The ASME B16.5 Class 150 Lap Joint (LJ) Flange is a specialized design engineered to cut structural costs, streamline bolt-hole alignment, and solve the unique challenges of exotic alloy piping systems.
- The Lap Joint Flange (Backing Flange): A metallic ring with an internal bore designed with a radius along the back edge. This radius accommodates the matching fillet of a companion stub end. The flange slips freely over the pipe before the stub end is attached.
- The Stub End: A short length of pipe featuring a flared outer lip (the "lap"). The stub end is butt-welded directly to the process piping. The outer face of the stub end provides the actual gasket seating surface.
HT PIPE supply all different types and scales of flanges. Please feel free to contact us for further product information and pricing.
Why Use a Lap Joint Design?
1. Rotational Alignment Freedom
In fixed-flange piping assemblies (such as weld necks), the bolt holes are locked in place once the flange is welded to the pipe. If the bolt holes are misaligned by even a few degrees during shop fabrication, field crews will face fit-up issues when connecting to valves, vessels, or existing runs.
Because a lap joint flange spins freely on the pipe axis, field technicians can rotate the flange to match any orientation. This rotational freedom eliminates bolt-hole misalignment stress during final tie-ins.
2. Significant Material Cost Reductions
In corrosive or ultra-high-purity applications, process piping requires expensive alloy materials such as 316/316L Stainless Steel, Duplex 2205, Hastelloy, or Titanium. Using standard weld neck or slip-on flanges means the entire heavy forging must be made from these high-cost alloys.
The lap joint configuration separates these duties:
- The Stub End (wetted) is fabricated from the required corrosion-resistant alloy.
- The Backing Flange (non-wetted) can be made from economical ASTM A105 Carbon Steel or A36 structural carbon steel.
On large-diameter projects or lines using exotic metals, this design approach cuts material procurement costs dramatically.
3. Simplified Maintenance and Inspection Protocols
Piping loops exposed to abrasive slurries or severe corrosion require frequent visual inspections and regular component replacement. A lap joint connection speeds up these workflows. Technicians can loosen the bolts, slide the backing flange away from the joint, inspect the butt-weld and internal lining, or swap out worn components without cutting the pipe line.
ASME B16.5 Class 150 Lap Joint (LJ) Flange
