Mechanical Seal Strategies for Ethane and Ethylene Service

The 2026 Turbomachinery and Pump Symposia kicked off with a session from John Crane on mechanical sealing advancements and strategies in ethane and ethylene applications. The key messages were that volatility is inevitable and must be addressed, and that each application needs to be custom engineered with regard to the type of seal and the materials deployed.

Brian Kalfrin, senior manager of regional engineering for North America for John Crane, led the discussion. He explained that natural gas liquids (NGLs) are critical components of the downstream refinery, petrochemical and specialty chemical processing industries. They are usually byproducts from upstream natural gas gathering. Ethane, which is one of the simplest molecules containing more than one carbon atom (C₂H₆), is the foundation of many of these compounds.

“Ethane is processed as either a purity product or blended with propane (known as EP mix) to be used in ethylene production,” Kalfrin said. “They are extremely volatile and difficult to seal, requiring mechanical seals with high seal-face stability and good lubrication.”

Because of the challenging environment, face materials tend to experience higher wear rates due to increased temperature and friction. Kalfrin laid out a variety of mechanical seal component and design strategies to improve reliability in these applications, particularly for midstream pipeline and other gas processing type applications.

NGL Fundamentals

NGLs are condensed hydrocarbons that facilitate transportation and storage. They include what are known as dry gases (ethane), liquefied petroleum gas (LPG – propane, butane and isobutane), and heavier fractions (pentanes, naphtha, natural gasoline and condensate). Almost all the ethane and NGL production in North America is sourced from natural gas processing plants. Worldwide, the percentage drops to around 60%.

To be considered purity-grade, ethane must be at least 95% pure. But even when dealing with extremely pure ethane – 98% or above – there is still particulate present that can cause severe problems for mechanical seals. The typical operating parameters for purity ethane are:

• Suction pressure of 41 to 97 barg (600 to 1,400 psig)
• Maximum discharge pressure of 152 barg (2,200 psig)
• Speed range of 1,800 to 3,600 rpm
• Temperatures of 10 C to 33 C (50 F to 90 F)

Low viscosity and low specific gravity are also the norm; two to three pumps in parallel are generally used in such applications.

Despite the challenging operating environment, advances in simulation technology have enabled John Crane to tailor mechanical seals more exactly to operating conditions. Modeling paired with in-depth lab and field testing has enabled designers to better understand the various phases that ethane and other NGLs experience. The accumulated know-how in recent years means that there is a much clearer understanding of how to adapt seals to suit subtle differences in phase state, temperature and pressure.

As problematic as ethane applications can be, though, ethylene is even more challenging as it has a lower critical temperature. Both are low-viscosity fluids with low film stiffness, high volatility and a tendency for pressure spikes. Designers must pay close attention to boundary lubrication and changes in fluid density to avoid chipping, cracking and degradation of mechanical seals.

Material Selection

Due to these factors, the choice of materials used in mechanical seals is crucial. Unfortunately, there is no one answer to the question of which material is best.

Carbon, for example, has plenty of advantages. It is compliant, resists thermal shock, can manage temperature loss within the lubricant and can tolerate full face contact without excessive heat being generated. However, it has lower strength compared to other materials, is porous and can’t be used in pressures above 1,200 psi. If carbon is being used, attention must be paid to how torque is transmitted so as not to induce stress.

Silicon carbide and tungsten carbide are further options. Both are harder than carbon and are suitable for high-pressure service. In John Crane’s experience, silicon carbide is preferred over tungsten carbide for ethane applications. There is also an alternative known as graphite-loaded silicon carbide, which offers improved performance under fluid film instability. However, the quality of the graphite must be kept to a high level.

Speakers from John Crane mentioned one other possibility – diamond-treated faces. Their advantages include strength, low friction, and suitability for applications where fluid films might collapse or vaporization is likely.But diamond-treated faces require longer lead times and are more expensive. Bottom line: no one material fulfills all needs and works for all applications. Skilled design, simulation and engineering are required to customize mechanical seals to the needs of the specific NGL and the application.

Installation and Operating Tips

The presentation continued with a discussion about installation criteria when fitting mechanical seals into pumps. This area is often overlooked. Yet it is a major contributing factor to seal failures, especially with ethane pumps. Slight deviations in the face surfaces, for example, can lead to instability and leakage, especially in static pressure scenarios. Those installing seals are advised to work closely with their supplier to ensure that the equipment and the seal are correctly aligned.

Finally, proper lubrication of mechanical seal faces is essential for prolonged reliability. John Crane recommends a flush rate of 2.5 gallons per minute per inch of seal. Even non-contacting seals need to be flushed, though the rate can be reduced to one or two gallons per minute.

“Even in pure ethane, there is other material that can cause problems, and it all needs to be flushed out,” Kalfrin said. “Additionally, most successful midstream installations use good filtration.”