What Is RTJ Flange?

Quick Answer

An RTJ (Ring Type Joint) flange has a precision-machined groove on its face that accepts a solid metal ring gasket. The ring deforms into the groove under bolt load, creating a metal-to-metal seal. RTJ facing is used for high-pressure, high-temperature service—typically Class 600 and above—where soft gaskets cannot maintain a reliable seal.

How RTJ Sealing Works

The RTJ groove is machined to a precise profile (R, RX, or BX per ASME B16.20). A softer metal ring sits in the groove. When stud bolts are tightened, the ring deforms plastically into the groove, filling microscopic imperfections and creating a pressure-energized seal. The ring material must always be softer than the flange groove material.

Property	Detail
Standard	ASME B16.5, B16.20 (ring gasket)
Groove types	R (octagonal/oval), RX (pressure-energized), BX (pressure-energized, higher pressure)
Ring materials	Soft iron, 304 SS, 316 SS, Inconel 625, Monel
Typical pressure classes	600, 900, 1500, 2500
Flange types	WN, blind (RTJ facing available on both)
Ring number	Standardized per ASME B16.20 (e.g., R-24 for NPS 2 Class 600)
Reusability	Ring is single-use; replaced at every joint opening

Ring Types

Ring Type	Profile	Pressure Range	Key Feature
R (oval)	Oval cross-section	Standard HP service	Line contact with groove
R (octagonal)	Octagonal cross-section	Standard HP service	Face contact (better seal)
RX	Modified octagonal	Higher pressure	Self-energizing under pressure
BX	Square cross-section with pressure passage	API 6A, wellhead	Highest pressure, vent hole

R-type rings (oval and octagonal) are interchangeable in the same groove. Octagonal rings provide a superior seal because they make face contact rather than line contact. RX and BX rings are NOT interchangeable with R-type grooves—they require specific groove profiles.

Common Mistake

Reusing RTJ rings after opening the joint. The ring deforms plastically during initial bolt-up and will not seal properly a second time. Always install a new ring at each assembly.

RTJ vs RF Facing

Feature	RTJ	RF (Raised Face)
Gasket	Solid metal ring	Spiral wound or sheet
Seal mechanism	Metal-to-metal deformation	Gasket compression
Typical class	600-2500	150-600
Bolt torque	Very high	Moderate
Cost	Higher (precision machining)	Lower
Temperature limit	>1000degF	Limited by gasket material
Flange face contact	Flanges do NOT touch (gap required)	Flanges contact gasket

Pro Tip

When tightening RTJ flanges, the metal faces must NOT contact each other. A visible gap between flange faces after bolt-up confirms the ring is properly seated in the grooves. If the faces touch, the ring may be incorrect, damaged, or the wrong size.

RTJ flanges are standard in subsea pipelines, wellhead equipment (API 6A), and high-pressure process piping in refineries and LNG plants.

Read the full guide to flanges