Pad flanges, also known as studding outlet flanges, are a type of flange that is designed to minimize the projection of equipment both inside and outside of the vessel. They are typically welded to the shell or head of a vessel to provide a connection point for equipment such as sight glasses, level gauges, and flow indicators.

What is Pad Flange

A pad flange is a specialized component used in industrial equipment, pipelines, and vessels to seal openings and maintain system integrity. What sets pad flanges apart is their compact design, which minimizes their projection both inside and outside the equipment, making them space-efficient.

Pad FlangeImage Source: TexasFlange

Pad flanges are essential in industries where space is at a premium and equipment needs to be securely mounted. They facilitate the direct mounting of instruments and devices onto vessels or pipelines, eliminating the need for additional nozzles or penetrations.

Types of Pad Flange

There are two main types of pad flanges:

  1. Flat Face Pad Flange:

The flat face pad flange, as the name suggests, has a flat and smooth sealing surface. It is commonly used in applications where the fluid or gas being handled does not require a raised face or a gasket. This type provides an effective seal in low-pressure, non-corrosive, and non-toxic environments.

  1. Raised Face Pad Flange:

Raised face pad flanges feature a raised surface around the opening. This raised face accommodates a gasket, which is compressed between the flange and the mating component, ensuring a tight and leak-free seal. These pad flanges are suitable for higher-pressure applications, as they enhance the sealing capability.

Materials used to make Pad Flange

Pad flanges are typically made of stainless steel, carbon steel, or alloy steel.

  • Stainless steel: Good corrosion resistance and abrasion resistance. Strong and durable. Good for high-pressure applications.
  • Carbon steel: Less expensive than stainless steel. Not as resistant to corrosion or abrasion. Good for low-pressure applications.
  • Alloy steel: Combination of carbon steel and other elements. Stronger and more corrosion-resistant than carbon steel. Good for medium- to high-pressure applications.

Key Characteristics of Pad Flange

The key characteristics of pad flanges are as follows:

  • Minimal projection inside and outside of the vessel: Pad flanges are designed to minimize the projection of equipment both inside and outside of the vessel. This is critical in some applications for mounting certain equipment to the vessel.
  • Easy installation and maintenance: Pad flanges are relatively easy to install and maintain. This is because they are typically welded to the vessel, which provides a strong and reliable connection.
  • Available in a variety of sizes and pressure ratings: Pad flanges are available in a wide range of sizes and pressure ratings, making them suitable for a variety of applications. This includes applications in the chemical processing, food and beverage processing, pharmaceutical manufacturing, power generation, and oil and gas production industries.
  • Can be used with a variety of types of equipment: Pad flanges can be used with a variety of types of equipment, such as sight glasses, level gauges, flow indicators, and other types of equipment. This makes them a versatile and adaptable flange solution.

Pad Flange Applications

Pad flanges are used in a variety of applications, including:

  • Mounting sight glasses: Pad flanges are commonly used to mount sight glasses to vessels and tanks. This allows operators to visually inspect the contents of the vessel without having to open it.
  • Mounting level gauges: Pad flanges can also be used to mount level gauges to vessels and tanks. Level gauges are used to measure the level of liquid or gas in a vessel.
  • Mounting flow indicators: Pad flanges can also be used to mount flow indicators to pipes and pipelines. Flow indicators are used to visually indicate the flow rate of a fluid or gas through a pipe or pipeline.
  • Mounting other types of equipment: Pad flanges can also be used to mount other types of equipment to vessels and tanks, such as temperature sensors, pressure sensors, and relief valves.

Pad flanges are particularly well-suited for applications where space is limited or where the equipment needs to be flush with the vessel wall. They are also relatively easy to install and maintain.

Design and Standards 

Pad flanges are designed in accordance with various industry standards, such as:

  • ASME B16.5: This standard covers the design and manufacture of pipe flanges and flanged fittings.
  • ANSI/AWWA C207: This standard covers the design and manufacture of steel pipe flanges and flanged fittings for water and wastewater service.
  • BS EN 1092-1: This European standard covers the design and manufacture of flanged joints for pipes, valves, fittings, and other equipment.
  • DIN 2501: This German standard covers the design and manufacture of flanged joints for pipes, valves, fittings, and other equipment.
  • JIS B2220: This Japanese standard covers the design and manufacture of steel pipe flanges and flanged fittings.

These standards specify the dimensions, materials, and construction requirements for pad flanges. They also specify the testing and inspection requirements for pad flanges.

How to Install and Maintain Pad Flange

Here are the steps to install and maintain pad flanges:

Installation:

  1. Prepare the vessel and pad flange. This involves cleaning the surfaces and making sure that they are properly aligned.
  2. Weld the pad flange to the vessel. This can be done using a variety of welding methods, such as arc welding or gas tungsten arc welding.
  3. Once the pad flange is welded to the vessel, it is important to test it to make sure that it is leak-tight. This can be done using a hydrostatic test or a pneumatic test.

Maintenance:

  1. Inspect the pad flanges regularly to identify any signs of wear or damage. Visual inspections should be performed to look for cracks, corrosion, and other defects. Nondestructive testing methods, such as ultrasonic testing and radiographic testing, can also be used to inspect pad flanges for internal defects.
  2. If any defects are found, the pad flange should be repaired or replaced immediately.

FAQs

Q1. Are there different types of pad flanges, and how do I choose the right one for my application?

Yes, there are various types of pad flanges, including flat face, raised face, ring type joint (RTJ), weld neck, slip-on, threaded, and socket weld pad flanges. The choice depends on factors such as pressure, temperature, compatibility, and application requirements.

Q2. What materials are pad flanges typically made of?

Pad flanges can be made from a range of materials, including carbon steel, stainless steel, and other corrosion-resistant alloys.

Q3. What is the significance of maintenance for pad flanges?

Regular maintenance is essential for ensuring the long-term reliability of pad flanges. It includes inspections, gasket replacement (if applicable), corrosion prevention, bolt tightening, leak detection, and comprehensive record-keeping. 

Q4. Can pad flanges be used in high-pressure and high-temperature applications?

Yes, pad flanges are available in designs like raised face and RTJ, specifically for high-pressure and high-temperature applications. 

Q5. Are pad flanges adaptable to different connection types?

Certainly, Pad flanges come in various connection types, including weld neck, slip-on, threaded, and socket weld, making them adaptable to different installation and system requirements.

Q6. Can I replace the gasket of a pad flange without professional assistance?

Gasket replacement requires careful consideration of material compatibility and proper installation. While some individuals may perform this task, it is often recommended to seek professional guidance to ensure an effective seal and system integrity.

Conclusion

In conclusion, Pad flanges are a type of flange that is designed to minimize the projection of equipment both inside and outside of the vessel. They are made of a variety of materials, including stainless steel, carbon steel, and alloy steel. Pad flanges are available in a variety of sizes and pressure ratings and offer a number of benefits, including minimal projection, easy installation and maintenance, and versatility. Pad flanges are commonly used in a variety of industries, including chemical processing, food and beverage processing, pharmaceutical manufacturing, power generation, and oil and gas production.

For all your flange steel requirements, consult with reputable manufacturers and suppliers like Texas Flange, who can provide the right flange solutions tailored to your application’s demands.