Lap Joint Flange
A Lap Joint Flange is a two-component piping connection assembly consisting of a rotatable loose ring flange and a stub end(welded permanently to the pipe).It is specifically engineered for easy bolt-hole alignment,frequent disassembly,and...
A Lap Joint Flange is a two-component piping connection assembly consisting of a rotatable loose ring flange and a stub end(welded permanently to the pipe).It is specifically engineered for easy bolt-hole alignment,frequent disassembly,and cost-effective material selection—especially for corrosive or specialty alloy piping systems,where the flange ring itself does not contact the process media.
Design&Core Features
Two-Piece Assembly:Stub end(lap end)is butt-welded to the pipe and forms the sealing face;the lap joint ring slides over the stub and is only clamped by bolts,not welded to the pipe.The ring can swivel 360°for fast bolt alignment,even on large-diameter pipes.
Sealing Configuration:Usually Flat Face(FF)or Raised Face(RF)via the stub end;gaskets sit between mating stub faces.No contact between the flange ring and fluid,allowing the ring to use lower-cost carbon steel(e.g.,ASTM A105)while the stub end uses corrosion-resistant material(e.g.,ASTM A182 304/316 stainless steel).
Radius Bore Transition:The ring’s bore has a smooth radius to fit the stub end’s flange lip,avoiding stress risers.
Reusability:The flange ring can be salvaged and reused after disassembly,reducing replacement costs for maintenance-heavy systems.
Standards&Sizes
ASME B16.5(NPS½”–24”,pressure classes 150–2500)
ASME B16.47(large diameters NPS 26”–60”)
EN 1092-1,DIN,JIS,BS for global industrial compatibility
Common materials:A105 carbon steel,A182 F304/F316 stainless steel,duplex stainless steel,alloy steel
Applications
Ideal for low-to-moderate pressure/temperature,maintenance-intensive,or corrosive systems:
Chemical processing&petrochemical plants(acid/alkali lines,stainless/non-ferrous piping)
Water/wastewater treatment,food&beverage,pharmaceutical(sanitary lines needing frequent cleaning)
Shipbuilding,offshore platforms,and modular skid systems
Piping with frequent nozzle reorientation or equipment replacement
Advantages&Limitations
Advantages
Effortless Alignment:360°rotation eliminates bolt-hole mismatch,cutting installation time for large pipes.
Material Cost Savings:Expensive alloy only needed for the stub end,not the entire flange.
Fast Maintenance:No pipe cutting/welding required for disassembly;reusable rings.
Reduced Corrosion Risk:Flange ring is isolated from aggressive media.
Limitations
Lower Fatigue&Pressure Rating:Not recommended for high-pressure(Class 1500+),high-temperature cyclic service(inferior to Weld Neck Flanges).
Dependent on Stub Weld Quality:The stub-to-pipe weld must be properly inspected(RT/UT)as it bears the pressure load.
Extra Component Cost:Requires purchasing both stub end and flange ring(offset by material savings).
