SELECTION CRITERIA FOR GASKETS

What is a Gasket?

A gasket is a mechanical component that seals gaps between two or more surfaces. Depending on their intended application, gaskets come in various shapes, sizes, and materials. They are commonly used in engines, pipes, and other mechanical systems to prevent fluid or gas leaks.

The primary function of a gasket is to create a tight seal between two surfaces, preventing the escape of liquids or gases. A proper seal is essential to maintain the integrity of a mechanical system and ensure that it operates efficiently. A gasket can also help reduce vibration and noise and prevent the ingress of contaminants such as dust and dirt.

Importance of selecting a right gasket

Gaskets are an integral part of many industrial and mechanical applications. They provide a leak-proof seal between two surfaces, preventing fluid or gas from escaping. Therefore, selecting the appropriate non-asbestos gasket ensures the equipment operates safely and effectively.

Choosing the wrong gasket can lead to leaks, which can cause accidents, increase downtime, and incur costly repairs. Gaskets must be compatible with the fluids or gases being transported and withstand the pressure and temperature requirements of the application. Using non-asbestos gaskets is crucial to prevent hazardous airborne fibres.

One of the critical factors in selecting the right non-asbestos gasket is the material. Gaskets are made from various materials, including rubber, silicone, metal, and compressed fibre. Each material has unique properties that make it suitable for specific applications.

Another crucial factor is the design of the gasket. The shape and size of the gasket must match the surfaces it is sealing. A poorly designed gasket can result in uneven distribution of pressure and leaks.

1.     Types of Gasket

• Flat Gaskets

Flat gaskets are the most common type of gasket, typically made of rubber, cork, or non-asbestos fibre. They are used in low-pressure applications and are effective at temperatures up to 200°C and pressures up to 1000 psi.

• Spiral Wound Gaskets

Spiral wound gaskets consist of a metal strip and a softer filler material wound together in a spiral. They are suitable for high-pressure and high-temperature applications, with a pressure range of up to 2000 psi and a temperature range of up to 1000°C.

• Ring Gaskets

Ring gaskets are circular, with a hole in the center for fluid or gas to flow through. They are typically made of rubber, silicone, or metal and are used in applications requiring a high-pressure seal. They can withstand temperatures up to 1000°C and pressures up to 1500 psi.

• Metal Jacketed Gaskets

Metal jacketed gaskets contain a soft filler material such as graphite or non-asbestos fibre enclosed in a metal jacket. They are used in high-pressure seal applications and can withstand temperatures up to 1000°C and pressures up to 2000 psi.

• Kammprofile Gaskets

Kammprofile gaskets are made of a solid metal core with serrations on both sides, covered with a soft filler material. They are suitable for high-temperature and high-pressure applications, with a temperature range of up to 1000°C and up to 2500 psi pressures.

 

2.     Gasket Performance Factor

• Chemical Compatibility

The gasket material must be compatible with the fluid or gas it will contact.

• Temperature and Pressure

The temperature and pressure at which the gasket will be used are critical factors in material selection. Therefore, operating temperature and pressure must be considered instead of the Maximum.

• Environmental Conditions

The gasket material must resist environmental factors such as moisture, UV exposure, and ozone.

• Mechanical Stress

Selecting a gasket that can withstand the mechanical stresses placed upon it is crucial for ensuring its effectiveness in sealing the joint. One should consider the bolt tightening capacity and stress exerted on the gasket to do so. Failure to choose a gasket that can handle the mechanical stresses can lead to deformation, bolt failure, and joint leakage. It's recommended to consult with experts to ensure the gasket chosen can withstand the mechanical stresses of the application.

3.     Most Commonly used gasket material

Gasket Material	Properties	Maximum Temperature	Maximum Pressure	Recommended Use
Non-Asbestos Fibers	Made from organic or synthetic fibres.	500°F	1500 psi	Low-pressure applications
Rubber	Suitable for use in low to medium-pressure applications.	400°F	1500 psi	Low to medium-pressure applications
Metal	Used in high-temperature and high-pressure applications.	1500°F	10,000 psi	High-temperature and high-pressure applications
Graphite	Used in high-temperature applications.	1800°F	10,000 psi	High-temperature applications
PTFE (Polytetrafluoroethylene)	Resistant to high temperatures, corrosive chemicals, and high pressures.	600°F	2500 psi	High-temperature, high-pressure, and corrosive chemical applications

 

4.     Temperature and Pressure Considerations for Gasket

A gasket that is exposed to temperatures or pressures outside of its recommended range can fail, resulting in leaks and potential equipment failure. However, the operating temperature and pressure are more important than the maximum temperature and pressure rating because the gasket will be subjected to those conditions continuously. Therefore, ensuring that the gasket material can consistently withstand operating conditions is essential to prevent leaks and equipment breakdowns.

The maximum temperature and pressure rating is typically determined under ideal laboratory conditions, which may not reflect the real-world environment. Thus, understanding the specific operating conditions is critical to select the appropriate gasket material for the application, ensuring safe and effective performance.

5.     Gasket Design Considerations

• Flange type and design considerations

Flange type and design are vital in selecting the right gasket. The flange face finish and flatness affect gasket sealing and influence gasket compression and deformation characteristics.

• Bolt and torque requirements

Proper bolt and torque specifications are essential to ensure the correct gasket compression and sealing pressure. The bolt load and torque must be sufficient to maintain the gasket's sealing integrity throughout the equipment's operation. The right bolt and torque specifications depend on the gasket material, flange type, and application.

• Gasket thickness considerations

Gasket thickness must be selected based on the application's operating conditions and the required gasket compression. Thicker gaskets are not always better, as they can reduce the bolt load and increase the relaxation risk. The gasket thickness must be sufficient to compensate for flange irregularities and surface finish imperfections.

• Size and shape considerations

The gasket size and shape must be selected based on the flange and equipment's dimensions. The gasket's inside and outside diameters must match the flange size and bolt circle diameter. In addition, the gasket shape must accommodate any bolt holes or obstructions on the flange.

 

6.     Application-Specific Considerations of Gasket

• Compatibility with media being sealed

The gasket must be compatible with its sealing media to prevent chemical reactions and ensure long-term performance. The gasket material should also resist fluid absorption, swelling, or degradation over time.

• Industry-specific requirements and standards

Different industries may have specific requirements or standards that need to be met, such as FDA compliance for the food and beverage industry or NORSOK standards for the oil and gas industry.

• Environmental and regulatory considerations

Environmental factors such as UV exposure, humidity, or ozone can impact gasket material performance. Regulatory like REACH, RoHS, or WEEE compliance should be considered.

• Operational considerations, including vibration and temperature cycling

Applications that experience vibration or thermal cycling may require gaskets with additional features like adhesives or coatings to maintain proper sealing under changing conditions. The gasket should also retain its mechanical properties under pressure and deformation.

7.     Gasket Testing and Certification

Gasket testing and certification standards ensure the reliability and performance of gasket materials in various applications. Typical standards include ASTM F104, ASME BPVC Section VIII, and API 6A.

Testing and certification ensure gasket materials meet specific performance criteria, such as pressure, temperature, and chemical resistance, reducing the risk of leaks and equipment failure.

Types of testing and certification available include pressure, temperature, fire, chemical resistance, and compression and recovery tests. Certification bodies include UL, FM Global, and NSF International.

8.     Gasket Installation and Maintenance

Proper installation and maintenance of gaskets are crucial to ensure leak-free performance and prevent costly downtime. Inadequate installation or neglected maintenance can lead to gasket failure, resulting in fluid or gas leaks that can compromise safety, contaminate the environment, and incur significant repair costs.

Best practices for gasket installation include ensuring that flanges are clean, properly aligned, and free of damage or distortion. The gasket should be installed in the correct orientation and at the recommended torque. A torque wrench and a tightening sequence are recommended to achieve the desired bolt load and gasket compression.

Maintenance considerations for gaskets include periodic inspections and replacements to prevent degradation from exposure to corrosive or abrasive media, thermal cycling, or environmental factors such as UV radiation or ozone. In addition, lubrication or anti-seize compounds can be applied to prevent galling or seizure of metal gaskets, and storage conditions should be optimized to avoid contamination or damage.

9.     Final thoughts and recommendations

Selecting the right gasket for an application can be complex, but ensuring any sealing system's reliability, safety, and efficiency is critical. Therefore, evaluating all selection criteria and consulting with a gasket specialist or supplier is essential to make an informed decision. Additionally, proper installation and maintenance are equally important in ensuring the longevity and effectiveness of the gasket. Following best practices and industry standards can achieve the best possible sealing performance and minimize the risk of failures and downtime.

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