Slip-On Flange
Slip-on flanges are designed to slide over the pipe end and are then fillet welded both inside and outside to secure the connection. This design offers lower material cost and easier alignment compared to weld neck flanges, making them popular for low to medium pressure utility and water service applications. The slip-on design reduces the accuracy needed in pipe cutting, as the pipe can be adjusted slightly within the flange bore before welding.
Our slip-on flanges are manufactured to ASME B16.5 with flat face (FF) or raised face (RF) options. They are available in Classes 150 through 1500, though they are most commonly used in Class 150 and Class 300 services. While they require two fillet welds and have a slightly lower fatigue life than weld neck flanges, they remain one of the most economical and widely used flange types in industrial piping.
ASME B16.5 / EN 1092-1
ASTM A105
DN15-DN1200, Class 150-1500
Applications
- Water distribution and utility piping
- Low-pressure steam and condensate lines
- Cooling water systems
- Fire protection piping
- General industrial process piping
Quality Assurance
All Slip-On Flange products undergo NDT testing with MTC per EN 10204 3.1. Third-party inspection by SGS, BV, TUV available.
Slip-On Flange Technical Specifications
Slip-on flanges (SO flanges) slide over the pipe and are attached with two fillet welds (one at the flange face, one at the hub). They offer easier alignment than weld neck flanges and are the most economical choice for low to medium pressure applications.
| Parameter | Specification |
|---|---|
| Standard | ASME B16.5 / EN 1092-1 Type 01 / JIS B2220 |
| Size Range | DN15 (1/2") to DN1200 (48") |
| Pressure Class | Class 150, 300, 600 (not recommended above Class 600) |
| Face Type | Raised Face (RF) standard, Flat Face (FF) for cast iron mating |
| Hub Type | Low hub (SO) or no hub (plate flange variant) |
| Material Grades | ASTM A105, A234 WPB, F304/F316, A350 LF2 |
| Welding | Double fillet weld (inside and outside), no bevel preparation needed |
Manufacturing Process
Slip-on flanges are produced through plate cutting and forging, offering faster production and lower cost than weld neck flanges:
- Plate Forging: Forged from round bar or cut from certified steel plate (ASTM A105, A516 Gr.70 for plate).
- Rough Turning: CNC lathes machine the flange blank to approximate dimensions, creating the hub and bore.
- Bore Sizing: The inside diameter is bored to slip-fit the pipe OD (typically 1.5-3mm clearance for alignment).
- Bolt Hole Drilling: CNC drilling per ASME B16.5 bolt circle patterns, with through-holes or tap-holes.
- Face Machining: Raised face or flat face finish to 125-250 Ra roughness.
- NDT Testing: Magnetic particle testing on all surfaces, ultrasonic testing on plate-cut flanges to detect lamination.
Slip-on flanges are marked with size, class, material grade, and heat number per MSS SP-82. MTC 3.1 certificates are provided with every shipment.
Installation & Welding Guidelines
Slip-on flange installation requires proper fillet welding technique for reliable service:
Welding Requirements
- Slide flange over pipe, leave 1.5-3mm root gap between pipe end and flange face.
- Back weld (inside fillet) first, then front weld (outside fillet) to minimize distortion.
- Fillet weld leg size should equal 1.4 times the pipe wall thickness for full strength.
- Use WPS per ASME Section IX; preheat not typically required for carbon steel at ambient above 5C.
Advantages & Limitations
- Advantage: easier pipe alignment, lower cost, faster welding, allows minor length adjustments.
- Limitation: not suitable for high-pressure cyclic service, lower fatigue resistance than butt-welded joints.
- Per ASME B31.3, slip-on flanges are limited to Category D service (non-hazardous, low pressure).