The failure mode most frequently associated with high fluid pressure is extrusion. Extrusion is the phenomenon of the O-ring being forced into the clearance gap, rendering damage to the seal and eventual leakage. The amount of pressure the O-ring can withstand is generally a function of the clearance gap and the material selection. Material properties which greatly contribute to resisting extrusion are hardness and modulus of elasticity.
Modulus of a compound is a measurement of the ability to recover from a localized force, such as pressure. In a laboratory setting, the modulus is the stress at either 50% or 100% elongation, stated in psi (pounds per square inch) or Mpa (MegaPascals). The higher the Modulus, the more resistant the material will have to extrusion.
Coupled with high modulus, the other physical property which helps a material resist extrusion is Shore A Hardness. Empirical data shown in the Limits for Extrusion Chart supports higher hardness materials will withstand significantly greater pressures within the same set of application conditions. Extrusion resistant O-ring materials include those shown in the chart below.
O-Ring with Back-Up Ring
Specialty seals are designed when hardware cannot be changed or controlled.
HPHT Double Chamfer Seals
High Pressure High Temperature (HPHT) Double Chamfer Seal, originally designed for the aggressive pressures and temperatures common in oil & gas applications, could work in many high pressure applications.