What Is an ASME B16.5 Slip-On Flange?
A slip-on (SO) flange slips over the pipe and is attached by two fillet welds, one on the outside and one on the inside of the hub. Covered by ASME B16.5, it requires less accurate pipe cutting than a weld neck flange and is easier to align, making it a common economical choice for low-to-medium pressure service.
Size & Pressure Class Range
- Sizes: NPS 1/2 through NPS 24, in Classes 150 through 2500
- Connection: pipe slips through the bore (dimension B2), welded outside and inside
- Standard bore: counterbored to clear the pipe OD with running clearance
Pressure-Temperature Ratings (Group 1.1 Carbon Steel, at 38°C)
| Class | 150 | 300 | 400 | 600 | 900 | 1500 | 2500 |
|---|---|---|---|---|---|---|---|
| Rating, bar | 19.6 | 51.0 | 68.0 | 102.0 | 153.1 | 255.1 | 425.1 |
Materials & Temperature Limits
| Material | Grade | Temperature Range |
|---|---|---|
| ASTM A105 | Carbon steel forging | -29°C to 425°C |
| ASTM A182 | F304 / F304L / F316 / F316L | Up to 538°C |
| ASTM A350 | LF2 | -46°C to 425°C (low-temperature service) |
Dimensions
Slip-on flange dimensions (outside diameter O, minimum thickness tf, hub diameter X, hub length Y and slip-on bore B2) are given per class in the dimensional tables of ASME B16.5-2025: Table 8 (Class 150), Table 11 (Class 300), Table 14 (Class 400), Table 16 (Class 600), Table 18 (Class 900), Table 20 (Class 1500) and Table 22 (Class 2500), SI units. Raised face is 1.5 mm on Classes 150/300 and 2.0 mm on higher classes unless otherwise specified.
Related Standards
- ASME B16.5 — Pipe Flanges Overview (NPS 1/2–24)
- ASME B16.5 Weld Neck Flanges
- ASME B16.5 Blind Flanges
- ASME B16.5 Socket Weld Flanges
- ASME B16.21 — Nonmetallic Flat Gaskets
- Our Flange Range
- ASTM A105 Carbon Steel Forgings
FAQ
How is a slip-on flange welded?
The pipe passes through the flange bore and the joint is made by two fillet welds — one around the outside and one around the inside of the hub. Full penetration butt welding is not used on slip-on flanges.
What pressure classes are slip-on flanges available in?
ASME B16.5 covers slip-on flanges from Class 150 through Class 2500, sizes NPS 1/2 to NPS 24. They are most commonly used in Classes 150 and 300.
What is the difference between slip-on and weld neck?
A weld neck flange is butt-welded with one inspectable full-penetration weld and handles high cyclic loads; a slip-on flange uses two fillet welds, is cheaper and easier to fit, but is limited to moderate service and is not typically radiographically inspected.
Which materials do you supply?
A105 carbon steel, A182 F304/F304L/F316/F316L stainless steel and A350 LF2 low-temperature carbon steel, forged to the corresponding ASTM specifications.
Can slip-on flanges be used with lap joint stub ends?
No — a lap joint flange is a separate, rotatable loose flange designed to bear against a stub end. Slip-on flanges are permanently welded to the pipe.