A Guide to the Application and Selection of Stub Ends in Flange Connection Systems

Overview of Stub Ends and Their Role in Flange Systems

Stub ends are an essential component in piping systems that are used in conjunction with lap joint flanges. They are designed to facilitate the connection of pipes, valves, and flanges, and their design plays a crucial role in ensuring a secure, leak-tight seal in high-pressure and high-temperature environments. Texas Flange offers two distinct types of stub ends: MSS-type and ASA-type, both designed to match specific flanges and piping configurations.

MSS-Type Stub Ends

The MSS (Manufacturers Standardization Society) type stub end is the industry-standard and the most commonly used type of stub end in flange systems. It is designed for use with lap joint flanges, which are particularly suited for applications where frequent disassembly and maintenance are required.

• Common Use: The MSS-type stub end is designed to work with flat-face lap joint flanges. It has a shorter length than the ASA-type stub end and is more prevalent in standard flange applications.
• Lap Thickness: The lap thickness of the MSS-type stub end typically corresponds to the thickness of the schedule pipe it accompanies. For example, if you are using Schedule 40 pipe, the stub end will have a matching thickness for seamless integration.
• Design Features: The exterior of the base of the MSS-type stub end has a curved machine radius to ensure that the lap joint flange mates properly and securely over the stub end. This ensures a smooth, leak-free connection.

ASA-Type Stub Ends

The ASA (American Standards Association)-type stub end is a less common, longer variant of the stub end, although it may be more appropriate for certain specialized applications that demand additional length or specific design features.

• Longer Length: The ASA-type stub end is typically longer than the MSS type. This additional length can be beneficial in certain high-pressure or high-temperature applications where extended lengths help meet certain mechanical or operational requirements.
• Less Common: ASA-type stub ends are less frequently used than MSS-type stub ends, but they are still relevant in specific industries where extended flanges or specific configurations are required.

Lap Joint Flanges and Stub Ends

A lap joint flange is designed to be used in conjunction with a stub end, and it is typically mounted on the stub end without being welded to it. The flange "laps" over the stub end, which allows for easy assembly and disassembly. This is ideal for situations where the connection needs to be made and broken frequently, such as in maintenance-heavy industries like pharmaceuticals, food processing, and chemical manufacturing.

• Mating Mechanism: The lap joint flange will mate flush over the stub end, using the radius on the exterior of the stub end to form a strong, leak-resistant seal.
• Hub Length: A typical lap joint flange has a longer hub length compared to a slip-on flange, which makes the connection more robust. However, in many applications, this extended hub length might not be necessary, and fabricators may opt for other options, such as machining the face of a slip-on flange to meet the radius requirements of the stub end.

Custom Stub Ends and Flange Solutions

At Texas Flange, custom solutions are available for unique or non-standard requirements. If a custom stub end is needed for a particular application, customers can provide technical drawings with the necessary dimensions and specifications, and Texas Flange can manufacture a solution tailored to those needs.

• Fabricators' Preference: Sometimes, fabricators or field workers may prefer custom stub ends, especially when the specific lap joint or material grade is unavailable in standard configurations.
• Custom Lap Joints: For specialized piping systems, fabricators might design custom lap joints or mounting flanges, and custom stub ends are fabricated to suit these applications.

Practical Considerations

• Lead Time and Customization: In some cases, lead time is a critical factor, and customers may prioritize quick delivery over strict adherence to specific ANSI/ASME standards. In these situations, customers may purchase slip-on flanges and machine the face to meet the radius requirements of the corresponding stub end.

  This is a common practice in projects where time constraints are critical, and it can offer a more expedient solution for getting the system up and running quickly, even if it means modifying standard flanges.

• Materials and Sizes: Stub ends, like other flanges, are available in various materials, including carbon steel, stainless steel, and alloys for specific applications. The material selected for the stub end must match the piping system and the operating conditions to ensure compatibility and durability.

Summary of Key Points

• MSS-type stub ends are the most commonly used in the flange industry and work with standard flat-face lap joint flanges.
• ASA-type stub ends are longer and may be more appropriate for certain high-pressure or high-temperature applications, though they are less common.
• Lap joint flanges are typically used with stub ends, and they offer advantages in applications where frequent disassembly is required.
• Customization is available for unique needs, with Texas Flange offering custom stub ends and lap joints to meet specific application requirements.
• In situations where lead time is critical, customers may opt to machine a slip-on flange to match the radius requirements of the stub end.

Choosing the right stub end and flange configuration is crucial for ensuring the integrity, safety, and efficiency of the piping system. Whether you're working with MSS or ASA types, custom fabrication is an option to ensure a tailored solution for your piping needs.