Seals that can withstand high temperature and pressure applications are required for safety and efficiency reasons in industries such as petroleum and food processing. Without using the right sealing technology, sealing materials deform or become completely damaged, leading to compromised seal integrity.

Confining fluids at pressures below 5,000 psi can be effectively accomplished using standard U-cup seal functions and energized urethane lip seals without the need for any special provisions. However, special sealing is required when dealing with pressure above this threshold.

Let’s examine the various factors to consider when selecting sealing technology for applications that require robust temperature and pressure management, along with an overview of four sealing technologies utilized in these scenarios.

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Seal considerations for high-pressure and high-temperature applications

To ensure the sealing technology used performs effectively, it is essential to choose the appropriate type. Common problems associated with incorrect use of seals include fluid or gas leaks, temperature rise, premature wear and maintenance difficulties. That said, below are five factors to consider when selecting seal materials.

Microscopic irregularities

Sealants must be suitable for the microscopic irregularities of the mating surfaces to prevent fluid passage or penetration due to pressure. Mating surfaces refer to parts or areas that come into contact with each other. When these surfaces are viewed on a microscopic level, they are not entirely smooth or flat. There would be imperfections such as scratches through which fluid molecules can escape.

Sealants used in demanding applications must be able to fill in the voids and gaps created by surface imperfections.

Clearance-gap adjustments

When sealing spaces between the piston and cylinder wall meet, high temperature from the heating process can cause the space between the two mating surfaces to grow. The size of the clearance gap can also change due to variations in the diameter and roundness of the cylinder parts.

If the sealing element can’t adjust to changes during a cylinder stroke, this leads to fluid leakage. Therefore, the ability to seal to maintain a compressive sealing force between the surfaces in question must be considered.

Resist extrusion

Pressure differences between the pressurized and unpressurized sides of the sealing can push a sealant into the clearance gap between surfaces, leading to leakages and damage to the seal material. The sealing material used must possess sufficient stiffness and strength to resist being deformed into the gap and damaged or destroyed.

Contamination

It's also important to ensure that the sealing material used does not leach its content or shed particles into the system, leading to fluid contamination.

Maintenance requirements

Lubrication is essential for seals to ensure optimal performance under high friction conditions. The design of the sealing material must be carefully considered for the frequency of lubrication. The seal must also withstand system vibration, otherwise it breaks down quickly.

Another important aspect of seal maintenance is the accessibility of replacing it. If the sealant isn’t something that can be procured and delivered quickly, system operators must make provisions in advance and store spares. This approach ensures that manufacturing is not overly dependent on unstable supply chain logistics.

Sealing technologies for high-temperature and high-pressure applications

Having seen five important considerations when selecting seals for manufacturing processes with high temperature and pressure, let’s consider four seals used in such environments.

Cartridge seals

Cartridge seals are mechanical seals used for containing fluids in rotating equipment such as mixers and pumps. Mechanical seals are used to prevent large amounts of pressurized fluids from escaping vessel systems with rotating shafts.

A cartridge mechanical seal is a preassembled, self-contained unit featuring components that are mounted on a single, easy-to-install sleeve. Unlike traditional seal technology that involves complex assembly typically done on-site, cartridge seals’ preinstallation helps reduce on-field assembly errors.

Parts that go into a cartridge seal are a sleeve, gland plate, seal faces, lock collar, and energizing force source.

Gaskets

A gasket creates a pressure-tight sealing between multiple stationary components under compression. It plays a crucial role in ensuring leak-free operations in many machines and equipment. Gasket material is deformed to match the surfaces for which it provides sealing.

Gaskets are manufactured using different materials including rubber, paper, metal, silicone, felt and cork. The gasket employed in mechanical sealing must be evaluated based on the intended application.

It's important to note that gaskets may not be considered sealants because they are not deployed in leakage prevention between moving parts such as rotating shafts. However, gaskets serve similar purposes as seals, particularly for static components.

Metal bellow seals

Metal bellows are metallic seals designed as leak-tight sealants to effectively separate two environments from one another. They are designed to compress, expand, and bend to absorb angular and axial movement. Metal bellows find application in beamlines, actuators, expansion joints, thermal expansion tanks and more.

All metal bellows are not manufactured the same. Edge-welded bellows are designed by succession welding of precut diaphragms, while formed bellows are manufactured through the process of hydroforming, mechanical forming, or elastomer-forming. Other types of bellows include electroformed, vacuum, and electrical contacts. The type used depends on the intended application.

Magnetic seals

Magnetic seals are sealing units used to prevent the leakage of gasses in rotating parts. Rotating mechanical systems come with a clearance between the rotating part such as the shaft and the static part such as the bearing.

The clearance prevents friction between the two parts, which can lead to overheating and premature wear. The clearance can also allow the gasses required for optimal system performance to escape, necessitating the need for some sort of sealing. Maintaining the pressurized condition and vacuum condition in a container requires the sealing of the clearance.

Conclusion

Sealing used in petroleum, food processing and other industries with demanding systems must suit the intended applications. This helps prevent leakages that can drive up waste. Appropriate use of sealing can also prevent system inefficiencies and premature breakdown.

The suitability of a sealant for the mating surfaces, protection against contamination, and ease of maintenance are important factors to consider when choosing sealing materials for high pressure and temperature environments. Depending on the machine or system, sealing can be carried out by cartridges, gaskets, metal bellows or magnetic seals.

By ensuring the right use of sealants, producers and manufacturers in different industries can ensure leak-free operation and increased system uptime.