Flange gaskets are mechanical seals; placed between two flanges to prevent liquid or gas leakage. Such gaskets can be made of diverse materials like rubber, cork, fiber, or metal and are available in various shapes and sizes.
Different flange gasket types and their usage in various applications:
Full-face gasket
Covers the entire face of the flange.
It consists of bolt holes matching the flange.
Ring-type gasket
The intended use is to fit inside the bolt circle of a flange.
Metals like stainless steel or carbon steel are used to make these gaskets.
Spiral wound gasket
It comprises metal winding with filler materials like graphite placed between the windings.
Suitable for high-pressure and high-temperature applications.
Kamm profile gasket
It consists of a serrated metal core with a soft material, such as graphite or PTFE, placed on either side.
Used in high-temperature and high-pressure applications.
Jacketed gasket
It has a metal casing around a soft filler material like graphite or PTFE.
They are common in heat exchangers and other applications with high temperatures and pressures.
Corrugated metal gasket
Made of a thin metal sheet corrugated or folded to create a seal.
Used in high-pressure and high-temperature applications.
Rubber gasket
For rubber gaskets, they use elastomeric materials and rubber.
Used in low-pressure applications.
Choose the Right Flange Gasket- What You Should Know
When selecting a flange gasket, piping engineers must account for four significant criteria. These include the type of fluid, temperature, and pressure of the process, fugitive emissions legislation, and other pertinent elements.
Let us dive into each of these factors:
Fluid Type
Selecting the correct type of gasket for a pipeline depends on the type of fluid that will flow through it. You can use different gasket materials for diverse fluids to ensure that the flanged joint lasts for a prolonged period.
In addition, sealing gases is more complex than sealing liquids, and the aggressiveness of certain fluids can increase when exposed to higher temperatures.
Therefore, opt for a gasket material that can withstand corrosive attacks from the system fluid and preserve its physical properties.
Process Temperature and Pressure
When selecting the proper gasket material, one should bear in mind the working temperature and pressure of the pipeline. Therefore, the material must have the ability to survive both the most extreme temperature-pressure scenario in the process (high temperatures for hot applications, low temperatures for cool ones).
In addition, the gasket must not suffer any creeping when subject to the maximum pressure in the system, which usually is the test pressure and can exceed twice the rating at ambient temperature.
The Flange Load
All gasket materials must experience enough flange pressure to compress the gasket. In addition, it helps to ensure that the gasket remains unbroken with secured sealing.
The flange pressure needs even distribution, also known as the “y” factor. However, during operation, the greatest force is usually exerted near the bolts, while the lowest is between two bolts.
Therefore, flange designers must remember when making their design decisions.
Flange Gasket Diameter and thickness
The size of a gasket’s outer Diameter plays a pivotal role in determining its pressure resistance; the larger it is, the greater the capacity. However, it would help if you considered the thickness of a gasket when selecting its material. Generally,
The thinner the gasket, the more compressive stress it can handle, though it will necessitate a higher surface finish quality of the flange faces. For optimum performance, the gasket should be four times thicker than the maximum roughness of the faces.
In conditions where vibrations occur, it is advisable to choose a thicker gasket than what is initially needed.
Gasket Surface Finish
Surface finishing is crucial to forming a successful physical barrier between two flanges. The finish can be either machined or pressed onto the gasket.
It contains grooves or channels. If the finish is too fine or shallow, it will lack the grip needed to maintain integrity.
The too-deep finish creates complications in forming a seal due to an excessive bolt load on large flanges.
Stress Relaxation
This metric evaluates a material’s resilience across a period, commonly indicated by a decrease in percent per unit of time.
Although any gasket material may succumb to wear and tear from the pressure, the remaining strain should stay steady after the initial relaxation period.
Fugitive Emissions Laws
When selecting an appropriate gasket for a process, one must consider the fugitive emission laws of the country.
Stricter fugitive emissions regulations may ultimately affect the type of flange and gasket you should use for the process’s flanged joints.
General Aspects To Consider When Selecting A Flange Gasket
Pipeline Oscillation and Vibration:
The expected performance of gaskets is to endure any oscillations and vibrations that could impact the pipeline.
Fluid Contamination Risk
In certain circumstances, gaskets can prove useful. When you use them, they do not taint the fluid transported through the pipeline. These are relevant across industrial sectors like food, pharmaceuticals, and gas.
Flanges Corrosion
Choosing the appropriate gasket type and material is imperative. It would help to consider that certain flange materials, such as austenitic stainless steel, may be susceptible to stress corrosion cracking.
Integrity
It is essential to prevent potential harm to human lives or prevent soil pollution, and the toxic fluids need to be completely leak-proof seals. Hence, it is necessary to opt for tighter and strong gaskets.
For instance, for these types of applications, you can go for a spiral wound gasket with an outer ring instead of non-asbestos gaskets.
Financial Risk
The selection of inappropriate gaskets can result in significant financial risk, despite their relatively low cost compared to other piping materials. Opting for cheaper gaskets to save costs can be a risky decision.
It threatens the contractor, who may face penalties, and the end-user. Hence, carefully consider the potential financial impact of gasket failure when deciding about gasket selection.
Conclusion
Although gaskets are economical in constructing a piping system, their role in preserving its trustworthiness and quality is pivotal. Thus, scrimping on gaskets may cause immense difficulties in the long run, so one should take care while selecting them for any application.