Re-engineering seal reliability in extreme temperature applications 

Reducing unplanned downtime, controlling operating costs and meeting environmental requirements all depend on how effectively rotating equipment is sealed. Non-contacting dual-gas-lubricated metal bellows mechanical seals offer an alternative that addresses these challenges while improving reliability, efficiency and long-term cost control. 

Why high-temperature sealing requires a different approach 
To manage heat and lubrication, conventional wet mechanical seals rely on complex liquid-based support systems that introduce additional equipment and increase operating costs. 

In these environments, sealing performance directly affects reliability, safety and environmental compliance. Extending the mean time between repairs (MTBR) while maintaining effective containment becomes a critical requirement for operators handling hot hydrocarbons or other hazardous process fluids. 

How non-contacting gas-lubricated metal bellows seals operate 
High-temperature corrosive-resistant (HTC) non-contacting metal bellows seals use a pressurised inert barrier gas between the seal faces rather than a liquid fluid film. A nitrogen, argon, or steam barrier is applied at a pressure higher than the process fluid pressure, reliably containing fluids at temperatures up to 425°C (800°F). 

This class of seal technology is exemplified by designs such as the Type 2874HTC, which combines a dual gas-lubricated, non-contacting sealing arrangement with a non-elastomeric metal bellows construction to support stable operation in both hot and cold hydrocarbon services. 

Because the seal faces operate without contact during normal operation, friction and wear are eliminated, extending MTBR and reducing energy costs. 

Principles of non-contacting operation 
Non-contacting gas-lubricated mechanical seals rely on a thin, stable gas film between the seal faces. A specialised face topology, such as a spiral groove, generates hydrodynamic lift when the shaft rotates and the barrier gas is applied. 

This operating principle delivers several performance advantages: 

The pressurised gas barrier both lubricates the seal faces and prevents process fluid from escaping to the atmosphere. 

Pressure-balanced designs also allow seals to accommodate full reverse pressure. 

Role of metal bellows and non-elastomeric secondary seals 
Metal bellows enable non-contacting mechanical seals to operate across a wide temperature range while HTC technology maintains excellent face stability. When paired with inert, flexible carbon-graphite secondary seals, the seal can accommodate both high- and low-temperature services. These secondary seals also eliminate the need for elastomeric O-rings, which can be vulnerable to thermal degradation and chemical attack. 

In mechanical seals such as the Type 2874HTC, this non-elastomeric design supports reliable operation over a temperature range from very low temperature conditions to 425°C (800°F). 

Cleaner operation with lower energy demand 
Using a pressurised gas barrier can enable non-contacting seals to achieve zero fugitive emissions when sealing hazardous fluids. This directly supports environmental compliance while reducing the risk of leaks, spills and associated clean-up costs. 

Further key benefits include: 

Compared with dual-wet-seal systems, non-contacting designs reduce auxiliary energy demand and lower the overall carbon footprint. 

Operating environments that benefit from non-contacting sealing 
High-temperature non-contacting metal bellows seals are applied across the hydrocarbon processing, chemical and petrochemical industries. These seals handle volatile organic compounds (VOCs) and other hazardous fluids, specifying API 610 7th- and 8th-edition pumps.  

Typical applications include: 

The same technology is also suitable for selected cold services down to –73°C (-100°F), including fluids such as ethane, methanol and methylene chloride. 

Installation and support considerations for non-contacting seals 
Non-contacting metal bellows seals are supplied as pre-assembled cartridge designs that require no centring or measuring during installation. For reliable operation, a minimum support system, API Plan 74 is required. 

Defining features of gas barrier support systems include: 

The Type 2874HTC utilises an API Plan 74 or steam panel configurations, supporting a simpler system architecture and lower operating complexity. 

Materials of construction for extreme services 
High-temperature non-contacting seals use materials selected for durability in corrosive and thermally demanding environments. Typical designs incorporate all-metal Inconel bellows combined with mechanical seal faces manufactured from silicon carbide, silicon carbide composites or tungsten carbide. 

Silicon carbide seal faces offer high hardness, corrosion resistance and thermal shock resistance, making them well-suited to the operating envelope of high-temperature hydrocarbon services.  

Life-cycle cost perspective 
Life-cycle cost analysis considers the total cost of owning and operating a sealing solution, including installation, operation, maintenance, downtime and disposal. When evaluated on this basis, non-contacting gas-lubricated seals, supported by API Plan 74, consistently demonstrate significantly lower total cost than dual-contacting wet seals supported by liquid-based systems. 

Cost reductions are driven by simpler support systems, elimination of barrier fluids, lower energy consumption and extended seal life. Estimates show that lifecycle costs for the Type 2874HTC are approximately 50% lower than those for dual wet seals that require support systems and flushes. This is verified by the FSA/ESA Lifecycle Cost Calculator. 

Expertise applied through proven HTC sealing technology 
Reliable sealing in extreme temperature services depends on applying non-contacting technology correctly. Solutions such as the Type 2874HTC—a patented dual gas-lubricated metal bellows seal—reflect John Crane’s expertise in supporting hot and cold hydrocarbon applications while reducing life-cycle costs and environmental risk.