How to specify Alloy 825 flanges to ASTM B564
Alloy 825 flanges are forged to ASTM B564 UNS N08825 (ASME SB-564) and supplied annealed. Dimensions follow ASME B16.5 up to NPS 24 and B16.47 Series A or B above it, in Class 150 to 2500. Specify type, size, class, facing, bore schedule and certificate.
Material: ASTM B564
Types of 825 flange
| Type | Use | Page |
|---|---|---|
| Weld neck (WN) | High pressure and cyclic service; butt-welded to pipe | 825 weld neck |
| Slip-on (SO) | Lower pressure; fillet-welded inside and out | 825 slip-on |
| Blind (BL) | Closing pipe ends and nozzles | 825 blind |
| Socket weld (SW) | Small-bore high-pressure lines | 825 socket weld |
| Lap joint (LJ) | With an 825 stub end; backing flange can be a cheaper alloy | 825 lap joint |
| Threaded, orifice, spectacle blind | Special duties | All 825 flanges |
Dimensions and pressure classes
ASME B16.5 covers NPS ½ to 24 in Class 150, 300, 400, 600, 900, 1500 and 2500. Above NPS 24, ASME B16.47 applies in Series A or Series B — the two do not bolt together, so the series must be stated. Alloy 825 has its own pressure–temperature ratings in B16.5 (Table 1A lists it in material group 3.8); check the rating at your design temperature rather than assuming the carbon-steel value.
Facing and finish
- Raised face (RF) is standard; flat face (FF) mates with cast or non-metallic flanges.
- Ring-type joint (RTJ) for high-pressure service, with the groove matched to the ring number.
- Serrated finish on the gasket face to suit spiral-wound or sheet gaskets.
Ordering checklist
- ASTM B564 UNS N08825 (ASME SB-564)
- Type, size and class — e.g. WNRF 6" Class 300
- Bore schedule to match the pipe (weld neck), e.g. Sch 40S
- Dimensional standard: B16.5, or B16.47 Series A / B
- Facing and finish
- Certificate EN 10204 3.1 / 3.2; NACE compliance if sour service
Bolting for 825 flanges
Stud bolts and nuts are chosen for the service: B7/2H for non-corrosive external conditions, B8M or duplex where corrosion is a concern, or 825 / 625 bolting for full alloy match. See 825 fasteners.