By Rebecca Phan (August 2021)
Elastomeric seals such as rubber gaskets and O-rings have long been the “default” sealing solution, finding use in virtually all industries as well as domestic applications. However, despite their ubiquitous presence, elastomeric seals are prone to failure at high temperatures and pressures. For the most demanding applications – such as in cryogenic space systems, nuclear power plants and commercial aircraft – metal-to-metal seals have been proven to provide the necessary resilience and performance. This technical article takes a closer look at the benefits and applications of metal-to-metal seals.
In a fluid containment system, interfaces between different components (for example, the joint between two pipes) present an opportunity for fluid to escape from the system. Therefore, any fluid containment system – whether a gas pipeline or a central heating system – typically requires sealing.
The conventional sealing solution to this problem is to sandwich a layer of soft elastomeric material in the interface between any two parts of the system. A simple example is using a rubber O-ring to seal the joint between two metal pipes: place an O-ring in a groove at the end of one pipe, then connect the pipes using a compressive force (e.g., via a bolted flange or screw connection). Compression deforms the soft elastomeric ring, causing it to conform to the shape of the interface between the two pipes, as well as acting as a load-bearing component.
Non-metal-to-metal seals such as these are typically easy to fit, require low compressive forces, and provide a water or air-tight seal in typical applications. Indeed, for many years, elastomeric seals provided sufficient versatility and performance to meet the needs of industry.
However, over the last 50 years or so, process requirements have evolved beyond the capabilities of elastomeric seals, with metal-to-metal seals taking their place in high-performance applications.
Metal-to-metal seals offer a much greater range of operating temperatures than elastomeric seals. If too cold such as below 50°C (32°F), elastomeric materials undergo a glass transition, losing elasticity and mechanical stress resistance. Too hot around 250°C (482°F) and an elastomer can melt or degrade. This is not the case with metal-to-metal seals, which can operate at temperatures in excess of 1,100°C (2,000°F). Elastomers also have strict pressure limits: if the differential pressure across a seal is too high, elastomers are prone to destruction by extrusion. Metal-to-metal seals easily outperform elastomers in this regard, providing effective seals beyond 25,000 psi.
Applications of Metal-to-Metal Seals
Since metal-to-metal seals offer required fatigue-resistance and sealing characteristics, they are widely used for the most demanding high-pressure and high-temperature applications.
Space & Aviation (Aerospace)
When referring to extreme environments or challenging operating conditions, space applications are at the top of the list. Due to cryogenic and very high temperatures as well as sealing and leakage control requirements, metal sealing solutions are relied upon in several critical systems.
Rocket engines (fuel lines and combustion chambers)
AS 5202 Ports (hydraulic ports with metal boss seals or fitting seals)
Fuel tanks (propellants)
Valves (fluids and gases)
In aviation applications, high operating temperatures in jet engines may pose a challenge to polymer seals. Instead, for these applications, metal-to-metal seals are selected, which offer low leak rates and resistance to thermal cycling.
Chemical, Plastics and Petrochemical
Metal-to-metal seals can easily handle the rapid thermal cycling that renders elastomer seals incompatible with many pressure vessels, pumps and valves in the petrochemical, chemical and plastics industries. Thanks to plating, metal-to-metal seals also offer the best chemical compatibility, providing a durable and corrosion-resistant seal.
Nuclear Power
The nuclear industry places huge demand on metal-to-metal seals: as well as exposing them to high temperatures and radiation, these seals must exhibit superior performance to prevent dangerous radioactive leaks. Metal-to-metal seals are a proven solution for the many valves, fittings, piping systems and large enclosure vessels used in nuclear reactor systems.
To find about more about our range of metal-to-metal seals for high pressure and temperature applications, get in touch with our experts today.
Metal-to-metal seals withstand extreme temperatures above 1,100°C (2,000°F) and pressures beyond 25,000 psi. They also resist radiation, corrosive chemicals, and fatigue, unlike elastomers or rubber seals that degrade, melt, or extrude under such operating conditions.
Metal sealing solutions are critical in aerospace (rocket engines, hydraulic ports, fuel systems), energy (gas turbines), industrial applications (pressure vessels, pumps, valves), semiconductor manufacturing (wafer fabrication, vacuum chambers) and nuclear power (reactors, piping, enclosures, spent fuel casks).
Elastomers lose elasticity below –50°C (–58°F), degrade structurally around 250°C (482°F), and fail under high differential pressures. These limits make them unsuitable for extreme temperatures, deep vacuum, and high-pressure environments.
The choice of seal material is key to ensure chemical compatibility. Seals can also be plated with specialized coatings that resist corrosion and chemical attack, making them durable in aggressive chemical environments.
They deliver low leak rates, maintain sealing under thermal cycling, and withstand radiation exposure, ensuring safety and performance in critical applications.
