Re-engineering mechanical seals and support systems for extreme services

Improving reliability in extreme service applications requires more than incremental improvements to conventional designs. For operators managing high-temperature or hazardous process fluids, sealing technology plays a criticl role in balancing safety, environmental performance and operating cost. Non-contacting, gas-lubricated metal bellows mechanical seals offer a unique approach that closely aligns with these priorities. 

Customer pressures shaping sealing decisions 
Operators across API 682 industries, such as refining, chemical and petrochemical, face a common set of pressures: 

In high-temperature services, conventional contacting wet mechanical seals often require complex auxiliary systems to manage heat and lubrication. These systems increase capital expenditure and introduce additional failure points, making it challenging to achieve predictable long-term performance. 

Limitations of conventional wet seal systems 
Dual-contacting wet seals supported by lubrication systems rely on continuous circulation of barrier fluids to condition and cool the seal faces. In extreme-temperature services, these fluids are exposed to catalysts that may degrade the barrier fluid and cause coking. 

Common challenges include: 

Over time, these factors drive up operating costs and increase the likelihood of unplanned shutdowns. 

Non-contacting seals as a cost-control strategy 
Non-contacting gas-lubricated metal bellows seals eliminate many of the cost drivers associated with wet seal systems. By using a pressurised inert gas rather than a liquid barrier, they simplify the sealing arrangement and reduce ongoing operating expenses. 

Primary cost-related advantages include: 

These factors combine to deliver a lower total cost of ownership throughout the seal's life. 

Impact on maintenance and reliability 
Because non-contacting seals operate without face contact, they experience minimal wear during normal operation. This directly supports a longer mean time between repair (MTBR), particularly in services where contacting seals suffer accelerated degradation. 

Advantages for maintenance teams include: 

Environmental compliance and emissions control 
Environmental performance is a critical consideration in sealing selection, particularly for services handling volatile organic compounds (VOCs) or hazardous fluids. Non-contacting gas-lubricated seals can provide zero fugitive emissions when operated with a pressurised barrier gas. 

This capability supports: 

In some cases, these seals may also reduce or eliminate the need for ongoing leak detection and repair programmes. 

Reducing energy demand through non-contacting operation 
Energy efficiency improvements are often overlooked in sealing decisions. However, the friction-free operation of non-contacting seals reduces parasitic losses within the pump system. 

By eliminating face contact and cooling requirements, these seals: 

These gains contribute to broader sustainability objectives while delivering tangible operating cost savings. 

Flexibility across temperature extremes 
The combination of metal bellows and inert secondary seals allows non-contacting designs to operate effectively across a wide temperature range. This flexibility makes them suitable for both high-temperature hydrocarbon services, such as oil refineries and selected low-temperature applications. 

Typical operating ranges include: 

This design approach provides several practical advantages: 

Mechanical deal designs such as the Type 2874HTC use this non-elastomeric metal bellows configuration. This delivers consistent sealing performance across extreme temperature ranges, aligning material selection with the demands of high-temperature and cold-service applications. 

Simplifying compliance with material regulations 
Eliminating elastomeric secondary seals reduces reliance on specialised perfluoroelastomers in lower-temperature applications, typically below 260°C (500°F). This has both cost and compliance implications, particularly as regulatory attention on certain materials increases: 

Reducing complexity in seal support systems 
Non-contacting gas-lubricated seals can reduce seal support complexity by using a gas barrier rather than a liquid-based support system. When a mechanical seal such as Type 2874HTC is applied with API Plan 74, the barrier gas typically comes from an existing plant nitrogen supply, reducing infrastructure requirements. 

Benefits of this approach include: 

Steam can also be used as a barrier gas in specific applications, with appropriate support systems. 

Evaluating total cost of ownership 
A comprehensive life-cycle cost model provides a clear framework for comparing sealing options. When all cost elements are considered, non-contacting gas-lubricated seals consistently deliver strong economic performance in extreme service conditions. 

Typical cost categories include: 

In high-temperature hydrocarbon applications, elimination of external flushes alone can result in substantial annual savings. 

Engineering expertise that supports long-term value 
Lower life-cycle costs and extended MTBR in extreme service conditions rely on non-contacting sealing strategies. Supported by John Crane’s application knowledge, the Type 2874HTC dual gas-lubricated metal bellows seal provides reliable, efficient, and regulation-aligned operation throughout the full lifecycle of the rotating equipment.