Zhejiang Chengjiu Pipeline Co., Ltd. is one of the most reliable manufacturers and suppliers of ansi slip on flange in China, also supports customized service. Please feel free to buy high quality ansi slip on flange from our factory. Good service and reasonable price are available.
An ANSI slip on flange is a forged pipe flange that slides over the pipe end and is secured by two fillet welds - one at the hub face and one inside the bore. Manufactured to ASME B16.5, it is available in pressure Classes 150 through 2500 and in nominal pipe sizes from 1/2" to 48". CNCJ produces these flanges in stainless steel grades SS304, SS316, SS304L, SS316L, SS321, and duplex alloys, making them suitable for demanding service in oil & gas, chemicals, water treatment, and marine piping systems.
1. What Is an ANSI Slip On Flange?
A slip-on flange (also written as SO flange) is distinguished by its inner bore diameter, which is sized slightly larger than the outer diameter of the mating pipe. This design allows the pipe to slip inside the flange hub before welding, reducing alignment demands during installation.
How the two-weld attachment works
Once positioned, the installer places one fillet weld at the top of the hub (where the pipe end meets the flange face) and a second fillet weld inside the bore. The dual-weld joint prevents fluid from entering the gap between pipe and flange, significantly reducing leak risk. This welding method delivers approximately two-thirds the strength of a weld neck flange, making it ideal for moderate-pressure services.
Governing standard: ASME B16.5
ASME B16.5 is the primary dimensional standard covering pipe flanges and flanged fittings for NPS 1/2" through 24" across pressure classes 150 to 2500. The standard defines bore tolerances, hub dimensions, bolt-hole patterns, raised face dimensions, and acceptable materials for each pressure class.
2. Key Specifications & Dimensions (ASME B16.5)
The table below summarises the principal dimensional parameters buyers need when ordering an ANSI slip on flange to B16.5.
|
Parameter |
Value / Range |
|
Standard |
ANSI / ASME B16.5 |
|
Type |
Slip-On (SO) |
|
Pressure Class |
150# · 300# · 400# · 600# · 900# · 1500# · 2500# |
|
Nominal Pipe Size (NPS) |
1/2" to 48" (DN15 to DN1200) |
|
Face Types |
Raised Face (RF) · Flat Face (FF) · Ring Type Joint (RTJ) |
|
Materials |
SS304 · SS316 · SS304L · SS316L · SS321 · SS310 · 2205 · 2507 · 254SMO |
|
Bore Tolerance |
Inner diameter slightly larger than pipe OD (per B16.5 Table) |
|
Certifications |
CE · ISO 9001 · SGS · PED available |
Pressure-temperature ratings
Under B16.5, pressure ratings are tied to both the flange class and the material group. For example, a Class 150 SS316 flange is rated at 275 psi (19 bar) at 100 °F (38 °C), while a Class 600 SS316 flange at the same temperature is rated at 1,450 psi (100 bar). Engineers must confirm the combined pressure-temperature condition against B16.5 Table 2 before selecting a pressure class.
Bore and hub dimensions
The bore inside a slip-on flange hub is drilled approximately 1/16" (1.6 mm) larger than the pipe's outer diameter. Hub length varies by pressure class - Class 150 hubs are shorter, while Class 900 and above feature taller hubs to accommodate the larger fillet welds required at higher pressures.
3. Material Options
CNCJ manufactures stainless steel ANSI slip-on flanges in the following alloy groups:
Austenitic Stainless Steel
SS304 / 1.4301 - general corrosion resistance, food-grade and water systems
SS304L / 1.4306 - low-carbon grade, reduces sensitisation risk post-welding
SS316 / 1.4401 - added molybdenum for chloride and acid resistance
SS316L / 1.4404 - low-carbon SS316; preferred for chemical process piping
SS321 / 1.4541 - titanium-stabilised for high-temperature service up to 850 °C
SS310 / 1.4845 - high-temperature oxidation resistance up to 1050 °C
Duplex & Super Duplex
2205 (UNS S31803) - balanced austenite/ferrite microstructure; excellent SCC resistance
2507 (UNS S32750) - higher chromium and molybdenum; oil & gas subsea service
254 SMO (UNS S31254) - 6% Mo; seawater and aggressive chloride environments
For full chemical composition and mechanical properties → check our Material Data Sheet
4. Face Types: RF, FF, and RTJ
Raised Face (RF)
The most common face type. A circular raised ring (1/16" for Class 150/300; 1/4" for higher classes) concentrates gasket load and improves sealing. Compatible with spiral-wound, ring, and sheet gaskets.
Flat Face (FF)
Used when connecting to cast iron or plastic flanges to prevent bending stress. The entire flange face contacts the gasket, distributing bolt load over a larger area.
Ring Type Joint (RTJ)
A machined groove in the flange face accepts a metallic ring gasket. RTJ faces are specified for high-pressure, high-temperature services (Class 600 and above) in oil & gas and petrochemical plants.
Why Choose CNCJ for ANSI Slip On Flanges?
- Full in-house forging, heat treatment, machining, and surface finishing - no subcontracting of critical processes.
- EN 10204 3.1/3.2 MTRs; hydrostatic testing, PMI, PT/MT/UT NDT all available.
- Covers ASME B16.5, ASME B16.47, EN 1092-1, JIS B2220, DIN 2527, GOST standards in one facility.
- Custom sizes, special alloys (Duplex, Super Duplex, 904L), and non-standard face machining accepted.
Process Flow
FAQ
Q: What is the difference between a slip-on flange and a socket weld flange?
A: Both designs slip over the pipe, but a socket weld flange has a deeper internal socket that accepts the pipe to a precise depth, with only one external fillet weld required. Socket weld flanges are rated for smaller bore sizes (typically NPS 3" and below) and higher-pressure applications than equivalent slip-on types. Slip-on flanges use two fillet welds and are available across the full NPS range.
Q: Can ANSI B16.5 slip-on flanges be used in Class 900 or Class 1500 service?
A: B16.5 permits slip-on flanges up to Class 2500, but most piping engineers recommend weld neck flanges for Class 900 and above. At those pressure levels, the tapered bore of a weld neck provides better stress distribution and allows radiographic inspection of the butt weld - neither of which is possible with a fillet-welded slip-on.
Q: What gasket should I use with a raised face ANSI slip-on flange?
A: For Class 150 and 300 in water or low-pressure gas service, a full-face or ring gasket in EPDM, PTFE, or non-asbestos compressed fibre is standard. For higher classes and process fluid services, a spiral-wound metallic gasket (304/316 SS winding, graphite filler) conforming to ASME B16.20 is recommended.
Q: How do I confirm the bore size when ordering?
A: The bore inside diameter is set by the nominal pipe size (NPS) and pipe schedule (wall thickness). For most standard schedules, ASME B16.5 Table A1 defines the exact bore per pipe size. When ordering, specify NPS, pressure class, pipe schedule, and whether the bore should be drilled to pipe OD or a specific ID. CNCJ can also custom-bore to your drawing.
Q: Do you supply mill test reports (MTRs)?
A: Yes. Material test reports (MTR / MTC) showing chemical composition and mechanical properties to ASTM A182 or equivalent are supplied with every order as standard. EN 10204 Type 3.1 inspection certificates are available on request.
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