Metal ring seals are static devices that can withstand high temperatures, pressures, and vacuums. They can also withstand cryogenic conditions and high face-to-face cycling. There are three basic types of metal ring seals: plain, self-energized, and pressure-filled. With spring-energized seals, compression deforms a plastic jacket that is more ductile than the flange materials. Flanges have a sealing face and an elastic core that includes a tightly wound helical spring whose coils have a specific compression resistance. During compression, the pressure forces the jacket to yield, fills the flange’s imperfections, and ensures positive contact with the flange’s sealing faces. Each coil in the helical spring acts independently.

Metal ring seals are available in a variety of shapes, sizes, and materials. Some are rounded, rectangular, or square. Others are oblong or oval. Metal ring seals vary by outer diameter and length, and are made from aluminum, copper, silver, nickel, steel, or stainless steel. Some metal ring seals are plated or coated with cadmium, copper, nickel, silver, gold, or indium. Others are heat-treated, age-hardened, or annealed. In terms of performance, metal ring seals have an operating temperature range, a pressure range, and a vacuum range. For example, metal ring seals that are designed for cryogenic conditions can withstand a range of low temperatures.  

Some metal ring seals have cross-sections that are shaped like letters. For example, O-rings have O-shaped cross-sections and are used as secondary seals or gaskets. C-rings are fully vented O-rings that are self-energizing under pressure. Typically, O-rings are interchangeable with C-rings of the same free height. U-rings and V-rings have similar geometries and are often regarded as one type. These robust seals are able to withstand a wide range of pressures and temperatures. Other lettered metal ring seals include E-rings and W-rings. Unlike other metal ring seals, metal wedge seals consist of a simple metallic chamfer ring. 

Metal ring seals are used in a variety of applications and industries. For example, they are used in aerospace, nuclear, and power generation applications. These devices are also used in industrial piping and valves, semiconductors, and cryogenics. Metal ring seals that are used in the oil and gas industry are rated for use with petrochemicals such as engine oil, gasoline, and diesel fuel. Chemical companies use seals with a high degree of resistance to corrosive substances such as acids and solvents. MIL-SPEC metal ring seals are designed in accordance with military specifications.