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Slip on flanges, also called SO flanges, are a popular type of pipe flange designed to accept pipe into the bore/center of the flange for welding around both the Outer Diameter (OD) of the pipe and on the interior side of the connection.
| Standard | ANSI, MSS, AWWA, DIN, UNI, JIS, BS, SABS, EN1092, GOST, also we can produce according to customers’ drawings. |
| Size | 15mm to 2,000mm. |
| Grade Range | 150, 300, 400, 600, 900, 1500, 2500 (# or LB). PN 2.5 to PN 250. |
| Flange Facing | RF, FF, RTJ. etc. |
| Materials | Carbon steel, stainless steel and alloy steel. |
| Process | Forged or Cast. |
| Painting | Yellow paint, black paint, anti-rust oil or zinc coated. |
| Packing | Sea-worthy Plywood cases or Pallet with polyethylene film or as customers’ request. |
Slip on flanges, also called SO flanges, are a popular type of pipe flange designed to accept pipe into the bore/center of the flange for welding around both the Outer Diameter (OD) of the pipe and on the interior side of the connection.
A Slip-On Flange is a commonly used pipe flange designed to slide over the pipe and be welded on both the inside and outside. This design provides sufficient strength and reliable sealing performance while offering easier alignment and installation compared to weld neck flanges. Slip-on flanges are widely used in low to medium pressure piping systems.
The slip-on flange is a straightforward alternative to a weld neck flange, offering flexibility in adjusting the pipe length relative to the flange’s position due to its lack of a weld bevel. This design provides ample clearance for the pipe and facilitates easier welding and fabrication.
Primarily used in lower pressure applications, slip-on flanges typically feature a hub that resembles a raised face but can also be supplied in a "ring style" without a hub if space constraints demand it. While the hub style is more prevalent, the ring style is also valid within the slip-on category. For higher pressure applications, slip-on flanges may be manufactured with a lap joint height for improved connection quality. In cases where a lap joint is unavailable or the hub height is not critical, a slip-on flange can be produced with a machined hub to resemble a lap joint style.
In general, slip-on flanges are less suitable for high-stress applications compared to weld neck flanges. The latter features a reinforced hub and a tapered weld bevel, providing a more robust connection to the pipe’s butt weld end, which is better suited for environments subject to significant mechanical stress.
The inner diameter of a slip-on flange is slightly larger than the outer diameter of the pipe, allowing the pipe to slip easily into position. After alignment, fillet welds are applied on both sides to secure the connection. This simple installation method reduces fabrication time and overall installation cost, making slip-on flanges a popular choice for large-scale projects.
Our slip-on flanges are manufactured in accordance with international standards to ensure compatibility with global piping systems:
ANSI / ASME B16.5 (NPS 1/2” – 24”)
ANSI / ASME B16.47 (Large Diameter Flanges)
AWWA C207 (Waterworks Flanges)
EN 1092-1 / ISO 7005 (European Standards)
Available sizes typically range from DN15 (1/2”) up to DN600 and above, depending on the applicable standard and project requirements.
Pressure Classes: Class 150, 300, 400, 600, 900, 1500, 2500 or PN6 – PN420
Facing Types:
Raised Face (RF): Most common facing type for general industrial applications.
Flat Face (FF): Typically used with flat-faced mating flanges such as cast iron systems.
Ring Type Joint (RTJ): Designed for high-pressure and high-temperature applications requiring superior sealing.
Slip-on flanges are available in a variety of materials to meet different service conditions:
Carbon Steel: Cost-effective and widely used for general industrial and municipal piping.
Stainless Steel (304 / 316): Excellent corrosion resistance for chemical, food, and marine applications.
Alloy Steel: Suitable for high-temperature and high-pressure systems.
Simple structure with lower manufacturing cost.
Easy alignment and installation on site.
Reduced welding preparation compared to weld neck flanges.
Wide compatibility with multiple international standards.
Suitable for a wide range of industrial and water pipeline applications.
Municipal water supply and drainage systems
Industrial process piping
Water treatment plants and pump stations
HVAC systems
Medium-pressure gas and utility pipelines
Midas is a leading manufacturer of slip-on flanges in China, offering Slip On Flanges that meet various standards including ANSI, MSS, AWWA, DIN, UNI, JIS, BS, SABS, EN1092, and GOST, as well as custom designs based on customer specifications. Our slip-on flanges are available in sizes ranging from 15mm to 2,000mm and can feature flange facings such as RF, FF, and RTJ. We provide flanges in materials like carbon steel, stainless steel, and alloy steel, with manufacturing processes including forging or casting. For protection and durability, we offer painting options such as yellow, black, anti-rust oil, or zinc coating, and pack our products in sea-worthy plywood cases or pallets with polyethylene film, tailored to customer requirements.
Slip-on flanges come in two main types: the slip-on welding plate flange and the slip-on welding hubbed steel pipe flange. These flanges offer mechanical properties that fall between those of integral flanges and looping flanges, featuring a straightforward design and ease of processing. As a result, slip-on flanges are commonly utilized in various fluid pipeline systems.
Slip-on flanges come in several types based on the flange face design, including Raised Face (RF), Ring-Type Joint (RTJ) and Flat Face (FF).
The raised face slip-on flange features a small protrusion on its bottom face. This raised face serves as a designated area for gasket placement during installation, enhancing the overall sealing performance.
The RTJ slip-on flange features a machined groove on the raised face, designed to accommodate a gasket ring for effective sealing. This RTJ design is specifically intended for high-pressure applications, offering a more robust sealing solution compared to the RF type. The groove allows for a secure placement of the gasket, enhancing the flange’s ability to withstand elevated pressures.
Slip on flange use slip welding to connect equipment, so either below of name is describing the same flange:
Slip on weld flange
Slip on flange weld
Weld slip on flange
Slip on flange welding
SO flange
The FF (Flat Face) slip-on flange has a flat, unraised sealing surface, which contacts the gasket directly. This type is often used in lower pressure applications and is preferred when a more uniform seal is needed across the flange face.
Lower Installation Costs: Slip-on flanges generally require less material and fewer manufacturing steps compared to other types of flanges, such as weld neck flanges. This simplicity results in reduced production and installation costs. The absence of a weld bevel also means that fewer preparatory steps are needed, further lowering overall expenses.
Easier Alignment During Installation: Slip-on flanges are designed to slide over the pipe, allowing for straightforward alignment with other components. This ease of alignment simplifies the installation process, reducing the time and effort needed to ensure that all parts fit together correctly.
Improved Leak Proofing: While slip-on flanges are not inherently leak-proof, their design facilitates better sealing when used with appropriate gaskets. The ability to weld both inside and outside the flange helps to secure the joint, minimizing the risk of leaks compared to flanges that only allow for external welding.
Inner and Outer Welding on Flange: Slip-on flanges support welding both inside the flange bore and on the outer surface. This dual welding provides additional strength and enhances the seal, making the connection more robust and reliable, especially in applications where joint integrity is crucial.
Faster Accurate Cutting for Pipelines: The design of slip-on flanges simplifies the cutting process for pipelines. Since the flange slides over the pipe, it is easier to achieve precise cuts and alignments, saving time during the preparation and installation stages.
Compatibility with Lower Hub: Slip-on flanges are designed to accommodate pipes sliding onto them, which means they are compatible with flanges that have a lower hub. This feature is beneficial in installations where space is limited or where a lower hub design is required for specific engineering or design constraints.
To install a slip-on flange, slide it over the end of the pipe, align it with the mating flange or component, and then weld it both inside and outside the flange. Proper alignment and welding ensure a secure and leak-proof connection.
A slip-on flange slides over the pipe and is welded externally and internally, making it easier and less costly to install. In contrast, a weld neck flange has a tapered neck that is welded directly to the pipe, providing a stronger and more durable connection, particularly for high-pressure and high-temperature applications.
Slip-on flanges are typically used in lower to moderate pressure applications. For high-pressure environments, other flange types such as weld neck flanges or RTJ flanges are generally recommended due to their superior strength and sealing capabilities.
To achieve a leak-proof seal, it is crucial to use appropriate gaskets and ensure that the flange is welded properly both inside and outside. Regular inspection and maintenance can also help in maintaining the integrity of the seal.
Yes, slip-on flanges can be manufactured to custom sizes and specifications based on customer requirements. Manufacturers can produce flanges in various dimensions, materials, and face types to meet specific project needs.
Slip-on flanges are commonly used in water and wastewater systems, general industrial pipelines, and low to moderate pressure applications. Their ease of installation and cost-effectiveness make them a popular choice for many piping systems.
Slip-on flanges are commonly used in Class 150 to Class 600 systems, but higher pressure classes are available depending on material and standard compliance.
Raised Face (RF) flanges provide enhanced sealing by concentrating gasket pressure, while Flat Face (FF) flanges are designed to mate with flat-faced components to avoid damage.
Slip-on flanges can be used in high-temperature applications when appropriate materials and pressure ratings are selected. For extreme conditions, weld neck flanges are often recommended.
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