Stainless Steel Flanges: Weld Neck, Slip-On, Blind, Socket Weld and How to Order Right

Stainless steel flanges are the most-ordered connection component in process piping — and also one of the most commonly mis-specified. Order the wrong flange type, pressure class or facing and your pipe spool won't mate up on site, or worse, leaks under pressure.

This guide covers the five flange types buyers ask for most, the standards that govern them (ASTM A182, ASME B16.5, EN 1092-1), pressure-temperature classes, facing types, and a step-by-step ordering checklist.

The Five Flange Types Buyers Specify

Choosing rule: for anything above class 300 or subject to bending/fatigue, specify weld neck. For utility lines up to class 150, slip-on is fine and cheaper.

Standards and Pressure Classes

Pressure classes (ASME): Class 150, 300, 600, 900, 1500, 2500. A flange's allowable pressure drops as temperature rises — always check the pressure-temperature rating chart for your design temperature, not just the class number.

Common Flange Grades

L vs non-L: for welded flanges, specify the L (low carbon) grade. Non-L 316 can sensitize in the heat-affected zone and lose corrosion resistance.

Facing Types

• Raised Face (RF) — most common; a raised ring concentrates gasket load
• Flat Face (FF) — for cast-iron or full-face gasket connections; never mate RF to FF without a spacer
• Ring Type Joint (RTJ) — metal ring in a groove for very high pressure (class 600+)
• Tongue & Groove / Male-Female — for specific gasket styles

Match the facing and gasket to your service: RF with spiral-wound gasket is the workhorse; RTJ for high-pressure hydrocarbons.

How to Write a Flange Enquiry

1. Type (WNRF / SORF / BLRF / SWRF)
2. Nominal size (NPS) and schedule of the connecting pipe
3. Class (150 / 300 / 600 …)
4. Standard (ASME B16.5 or EN 1092-1 — they are not interchangeable!)
5. Facing (RF / FF / RTJ) and gasket style if known
6. Grade + UNS (L-grade for welding)
7. Bore: standard (B16.5) vs long-stem / reducing if needed
8. Certification: EN 10204 3.1 minimum, 3.2 for code work, NACE if sour

Europe vs US trap: EN 1092-1 PN-flanges (PN10/16/25/40) do not dimensionally match ASME class flanges. Mixing them is the single most common flange ordering error on export projects.

Frequently Asked Questions

What's the difference between flange class and pressure? Class is a nominal rating; the actual allowable pressure depends on temperature. A Class 300 flange holds ~51 bar at 38°C but less at 200°C — read the rating chart.

Can I weld 316 flange to 316L pipe? Yes — 316L pipe with a 316 (or 316L) flange is normal and acceptable; the low-carbon piped side avoids sensitization.

Do you stock both ASME and EN flanges? Yes — we stock ASME B16.5 (Class 150–1500) and EN 1092-1 (PN10–PN40) in 304/316L and duplex, with 3.1 MTCs.

What lead time for exotic-grade flanges? 316L/304L from stock (days). Duplex, 904L, nickel alloy and large sizes: typically 3–8 weeks.

Order Stainless Steel Flanges

Shanghai Hangbo Alloy Group supplies weld neck, slip-on, blind, socket weld and lap joint flanges in 304/316L, 321/347, duplex 2205/2507, 904L and nickel alloys, to ASTM A182 / ASME B16.5 / EN 1092-1 with EN 10204 3.1/3.2 certification. Send type, NPS, class, facing and grade — we quote within 24 hours, including MTC preview.