Understanding Lap Joint Flanges
A Lap Joint Flange consists of two components: a stub end and a backing flange. The stub end is butt-welded to the pipe, while the backing flange rotates freely around it, allowing for easy bolt hole alignment during assembly.
Design Features
- Two-piece construction: stub end + backing flange
- Backing flange rotates freely for bolt alignment
- Stub end provides pressure containment
- Available in various materials and finishes
Key Advantages
- Easy Alignment: Rotating flange simplifies bolt hole matching
- Cost Savings: Backing flange can be lower-grade material
- Quick Disassembly: Ideal for systems requiring frequent maintenance
- Reduced Installation Time: No need to rotate pipe for alignment
- Versatility: Compatible with various stub end materials
Typical Applications
- Low-pressure piping systems
- Systems requiring frequent disassembly
- Large diameter piping where alignment is challenging
- Water treatment and distribution systems
- HVAC and fire protection systems
- Process piping with expansion joints
Material Combinations
| Component | Material Options |
|---|---|
| Stub End | 304/316 Stainless, Carbon Steel, Duplex |
| Backing Flange | Carbon Steel (cost-effective option) |
Standards
- ASME B16.5: Class 150-2500
- EN 1092-1: PN6-PN100
- GB/T 9115: Chinese lap joint flange standard
Installation Tips
- Ensure stub end is properly welded to pipe
- Verify backing flange rotates freely
- Check gasket seating surface is clean
- Tighten bolts in cross pattern
Lap joint flanges offer an economical and practical solution for piping systems requiring frequent maintenance or where precise bolt alignment is challenging.
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