Spiral wound and ring type joint (RTJ) gaskets both sit at the high end of the flange sealing chart, but their materials, sealing mechanics, and pressure envelopes are not interchangeable [S7]. A wrong spec between the two usually shows up as a leak on heat-up, a crushed filler, or a galled groove.
For process engineers, the material decision is binary: a solid metal ring that plastically deforms into a flange groove, or a wound metal-and-filler strip that seals under controlled compression. Both have their place; the boundary is set by pressure class, temperature swing, and media compatibility.
How RTJ and Spiral Wound Gaskets Seal Differently
An RTJ gasket works by being softer than the flange face, so the bolt load plastically deforms the ring into the groove walls and creates a metal-to-metal seal; stainless on carbon steel is a common mismatch that inverts the intended yield behaviour [S2]. The standard RTJ body material is soft iron or low carbon steel, with harder grades (304/316 SS, Monel 400, Inconel) reserved for media that would corrode the standard stock [S1][S4].
A spiral wound gasket depends on the mechanical characteristics of a formed metal spiral strip rather than the compressive virtues of a homogeneous sheet; stainless steel is the default winding, while graphite is the most common filler, with PTFE used where graphite is unsuitable [S5]. The wound body is usually contained inside an inner and outer guide ring (typically carbon steel, sometimes called a centering ring) that limits how far the bolt load can crush the windings [S6][S8].
Pressure and Temperature Operating Bands
RTJ connections become the default specification at ASME B16.5 Class 900# and above and are available through 2500#; API 6A wellhead and Christmas tree service extends the rating to 20,000 PSI, with BX rings dedicated to API 6BX flanges at 5,000 PSI and above [S4]. Above those classes, the metal-to-metal seal is the only mechanism that holds line pressure against the flange without extrusion failure.
Spiral wound gaskets with an inner ring are the more forgiving option in services with temperature or pressure cycling, shock, and vibration, where a homogeneous RTJ ring would creep and lose line contact [S3]. The wound geometry recovers small movements because the metal windings flex while the filler (graphite rated for typical oxidising service to roughly 450 deg C in steam, or PTFE capped near 260 deg C) maintains seal contact [S5].
Material Comparison Across the Two Designs
The two products diverge on at least four decision criteria. On sealing mechanism, RTJ uses plastic deformation of a solid metal ring; spiral wound uses controlled compression of a wound metal-plus-filler strip. On material, RTJ defaults to soft iron or low carbon steel with optional SS/Monel/Inconel upgrades [S1], while spiral wound pairs a stainless steel winding (most often 316L or 304) with graphite, PTFE, ceramic, or non-asbestos filler [S5]. On pressure class, RTJ is specified from ASME B16.5 Class 900# up to 2500# and into API 6A at 20,000 PSI, whereas spiral wound covers the bulk of Class 150#-600# and overlaps into 900# where bolt load is limited [S4]. On cycling behaviour, RTJ is preferred for steady-state high pressure but needs hard-on-soft material pairing to avoid galling, while spiral wound is the better match for thermal cycling, vibration, and shock-loaded lines [S2][S3].
Where Each Type Fits, and Where It Does Not
Specifying RTJ on a Class 150# or 300# raised face flange is over-engineered and often impossible because the flange face has no ring groove machined into it [S4]. The flange itself must be ordered as an RTJ face (R, RX, or BX groove per ASME B16.5 or API 6A) before an RTJ ring can even seat. Specifying a soft-iron RTJ on a stainless lined chlorine or sour (H2S) line will fail by general or pitting corrosion, so 316L, Monel 400, or Inconel 600/625 are the typical upgrades for those media [S1][S4].
Specifying a spiral wound gasket on a 2500# API 6A wellhead is equally wrong, because the bolt load will over-compress the windings and destroy the filler even with the inner and outer guide rings fitted [S5]. Within spiral wound, omitting the inner ring in a service with aggressive media exposes the graphite filler to direct process attack, which is why inner-ring SWGs are mandatory for most hydrocarbon and chemical duties [S6]. For broader flange, valve, and pump sealing decisions, the gasket selection encyclopedia entry and the expansion joint material guide give additional context on how RTJ and spiral wound fit alongside soft-cut sheet and kammprofile products.
Ring Styles, Standards, and Interchange Rules
Three RTJ ring geometries dominate the spec sheet. R-type oval and R-type octagonal both seat in the same ASME B16.20 R-groove, with octagonal preferred for new construction because it makes line contact instead of area contact with the groove walls [S4]. RX rings are pressure-energised modified octagals that drop into a standard R-groove and give better performance under thermal cycling without changing the flange [S4]. BX rings are square/rectangular, use a dedicated BX groove, and are reserved for API 6BX wellhead and tree service at 5,000 PSI and above [S4].
Spiral wound gaskets are governed by ASME B16.20 for dimensions and materials, with the filler and winding pairing chosen against ASME B16.5 flange class and the process media [S5]. Material cross-reference is straightforward: the same 316L/304 SS winding used in the wound body frequently appears as the metallic component in adjacent sealing devices, and the same graphite filler used in spiral wound gaskets often pairs with metallic winding in high-temperature piping. A common point of confusion is that an RTJ ring must be softer than the flange groove, so a 316L ring on a carbon steel flange is acceptable while a 316L ring on a 316L groove will gall rather than seal [S2].
Installation, Reuse, and Common Failure Modes
RTJ rings are single-use in practice. Once the ring has deformed into the groove, a second torque-up will not reseat cleanly because the previous plastic strain is already locked into the cross-section [S4]. Spiral wound gaskets can occasionally be re-torqued if the windings have not been over-compressed and the flange faces have remained parallel, but reuse is service-specific and most plant procedures still treat them as a single-use consumable [S5].
The two failure modes to watch for are opposites. RTJ failure typically presents as a leak at the groove wall, almost always caused by a material mismatch (hard ring on a soft groove, or galvanic incompatibility in wet service) [S2]. Spiral wound failure typically presents as a leak at the winding-filler interface or as a crushed outer ring, almost always caused by over-torque or by omitting the inner ring on a service that attacks the filler [S6]. In both cases, the root cause is a material or geometry spec error rather than a manufacturing defect.
Selection Workflow by Service Condition
A practical spec path: confirm the flange face type first (RTJ groove or raised face) before choosing the gasket style, because the face geometry locks in the option set. If the flange is ASME B16.5 Class 900# and above with a steady-state hydrocarbon or steam service, default to RTJ with soft iron for non-corrosive media or 316L/Monel/Inconel for sour, chloride, or acid service [S1][S4]. If the flange is Class 150#-600# with thermal cycling, vibration, or shock, default to a spiral wound with 316L/304 winding, graphite filler, and inner and outer guide rings of carbon steel, and consider PTFE filler only if the media is incompatible with graphite at the design temperature [S3][S5]. For balanced, repeatable torque behaviour across actuator and valve assemblies, the universal joint material pairing guide applies a similar soft-on-hard principle to a different sealing class, and is worth reading once you have locked the flange spec.
Trackable signals for the next planning cycle: ASME B16.5/B16.20 and API 6A ring and groove revisions in committee, plus the ongoing industry move toward low-carbon stainless and higher-Nickel alloys (Inconel 625, C276) for sour and CCUS service; both will tighten the material list for both RTJ and spiral wound builds in 2026-2027.
This topic is covered further in Rail-Mounted vs Aisle Stacker Cranes: Warehouse Layout Decision Guide.