by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Rotary Shaft Seals in the Oil and Gas Industry

Seals in the oil and gas industry face some of the most intense challenges, HPHT (High Pressure, High Temperature) and corrosive media. Trying to find the right rotary shaft seal for such an application can be challenging but is far from impossible.

Introduction to Oil and Gas Seals

Seals are needed in many different areas of the petrochemical industry. They can be found in compressors, motors, gearboxes, pumps, top drives, and steam turbines. Seals are required for mixers, extruders, fans, cooling towers, and blowers. Swivel stacks, wellhead connectors, subsea connectors, and rotary drill bits are also in need of reliable seals to do their job safely and effectively.

And whether these seals are for upstream, midstream, or downstream petrochemical processing, they often serve in a critical application: when a seal in the oil and gas industry fails, it is more than an inconvenience. Seals failures can quickly prove devastating to personnel, the equipment, and the environment. And the costs of seal failure can easily extend beyond equipment downtime and repair costs, as there may be fines related to environmental damage as well as costly lawsuits and out-of-court settlements involved.

With all that said, it can be agreed that seals for rotary shaft applications must be especially reliable, extremely rugged, and able to provide excellent performance in some of the most hostile operating environments in existence.

Spring-Energized Seals

Spring-energized seals include a spring energizer that keeps the seal lip in contact with the sealing surface when other seals would fail. They can maintain a seal even in the presence of wear, out of roundness, eccentricity, and runout. In addition, spring-energized seals outperform traditional lip seals in extreme pressures (including vacuum pressures) and extreme temperatures (including cryogenic temperatures). 

Most oil and gas applications using spring-energized seals take advantage of canted coil springs and their ability to provide a consistent load on the seal lip over a wide deflection range. In addition, canted coil springs are also highly resistant to damage unless they are stretched upon installation.

Labyrinth Seals

Labyrinth seals do an excellent job of sealing and are very effective at contaminant exclusion. They accomplish this through a barrier with a complicated set of maze-like paths (hence the term “labyrinth”) that (1) restricting the clearance through which leaks can occur and (2) creates areas of turbulent flow and high flow friction to further prevent leaks and contamination.  They are considered a dynamic mechanical clearance seal.

One of the benefits of labyrinth seals is their ability to provide sealing without making contact with the sealing surface. This means they experience far less wear than traditional lip seals and generate less frictional losses, as well. They are highly efficient, extremely reliable, and are even easy to install.

Seal Materials

Rotary shaft seals can be exposed to highly corrosive chemicals including methanol, H2S, aromatic hydrocarbons, oil, and supercritical CO2. Many of the chemicals that seals must interact with are also highly flammable gases and liquids. Operating temperatures can range from cryogenic below zero temperatures all the way up to 800°F, depending on the application and media involved. To complicate matters further, some liquid products are handled near their vapor temperature where they can unexpectedly flash into vapor. In addition, the materials used need to be resistant to chemical permeation while also being extremely wear-resistant and flameproof.

Two options typically lie at the top of the list for seal jacket materials: PEEK and PTFE. Both of these high-performance polymer materials are extremely compatible with a wide range of chemicals. They offer excellent performance in the HPHT environment found in most oil and gas applications: PEEK has a maximum operating temperature of  500°F and PTFE can handle temperatures up to 575°F. They also perform well in below-zero cryogenic temperatures, such as those used with LNG.

These engineering polymers are also wear-resistant and flame resistant with low coefficients of friction and thermal expansion. In addition, they are dry-running so no additional lubricants are required.  And PEEK in particular offers excellent performance even in sour gas environments, which often destroys other seal materials.

For spring-energized seals, both PEEK and PTFE are excellent choices. For labyrinth seals, however, PEEK or Flourosint (enhanced PTFE) usually performs more effectively. And keep in mind that these materials can be enhanced with fillers to increase their mechanical properties, including stiffness, strength, and wear resistance.

Conclusion

When traditional rotary shaft lip seals fail in oil and gas operations, consideration should be given to spring-energized seals and labyrinth seals combined with PTFE, PEEK, or enhanced PTFE. This combination of sealing technology and engineering polymers can provide the reliable performance needed in critical applications where seal failure is simply not an acceptable option. Both types of seals and the materials described here have proven performance records for their ability to handle the rugged, corrosive, HPHT environments of the petrochemical industry.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Spring Energized Seals in the Oil and Gas Industry

The oil and gas industry is home to some of the most intense operating conditions for seals: HPHT (High Pressure, High Temperature), corrosive chemicals, and very dangerous repercussions if seals fail. When all other sealing solutions fail, spring-energized seals are often the answer.

How are spring energized seals used in the oil and gas industry? Spring energized seals are used for a variety of applications including valves, well head connectors, couplings, loading swivels, and more.

Spring Energized Seals in Oil and Gas Applications

Seals are used throughout the oil and gas industry, including applications as diverse as …

  • Anti-Blow Out Seals
  • Couplings
  • Downhole Tools
  • Emergency Release Systems
  • Loading Swivels
  • Logging Tools
  • Quick Connect/Disconnect Couplings
  • Rotary Drill Bits
  • Surface and Subsea Well Heads
  • Swivel Stack Seals
  • Top Drive Units
  • Valves
  • Well Head Connectors

A seal failure in any of these areas could quickly lead to injured personnel, environmental damage, and ruined equipment. Seals for such applications must be rugged, reliable, and chemically resistant. They must be compatible with corrosive chemicals such as H2S, aromatic hydrocarbons, supercritical CO2, oil, and methanol,–and they need to be resistant to chemical permeation, as well. They generally need to be flameproof, tough, and wear-resistant as well.

Spring-Energized Seals

A spring-energized seal has a spring (the energizer) that applies additional force to the seal lip to maintain contact between the lip and the sealing surface. This energizing effect can account for issues related to dimensional changes, extreme pressure variations, wear on the edge of the seal lip, and other phenomena that can lead to a leaking seal. 

With the right choice of spring geometry, a constant force can be applied to the sealing lip to ensure its full engagement with the sealing surface, even through extreme pressure variation, temperature changes, wear on the shaft, and alignment issues. Spring energized seals can also be used with backup rings, or BURs, to prevent extrusion problems with the seal lip.

Lip Materials for Spring-Energized Seals

The seal lip material is also key, with the most commonly used polymers for oil and gas sealing challenges being PEEK and PTFE. They are both chemically inert, tough, wear-resistant, flame resistant, and offer outstanding performance even in the presence of extreme temperatures. Both of these materials work extremely well with spring energizer to result in excellent spring-energized seals for the oil and gas industry. They also have very low coefficients of friction and low CTEs (coefficient of thermal expansion).

PEEK performs well at pressures up to 20 kpsi, has a maximum temperature operating temperature of 500°F, and is also available will fillers to provide additional strength and hardness. Many grades PTFE has a maximum operating temperature close to 575°F and can handle high pressures. They are both dry running, as well, which makes them ideal for situations where traditional lubrication is not feasible.

Conclusion

If you are in the market for a reliable sealing solution for an oil and gas application, be sure to consider spring energized seals. They perform where many other types of seals fail, can be used with backup rings, are commonly used in petrochemical applications, and can be designed with a PEEK or PTFE seal lip for maximum performance.