What is a Slip-On Flange: Types, Specifications & Applications

Slip-on flanges are essential components in piping systems, valued for their simplicity, versatility, and cost-effectiveness. Whether it is connecting steel pipes or ensuring a secure seal with a raised face or flat face, slip-on flanges offer practical solutions for various industrial needs. 

In this guide, we will explore their design, types, technical specifications, and applications, helping you understand why they remain a trusted choice in many industries. Keep reading to learn more!

1. What is a Slip-On Flange?

A slip-on flange is a widely used pipe connection component in the piping industry. It is designed to slide over the end of a steel pipe and is secured in place using fillet welds on both the outer and inner edges. Known for its ease of installation, cost-effectiveness, and versatility, the slip-on flange is a staple in many piping systems, particularly those operating under low to moderate pressure.

Components and Design Features

Slip-on flanges consist of several key components:

• Flange Face: The surface area that mates with the gasket for a secure seal. Types include flat-faced (FF) and raised-faced (RF).
• Inner Bore: The diameter of the opening, designed to fit the outer diameter of the pipe.
• Hub: Some slip-on flanges include a hub to provide additional strength and distribute stress evenly.
• Bolt Holes: Pre-drilled holes to align with corresponding bolts for attachment to other flanges or equipment.

Why Slip-On Flanges Are Commonly Used

The slip-on flange is popular due to its simplicity and flexibility. Unlike other flange types, it doesn’t require precise pipe cutting or beveling, making it easier to align during installation. This feature, combined with its affordability, makes the stainless steel slip-on flange and similar variations an excellent choice for general industrial and low-pressure applications.

Raised Face vs. Flat Face Slip-On Flanges

• Raised Face Slip-On Flange: Includes a raised area around the bore to improve gasket compression and sealing. These are suitable for higher-pressure systems.
• Flat Faced Slip-On Flange: The face lies flat without a raised surface, commonly used in systems where the flange must mate with flat surfaces or soft gaskets. Ideal for low-pressure applications.

2. Technical Specifications

Dimensional Characteristics

The design and dimensions of a slip-on pipe flange are standardized to ensure compatibility and performance across various applications:

• Outer Diameter Specifications: The outer diameter is critical for aligning the flange with mating components. It varies by flange size and pressure rating, typically adhering to ASME/ANSI standards.
• Inner Bore Requirements: The bore is slightly larger than the pipe’s outer diameter, allowing the flange to slip over the pipe before welding.
• Hub Dimensions: For flanges with hubs, dimensions are calculated to enhance strength without adding unnecessary bulk.
• Face Types: Options include flat-faced and raised-faced, with each serving specific sealing and application requirements.

Pressure Ratings

The pressure-handling capabilities of a slip-on weld flange are categorized into distinct classes, such as 150, 300, and 600, as defined by ANSI/ASME standards:

• Class 150: Suitable for low-pressure applications with minimal temperature variations.
• Class 300: Handles moderate pressures and temperatures, commonly used in medium-duty systems.

Operating Limitations

While versatile, slip-on flanges have some constraints:

• Not ideal for high-pressure systems where leak prevention is critical.
• Limited performance in high-temperature environments compared to weld neck flanges.
• Material grades, such as stainless steel, significantly affect the flange’s durability, corrosion resistance, and temperature tolerance.

3. Piping System Integration

System Design Considerations

Incorporating a slip-on flange into a piping system requires careful consideration of several factors:

• Load Bearing Capacity: The flange must support the mechanical loads imposed by the system, such as pipe weight and thermal expansion.
• Pressure Containment: Slip-on flanges are ideal for systems with moderate pressure requirements. They rely on fillet welds for sealing, which may limit their pressure resistance compared to alternatives.
• Temperature Effects: Elevated temperatures can affect the flange material and gasket, potentially leading to leaks.
• Stress Distribution: Proper welding ensures uniform stress distribution, preventing failure at high-stress points.

Below is a table detailing the maximum pressure and temperature ratings for steel pipe flanges:

Applications

Slip-on flanges excel in a variety of settings due to their adaptability:

• Low-Pressure Systems: Commonly used in water treatment, HVAC, and light industrial processes where pressure demands are minimal.
• High-Pressure Limitations: While they can handle moderate pressure, their design makes them less suitable for systems requiring stringent pressure containment.
• Temperature Constraints: Best suited for moderate temperature ranges; stainless steel slip-on flanges provide added resistance to thermal and chemical stress.
• Environmental Factors: Corrosion-resistant materials like stainless steel make them ideal for marine, chemical, and other corrosive environments.

4. Advantages of Slip-On Flanges

• Ease of Installation: No need for precise pipe end preparation.
• Cost-Effectiveness: Lower material and labor costs compared to other flange types.
• Versatility: Applicable across a wide range of systems and materials.

5. Disadvantages

• Welding Requirement: Needs two fillet welds, increasing labor in comparison to some flanges.
• Pressure Limitation: Less robust than weld neck flanges for high-pressure applications.

Frequently Asked Questions

Are slip-on flanges appropriate for underground sewage systems?

Slip-on flanges are not recommended for underground sewage systems. This is due to the required welding process in such a context. According to experts, it is better to use flange adapters. Looking for other more suitable flanges may also work.

Is any specific surface preparation needed before welding slip-on flanges?

For better results, you may thoroughly clean slip-on flange surfaces. This practice ensures that the flange is free of debris or contaminants before welding.

Are slip-on flanges suitable for steam systems?

You may use slip-on flanges for steam piping systems. However, remember that their suitability still depends on the specific pressure and temperature conditions. Before buying slip-on flanges for steam systems, first, verify the application requirements. Consulting relevant standards may also help.

Do slip-on flanges provide a leak-proof connection?

When properly installed and welded, slip-on flanges can provide a secure connection that minimizes the risk of leaks.

Reference

Sealing Performance Test of Slip-On Type Pipe Flange Connections Subject to Internal Pressure and Bending Moment; Satoshi Nagata, Takashi Kobayashi, Hirokazu Tsuji, and Toshiyuki Sawa; 2010 (https://www.researchgate.net/publication/267611972)

Some research results on the tightness and strength of flange joints; Georgeta Roman and mIon Durbaca; 2018 (https://www.researchgate.net/publication/368328335)