Bolted Joint Integrity: How to Match Gasket, Stud Bolt and Nut to Pipe Flange Facing in Oil & Gas, Petrochemical, Power and Marine Service

A practical procurement and engineering guide for selecting gasket stud bolt nut sets as a system — not as three separate line items — for ASME B16.5 / B16.47 pipe flanges in real plant service.

Most flange leaks in a refinery, power block, FPSO or chemical plant are not "gasket failures" in isolation. They are mismatches between the gasket, the stud bolt, the nut, the flange facing, and the operating envelope. A spiral-wound gasket paired with a Class 150 flat face, a B7 stud bolt in a −40 °C LNG service, or a 70/30 copper-nickel flange bolted with carbon-steel hardware in seawater will all leak — even though every component on its own passed the MTC.

This guide is written for B2B buyers, project engineers, and EPC procurement teams who need to specify gasket stud bolt nut sets that actually stay tight. We will work from the flange facing outward — because the facing dictates the gasket, and the gasket dictates the bolting.

1. Start With the Flange Facing — It Decides Everything Else

ASME B16.5 defines the most common raised face (RF), flat face (FF), ring-joint face (RTJ), tongue-and-groove (T&G), and male-and-female (M&F) facings. Each one is matched to a specific gasket style and pressure class. If you skip this step and order gaskets by part number alone, you will get a stack-up that does not seal.

1.1 Raised Face (RF) — the default for Class 150 to Class 600

The RF has a 1/16" or 1/4" serrated finish and is the most common facing on carbon and stainless pipe flanges. It is designed to be used with soft cut gaskets (compressed non-asbestos, graphite, PTFE) at low pressure, and with spiral-wound (SWG) or flexible graphite gaskets for higher pressure and temperature. The gasket sits inside the bolt circle and is centered on the RF.

1.2 Flat Face (FF) — required when the mating flange is non-metallic or cast iron

FF flanges are used with cast iron, fiberglass, or lined flanges. Because the full gasket stress goes into a flat surface, FF flanges need a full-face gasket that extends to the bolt holes. A standard RF gasket on a FF flange will blow out the moment you pressurize the line.

1.3 Ring-Joint Face (RTJ) — the only choice for Class 600 and above in high-pressure service

RTJ is a metal-to-metal seal. The RTJ gasket (oval or octagonal) sits in a precision-machined groove. Once you pressurize, the gasket is wedged into the groove and the harder of the two flange faces bites into the softer. RTJ gaskets are reusable, fire-safe, and standard for hydrocarbon, high-pressure steam, and offshore. The flange facing, the groove dimensions, and the gasket hardness (typically softer than the flange — Brinell 30 less) all have to be matched.

Procurement rule: never specify a gasket without specifying the facing, the groove (for RTJ), and the class. The facing is not a detail — it is the start of the bill of materials.

2. Gasket Selection by Service — Non-Metallic, Semi-Metallic, or Metallic

Once the facing is fixed, the next decision is the gasket family. Each family is engineered for a different pressure–temperature–media envelope.

Gasket Family	Typical Standards	Service Envelope	Best Match on EZ Steel Catalog
Non-metallic (compressed fiber, graphite sheet, PTFE)	ASME B16.21, ASTM F104	Class 150 / 300, low pressure, water, oils, mild chemicals	RF flanges in utility, HVAC, low-pressure water service
Semi-metallic — spiral wound (SWG)	ASME B16.20	Class 300 to Class 1500, high temperature, refinery and steam	RF and tongue-and-groove on carbon and alloy steel flanges
Semi-metallic — kammprofile / Camprofile	ASME B16.20, EN 1514	Class 300 to 600, heat exchangers, where reusability matters	Heat-exchanger channel covers, vessel heads
Metallic — RTJ (oval / octagonal)	ASME B16.20, API 6A	Class 600 and above, high-pressure hydrocarbon, offshore	Wellhead and Christmas tree equipment, high-pressure steam
Metallic — corrugated metal / flat metal	EN 12560, DIN 2690	High temperature, exhaust, boiler	Boiler manways, economizer headers

Common mistake: substituting a flexible graphite sheet for a spiral-wound gasket in a Class 600 hot oil line. Graphite sheets creep under sustained load at elevated temperature — within weeks the bolt load drops, the seating stress drops, and the line begins to weep. The spiral-wound design with its inner and outer rings holds its geometry far longer.

3. Stud Bolt and Nut Selection — Match the Material to Temperature, Not to the Flange

A stud bolt is not "a piece of threaded rod." It is a precisely engineered load-bearing element that has to hold the gasket under stress for the entire maintenance cycle. The grade is determined by the minimum design metal temperature (MDMT) and the maximum design temperature, not by what the pipe is made of.

3.1 The high-temperature workhorses: ASTM A193 B7 / B16

ASTM A193 B7 is a chromium-molybdenum alloy steel stud bolt (Cr 0.80–1.10 %, Mo 0.15–0.25 %), quenched and tempered to 860–1,000 MPa tensile. It is rated for service from −29 °C up to 482 °C continuous, with short excursions higher. B16 is the higher-temperature variant (up to 593 °C) with elevated vanadium, used in turbine piping and superheater connections. Both are paired with ASTM A194 Grade 2H heavy hex nuts.

3.2 The low-temperature workhorses: ASTM A320 L7 / L7M

For LNG, ethylene, ammonia, and cold-climate service (−46 °C and below), specify ASTM A320 L7 or L7M. L7M uses a Charpy impact-tested modified version — mandatory for most refinery and offshore low-temperature service. Pair with A194 Grade 7 or 7M nuts. A B7 stud bolt at −46 °C is a brittle-fracture risk and is explicitly forbidden by ASME B31.3 in low-temperature service.

3.3 The corrosion-resistant workhorses: ASTM A193 B8 / B8M, B8C

For stainless bolting on stainless pipe flanges in chloride or hygienic service, use A193 B8 (304) or B8M (316) Class 1 or Class 2, with A194 Grade 8 or 8M nuts. Avoid B8 below Class 2 in pressure-boundary service — the lower strength class 1 can yield under sustained bolt load.

3.4 Copper-nickel bolting for marine service

On 90/10 and 70/30 copper nickel flanges in seawater, fire-fighting, or sanitary marine service, the standard is aluminum-bronze or silicon-bronze stud bolts (typical grades CuAl / CuSi per DIN 17660 or naval brass equivalents) paired with matching bronze or monel nuts. Carbon steel B7 will fail by galvanic corrosion in seawater within months. The right call is bronze through-and-through, and the right source is a mill that stocks the matching bronze nuts.

Spec tip: when you write the RFQ for gasket stud bolt nut sets, list the standard, the grade, the class (where applicable), the thread (UNC / UN8 / BSW / metric), and the length — never ask a supplier to "recommend" a stud bolt grade based on the flange. That decision belongs to the engineer of record, not the warehouse.

4. Length, Thread Engagement, and the Bolt-Up That Actually Works

Specifying the right grade is half the job. The other half is making sure the stud bolt has the right length, the right thread engagement, and is installed using a controlled bolt-up sequence.

4.1 Stud bolt length

ASME B16.5 Table 1 (or B16.47 Appendix) gives the stud bolt length for each flange class and facing. The general formula is: stud length = 2 × (flange thickness) + 2 × (nut thickness) + 4–6 threads of stick-out. For RTJ flanges, add the groove depth. Buy the bolts pre-cut to length with two heavy-hex nuts, machined and chamfered — do not cut threaded rod on site.

4.2 Thread engagement and washer usage

A minimum of 4–6 threads must protrude beyond the nut after tightening. On RTJ and high-cycle service, a hardened washer under the nut and under the bolt head prevents galling on the flange serration and keeps the load uniform. For stainless bolting, always use PTFE or Xylan-coated nuts to prevent thread seizure — otherwise the next shutdown becomes a cutting-torch job.

4.3 Controlled bolt-up sequence (ASME PCC-1)

ASME PCC-1 is the industry standard for controlled bolt-up. The pattern is: (a) hand-tighten all bolts in a star/cross pattern, (b) torque to 30 % of target in a second pass, (c) 60 % in a third pass, (d) 100 % in a final pass, and (e) a final round pass at 100 % clockwise. Skip the round pass and you get uneven gasket stress — the leak path is set. Use a calibrated hydraulic torque wrench or a tensioning tool, not an impact gun.

5. RFQ Spec Callout — What a Clean Buyer Spec Looks Like

A clean specification removes every ambiguity from the supplier's quote. Here is the callout we recommend for a typical refinery hydrotreater service:

Flange standard: ASME B16.5, Class 300, RF, 4" NPS, A182 F316L weld-neck (matches the pipe from the stainless steel pipe list).
Gasket: spiral-wound, 304 stainless windings + graphite filler, inner ring 304, outer ring carbon steel, per ASME B16.20, with the manufacturer's name and the heat number on the MTC.
Stud bolt: ASTM A193 B7, 3/4"–10 UNC × length per B16.5 Table 1, fully thread rolled, chamfered ends, with a permanent color-code on the protruding end per ASME PCC-1.
Nut: ASTM A194 Grade 2H, heavy hex, 3/4"–10 UNC, each bagged with its bolt and tagged with the heat number.
Washer: hardened, ASME B18.21.1, Type A, flat, 3/4" ID.
Quantity, packaging, traceability: full MTC per EN 10204 3.1, marking per ASME B16.5, each set shrink-wrapped and labeled with project tag number, flange tag, and line number.

The same callout pattern applies to a copper-nickel seawater line on an FPSO — just swap the gasket to a kammprofile with a 90/10 Cu-Ni core, and the stud bolt and nut to aluminum-bronze per DIN 17660 (Werkstoff 2.0932 / 2.0966). The discipline is identical.

6. Where Bundled Sourcing Pays Off

Bolted joints are sold as three separate line items in most catalogs. In the field, they are one system. When the gasket, stud bolt, and nut are shipped from different warehouses — different heat numbers, different MTC batches, different packaging — the QA burden on your site engineer is enormous. Every joint has to be re-verified.

A mill-direct bundled supplier, by contrast, will cut the stud bolts and pre-bag them with the matching nuts and the matching gasket, all with a single project MTC pack. For large refinery, power, or offshore projects, this is the difference between a one-month and a three-month bolt-up cycle. For LNG and nuclear service, the bundled approach is mandatory.

EZ STEEL INDUSTRIAL has been supplying gasket stud bolt nut sets, pipe flanges, and industrial valves as bundled mill shipments since 1994. Stocks include A193 B7 / B16 / B8 / B8M / L7 stud bolts, A194 2H / 7 / 8 / 8M nuts, ASME B16.20 spiral-wound and RTJ gaskets, and the matching flanges from 1/2" through 60" in carbon, stainless, alloy, and copper-nickel grades. The mill test certificates cover every heat, the third-party inspection (API, EN, ASME) is on file, and the bundled project packaging is project-tagged on the wooden crate.

7. Quick Decision Matrix — Use This When You Only Have Five Minutes

Service	Flange Facing	Gasket	Stud Bolt / Nut
Utility water, Class 150	RF	Compressed non-asbestos, 1/16" thick	A193 B7 / A194 2H (carbon steel)
Steam, 400 °C, Class 300	RF	Spiral-wound 304 + graphite, with inner/outer ring	A193 B7 / A194 2H
Refinery hydrotreater, Class 600, 450 °C	RTJ	RTJ octagonal, soft iron (Brinell 90 max)	A193 B7 / A194 2H, controlled bolt-up
LNG / ethylene, −46 °C	RF	Spiral-wound 316L + PTFE, inner ring 316L	A320 L7M / A194 7M (mandatory)
Seawater cooling, 90/10 Cu-Ni pipe	FF / RF	Kammprofile with 90/10 Cu-Ni core, EPDM	Aluminum-bronze (CuAl10Ni) / matching bronze nut
Sanitary pharma / food	RF	PTFE envelope, virgin grade	A193 B8M Class 2 / A194 8M, with PTFE-coated nut

Hard rule: never pair a copper-nickel flange with carbon-steel bolting in seawater. The galvanic potential difference is 0.4 V or more — the carbon steel will be the sacrificial anode and will fail in months. The bronze bolt costs a bit more and lasts the life of the pipe.

8. Common Procurement Pitfalls to Avoid

Buying by part number, not by service. "SWG 4" 300# 304/GR" tells you nothing about the filler, the rings, the wind density, or the operating envelope. Specify filler (graphite, PTFE, mica), ring material, and ASME B16.20 group.
Mixing standards on the same joint. ASME B16.5 stud bolt length on a B16.47 Series A flange is the wrong length. ASME B16.47 Series A and Series B are not interchangeable.
Re-using gaskets on RTJ. An RTJ gasket is a metal gasket — it does not "settle" the way a soft gasket does, but it does brinell the flange face. After a re-make, the gasket has to be replaced. Re-using a brinelled RTJ is a leak waiting to happen.
Specifying the wrong nut grade. A193 B7 stud bolts must be paired with A194 2H nuts — not A194 2, not B8. A 2H nut is heavy-hex and proof-loaded for high temperature.
Skipping the MTC review. Every batch of gasket stud bolt nut hardware must come with a 3.1 MTC that names the standard, the grade, the heat number, and the test results. Without it, you have no traceability for the next plant audit.

Source Your Bolted Joint Hardware from a Mill-Direct Bundled Supplier

If you are about to release an RFQ for an oil & gas, petrochemical, power, marine, or offshore project, send your flange schedule, the facing schedule, and the operating envelope to the EZ STEEL engineering desk. We will return a bundled quotation for gasket stud bolt nut sets, matched to your pipe flanges (carbon, stainless, alloy, and copper nickel flanges), with the steel flanges, steel flanges tags and 3.1 MTCs already aligned to your project BOM.