Views: 1 Author: Monica Publish Time: 2026-03-09 Origin: Site
Slip On Flange, also called SO Flange, is a type that slides over the pipe before being welded into place. The pipe inserts completely into the inner bore of the flange, which has a diameter slightly larger than the outside diameter of the pipe to allow for easy insertion.
In this article, we will introduce various types of sliding flanges, detailed dimension tables, advantages, installation steps, applications for beginners.
Slip On Flange is essentially a ring that is placed over the end of a pipe. The internal diameter of the flange is slightly larger than the external diameter of the pipe, allowing it to "slip" into position before being secured via fillet welds. While the basic design remains consistent, they are categorized primarily by their "face" type, which determines how they seal against a gasket.
Raised Face (RF)
The Raised Face is the most common type used in industrial applications. It features a small area surrounding the bore that is elevated above the bolting circle face. This design concentrates more pressure on a smaller gasket area, enhancing the seal's pressure-containment capability.
Flat Face (FF)
Flat Face flanges are used when the mating flange or filing is also flat-faced. This is common in low-pressure applications or when connecting to cast iron equipment. Because the entire surface is flush, there is no risk of the flange bending when bolts are torqued, which is critical for brittle materials.
Ring Type Joint (RTJ)
While less common for Slip On designs compared to Weld Neck flanges, RTJ faces feature a machined groove for a metal ring gasket. These are utilized in high-pressure and high-temperature environments where a mechanical seal is required to prevent leaks under extreme stress.
Material-Based Types
Beyond the physical shape, Slip On Flanges are categorized by their metallurgy. In our facility, we focus on:
Stainless Steel (304L, 316L): Offers excellent corrosion resistance and durability.
Nickel Alloys (Inconel, Monel, Hastelloy): Designed for extreme environments involving high heat or highly corrosive chemicals.
Slip On Flanges are manufactured to ASME B16.5 standard. This standard covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24.
Dimensions are determined by two primary factors: the Nominal Pipe Size (NPS) and the Pressure Class 150, 300, 600, 900, 1500, and 2500.
Dimensions Introduction
Outside Diameter (OD): The total width of the flange.
Inside Diameter (ID): Slightly larger than the pipe OD to allow for the "slip."
Thickness (C): The minimum thickness of the flange to withstand pressure.
Bolt Circle Diameter: The diameter of the circle on which the bolt holes are positioned.
Class 150 Slip On Flange Dimensions
NPS | DN | OD (mm) | Flange Thick. (mm) | Hub OD (mm) | Flange Length (mm) | RF Dia. (mm) | RF Height (mm) | PCD (mm) | Socket Bore (mm) | Bolt Holes | Bolt Size UNC | Weight (kg) |
1/2" | 15 | 90 | 9.6 | 30 | 14 | 34.9 | 2 | 60.3 | 22.2 | 4 | 1/2" | 0.8 |
3/4" | 20 | 100 | 11.2 | 38 | 14 | 42.9 | 2 | 69.9 | 27.7 | 4 | 1/2" | 0.9 |
1" | 25 | 110 | 12.7 | 49 | 16 | 50.8 | 2 | 79.4 | 34.5 | 4 | 1/2" | 0.9 |
1 1/4" | 32 | 115 | 14.3 | 59 | 19 | 63.5 | 2 | 88.9 | 43.2 | 4 | 1/2" | 1.4 |
1 1/2" | 40 | 125 | 15.9 | 65 | 21 | 73.0 | 2 | 98.4 | 49.5 | 4 | 1/2" | 1.4 |
2" | 50 | 150 | 17.5 | 78 | 24 | 92.1 | 2 | 120.7 | 61.9 | 4 | 5/8" | 2.3 |
2 1/2" | 65 | 180 | 20.7 | 90 | 27 | 104.8 | 2 | 139.7 | 74.6 | 4 | 5/8" | 3.2 |
3" | 80 | 190 | 22.3 | 108 | 29 | 127.0 | 2 | 152.4 | 90.7 | 4 | 5/8" | 3.7 |
3 1/2" | 90 | 215 | 22.3 | 122 | 30 | 139.7 | 2 | 177.8 | 103.4 | 8 | 5/8" | 5.0 |
4" | 100 | 230 | 22.3 | 135 | 32 | 157.2 | 2 | 190.5 | 116.1 | 8 | 5/8" | 5.9 |
5" | 125 | 255 | 22.3 | 164 | 35 | 185.7 | 2 | 215.9 | 143.8 | 8 | 3/4" | 6.8 |
6" | 150 | 280 | 23.9 | 192 | 38 | 215.9 | 2 | 241.3 | 170.7 | 8 | 3/4" | 8.6 |
8" | 200 | 345 | 27.0 | 246 | 43 | 269.9 | 2 | 298.5 | 221.5 | 8 | 3/4" | 13.7 |
10" | 250 | 405 | 28.6 | 305 | 48 | 323.8 | 2 | 362.0 | 276.2 | 12 | 7/8" | 19.5 |
12" | 300 | 485 | 30.2 | 365 | 54 | 381.0 | 2 | 431.8 | 327.0 | 12 | 7/8" | 29.0 |
14" | 350 | 535 | 33.4 | 400 | 56 | 412.8 | 2 | 476.3 | 359.2 | 12 | 1" | 41.0 |
16" | 400 | 595 | 35.0 | 457 | 62 | 469.9 | 2 | 539.8 | 410.5 | 16 | 1" | 54.0 |
18" | 450 | 635 | 38.1 | 505 | 67 | 533.4 | 2 | 577.9 | 461.8 | 16 | 1 1/8" | 59.0 |
20" | 500 | 700 | 41.3 | 559 | 71 | 584.2 | 2 | 635.0 | 513.1 | 20 | 1 1/8" | 75.0 |
24" | 600 | 815 | 46.1 | 663 | 81 | 692.2 | 2 | 749.3 | 616.0 | 20 | 1 1/4" | 100.0 |
Class 300 Slip On Flange Dimensions
NPS | DN | OD (mm) | Flange Thick. (mm) | Hub OD (mm) | Flange Length (mm) | RF Dia. (mm) | RF Height (mm) | PCD (mm) | Socket Bore (mm) | Bolt Holes | Bolt Size UNC | Weight (kg) |
1/2" | 15 | 95 | 12.7 | 38 | 21 | 34.9 | 2 | 66.7 | 22.2 | 4 | 1/2" | 1.2 |
3/4" | 20 | 115 | 14.3 | 48 | 24 | 42.9 | 2 | 82.6 | 27.7 | 4 | 5/8" | 1.4 |
1" | 25 | 125 | 15.9 | 54 | 25 | 50.8 | 2 | 88.9 | 34.5 | 4 | 5/8" | 1.4 |
1 1/4" | 32 | 135 | 17.5 | 64 | 25 | 63.5 | 2 | 98.4 | 43.2 | 4 | 5/8" | 1.8 |
1 1/2" | 40 | 155 | 19.1 | 70 | 29 | 73.0 | 2 | 114.3 | 49.5 | 4 | 3/4" | 2.7 |
2" | 50 | 165 | 20.7 | 84 | 32 | 92.1 | 2 | 127.0 | 61.9 | 8 | 5/8" | 3.2 |
2 1/2" | 65 | 190 | 23.9 | 100 | 37 | 104.8 | 2 | 149.2 | 74.6 | 8 | 3/4" | 4.6 |
3" | 80 | 210 | 27.0 | 117 | 41 | 127.0 | 2 | 168.3 | 90.7 | 8 | 3/4" | 5.9 |
3 1/2" | 90 | 230 | 28.6 | 133 | 43 | 139.7 | 2 | 184.2 | 103.4 | 8 | 3/4" | 7.7 |
4" | 100 | 255 | 30.2 | 146 | 46 | 157.2 | 2 | 200.0 | 116.8 | 8 | 3/4" | 10.0 |
5" | 125 | 280 | 33.4 | 178 | 49 | 185.7 | 2 | 235.0 | 144.4 | 8 | 3/4" | 12.7 |
6" | 150 | 320 | 35.0 | 206 | 51 | 215.9 | 2 | 269.9 | 171.4 | 12 | 3/4" | 17.7 |
8" | 200 | 380 | 39.7 | 260 | 60 | 269.9 | 2 | 330.2 | 222.2 | 12 | 7/8" | 26.0 |
10" | 250 | 445 | 46.1 | 321 | 64 | 323.8 | 2 | 387.4 | 276.3 | 16 | 1" | 36.0 |
12" | 300 | 520 | 49.3 | 381 | 71 | 381.0 | 2 | 450.9 | 327.1 | 16 | 1 1/8" | 52.0 |
14" | 350 | 585 | 52.4 | 413 | 74 | 412.8 | 2 | 514.4 | 359.2 | 20 | 1 1/8" | 68.0 |
16" | 400 | 650 | 55.6 | 470 | 83 | 469.9 | 2 | 571.5 | 410.5 | 20 | 1 1/4" | 91.0 |
18" | 450 | 710 | 58.8 | 533 | 89 | 533.4 | 2 | 628.7 | 461.8 | 24 | 1 1/4" | 111.0 |
20" | 500 | 775 | 63.5 | 584 | 95 | 584.2 | 2 | 685.8 | 513.1 | 24 | 1 1/4" | 141.0 |
24" | 600 | 915 | 70.0 | 692 | 106 | 692.2 | 2 | 812.8 | 616.0 | 24 | 1 1/2" | 211.0 |
Lower Initial Cost
Slip On Flanges are generally less expensive to manufacture than Weld Neck flanges. Because they do not have a complex "hub" or neck, they require less raw material, which translates to direct savings for the procurement team.
Ease of Alignment
Since the flange slides over the pipe, it is much easier to align the bolt holes with the mating flange. The pipe does not need to be cut to an exact length with extreme precision, as the flange can be adjusted slightly along the pipe's axis before welding.
Simplified Installation
The "slip-over" nature of this component simplifies the fabrication process. It does not require a beveled pipe end for a butt weld; instead, it relies on fillet welds, which are often faster and easier for welders to execute in the field.
Space Efficiency
Slip On Flanges have a lower profile than many other flange types. In tight spaces or compact piping skids where vertical or horizontal clearance is a premium, the SO flange provides a reliable connection without the bulk of a long neck.
The Slip On Flange requires two fillet welds: one on the outside and one on the inside.
Step 1: Preparation
Ensure the pipe end is cut square and is free of burrs, rust, or debris. Clean the inside of the flange bore and the outside of the pipe to ensure a high-quality weld.
Step 2: Position the Flange
Slide the flange onto the pipe. The standard practice is to leave a small gap between the end of the pipe and the face of the flange. This gap is typically equal to the wall thickness of the pipe plus 3mm. This ensures the pipe end does not damage the flange face during expansion or cause interference with the gasket.
Step 3: External Fillet Weld
Perform a fillet weld around the outer circumference where the hub of the flange meets the pipe. This weld provides the primary structural strength for the connection.
Step 4: Internal Fillet Weld
Perform a second fillet weld on the inside of the flange, where the pipe end meets the internal bore. This weld prevents fluid from seeping between the pipe and the flange, protecting against crevice corrosion.
Step 5: Inspection
Once the welds have cooled, they should be inspected (often via Dye Penetrant or Magnetic Particle testing) to ensure there are no cracks or porosities.
Slip On Flanges are often used in low-to-medium pressure systems.
Water and Firefighting Systems: Their ease of installation makes them ideal for large-scale municipal water lines and fire suppression systems where pressures are manageable.
Cooling Water Circuits: In power plants and refineries, SO flanges are used extensively in secondary cooling loops.
Chemical Processing: When fabricated from 316L stainless steel or nickel alloys, Slip On Flanges are perfect for transporting non-hazardous chemicals or fluids at moderate pressures.
HVAC Systems: Used in large-scale heating and air conditioning piping for commercial buildings.
Low-Pressure Steam: They are suitable for steam lines where the pressure and temperature do not fluctuate violently, reducing the risk of fatigue at the weld point.
For a beginner, one of the most common points of confusion is choosing between a Slip On Flange and a Weld Neck Flange. The lists below summarizes the main differences.
Design And Connection Method: Slip On Flanges slide over the pipe and use two simple fillet welds. Weld Neck Flanges feature a long tapered hub that butt-welds directly to the pipe.
Installation Ease And Speed: Slip On Flanges install faster and require less skill and pipe preparation. Weld Neck Flanges need precise beveling and more time for alignment and full-penetration welding.
Cost: Slip On Flanges cost less. Weld Neck Flanges has a higher initial price.
Strength And Pressure Rating: Slip On Flanges offer moderate strength—about two-thirds that of Weld Neck—and suit low- to medium-pressure service. Weld Neck Flanges provide superior strength, better fatigue resistance, and excel in high-pressure and high-temperature applications. Their life is roughly three times longer.
Leak Resistance And Durability: Slip On Flanges perform well in steady conditions. Weld Neck Flanges deliver excellent long-term leak resistance under extreme cycling or vibration.
Best Applications: Choose Slip On Flanges for budget-conscious projects with low to medium pressure, such as water lines or HVAC. Select Weld Neck Flanges for critical high-pressure systems in oil refineries or power plants.
As specialists in stainless steel and nickel alloy products, we are ready to help you select, specify, and supply the perfect Slip On Flanges for your project. Contact our team to discuss your requirements.
