What Is an RTJ Metal Ring Gasket?
An RTJ gasket is a solid metallic sealing ring with a precision-machined cross-section.
The gasket is installed into the ring groove of an RTJ flange. When the flange bolts are tightened, the ring gasket is compressed between the mating groove surfaces.
The sealing mechanism relies primarily on:
Controlled Metal Deformation + Contact Pressure + Pressure Containment
As the internal pressure increases, the sealing system can maintain a high contact pressure when the correct gasket, flange groove and installation procedure are used.
This makes RTJ sealing particularly suitable for demanding pressure applications.
Important:
An RTJ gasket must be used with a matching RTJ flange groove.
It is not a replacement for an RF or FF gasket.
A conventional raised-face flange does not have the ring groove required to accommodate an RTJ gasket.
Main Standards
The two most important standards for this type of product are:
ASME B16.20
ASME B16.20 – Metallic Gaskets for Pipe Flanges
The standard covers metallic ring-joint gaskets as well as spiral-wound and metal-jacketed gaskets. For ring-joint gaskets, it defines requirements such as:
Materials
Dimensions
Tolerances
Marking
Ring gasket types
Hardness requirements
ASME states that its ring-joint gaskets are dimensionally suitable for use with the referenced flange standards, including ASME B16.5, ASME B16.47 and API 6A.
API 6A
API Specification 6A – Wellhead and Tree Equipment
API 6A is particularly important for oil and gas wellhead and Christmas tree equipment.
The specification contains requirements for ring gaskets used with API 6A flange connections, including R, RX and BX gasket types. API's current 6A information identifies the specification as covering wellhead and tree equipment and includes quality requirements for ring gasket materials and related components.
RTJ Flange vs RF Flange
One of the most important points when selecting an RTJ gasket is understanding the difference between RTJ and Raised Face (RF) flanges.
|
Item |
RTJ Flange |
RF Flange |
|
Sealing surface |
Machined ring groove |
Raised flat sealing face |
|
Gasket location |
Inside ring groove |
On raised face |
|
Typical gasket |
Metallic RTJ ring |
Spiral wound, graphite, soft gasket, etc. |
|
Sealing mechanism |
Metal-to-metal ring sealing |
Gasket compression |
|
Typical application |
High-pressure service |
General pressure piping |
|
Common applications |
Oil & gas, wellhead, high-pressure piping |
Process piping, chemical, utility systems |
RTJ Ring Gasket Types
The three major RTJ gasket configurations are:
Type R
Type RX
Type BX
However, the selection is determined by the mating flange design and applicable standard.
Type R Ring Gasket
The R Type RTJ gasket is one of the most common ring-joint gasket designs.
It is manufactured with either:
Oval cross-section
Octagonal cross-section
Type R gaskets are commonly used in conventional RTJ flange connections.
Under API 6A, R and RX gaskets are used with 6B flanges.
Oval vs Octagonal RTJ Gaskets
R-type ring gaskets are commonly available in oval and octagonal cross-sections.
Oval RTJ Gasket
The oval ring has a curved sealing profile.
It is an established RTJ design used with compatible flange grooves.
Octagonal RTJ Gasket
The octagonal gasket has a polygonal cross-section and provides controlled contact between the gasket and groove surfaces.
When ordering, customers should specify the exact gasket type and applicable standard rather than simply requesting an "RTJ gasket."
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Typical applications
High-pressure piping
Oil and gas pipelines
Refineries
Petrochemical equipment
Process piping
Valve connections
Main features
Simple metallic construction
Precision-machined sealing surface
Good high-pressure sealing performance
Available in multiple materials
Suitable for repeated industrial applications when properly specified
Type RX RTJ Gasket
The RX gasket is a pressure-energized ring gasket design.
As system pressure increases, internal pressure acts on the gasket configuration and contributes to the sealing force.
This provides a useful pressure-energizing effect in high-pressure applications.
API 6A specifies that R and RX gaskets are used with 6B flanges, while BX gaskets are reserved for 6BX flanges. It also states that RX and BX are pressure-energized designs but are not interchangeable.
Typical applications
High-pressure oil and gas systems
Wellhead equipment
Christmas tree equipment
High-pressure valves
Drilling and production equipment
Advantages
Pressure-energized sealing
Suitable for demanding pressure service
Designed for compatible API 6A flange systems
Improved sealing capability as internal pressure increase
Type BX RTJ Gasket
BX RTJ gaskets are designed specifically for 6BX flange connections.
This is an important distinction:
6BX flange → BX gasket
According to API 6A, only BX gaskets shall be used with 6BX flanges. RX and BX gaskets are not interchangeable.
BX gaskets are commonly associated with very high-pressure wellhead and production equipment.
Typical applications
6BX wellhead flanges
High-pressure wellhead equipment
Christmas trees
High-pressure valves
Oil and gas production equipment
Critical pressure-containing connections
BX gaskets also incorporate a pressure-passage feature in their design. API 6A specifies a pressure-passage hole for BX gaskets, along with dimensional and surface-finish requirements.
|
Feature |
R |
RX |
BX |
|
Cross-section |
Oval / Octagonal |
Special pressure-energized profile |
Pressure-energized profile |
|
Typical API flange |
6B |
6B |
6BX |
|
Pressure energizing |
Conventional |
Yes |
Yes |
|
Typical use |
High-pressure piping |
High-pressure wellhead |
Very high-pressure wellhead |
|
Interchangeable with BX? |
No |
No |
No |
|
Typical standard |
ASME B16.20 / API 6A |
ASME B16.20 / API 6A |
ASME B16.20 / API 6A |
RTJ Gasket Materials
RTJ gaskets are manufactured from metallic materials selected according to:
Flange material
Operating temperature
Pressure
Process medium
Corrosion environment
Sour-service requirements
Required hardness
Common materials include:
Soft Iron
Soft iron is commonly used for suitable carbon-steel flange applications.
Its relatively low hardness helps protect the flange sealing groove while allowing the gasket to deform sufficiently during assembly.
Low-Carbon Steel
Low-carbon steel ring gaskets can be used for certain conventional applications where the temperature, pressure and medium are compatible with the material.
316 Stainless Steel
316 stainless steel provides improved corrosion resistance compared with carbon steel and may be selected for corrosive service.
Nickel Alloys
Nickel-based alloys may be required for severe corrosion or sour-service environments.
For example, API 6A's ring-gasket marking requirements identify nickel alloy UNS N08825 and other corrosion-resistant alloy materials among the possible gasket material designations.
Gasket Hardness Is Critical
One of the most important technical requirements for an RTJ gasket is hardness control.
The gasket should generally be softer than the mating flange sealing surface so that the gasket can deform and establish the required sealing contact without damaging the flange groove.
Therefore, when selecting an RTJ gasket:
Gasket Hardness < Flange Groove Hardness
The exact hardness limits should be determined according to the applicable standard and project requirements rather than using a universal hardness value.
ASME B16.20 includes specific maximum hardness requirements for ring gaskets.
API 6A also requires records for ring gaskets covering items including chemical analysis/heat number, hardness testing, job-lot traceability and dimensional inspection.
RTJ Gasket Manufacturing Process
A typical manufacturing process is:
Raw Material → Material Verification → Forging / Bar Stock Preparation → Heat Treatment → CNC Machining → Groove/Profile Machining → Surface Finishing → Dimensional Inspection → Hardness Testing → PMI → Marking → Final Inspection → Packaging
For critical oil and gas applications, traceability should be maintained from the raw material through the finished gasket.
Can RTJ Gaskets Be Reused?
No. RTJ ring gaskets should generally not be reused.
The gasket is designed to deform into the flange groove during installation. Reusing a previously compressed ring can compromise sealing performance.
The referenced API 6A requirements explicitly state that ring gaskets have limited positive interference and shall not be reused.
Therefore, when a flange connection is opened during maintenance, a new compatible RTJ gasket should normally be installed.
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