Flanges are an integral component in piping systems, playing a vital role in connecting pipes, valves, pumps, and other equipment. Among the various specifications and terminologies related to flanges, two terms frequently arise – PCD in flange and blind flange types. This detailed guide explores these terms, diving into the nuances of flange design and classification to help engineers, technicians, and industry professionals gain a clear understanding.

Table of Contents

1. Introduction to Flanges

2. What is PCD in Flange?

   • Definition of PCD

   • Importance of PCD in flange design

   • How to measure PCD in flange

   • PCD vs Bolt Circle

3. Common Standards and Dimensions for PCD

4. Applications of Flanges with Correct PCD

5. Overview of Blind Flanges

   • What is a Blind Flange?

   • Importance of Blind Flanges

6. Blind Flange Types

   • Raised Face Blind Flange

   • Flat Face Blind Flange

   • Ring Type Joint Blind Flange

   • Threaded Blind Flange

   • Custom Blind Flanges

7. Materials Used in Blind Flange Types

8. Applications and Uses of Blind Flanges

9. Differences Between Blind Flanges and Other Flanges

10. How to Choose the Right Blind Flange

11. Conclusion

1. Introduction to Flanges

Flanges are mechanical devices used to join sections of pipes or to connect pipes to a pressure vessel, valve, pump, or other integral component of a piping system. The design and proper selection of flanges are crucial for safe and effective operations across industries such as oil and gas, petrochemicals, water treatment, and construction.

2. What is PCD in Flange?

Definition of PCD

PCD in flange stands for "Pitch Circle Diameter." It is the diameter of the circle that passes through the center of all the bolt holes in a flange. In simpler terms, if you imagine a circle that connects the centers of all the bolt holes, the diameter of this circle is called the PCD in flange.

Importance of PCD in Flange Design

The PCD in flange is critical in ensuring that bolts align correctly during installation. A mismatch in PCD can lead to improper installation, leaks, and potential mechanical failure. Since flanges are manufactured according to various standards such as ASME, ANSI, DIN, and BS, the PCD must be consistent with the mating component for seamless integration.

How to Measure PCD in Flange

To measure the PCD in flange, follow these steps:

1. Identify and mark the center of each bolt hole.

2. Use a vernier caliper or measuring tape to measure the diameter between the centers of opposite bolt holes.

3. For even bolt holes, measure center-to-center directly.

4. For odd bolt holes, measure from one hole to the farthest bolt hole and use trigonometric calculations or specialized tools.

Accurate measurement of PCD in flange ensures compatibility with other flange components.

PCD vs Bolt Circle

The PCD in flange is sometimes also referred to as the bolt circle diameter. Though used interchangeably, it's important to note that both refer to the same measurement – the circle that runs through the center of the bolts.

3. Common Standards and Dimensions for PCD

Various flange standards have their own specific PCD measurements. For instance:

• ANSI/ASME B16.5 – Common in North America

• DIN Standards – Common in Europe

• BS Standards – British Standard flanges

Each flange standard provides a unique set of PCDs based on pressure class and nominal size.

Example PCDs:

• ANSI 150# 4” Flange = 190.5 mm PCD

• DIN PN16 DN100 Flange = 180 mm PCD

Understanding these values ensures the right flange is selected for a specific application.

4. Applications of Flanges with Correct PCD

• Oil & Gas Industry: PCD ensures tight sealing for high-pressure pipelines.

• Water Supply Systems: Correct PCD allows for proper alignment during installation.

• Chemical Plants: Reduces chances of leaks and mechanical wear.

• HVAC Systems: Maintains airflow integrity and pressure control.

• Power Plants: Ensures secure connections in high-temperature zones.

Correctly measuring and applying the PCD in flange avoids costly delays and system failures.

5. Overview of Blind Flanges

What is a Blind Flange?

A blind flange is a type of flange used to close the end of a piping system or a pressure vessel. Unlike other flanges, it does not have a bore or opening for fluid passage. Instead, it acts like a plug, blocking the flow in a pipeline.

Blind flanges are commonly used in testing, maintenance, and temporary shutoffs in pipelines and pressure vessels.

Importance of Blind Flanges

Blind flanges allow for easy access to the end of a piping system. They are essential in systems where the pipeline may need to be extended, inspected, or cleaned periodically.

6. Blind Flange Types

There are several blind flange types used in industry depending on application, pressure, and environmental factors.

1. Raised Face Blind Flange

This is the most common of all blind flange types. It has a small raised portion around the sealing area, which concentrates pressure on a smaller surface to ensure a tight seal.

Applications: Suitable for high-pressure systems.

2. Flat Face Blind Flange

This type has a flat sealing surface and is used when the mating flange is also flat-faced. It prevents overstressing brittle materials.

Applications: Low-pressure systems, especially in water treatment and HVAC.

3. Ring Type Joint (RTJ) Blind Flange

This type features a groove in which a metal ring gasket sits, allowing a metal-to-metal seal.

Applications: High-pressure and high-temperature applications in oil and gas.

4. Threaded Blind Flange

Though rare, threaded blind flange types have threads inside the bore for connecting to a male threaded pipe without welding.

Applications: Temporary or low-pressure connections.

5. Custom Blind Flanges

Custom blind flange types are designed for specialized applications, often including tapped holes or extensions for instrumentation.

Applications: Unique equipment, specialized vessels, or instrumentation access.

7. Materials Used in Blind Flange Types

The material selection of blind flange types plays a critical role in system integrity. Common materials include:

• Carbon Steel: Ideal for high-strength applications.

• Stainless Steel: Corrosion-resistant, suitable for aggressive chemicals.

• Alloy Steel: High temperature and pressure resistance.

• PVC/Plastic: Used in low-pressure applications with non-corrosive fluids.

• Duplex & Super Duplex Steel: High strength and corrosion resistance.

8. Applications and Uses of Blind Flanges

• Testing Pipeline Integrity: Temporarily seals the system during pressure testing.

• Future Pipeline Extensions: Allows for future piping extensions.

• Maintenance: Provides easy access to clean or inspect the pipeline.

• End of Line Shut-off: Permanently or temporarily shuts off unused pipe ends.

Each of the blind flange types is selected based on these applications to optimize performance and cost.

9. Differences Between Blind Flanges and Other Flanges

Understanding these differences helps in making informed decisions in flange selection.

10. How to Choose the Right Blind Flange

Choosing from various blind flange types requires considering several factors:

• Operating Pressure and Temperature

• Material Compatibility

• Corrosion Resistance

• Industry Standards (ASME, ANSI, DIN)

• Bolt Hole PCD Compatibility

Also, the PCD in flange of the blind flange must match the mating flange to ensure a proper seal and ease of installation.

11. Conclusion

In conclusion, understanding what is PCD in flange and the various blind flange types is fundamental for professionals working with piping systems. The PCD in flange determines the compatibility and fitment of flange components, directly influencing the reliability and safety of the entire system. At the same time, choosing the right type from the many blind flange types ensures that the pipeline or vessel meets its intended function, whether it is sealing off flow, preparing for future expansion, or facilitating maintenance.