Ring-joint flange is a high-pressure flange that achieves sealing through a ring groove structure. Its sealing surface is in the shape of an annular groove, used with a metal ring gasket (such as octagonal gasket, oval gasket), suitable for high temperature, high pressure, and flammable and explosive harsh working conditions. The following is an introduction from the aspects of structure, performance, and application:

Structural Features and Sealing Principle

1. Sealing Surface Design

Ring groove structure: A ring groove (RJ surface) with a trapezoidal cross-section is machined on the flange sealing surface. The groove depth is usually 6-12mm, and the groove width is adjusted according to the pressure level and diameter (e.g., the groove width of DN100, Class 900 is about 16mm).

Gasket matching: Metal octagonal gaskets or oval gaskets (materials include low carbon steel, stainless steel, Monel alloy, etc.) are used. During installation, they are tightened by bolts, causing the gasket to embed in the groove and undergo plastic deformation, forming a metal-to-metal line contact seal. The sealing pressure can reach over 100MPa.

2. Flange Main Body Structure

It is often combined with a weld neck flange (WNRF) or integral flange (IF). The neck design is thicker to withstand bending moments and axial forces under high pressure, preventing flange deformation that could lead to sealing failure.

Core Materials and Manufacturing Process

1. Commonly Used Materials

Flange body:

Carbon steel: A105, WCB (suitable for Class 150-Class 600, temperature ≤425℃);

Alloy steel: F11, F22 (high temperature and high pressure resistant, suitable for steam pipelines, hydrogenation devices, temperature ≤540℃);

Stainless steel: 316L, 347 (corrosion resistant, suitable for chemical and seawater media);

Special alloys: Hastelloy C-276, titanium alloy (highly corrosion resistant, such as concentrated nitric acid, wet chlorine gas environments).

Gasket material: Needs to be compatible with the medium. Commonly used are 304, 316 stainless steel, or soft iron (suitable for non-corrosive media).

2. Manufacturing Process

Mainly forging (DN≤600) to ensure material density; large diameter (DN＞600) can use cast steel + machining. The groove surface needs to be precisely machined by CNC lathe or boring machine, with surface roughness Ra≤3.2μm, ensuring gasket fit.

Performance Advantages

High sealing performance: Metal hard seal structure, suitable for high pressure (up to Class 2500, about 42MPa), vacuum systems, or highly toxic media (such as phosgene, liquid ammonia), with extremely low leakage rate.

Resistance to harsh working conditions: High temperature resistance (up to 650℃), vibration resistance (such as compressor inlet and outlet pipelines), no gasket aging problem (compared to rubber gaskets), long service life.

Reusability: Under some conditions (such as small pressure fluctuations), metal gaskets can be reused, but the groove surface and gasket surface should be checked for damage.

Application Fields

Wind power industry	Shipbuilding	Mechanical manufacturing
Nuclear power industry	Oilfield industry	Chemical industry