An In-depth Look at UNS N06625 Inconel 625 Ring Joint Gasket and Application Examples

author: Qishine Industry

2023-10-03

One-Minute Overview

RTJ gaskets seal by line contact under bolt load, not by a soft compressed face.
Inconel 625 resists corrosion, heat, and fatigue in sour and seawater service.
NORSOK L-005 Type IX / IX-350 calls for a corrosion-resistant alloy with a hardness cap.
One seating is final - an RTJ is not re-torqued like a spiral-wound gasket.

What an Inconel 625 Ring Joint Gasket Is

A ring joint gasket in UNS N06625 (Inconel 625) is a solid metal seal made for the highest-pressure flanged joints - wellheads, subsea trees, and pipeline risers. Forged to a ring shape and often built to the NORSOK L-005 Type IX / IX-350 specification, it seats by line contact and stays tight where soft gaskets would fail. This article covers the alloy, the ring types, how the gasket meets the flange groove, and where it is used.

Why Inconel 625

Why Inconel 625 is chosen for the ring:

Nickel-chromium-molybdenum chemistry resists pitting, crevice, and chloride stress cracking.
It keeps strength to about 980 deg C and stays tough in cryogenic cold.
Good fatigue resistance suits the thermal and pressure cycles of wellhead service.
It welds and repairs cleanly, which matters for field-modified components.

Ring Types and the NORSOK L-005 Standard

Ring type	Shape	Typical use
R	Oval or octagonal	Standard ASME B16.20 RTJ flanges
RX	Octagonal, pressure-energized	Higher pressure within B16.20
BX	Octagonal, full bore	API 6BX wellhead and choke
IX / IX-350	Corrosion-resistant alloy ring	NORSOK L-005 sour and subsea

How the Ring Seals

How the ring actually seals:

The ring sits in a precision-machined groove on the flange face.
Bolt load drives the ring into the groove until it makes line contact on both sides.
That metal-to-metal line carries the full pressure without a soft filler.
Once plastically seated, the joint is made up and not re-torqued in service.

Where It Is Used

Where it earns its cost:

Subsea trees and templates exposed to seawater and H2S.
Wellhead and Christmas-tree flanges rated to API 6A / 6BX.
Pipeline risers and tie-in spools on offshore structures.
Heat exchangers and reactors with high pressure and corrosive fluid.

Sizing and Hardness Rules

Sizing and hardness you must respect:

Match the ring number and style to the flange groove - R, RX, BX, or IX do not interchange.
The gasket must be softer than the flange so the ring deforms, not the groove.
For IX-350 the hardness is capped (about 350 HB) to protect the mating face.
Confirm material cert (EN 10204 3.1) names UNS N06625 and the heat.

Installation Notes

Install so it seats once:

Clean the groove; no old sealant, scale, or debris that would stop full seating.
Lubricate the ring lightly so it slides into the groove without galling.
Torque the bolts in a cross pattern to the flange specification, in passes.
Do not reuse a ring that has already been plastically seated - fit a new one on breakout.

FAQ

What is the difference between R, RX, BX, and IX rings?

R is the classic oval or octagonal ring for ASME B16.20; RX is pressure-energized; BX is full-bore for API 6BX wellhead; IX / IX-350 is the NORSOK L-005 corrosion-resistant alloy ring for sour and subsea.

Why Inconel 625 and not soft iron?

Soft iron seals well but rusts in seawater and sour gas; Inconel 625 keeps the ring intact and corrodible-free in those services.

Can I re-torque an RTJ gasket?

No. Once the ring has plastically seated to the groove, the joint is made up; you fit a new ring on breakout rather than re-torque the old one.

What does IX-350 mean?

It is the NORSOK L-005 ring style (IX) with a hardness cap around 350 HB, so the corrosion-resistant ring stays softer than the flange face.

Do RTJ and spiral-wound gaskets interchange?

No. An RTJ needs a ring groove; a spiral-wound needs a different facing and a centering ring. Match the gasket to the flange facing.

How do I verify the material on delivery?

Read the marking and match it to an EN 10204 3.1 certificate that names UNS N06625 and the heat number, plus the hardness value.

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