Lap Joint Flange

Lap Joint Flange is a detachable pipeline connection composed of a flange ring and a flanged short section. The flange ring can be freely fitted onto the flanged short section and sealed by bolt fastening. It is widely used in low-pressure, corrosive media or pipeline systems that require frequent disassembly. Its core advantages are flexible installation, adaptability to slight displacement of pipelines, and low maintenance costs.

Structure and Composition

The loose flange consists of two parts:

Flange ring: usually a flat ring with an inner diameter slightly larger than the outer diameter of the pipeline, without a long neck design. The material can be selected from carbon steel (A105), stainless steel (304/316), etc., and even different materials from the pipeline can be used (such as expensive corrosion-resistant alloys for pipelines and carbon steel for flange rings to save costs).

Flanged short section: a short pipe with a flanged edge, the flanged part is in contact with the sealing surface of the flange ring, and the material needs to be consistent with the pipeline (to ensure corrosion resistance). The thickness of the flanged edge is usually 1.5 times the wall thickness of the pipeline to ensure sealing strength.

During installation, the flange short section is welded to the pipeline, and the flange ring is fitted onto the flange. The flange ring is tightened with bolts to achieve sealing with the flange. The sealing surface is mostly flat (FF) or protruding (RF), and is compatible with non-metallic gaskets (such as rubber and PTFE).

Performance characteristics

Flexible installation: The flange ring can slide axially along the flanged short section, allowing for ± 3mm axial displacement or slight angular deviation of the pipeline, reducing installation stress, and suitable for scenarios with large temperature differences.

Cost controllable: The flange ring can be made of low-cost materials, and only the flanged short section uses corrosion-resistant materials. Especially in large-diameter (DN500 or above) or high alloy pipeline systems, the cost is 40% -60% lower than that of welded flanges.

Easy to maintain: When disassembling, simply loosen the bolt to remove the flange ring, without cutting the pipeline, making it easy to replace gaskets or inspect the interior of the pipeline.

But its pressure resistance level is relatively low (usually Class 150 to Class 300, corresponding to 1.6-5.0MPa), and the strength of the flange part is weak, which is not suitable for systems with high pressure or severe vibration.

Applicable scenarios

Corrosive medium pipelines in the chemical industry (such as conveying hydrochloric acid and sulfuric acid, using 316L stainless steel for flanged short sections, and carbon steel for flange rings);

Low temperature pipelines (such as LNG storage tank connecting pipes, adapted to cold shrinkage displacement);

Municipal water supply and drainage, sewage treatment system (with high demand for frequent maintenance).