A Practical Guide to Gasket Thickness Decisions

In the field of industrial sealing, gaskets are ubiquitous, playing a crucial role in ensuring sealing performance and preventing leaks, from delicate chemical pipelines to massive pressure vessels. However, selecting the appropriate gasket thickness for specific applications is a complex and frequently asked question. This article will delve into the scientific basis for gasket thickness selection, the considerations in engineering practice, and how to make optimal decisions under various operating conditions.

The selection of gasket thickness is not a one-size-fits-all solution; it is influenced by a combination of factors. Firstly, the material, size, and shape of the flange are fundamental considerations. For instance, thin flanges are prone to deformation after bolt tightening, while large-diameter flanges require more bolt force to maintain a seal. Secondly, the properties of the working medium, such as pressure, temperature, and chemical nature, also impose different requirements on gasket performance. Additionally, the characteristics of the gasket material itself, such as compression rate and creep relaxation properties, determine the applicable thickness range. These factors are interwoven, making gasket thickness selection a decision-making process that requires a comprehensive trade-off.

In many cases, thin gaskets are the preferred choice. The advantages of thin gaskets lie in their smaller contact area with internal pressure, which enhances their blowout resistance and reduces leak rates. Moreover, thin gaskets have lower creep relaxation characteristics, allowing them to better maintain the torque of fasteners and thus sustain sealing performance. Additionally, thin gaskets are relatively less expensive. For example, in the design of flanges for higher pressures, thick flanges can typically maintain flatness after bolt tightening, with a flatness level of 0.1 mm. In such cases, the "the thinner, the better" recommendation is appropriate.

Thin gaskets, due to their smaller contact area with internal pressure, experience less blowout force. Under high-pressure conditions, this enables thin gaskets to better withstand the impact of internal pressure and maintain sealing performance. For instance, in the high-pressure pipelines of the oil and gas industry, the use of thin gaskets can effectively reduce the risk of leaks and ensure production safety.

Similarly, because of the smaller contact area with internal pressure, thin gaskets have shorter leak paths, thereby reducing leak rates. In the chemical industry, many media are corrosive or toxic. Using thin gaskets can effectively minimize leaks, protecting the environment and the safety of operators.

Thin gaskets have lower creep relaxation characteristics, meaning that over long-term use, the gasket can better maintain its compressive load, reducing seal failure due to creep relaxation. In equipment that requires long-term stable operation, such as steam pipelines in power plants, the advantages of thin gaskets are particularly evident.

Despite the preference for thin gaskets in many situations, there are certain special operating conditions where thick gaskets are a better choice. These include:

When flanges are prone to deformation after bolt tightening, thick gaskets can better accommodate the flange's unevenness. For example, 6.4 mm thick angle iron or steel plate flanges, being relatively thin, can easily become uneven after bolt tightening. In such cases, a 3.2 mm thick gasket is necessary because thin gaskets cannot provide sufficient compression to compensate for the flange deformation.

Large-diameter flanges, such as those in AWWA standard water pipelines and 3-meter diameter pressure vessel flanges, require more bolt force to maintain a seal due to their size. In these situations, thick gaskets can provide greater compression, better accommodating the flange's unevenness. Additionally, the limited number of bolts in large-diameter flanges means that thick gaskets can offer better sealing performance with the available bolt force.

Many low-pressure full-face large-diameter flanges have limited bolt force, which also means limited gasket compression. In such cases, thick gaskets can better adapt to the flange's unevenness and provide sufficient sealing performance. For example, a 66 flange with a flange thickness of about 6.4 mm and 20 bolts of 5/8 inch. For such a large flange, the number and size of bolts are insufficient. In this case, a 3.2 mm thick gasket is more suitable than a 1.6 mm thick gasket because the large bolt spacing means that thin gaskets cannot provide enough compressive load to accommodate the curved flange.

Old flanges may have a certain degree of pitting, bending, or damage. Thick gaskets can better fill these defects and provide better sealing performance. For example, in some aged chemical pipelines, using thick gaskets can effectively reduce leaks and extend the service life of the equipment.

Although thick gaskets are necessary in certain situations, they also bring some potential problems. Firstly, thick gaskets have higher creep relaxation characteristics, meaning that over long-term use, the gasket may gradually lose its compressive load, leading to seal failure. Secondly, thick gaskets have greater blowout force, which increases the risk of the gasket being blown out, especially under high-pressure conditions. Additionally, thick gaskets have larger permeation channels, which may result in higher leak rates. Therefore, when selecting thick gaskets, it is necessary to consider these potential issues comprehensively and take corresponding measures to reduce risks.

Thick gaskets have higher creep relaxation characteristics, meaning that over long-term use, the gasket may gradually lose its compressive load, leading to seal failure. To address this issue, regular inspection and retightening of bolts are required to maintain the gasket's compressive load. Additionally, selecting gasket materials with lower creep relaxation characteristics is an effective way to reduce risks.

Thick gaskets have greater blowout force, which increases the risk of the gasket being blown out, especially under high-pressure conditions. To address this issue, gasket materials with higher blowout resistance should be selected, and the flange design should provide sufficient bolt force to counteract the blowout force. Moreover, rational flange structure design, such as increasing the number of bolts or using thicker flanges, can also effectively reduce blowout risks.

Thick gaskets have larger permeation channels, which may result in higher leak rates. To address this issue, gasket materials with lower permeability should be selected, and the gasket's compression should be sufficient to effectively fill the flange's defects. Additionally, rational flange structure design, such as increasing the flange's flatness or using thinner gaskets, can also effectively reduce leak rates.

In some special cases, gaskets with very specific thicknesses are required. These include:

The final thickness of split pumps is critical as it affects the gap between the two sides of the pump. These pumps typically use 0.4 mm non-asbestos compressed gaskets. Customers sometimes require sheets with very small thickness tolerances and minimal thickness variations. In such cases, special attention must be paid to the gasket's compression to ensure that the final thickness meets the requirements.

In long-distance pipeline systems, there may be spacing issues. For example, a standard spiral-wound gasket, when compressed, measures approximately 3.2 mm in thickness. If a thinner gasket is used and there are many flanges along a pipeline, a large gap will form between the last two flanges. In such cases, the gasket thickness must be selected based on the actual spacing.

When using tongue-and-groove flange structures or concave flanges, the gasket must fill the entire space and be compressed before the flange metals come into contact. The compressed thickness of the gasket after loading must be calculated and must be greater than the gap produced after the flanges come into contact. For example, if the groove is 3.2 mm deep and the tongue is 0.6 mm high, the compressed thickness of the gasket must exceed 2.6 mm; otherwise, the flanges will come into contact before the gasket is fully compressed.

The type of gasket material and the allowable compressive load also affect the gasket thickness required to seal a specific flange connection. Under the ASTM F36 standard test, gaskets with higher compression rates compared to those with lower compression rates do not require the same gasket thickness. This is because a more easily compressible gasket does not need to be as thick to adapt to flange imperfections. Therefore, when selecting gasket material, it is necessary to choose the appropriate material and thickness based on actual operating conditions.

The compression rate of a gasket refers to the amount of compression the gasket undergoes under a given load. Gaskets with higher compression rates can provide greater compression with a smaller load, thereby better accommodating flange unevenness. Therefore, when selecting a gasket, the compression rate should be chosen based on the flange's flatness and bolt force.

The allowable compressive load of a gasket is the maximum load the gasket can withstand without damage. Selecting the appropriate compressive load ensures that the gasket will not be damaged by overloading during use while also providing sufficient sealing performance. Therefore, when selecting a gasket, the allowable compressive load should be chosen based on the flange's bolt force and operating pressure.

Proper installation and maintenance are key to ensuring the sealing performance of gaskets. During installation, it is necessary to ensure that the flange surface is clean and flat and that the bolts are tightened to the specified torque. Additionally, regular inspection and maintenance of flange connections, timely detection, and handling of potential problems can effectively extend the service life of gaskets and ensure sealing performance.

Clean the flange surface: Before installing the gasket, the flange surface must be thoroughly cleaned to remove oil, rust, and impurities to ensure that the gasket can closely adhere to the flange surface.

Check flange flatness: Before installing the gasket, the flatness of the flange should be checked to ensure that there are no obvious pits, bends, or damages on the flange surface. If the flange surface is uneven, it should be repaired or replaced.

Tighten bolts evenly: When installing the gasket, the bolts should be tightened evenly to the specified torque to avoid flange deformation or gasket damage due to uneven bolt force. Additionally, the bolts should be tightened in a diagonal sequence to ensure even force distribution on the flange.

Regular inspection: Regularly inspect the sealing performance of flange connections to promptly detect and address potential problems. If leaks or gasket damage are found, the gasket should be replaced in a timely manner.

Retighten bolts: Over long-term use, gaskets may gradually lose their compressive load, leading to seal failure. Therefore, it is necessary to regularly retighten the bolts to maintain the gasket's compressive load.

Replace gaskets: If a gasket is damaged or aged, it should be replaced promptly. When replacing a gasket, the appropriate gasket material and thickness should be selected, and the installation should be carried out according to the correct method.

Selecting the appropriate gasket thickness is a decision-making process that requires a comprehensive consideration of various factors. In many cases, thin gaskets are the preferred choice due to their smaller contact area with internal pressure, lower creep relaxation characteristics, and lower cost. However, in certain special operating conditions, thick gaskets are a better choice because they can better adapt to flange unevenness and provide sufficient sealing performance. When selecting gaskets, it is necessary to choose the appropriate gasket material and thickness based on actual operating conditions and ensure proper installation and maintenance to ensure the sealing performance and service life of flange connections. Through an in-depth analysis of the scientific basis for gasket thickness selection and the considerations in engineering practice, we can better understand how to select the appropriate gasket thickness for specific applications. It is hoped that this article will provide useful references for engineers and technicians in the industrial sealing field, helping them make scientifically sound and rational decisions in their actual work.