fillers, all in the standard sizes you need. For project schedules we ship from floor stock in 1–2 weeks; for custom orders our typical lead time is 4–6 weeks. The export team handles seaworthy packaging, customs paperwork and on-time dispatch from Changsha, China.

Our laboratory is ISO 9001 certified, and our pipe, fittings, flanges and bolting carry API, EN and ASME third-party approvals. For projects that need nuclear-grade traceability, our RCC-M II line and our PWR nuclear material guide demonstrate the documentation depth that nuclear and aerospace buyers require.

A bolted joint is a system, and a system fails as a system. The gasket, the stud bolt, the nut, the flange, the pipe and the fitting have to tell the same metallurgical story, be documented against the same standard, and arrive at site in the same packaging batch. Working with a manufacturer that can deliver that bundle — and stand behind it with a single point of accountability — turns the bolted-joint stack from a long list of small parts into a clean, auditable assembly.

If you are matching gaskets to flanges, comparing stud-and-nut standards, or trying to consolidate pipe, fittings, flanges and bolting into a single shipment, our engineering desk is happy to walk through your line list with you. Send your class, size, fluid and quantity table and we will return a clean, fully-documented bid within five working days.