RTJ Ring Type Joint flanges

Single (R, RX) and double (BX) ring-joint, ANSI B16.5 / B16.20 / API 6A. Classes 150–2500. Permanent metal sealing for high-pressure service: hydrogen, ammonia, oil & gas, superheated steam. F316L, F22, Inconel 625 materials with MTR 3.1/3.2.

Metal sealing for severe service

Ring-joint RTJ flanges are the standard solution for plants where sealing must be absolute and permanent: high pressure, high temperature, hazardous fluids (hydrogen, ammonia, H2S), cryogenics. The groove on the flange face houses an oval or octagonal metal ring that, under tightening, deforms plastically and creates a metal-on-metal seal that resists over 1,000 °C, passes fire-safe tests, and maintains integrity at Class 2500 (~420 bar at ambient temperature).

Roffia supplies RTJ flanges in the full ANSI range (B16.5 and B16.47 series A/B for large diameters), in the three standard geometries R, RX, BX codified in ASME B16.20 and API 6A, with materials selected for each service: F316L for hydrogen and food, F22 for refining and steam, Inconel 625/718 for HRS and ammonia, Monel 400 for cryogenics. All flanges are supplied with MTR 3.1 as standard and 3.2 on request, reinforced dimensional control on grooves and complete heat traceability.

This page is dedicated to ring-joint flanges; for standard raised-face flanges (RF) consult ANSI/ASME raised face flanges.

Ring-joint types — standard geometries

Type Standard ANSI Classes Features
R (single ring-joint)ASME B16.20150 – 2500Oval or octagonal ring, historic geometry, interchangeable with RX. Optimal for Class 150–600.
RX (pressure-energized)ASME B16.20600 – 2500Modified octagonal ring: internal pressure pushes the ring against the walls, increasing sealing. Interchangeable with R.
BX (double ring-joint)API 6A / ASME B16.201500 – 2500 ANSI / API 6A 2,000–20,000 psiNot interchangeable with R/RX. Sealing on both sides of the ring, for very high pressures and HRS H2.

Technical specifications

Parameter Specification
Construction standardsASME B16.5 (NPS 1/2 – 24), ASME B16.47 series A/B (NPS 26 – 60), API 6A
Sealing standardsASME B16.20 (RTJ rings), API 6A (BX/SBX rings)
TypeWelding Neck (WN), Slip-On (SO), Blind, Lap Joint — all with RTJ ring-joint
DNDN 15 – DN 1500 (NPS 1/2 – 60)
Pressure classes150, 300, 600, 900, 1500, 2500 lb (ANSI). API 6A: 2,000–20,000 psi
Standard materialsA105, F11, F22, F304/L, F316/L, F347, Duplex F51 / F55, Inconel 625/718
Rings (gasket)Soft iron, F5 (5% Cr), 304/316/316L SS, Inconel 625/718, Monel 400
Groove finishRa 1.6 μm (63 μin) — certified profile control
DocumentationMTR 3.1 standard, 3.2 on request, 100% dimensional inspection, hardness test, NACE MR0175 on request

Typical applications

Hydrogen and biomethane upgrading

For high-pressure H2 plants, refining, blending, biomethane upgrading and HRS 350/700 bar. F316L or Inconel materials with 316L/Inconel rings. BX geometry for Class 1500+. See ANSI flanges for hydrogen.

Oil & Gas and refining

High-pressure hydrocarbon lines, sour service (H2/H2S), wellhead. F22, F11, Inconel 625 materials per NACE MR0175. R/RX geometry for Class 600–900, BX for API 6A pressure rating.

Superheated steam and power

Thermoelectric plants, cogeneration, process steam at temperatures >500 °C. F22, F91 materials (creep-resistant). Soft iron or F5 rings for standard services, AISI 316 for corrosive environments.

Ammonia and LNG

Anhydrous NH3 storage, LNG terminals and cryogenic liquefied gases (T down to −196 °C). 316L austenitic, Inconel 625, Monel 400 materials. SS 316 or Inconel rings.

Related components

Klinger rings and gaskets →

Klinger RTJ rings (R, RX, BX) in soft iron, SS 316L, Inconel — lot traceability and full MTR.

ANSI flanges for hydrogen →

B16.5 and B16.47 dedicated to H2 service with ISO 11114 certified materials.

Hydrogen safety valves →

PED category IV, free EN ISO 4126 sizing, Ribel brand.

Hydrogen ball valves ANSI →

Trunnion-mounted, fire-safe API 607, ANSI Class 150–1500, Ribel brand.

Domande frequenti

What are RTJ (Ring Type Joint) flanges?
Ring-joint flanges — also called RTJ (Ring Type Joint) in ANSI/ASME standard — are flanges characterized by a groove on the mating face that houses an oval or octagonal metal ring (gasket). When the flanges are tightened, the ring deforms plastically into the grooves of the two facing flanges, creating a permanent metal seal of the highest reliability. "Single ring-joint" indicates a single groove (standard R geometry of B16.5), while "double ring-joint" refers to BX or RX geometry (for higher pressures, up to Class 2500). They are the standard for high-pressure, high-temperature, hazardous gas and severe service applications: hydrogen, ammonia, LNG, refining, oil & gas, superheated steam.
Difference between simple (R) and double (RX/BX) ring-joint?
The three standard ANSI types are codified in API 6A and ASME B16.20: (1) R type — simple ring-joint, oval or octagonal section, for Class 150–2500. The historic type, still used in many standard applications. (2) RX type — pressure-energized geometry: internal pressure presses the ring against the groove walls, increasing sealing as pressure increases. Replaces R type for Class 600+ in ASME B16.20. Interchangeable with R flanges (same dimensions). (3) BX type — double ring-joint for higher pressures (Class 1500, 2500 and API 6A 2,000–20,000 psi). The ring is octagonal contacting both sides with the flange. Geometry not interchangeable with R/RX: requires dedicated BX flanges. For high-pressure hydrogen (HRS 350/700 bar) BX flanges or welded connections are typically used to eliminate the sealing point.
When to use RTJ instead of flat (RF) or spiral wound gaskets?
The choice between RF (Raised Face with flat or spiral wound gasket) and RTJ depends on pressure, temperature, fluid and criticality: Class 150–300 with spiral wound or flat gasket → adequate for standard services, low cost, simple maintenance. Class 600 → transition zone: spiral wound with centering ring for industrial services, RTJ for hazardous fluids (H2, H2S, ammonia) and high temperatures. Class 900–1500–2500 → almost always RTJ mandatory: pressure requires permanent metal seal; soft gaskets risk blow-out. Fire-safe service: RTJ recommended because metal sealing resists over 1,000 °C without degrading. Hydrogen and LNG: RTJ de facto standard for sealing on tiny molecules (H2 = 0.29 nm) and for cryogenic temperatures of LNG/liquid H2.
Standard materials for RTJ flanges and rings (ring gasket)?
Materials must be softer than the flange to deform plastically in the groove without damaging it. Standard combinations are: Soft Iron (BHN ≤ 90) — most economical material, for standard service up to 200 °C. Low alloy 4–6% Cr (F5) — for steam lines and refining. AISI 316L / 316 SS (BHN ≤ 160) — standard for hydrogen, corrosive environments, food; excellent H2 compatibility (austenitic). Inconel 625 / 718 — for severe services: high-pressure H2, H2S, ammonia, high temperature. Monel 400 — for acids and cryogenic environments. The flange must have hardness at least 30 BHN higher than the ring (rule of thumb): typically F22, F11, F316L or ASME B16.5 materials. For NACE MR0175 service (H2/H2S) limit hardness to HRC 22 max on both ring and flange.
How to correctly install an RTJ flange?
Installation is the most critical phase for sealing. Procedure: (1) Thorough cleaning of the grooves on both flanges — any particle or impact mark compromises sealing. (2) Visual inspection of grooves and ring: no dents, corrosion, residue from old rings. (3) Ring positioning in the lower groove (do not lubricate, do not use grease). (4) Flange approach ensuring perfect alignment — misalignment >0.5 mm can ruin the ring on first tightening. (5) Cross-pattern sequence tightening in progressive stages: 30%, 60%, 100% of final torque. Tightening torque must follow ASME PCC-1 standard and project-specific values (variable for Class and material). (6) Final verification: hydrostatic and/or pneumatic test per line specifications. RTJ rings are single use — never reuse a ring that has undergone previous tightening.
Does Roffia supply RTJ flanges with MTR and complete dossier?
Yes. All Roffia RTJ flanges are supplied with: MTR 3.1 certificate as standard (laboratory test on the specific material supplied) or 3.2 on request (countersigned by Notified Body), heat and lot traceability, 100% dimensional inspection on grooves (depth, width, surface finish Ra), hardness test, visual groove inspection. For hydrogen service we provide H2 compatibility declaration per ISO 11114-1, for sour service NACE MR0175 / ISO 15156 certificate with hardness verification. On request: ultrasonic test, radiographic test, liquid penetrant test on grooves, reinforced dimensional inspection for HRS or HSE-critical applications. Sector coverage includes H2, ammonia, LNG, refining, chemical, superheated steam, biomethane upgrading.

RTJ flange supply with complete dossier

Send us line specifications (DN, ANSI class, material, R/RX/BX type, fluid service, applicable standards). We supply RTJ flanges with MTR 3.1/3.2, reinforced dimensional inspection, NACE MR0175 and H2 compatibility declaration on request.

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