Loose flange with welded ring is a special flange structure that connects the welded ring and the pipe through butt welding, and the flange body can be freely fitted on the pipe. It combines high-strength connection and flexible installation characteristics, suitable for medium and high pressure, high temperature and corrosive medium scenarios. The core characteristics are analyzed below from the dimensions of structure, performance and application:

Structure Design and Working Principle

1. Core Components

Loose flange body: The inner diameter is larger than the outer diameter of the pipe, and can be freely fitted on the pipe. It does not directly participate in pressure bearing, only plays the role of pressing and sealing the gasket. The material can be low-cost carbon steel.

Welded ring (welding neck): Connected to the pipe by butt welding. Its cross-section is conical (similar to the neck of a weld neck flange), and the outer diameter is consistent with the flange sealing surface, forming the main pressure-bearing structure.

Sealing surface form: Commonly used concave-convex surface (MFM), tongue and groove surface (TG), ring groove surface (RJ) can be used in high-pressure scenarios. The sealing performance is better than that of loose flange with flat welded ring.

2. Working Principle

The pipe and the welded ring are connected by butt welding (the weld strength is equivalent to the pipe body), and the flange body seals the pipe by bolting and pressing the gasket. The conical design of the welded ring can disperse the axial force generated by the medium pressure, and improve the fatigue resistance.

Core Product Characteristics

1. Outstanding Mechanical Properties

High-strength connection: Butt welding (full penetration process) between the welded ring and the pipe. The weld strength reaches more than 90% of the pipe base material, suitable for medium and high pressure conditions of PN16-PN100 (Class 300-Class 2500).

Strong stress resistance: The conical welded ring can buffer the axial stress generated by the thermal expansion and contraction of the pipe (e.g., when the temperature difference of the steam pipe is ≥100℃), reducing the risk of weld cracking.

2. Corrosion Resistance and Cost Balance

Flexible material configuration:

Welded ring: In contact with the medium, corrosion-resistant materials (such as 316L, Hastelloy C-276) should be selected;

Flange body: Not in contact with the medium, carbon steel (Q345B) or low alloy material can be used, the cost is reduced by 40%-60% compared with the overall stainless steel flange.

Easy maintenance and replacement: The welded ring can be individually cut and replaced after corrosion, without removing the flange body and bolts, improving maintenance efficiency by 50% (such as online maintenance of chemical pipelines).

3. Convenient Installation and Disassembly

Axially slidable: The flange body can slide slightly along the axial direction of the pipe, suitable for on-site pipe alignment adjustment (e.g., when the construction error of long-distance pipelines is ≤5mm).

Easy bolt hole alignment: The body can rotate, avoiding bolt hole misalignment caused by pipe installation deviation (allowing circumferential deviation ≤2°), especially suitable for ships, offshore platforms and other vibration environments.

4. High Temperature and High Pressure Adaptability

Wide temperature range: Carbon steel welded ring ≤425℃, stainless steel welded ring ≤650℃ (such as high-temperature heat transfer oil pipeline);

Suitable for high-pressure scenarios: In Class 600 (PN100) and above conditions, the conical design of the welded ring can effectively disperse the bolt pre-tightening force, avoiding deformation of the sealing surface.

Comparison with Other Flange Types

Application Fields

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