Full definition
Seal extrusion is a critical failure mode that occurs when the sealing material, typically elastomeric, is forced into the clearance between two mating metal surfaces due to fluid pressure. This phenomenon can lead to permanent damage to the seal, resulting in leakage and system failure. The mechanics behind this issue involve the interplay of pressure, material properties, and geometrical tolerances. When the pressure exceeds the capability of the sealing material, especially in high-pressure applications, the material can extrude into the gap, compromising the integrity of the seal. This failure is particularly prevalent in dynamic sealing applications where there is relative motion between the sealing surfaces. The severity of extrusion is influenced by multiple factors, including the hardness of the seal material, the geometry of the sealing profile, and the presence of backup rings. Materials with lower hardness are more susceptible to extrusion, particularly when they are subjected to high pressures. For instance, at fluid pressures exceeding 7 MPa (approximately 70 bar), the risk of extrusion increases significantly if backup rings are not utilized. Backup rings, typically made of PTFE or PEEK, serve to reinforce the sealing system by providing additional support and preventing the elastomer from being forced into the clearance. Reducing the diametral clearance to less than 0.1 mm at high pressures, such as 350 bar, is another effective strategy for minimizing extrusion risk. This tight tolerance helps ensure that the seal remains adequately compressed and less prone to being forced out of position. Understanding these factors is essential for engineers and maintenance personnel to design and select seals that can withstand specific operational conditions without failing due to extrusion.