Exploring Flange Gaskets: A Deep Dive into Types and Uses

Flange gaskets are sealing elements used between mating flanges to ensure a tight seal, and they come in three main types: non-metallic (soft), metallic (hard), and semi-metallic (composite). 

Each type has its specific applications, from industrial systems to automotive exhaust systems like exhaust flange gaskets. In this blog, we’ll explore how flange gaskets work and help you choose the right one for your needs.

What is a Flange Gasket?

A flange gasket is a sealing element placed between mating flanges to prevent leaks. It fills any imperfections on the flange surfaces. By so doing a flange gasket ensures a tight seal when bolts are tightened.

Flange gaskets are essential in piping systems, from industrial plants to automotive exhaust systems, like exhaust flange gaskets in vehicles.

Flange gaskets are classified into three main types based on material and application: 

• Non-metallic (soft) 
• Metallic (hard) 
• Semi-metallic (composite)

How Does a Flange Gasket Work?

A flange gasket compresses between two flange faces as the bolts are torqued. This compression allows the gasket to form a tight seal, preventing leakage. The choice of gasket depends on the application.

Different Types of Flange Gaskets

Non-Metallic Gaskets (Soft)

Made from materials like rubber, PTFE, or compressed non-asbestos fiber (CNAF), these gaskets are used in low-pressure applications. They are typically used in flat-face or raised-face flanges. For example, exhaust flange gaskets are often made from soft materials that can seal effectively at lower pressures.

Metallic Gaskets (Hard)

These gaskets are made entirely from metals like stainless steel or copper. They are ideal for high-pressure, high-temperature systems. Ring-type joint (RTJ) gaskets are commonly used in petrochemical industries, where durability is crucial.

Semi-Metallic Gaskets (Composite)

Semi-metallic gaskets offer the strength of metal with the sealing capability of softer materials. As the name implies, a semi-metallic gasket combines metal and non-metal elements.

How to Choose the Right Flange Gasket

Choosing the right flange gasket depends on factors such as pressure, temperature, and the type of fluid or gas in the system. For low-pressure systems, non-metallic gaskets are sufficient. For high-pressure or high-temperature systems, semi-metallic or metallic gaskets are more suitable.

For example, in automotive exhaust systems, a durable exhaust pipe flange gasket must be able to resist both high heat and vibrations to prevent leaks effectively.

Screw Thread Sealing Agents

Threaded joints often have minor imperfections due to the machining process. These imperfections can lead to leaks if not properly sealed. Below are some of the most common types of sealing agents used in threaded joints:

Liquid Sealant

Liquid sealants act as lubricants and are often combined with compounds like zinc, copper, or nickel to enhance their sealing capabilities. Liquid sealants work by filling gaps and reducing friction during assembly.

Plumber’s Hemp and Paste

Also known as “horse hair and paste,” this traditional sealing method is ideal for sealing poorly manufactured threads.

Thread Seal Tape

This is also called plumber’s tape or PTFE tape. The sealing agent is wrapped around the threads before assembly. PTFE tape acts as a lubricant rather than an adhesive. Thus, it enables the male and female threads to bind tightly, similar to a gasket.

Pipe Dope

Pipe dope is a paste-like combination of sealing material and a solvent carrier. It is applied to the male thread with a brush or spatula before assembly. Pipe dope is ideal for plumbing applications but may shrink or crack over time as it cures.

Anaerobic Resin Compounds

These compounds cure in the absence of air, making them excellent for threaded joints where air is excluded after assembly. A well-known example is superglue, which shares the same curing mechanism.

Conclusion

In summary, flange gaskets play a critical role in ensuring leak-free connections in a variety of systems, from industrial piping to automotive exhaust systems. Whether you choose non-metallic, metallic, or semi-metallic gaskets depends on the specific application, pressure, and temperature requirements. Soft gaskets work best for low-pressure applications, while metallic and composite gaskets are ideal for high-pressure and high-temperature environments.

For reliable, high-quality flanges, Longan Flange is a trusted manufacturer that provides durable solutions for all types of piping systems, ensuring maximum performance and safety.

Resources

A study on the sealing performance of bolted flange joints with gaskets using finite element analysis – ScienceDirect (1)

Corrosion failures of flanged gasketed joints: A review – ScienceDirect (2)