Dimension of ASME B16.5 Slip On Flange

In industrial pipeline system construction, forged flanges are important components for connecting pipes, valves, and equipment to ensure reliable system operation. Shanghai Zhucheng Pipe Fitting Manufacturing Co., Ltd., as a professional supplier of ASME B16.5 forged flanges in China, can provide domestic and international customers with forged flange products in various sizes, types, and materials. The Slip-On Flange (SO Flange) is one of the most widely used types of ASME B16.5 forged flanges. Due to its simple structure, easy installation, and low cost, it has become an important part of low-pressure, normal-temperature industrial piping systems.

What is Slip-On (SO) Flange

Appearance Features of ASME B16.5 Slip-On Flanges

The Slip-On flange has a simple structure. Its main body is disc-shaped, with a center bore matching the pipe size. Multiple bolt holes are evenly distributed around the flange disc, used with bolts, nuts, and gaskets for connection.

The Slip-On flange has a short neck at the connection between the flange disc and the pipe, which improves the flange’s rigidity and load-carrying capacity. Common sealing faces are Flat Face (FF) and Raised Face (RF). The neck is short, and when welding to the pipe, the pipe end is flush with the flange sealing face, with the weld located on the outside of the flange.

Main Uses

The Slip-On flange (SO flange) is one of the most common flange types in piping systems. Its core features are simple structure, easy installation, and low cost. The flange bore is slightly larger than the pipe outer diameter, allowing the pipe to “slip on” into the flange (hence the name). After installation, fillet welds are made on both the inside and outside of the flange. This provides pipe connection and sealing, and is widely used in medium-to-low pressure, normal-temperature, or low-temperature fluid transport applications.

Characteristics of Slip-On Flanges

• Easy installation: Simple welding process, less demanding on pipe cutting accuracy and alignment, high on-site construction efficiency.

• Cost-effective: Simple structure, low manufacturing cost, suitable for batch purchasing and large-scale application.

• Wide applicability: Can be used with carbon steel pipes, stainless steel pipes, and many other materials. Common in water treatment, HVAC, low-pressure steam, compressed air systems, and many chemical processes.

• Weak pressure resistance: Due to its structural characteristics, its pressure resistance is lower than that of weld neck flanges. Not recommended for applications with large pressure fluctuations, severe vibration, or high temperature and high pressure.

Introduction to the ANSI/ASME B16.5 Standard

ANSI stands for the American National Standards Institute, founded in 1918. At that time, many U.S. companies and technical groups had begun standardization work, but due to lack of coordination, there were many conflicts and problems. To improve efficiency, hundreds of technical societies, associations, and groups felt the need to establish a specialized standardization body and create unified general standards.

ASME generally refers to the American Society of Mechanical Engineers. ASME B16.5 is a standard for pipe flanges and flanged fittings recommended by ASME. It is an authoritative and widely used international standard and also meets ANSI requirements, so it is also called the ANSI B16.5 flange standard.

Simply put, ANSI is a national coordinating body in the U.S., while ASME is an organization that develops specific technical standards. The relationship is one of recognition.

ANSI (American National Standards Institute): A coordinator and recognizer of the U.S. voluntary standards system. It does not develop standards itself but provides a platform and rules for professional organizations (such as ASME, ASTM, API) to develop standards and recognizes them as “American National Standards.”

ASME (American Society of Mechanical Engineers): A professional technical organization and an ANSI-recognized standards developer. It drafts and publishes specific engineering standards. ASME B16.5 is also an American National Standard recognized by ANSI.

Therefore, the standard number “ANSI/ASME B16.5” indicates that the standard was developed by ASME and approved by ANSI as a national standard.

Types  of ASME B16.5 Forged Steel Flange

ASME B16.5 is published by the American Society of Mechanical Engineers for “Pipe Flanges and Flanged Fittings” and is one of the most widely used flange standards in global petrochemical, power, and other industries. It includes:

• Size range: 1/2" to 24"

• Pressure classes: Class 150, 300, 400, 600, 900, 1500, 2500

• Materials: Forged carbon steel (ASTM A105), alloy steel (ASTM A182 F11/F12), stainless steel (ASTM A182 F304/F316), etc.

• Core value of ASME B16.5: Ensures safe sealing and strength interchangeability of flanges under specified pressure and temperature. A flange marked “ASME B16.5 SO” means its design, manufacturing, and inspection comply with this standard.

Dimensions of ASME B16.5 Slip-On Flanges

ASME B16.5 specifies strict dimensions for Slip-On flanges, mainly including:

Flange outside diameter (O): Increases with pressure class and nominal pipe size (NPS)

Bolt circle diameter (PCD): Determines bolt alignment with the mating flange

Flange inside diameter (B): Slightly larger than pipe OD (e.g., for NPS 4″ Sch40 pipe, flange bore approx. 116.1 mm)

Flange thickness (T): Increases with Class rating

Sealing face height (approx. 2mm for RF)

Neck diameter and fillet radius

Example: Class 150, NPS 4″, RF face SO flange (units: mm):

Flange OD: 228.6

Bolt circle diameter: 190.5

Number of bolt holes: 8

Bolt hole diameter: 19

Flange thickness: 22.3

Flange bore: approx. 116.1 (matching pipe)

The standard clearly provides all key dimensions for each pressure class and size — no calculations needed.

Dimension and Weight of Class 150 SO Flange

Dimension and Weight of Class 300 SO Flange

Dimension and Weight of Class 400 SO Flange

Dimension and Weight of Class 600 SO Flange

Dimension and Weight of Class 900 SO Flange

Dimension and Weight of Class 1500 SO Flange

Slip-On flange vs. Weld Neck flange (SO vs. WN)

In actual industrial piping design and selection, Slip-On (SO) and Weld Neck (WN) flanges are often compared.

For general water, air, or oil lines without severe cyclic loads, ASME B16.5 Slip-On flanges are recommended for cost-effectiveness. For high temperature/pressure, toxic media, or critical equipment connections, Weld Neck flanges should be selected.

Application Range and Characteristics of ASME B16.5 Forged Flanges

ASME B16.5 Slip-On flanges are typically manufactured by forging: the steel billet is heated, forged into a flange blank, then machined into the finished product.

Main Characteristics of Forged Flanges:

Dense structure, no casting defects (porosity, shrinkage)

Better mechanical properties than cast flanges, especially impact toughness and fatigue resistance

Suitable for carbon steel, stainless steel, alloy steel, etc.

High precision of sealing face, low leakage risk

Application

Petrochemical industry: atmospheric/vacuum distillation, catalytic cracking, tank piping

Industrial gases: nitrogen, compressed air lines

Municipal engineering: water supply, heating networks

Water treatment: sewage, reclaimed water pipes

Marine piping systems (some low-pressure areas)

ASME B16.5 Slip-On flanges, with their standardized design, easy installation, and cost advantages, are one of the most widely used flange types in industrial piping. For selection, just confirm pressure class (Class), nominal pipe size (NPS), sealing face type (RF/FF), and material — then standard parts can be matched quickly. For non-high-temperature, non-high-pressure, and no severe cyclic load conditions, ASME B16.5 SO flanges provide safe, economical, and efficient connections for industrial pipelines.