Weld Neck (WN) flanges manufactured to ASME B16.5 Class 150 standards are among the most specified piping components across North American industrial facilities, chemical processing plants, and commercial mechanical systems. Designed with a long tapered hub that transitions stress directly into the connected pipe, Class 150 WN flanges provide dependable performance under low-to-medium pressure conditions.
HT PIPE supply all different types and scales of flanges. Please feel free to contact us for further product information and pricing.
Critical Engineering Parameters Explained
1. Bore Matching and Schedule Selection
Unlike Slip-On or Socket Weld flanges, a Weld Neck flange must be specified with an inside bore dimension that precisely matches the internal diameter of the matching pipe wall thickness.
Common pipe wall schedules include Standard Weight, Schedule 40, Schedule 80, Extra Strong, and Schedule 160.
Matching the inner bore eliminates steps at the circumferential weld joint, reducing turbulence and preventing localized erosion-corrosion.
2. Tapered Hub Functionality
The distinguishing feature of the WN flange is its long tapered hub profile:
Stress Redistribution: The gradual transition from the thick flange ring down to the thinner pipe wall redistributes bending stresses caused by pipe thermal expansion, pressure surges, and weight loads.
Weld Prep: The tip of the hub is machined with a standard 37.5-degree weld bevel to ensure full-penetration butt welding directly to the pipe.
3. Pressure-Temperature Ratings
While labeled as Class 150, the maximum pressure capability depends heavily on operating temperature and material selection:
Carbon Steel (ASTM A105): Standard cold non-shock rating is 285 psi at temperatures ranging from minus 20 degrees Fahrenheit up to 100 degrees Fahrenheit.
Temperature Derating: As temperatures rise to 400 degrees Fahrenheit, the pressure capability drops down to approximately 200 psi. Always consult the material pressure-temperature rating tables within ASME B16.5 for specific operational boundaries.
ASME B16.5 Fabrication Tolerances
During receiving inspection or field quality checks, verify that incoming flanges meet allowable manufacturing tolerance ranges:
Flange Outside Diameter: ±0.06 inches (approx. 1.6 mm) for sizes NPS 24 and under.
Flange Inside Bore:
NPS 1/2" through 10": ±0.03 inches (approx. 0.8 mm).
NPS 12" through 18": ±0.06 inches (approx. 1.6 mm).
NPS 20" through 24": +0.12 inches / -0.06 inches (+3.2 mm / -1.6 mm).
Overall Length Through Hub:
NPS 10" and smaller: ±0.06 inches (approx. 1.6 mm).
NPS 12" and larger: ±0.12 inches (approx. 3.2 mm).
Bolt Circle Diameter: ±0.06 inches (approx. 1.6 mm).
Bolt Hole Displacement: Maximum eccentric offset relative to the true bolt circle center line must not exceed 0.03 inches (approx. 0.8 mm).
Regional Sourcing & Local Supply Chain Management
When specifying ASME B16.5 Class 150 Weld Neck flanges for local construction and maintenance turnarounds:
Regional Availability: Ensure local stocking partners maintain adequate inventory across common carbon steel, stainless steel, and alloy material grades.
Material Traceability: Request Mill Test Reports conforming to standard EN 10204 3.1 compliance to verify chemical composition, heat treatment, and mechanical properties prior to field installation.
Logistics and Dispatch: Verify supplier capabilities for rapid jobsite delivery within project execution radii to mitigate critical path piping downtime.
