A spiral wound gasket combines the elasticity of metal with the plasticity of soft filler materials. It is constructed by alternately winding V-shaped metal strips and soft filler tapes (graphite or PTFE) into a composite structure. Its sealing performance is achieved through three stages.
1. Initial Sealing – Soft Filler Conforms to Flange Surfaces
When flange bolts are tightened, the applied load compresses the gasket. The soft filler material (graphite or PTFE) deforms plastically under pressure and flows into the fine machining grooves, scratches, and localized corrosion pits on the flange sealing faces, blocking potential leak paths at the source. Simultaneously, the V-shaped metal strips are compressed with their opening angle reduced, yet the metal itself is not crushed-it remains in a compressed state with elastic energy stored. The key principle here is: the soft filler conforms to the flange face imperfections, rather than relying on the flange surface being perfectly smooth.
2. Thermal Compensation – Metal Elasticity Responds to Expansion and Contraction
This is the primary advantage of spiral wound gaskets over non-metallic gaskets (such as compressed asbestos or solid PTFE). Once equipment is in operation, temperature fluctuations, pressure variations, and long-term bolt stress relaxation can cause minor separation between flange faces.
Non-metallic gaskets, once compressed, lack sufficient recovery-any flange separation immediately results in leakage. In contrast, the V-shaped metal strips in a spiral wound gasket act as built-in springs. The elastic energy stored during compression is released as needed, continuously pushing the soft filler against the flange faces to maintain sealing stress, effectively compensating for gaps caused by thermal distortion and bolt relaxation. Industry test data typically shows a recovery rate of 15%–20% for spiral wound gaskets, which is a critical parameter for their long-term reliability.
3. Extended Leak Path – High Flow Resistance
The gasket is not a solid barrier. For any medium to migrate outward, it must traverse multiple alternating layers of metal and filler materials. This multilayer construction creates a lengthy and tortuous leak path with significant resistance. The medium's pressure drops progressively along this route; when it is no longer sufficient to overcome the exit resistance, leakage is effectively contained. Moreover, even though metal and filler have different coefficients of thermal expansion, the multilayer structure accommodates these differential movements through localized micro-deformations, preventing overall seal failure due to temperature changes.
Installation Recommendations:
Control the compression rate within 30%–40% . Over-compression will destroy the elastic reserve of the metal strips, causing the gasket to lose its recovery capability and fail prematurely.
For high-temperature, high-pressure steam or highly corrosive media, a gasket with an inner ring is recommended. The inner ring prevents radial misalignment during installation and protects the inner layers of soft filler from being blown out.
