Pipe Flanges (ASME B16.5)
ASME B16.5 flanges in weld neck, slip on, blind, socket weld, threaded, and lap joint configurations. NPS ½"–24", Classes 150–2500, all standard materials.
Flange Types
Weld Neck (WN)
Long tapered hub, single butt weld to pipe. Preferred for high-pressure/temperature, cyclic, and critical service. Hub provides gradual bore transition and excellent fatigue resistance.
Slip On (SO)
Slips over pipe end, double fillet welded inside and outside. Lower cost than WN, suits Class 150–600 standard service. Weaker under cyclic load.
Blind (BL)
Solid plate flange used to close a pipeline end or isolate a branch. Subject to full pressure differential across its face — heavier than WN of the same size and class.
Socket Weld (SW) / Threaded (TH)
Socket weld: pipe inserts into socket, single fillet weld. Threaded: no welding, screwed to threaded pipe end. Both suited to small bore NPS ½"–2", non-corrosive service only for threaded.
Size and Pressure Classes
| Parameter | Range |
|---|---|
| Standard | ASME B16.5 (½"–24") / ASME B16.47 (26"–60") |
| Pressure Classes | 150, 300, 400, 600, 900, 1500, 2500 |
| NPS range (B16.5) | ½" to 24" (DN15–DN600) |
| Facing types | RF (raised face), FF (flat face), RTJ (ring type joint) |
| Material groups | Group 1.1–1.15 (per B16.5 Annex A) |
Materials
Carbon Steel
ASTM A105 (forgings), Group 1.1 — most common industrial piping
Stainless Steel
ASTM A182 F304/F304L, F316/F316L, F321 — corrosion-resistant service
Alloy Steel
A182 F11, F22, F5, F9, F91 — high-temperature power and process
Duplex / Super Duplex
A182 F51, F53, F60 — offshore, sour service, high-chloride environments
Calculate Flange Weight
ASME B16.5 geometric modeling — full hub + disc + raised face. Every NPS, every class, every flange type.
FAQ
Which flange type should I use — weld neck or slip on?
Weld neck flanges are the preferred choice for high-pressure, high-temperature, and cyclic service. The tapered hub provides a smooth bore transition and the single weld is easier to inspect radiographically. Slip on flanges require two welds (inside and outside), are cheaper, and suit lower-pressure, non-critical service. For any Class 600+ application, specify weld neck unless the engineer of record approves otherwise.
What does ASME B16.5 cover?
ASME B16.5 covers pipe flanges and flanged fittings from NPS ½" through 24" in Classes 150, 300, 400, 600, 900, 1500, and 2500. It specifies dimensions, tolerances, pressure-temperature ratings, materials, and marking requirements. For NPS 26" and above, ASME B16.47 (Series A and B) applies.
What is the difference between raised face (RF) and ring type joint (RTJ) facing?
A raised face (RF) flange has a raised seating surface that contacts a soft gasket (spiral wound, ring, or full face). An RTJ flange has a machined groove in the sealing face that accepts a solid metal ring gasket. RTJ is preferred for high-pressure Class 900+ or where zero leakage is required under cyclic loads. See our flange facing types guide for full details.