Gasket Selection: Sheet, Spiral Wound and Ring Joint

Gasket Selection: Sheet, Spiral Wound and Ring Joint is the process of matching a sealing element to a flange's pressure class, facing, temperature and process media so the joint holds pressure without leaking, creeping, or blowing out. A gasket fills the microscopic irregularities between two flange faces and holds a seal against bolt load, thermal cycling and pressure. Picking the wrong type is one of the most common causes of repeat flange leaks and fugitive emissions.

The Three Families of Gasket

Almost every industrial gasket falls into one of three families, based on how much metal the seal contains.

• Non-metallic sheet: compressed fibre, PTFE, and rubber-bonded materials, cut flat with no metal reinforcement. Used on Class 150 and 300 flanges.
• Semi-metallic: spiral wound and kammprofile, where a metal winding or grooved core carries the load while a soft filler (PTFE, graphite, mica) seals. Handles higher pressure and temperature.
• Metallic ring-type joint (RTJ): solid metal rings (soft iron, carbon steel, stainless, or alloy) seating into machined grooves, typically Class 600 up.

Selection starts with the flange facing already installed: an RTJ gasket cannot go on a raised-face flange, and a flat sheet gasket is wrong for a grooved RTJ face.

Gasket Factors: m and y

ASME BPVC Section VIII, Division 1, Appendix 2 assigns each gasket material two design factors for sizing bolt load. ASME B16.20 is a separate standard for gasket dimensions, not m and y.

• m, the maintenance factor: the pressure multiplier needed to keep the gasket sealing once pressurized. Soft sheet runs low (roughly 2 to 3.5); spiral wound defaults to about 3.0; solid RTJ needs the highest values (5.5 or more), since the ring must yield into the groove.
• y, the minimum seating stress: the stress needed to seat the gasket before pressure is applied. Soft sheet needs only a few MPa; spiral wound needs substantially more; RTJ needs the highest, often an order of magnitude above sheet.

These factors feed the bolt load calculation, so gasket selection and flange bolt torque must be done together. A high-y gasket torqued for soft sheet will never seat.

Typical Gasket Selection by Service

Treat this as a starting point, not a substitute for the manufacturer's data sheet and the flange rating per ASME B16.5 or B16.47. Sour and hydrogen service add material restrictions, such as NACE MR0175 / ISO 15156.

Matching Gasket to Media and Flange Facing

• Chemical compatibility: oxidizers, strong acids and some solvents attack elastomer binders in compressed fibre. PTFE and graphite-filled spiral wound resist more, but graphite is unsuitable in hot oxidizing service.
• Flange facing: raised-face flanges accept sheet or spiral wound. Flat-face flanges, common on cast iron, need a full-face sheet gasket; grooved RTJ faces need a matching ring.
• Cyclic service: spiral wound and kammprofile hold stress better under movement than sheet, key on reciprocating compressor maintenance, where valve cover joints see continuous pulsation.
• Machined finish: soft sheet tolerates a rougher flange face; RTJ and kammprofile need the groove machined to spec.

Failure Modes: Blowout and Creep Relaxation

Blowout happens when pressure and inadequate residual bolt load push the gasket sideways or extrude it from the joint, more common with soft sheet on high-pressure service, undersized gaskets, or bolts loosened by vibration.

Creep relaxation is the gradual loss of gasket thickness and stress over time, accelerated by heat. As stress drops below the m-factor requirement, the joint weeps, often first noticed as staining. Compressed fibre and elastomeric sheet are most susceptible; metallic and semi-metallic gaskets creep far less.

A gasket is a wear item with a defined re-torque and inspection interval, not install-and-forget. In a Fabrico-based CMMS workflow, each flange joint carries its own gasket spec and inspection interval, so technicians pull the right data at the job site.

Gasket Choice and Bolt Load Work Together

Gasket selection is incomplete without a matching bolt load calculation: bolt size, grade, quantity and torque must reach the joint's m and y stress uniformly around the flange. Under-torquing a correctly selected gasket leaks the same as picking the wrong gasket. On critical joints, hydraulic tensioning often replaces torque wrenching for a more even load.

See flange bolt torque for the tensioning side. To track gasket and torque specs against your flange inventory, book a Fabrico demo.

Frequently Asked Questions

Can a spiral wound gasket be used on a Class 150 raised-face flange?

Yes. Spiral wound gaskets span Class 150 to 2500 on raised-face flanges and are often chosen at lower classes when cyclic loading or heat makes sheet unsuitable.

Why does an RTJ gasket need a much higher bolt load than a sheet gasket?

It seals by the metal ring yielding plastically into the machined groove, needing far higher seating stress than a gasket that seals by conforming to surface irregularities.

How often should a bolted flange gasket be replaced?

There is no fixed interval; it depends on material, temperature and pressure cycling. As a rule, replace the gasket whenever the joint is opened, since it has already taken a compression set.

Is PTFE sheet suitable for high-temperature steam service?

Generally no. PTFE sheet is limited to roughly 260 C, and its creep resistance drops sharply near that limit. High-temperature steam is better served by a graphite-filled spiral wound gasket.