What is a Blind flange? Types, Thickness Calculation & Dimensional Standards

A blind flange is a solid, circular component used to close off the end of a pipeline, valve, or nozzle, effectively halting the flow of fluids or gases. Blind flanges are widely employed across various industries, including oil and gas, chemical processing, and water treatment.

This blog will discuss more about blind flanges. You’ll learn more about what a blind flange is, its types, industrial applications, and key factors like flange thickness calculation and dimensional standards. All of which will help you understand its versatile functionality.

1. Understanding the Blind Flange

A blind flange is a type of pipe flange used to seal the end of a piping system or block off a pipeline entirely. Unlike other flanges, it does not have a central bore, making it ideal for isolating piping systems during maintenance, testing, or when expansion of the system is planned. In piping, blind flanges provide a secure closure that prevents leakage and maintains system integrity under varying pressure and temperature conditions.

Applications Across Industries

Blind flanges are indispensable in industries like:

• Oil and Gas: For isolating sections of pipelines during repairs or testing.
• Chemical Processing: To ensure safety by securely sealing hazardous fluid systems.
• Water Treatment: For terminating unused pipeline sections or facilitating maintenance operations.

2. Types of Blind Flanges

Raised Face (RF) and Flat Face (FF) Blind Flanges

• RF Blind Flanges:
  Feature a slightly raised area around the sealing face to enhance gasket compression. These are commonly used in systems with higher pressure ratings.
  Use Case: Suitable for moderate to high-pressure piping where leakage prevention is critical.

• FF Blind Flanges:
  Have a flat sealing face that comes in full contact with the gasket. They are generally used in low-pressure systems where uniform load distribution is required.
  Use Case: Ideal for lightweight, non-critical applications like water pipelines.

Ring Type Joint (RTJ) Blind Flanges

These flanges include a precision-machined groove for a metallic gasket, providing a leak-proof seal in high-pressure and high-temperature environments.
Use Case: Widely used in oil and gas or chemical industries for pressure ratings exceeding 900#.

Spectacle Blind Flange

A spectacle blind flange consists of two metal discs connected by a hinge or strap—one solid and one with a central hole. This design allows switching between open and closed states by rotating the flange.
Use Case: Common in situations requiring frequent isolation and reconnection of pipelines.

Customizable Options

Blind flanges can be tailored to specific needs, including unique flange dimensions, material grades, and compatibility with various pressure ratings. Customizations are especially relevant for non-standard systems or extreme environments.

In response to growing demand, many blind flange manufacturers now offer customization options, enabling clients to specify parameters like material composition, surface coatings, and dimensional adjustments. These services ensure that the flanges align perfectly with system requirements.

3. What is the Difference Between a Blind Flange and a Blank Flange?

Blind Flange: A blind flange is a standalone component that bolts onto piping systems to seal the end of a pipeline or valve.
Use Case: Common in systems requiring frequent access for maintenance or testing.

Blank Flange: A blank flange is not bolted onto a system; instead, it is a disk used within flanges or between flange pairs.
Use Case: Primarily for temporary closures or sealing an unused flange.

4. What is a Blind Flange Used For?

Blind flanges are primarily used for:

• Sealing pipeline ends: To prevent leakage and allow system shutdown.
• Pressure testing: Isolating a section for testing pressure integrity.
• Maintenance access: Providing a removable barrier for pipe cleaning or modifications.

5. How to Calculate Blind Flange Thickness

To ensure safety and durability, the thickness of a blind flange is calculated by considering factors like pressure ratings, flange dimensions, and material grade. A common formula is:

Where:

• t: Flange thickness
• P: Internal pressure (psi)
• D: Flange outer diameter (inches)
• S: Allowable material stress (psi)
• C: Corrosion allowance (inches)

The ASME B16.5 standard provides guidelines to refine calculations, ensuring compliance with operational demands.

5. Detailed Dimensions Chart

Overview of Standard Dimensions

Blind flange dimensions are governed by standards like ASME B16.5 and ASME B16.47, specifying parameters like bolt circle diameter, flange outer diameter, and thickness for pressure ratings from 150# to 2500#.

Thickness Calculation for Various Applications

Using the ASME guidelines, the thickness of blind flanges can vary with pressure ratings:

• Low-pressure systems: Minimal thickness with basic corrosion allowance.
• High-pressure systems: Thicker flanges and robust materials like stainless steel or alloy steel.