If you have ever chased a small leak on a 600# RF flange and watched it grow into a hot work permit, you already know the truth: a bolted joint is a system, not a bag of parts. The flange, the gasket, the stud, the nut, the washer and the tightening method all share the load. Treat them as separate purchases and the joint will tell you about it the first time it cycles.

This guide walks through how a procurement or project engineer can specify a complete bolting package for pressure-boundary pipe flanges in line with ASME PCC-1-2019, the current industry baseline for pressure boundary bolted flange joint assembly, while still keeping the bill of materials practical for a real project.

Before you ｓｅｌｅｃｔ a gasket style, it helps to be honest about why bolted joints fail in service. Field experience and the analysis work behind ASME PCC-1-2019 (which replaced the 2013 edition) point to three dominant drivers.

• Improper assembly sequence. A star pattern with multiple controlled torque passes is the minimum. A single pass to "feel right" is how you get uneven gasket stress and a joint that relaxes on the first thermal cycle.
• Wrong bolt material for the service. Plain carbon steel studs in a service above about 425 °F will creep, lose preload, and the gasket will follow them down. ASME PCC-1 makes bolt grade selection tied to design temperature a non-negotiable part of the assembly spec.
• Gasket-flangeseat mismatch. A soft non-asbestos sheet on a Class 600 RF face looks fine on day one and disappears by month six. Seat hardness, gasket stress, and the flange's face finish have to be designed together.

Gasket choice is downstream of the flange rating and the design temperature. ASME B16.5 defines the geometry for pipe flanges from Class 150 through Class 2500, and ASME B16.20 covers the spiral-wound and ring-joint gaskets that pair with them. Working backwards from a vendor catalog usually produces a soft joint; working forward from the pressure–temperature rating gives you a seat that stays.

A real specification, not a marketing list, usually looks like the table below. Pressure class, temperature, fluid, and the flange face type all have to line up.

A spiral-wound gasket is usually the default for anything above Class 150 because it combines a metallic winding (the spring-like recovery that follows thermal movement) with a softer filler (graphite, PTFE, mica) that actually seals. RTJ gaskets are for high-pressure, high-temperature or hydrocarbon service where the soft filler would creep.

The stud bolt is what holds the gasket under load. ASME PCC-1-2019 reinforces what the 2013 edition already required: bolt grade has to be matched to the design temperature, and the nut has to be matched to the stud. The most common combinations a specifier will see are:

• ASTM A193 B7 with ASTM A194 2H — the workhorse for high-temperature, high-pressure service up to about 425 °F. Most spiral-wound and RTJ applications in oil and gas, petrochemical and power generation fall here.
• ASTM A193 B16 with ASTM A194 7 or 8 — for higher-temperature creep resistance, typical in steam and refinery service above 425 °F.
• ASTM A320 L7 with A194 L7 or L7M — required for low-temperature service below -46 °C, including LNG and refrigeration lines.
• ASTM A193 B8 / B8M (stainless) — used when corrosion resistance is needed. Note that stainless bolts stretch more under load; torque values have to be revised downward to stay within the elastic range of the stud.

A few practical things to put in the purchase order: stud length must allow at least one and preferably two full threads to project past the nut face; nuts should be the heavy hex series, not standard hex, because the bearing surface matters for even load; and washers, where used, must be through-hardened so they do not dish under the nut.

A gasket does not seal because you tightened the bolts hard. It seals because the joint reached a uniform target gasket stress before it was put in service. ASME PCC-1-2019 lays out the standard four-step tightening sequence for multi-bolt flanges:

• Pass 1 — snug. Hand-tighten or torque to roughly 30 % of target using a star (cross) pattern. The goal is to bring the flange faces together evenly, not to load the gasket yet.
• Pass 2 — torque to about 60 % of target using the same star pattern.
• Pass 3 — torque to 100 % of target in the same pattern.
• Pass 4 — final round pass at 100 % target to take out any relaxation from the previous round. This is the round most people skip and the one that prevents the leak that shows up the next morning.

The 2019 revision of PCC-1 added Appendix Q covering considerations for powered equipment (hydraulic torque wrenches, tensioners) and refreshed the reference torque tables in Appendix O. Both are worth a careful read before a hydrostatic test. A hydraulic tensioner is preferred over a torque wrench for high-pressure or high-cycle joints because it loads the stud in pure tension rather than torsion, which is gentler on both the stud and the gasket.

On a real project, the bolting package is rarely sourced as a single line item. The flange, the gasket, and the stud-and-nut set are usually purchased separately and arrive on site at different times. A few coordination points worth pushing into the procurement document:

• Confirm the stud length and thread pitch against the actual flange and nut combination before release. A Class 600 WN flange with a 4-inch pipe will not use the same stud length as a Class 300 weld neck of the same nominal size, even though both share an NPS label.
• When a forged steel butt weld fittings is welded into the line, the flange-to-fitting interface usually defines the highest bolt count in the system. Pull that spec forward so the stud bolt quantity per flange is correct in the MTO.
• Match fastener traceability to the flange's MTR. If the flange is supplied with EN 10204 3.1 certification, the studs and nuts should be supplied the same way. A 2.2 cert on the studs beside a 3.1 cert on the flange is a common cause of inspector comments.
• Package the stud, two heavy hex nuts, and a washer in the same bag with the gasket and the flange. The site foreman will thank you, and you will not lose half the studs to a rainy laydown yard.

Three errors show up over and over on bolted-joint review, and all of them are easier to fix on paper than in the field.

• Stud grade drift. A193 B7 is ordered in the RFQ, but B7M (which has reduced tensile strength for sour service) arrives on site. Both are valid, but only one is correct for the service.
• Gasket without outer guide ring on a tongue-and-groove or RF face that needs one. Without the centering ring the gasket can extrude inward on the first pressure cycle.
• Mixing stud bolt and stud rod terminology in the BOM. Stud bolts are fully threaded both ends; stud rods (threaded one end) are not, and they are not a ｄｒｏｐ-in replacement for stud bolts on standard ASME flanges.

Before you release a purchase order for a bolted joint, walk through the following.

• Confirm the design pressure, design temperature and fluid for the line.
• ｓｅｌｅｃｔ the flange class and face type per ASME B16.5 (or EN 1092-1 for European projects).
• ｓｅｌｅｃｔ the gasket style per ASME B16.20 for spiral-wound and RTJ, or per ASME B16.21 for sheet gaskets.
• Match the stud bolt and nut grade to the design temperature and any sour-service requirements.
• Verify the tightening sequence and target torque against ASME PCC-1-2019.
• Confirm traceability, MTR requirements, and packaging so the whole package arrives together on site.