In the industrial field, sealing of pipelines and equipment has always been a key link to ensure safe operation. Flexible graphite composite gaskets, with their excellent sealing performance and wide applicability, have become the first choice for many engineers and technicians. Today, we will take an in-depth look at three common types of flexible graphite composite gaskets: metal-graphite spiral wound gaskets, metal corrugated composite gaskets, and metal contact graphite gaskets. By analyzing their structural forms and performance characteristics, this article aims to help you better select the appropriate gasket type.
Among the many flexible graphite composite gaskets, the metal-graphite spiral wound gasket is considered a classic. With its unique structure and excellent performance, it has long been a popular choice in the industrial sealing field. This type of gasket is favored by many engineers and technicians due to its outstanding sealing effect, wide applicability, and flexible customization capability.
Metal-graphite spiral wound gaskets are a classic structure among flexible graphite composite gaskets. Their body consists of V-shaped, U-shaped, or W-shaped metal winding strips and graphite winding strips alternately layered and wound on the same core. This unique structural design gives the gasket excellent sealing performance. Depending on the application, spiral wound gaskets can also be divided into inner ring, outer ring, and inner-outer ring types, suitable for different flange sealing surfaces:
Inner ring gaskets: Suitable for raised-face flanges. The inner ring effectively prevents radial displacement of the gasket under high pressure, ensuring sealing stability.
Outer ring gaskets: Mainly used for flat-face flanges. The outer ring increases the rigidity of the gasket, preventing deformation during installation.
Inner-outer ring gaskets: Combine the advantages of inner and outer rings, suitable for conditions with large pressure fluctuations or frequent temperature changes, providing more reliable sealing.
The main performance advantages of metal-graphite spiral wound gaskets lie in their multi-seal structure and excellent compressibility and recovery. The metal strip serves as the supporting framework, ensuring the gasket's compressive strength, while the graphite strip provides reliable sealing. This combination allows the gasket to maintain good sealing performance under various conditions:
Multi-seal structure: Due to the alternating winding of metal and graphite strips, the gasket can form multiple sealing lines during compression, effectively preventing medium leakage.
Good compressibility and recovery: The graphite strip has excellent compressibility and recovery, maintaining good sealing even after multiple compression and relaxation cycles.
Strong adaptability: By adjusting the structure and process parameters, spiral wound gaskets can meet different requirements, suitable for various media and working conditions.
Although metal-graphite spiral wound gaskets have many advantages, the following points should be noted during use:
Sealing element width: The width of the sealing element in metal spiral wound gaskets should be smaller than that of non-metallic soft gaskets. When making metal spiral wound gaskets for raised-face, flat-face, and protruding flanges, one should not arbitrarily use the width of non-metallic soft gaskets as a replacement. This is because metal spiral wound gaskets are semi-metallic, and the standard gasket achieves reasonable compression deformation and good sealing only when the compressive stress is about 70 MPa. If the width of the gasket sealing surface is arbitrarily increased, the compressive force will decrease, and the gasket cannot reach the standard compression deformation, failing to provide good sealing. Excessive compressive force may cause substantial deformation of flanges and bolts, ultimately leading to leakage.
Application of basic-type gaskets: Basic-type gaskets are best not used on raised-face flanges. Under flange axial compressive force, the inner ring/layer points of the gasket can weld open, which may not only cause leakage but also scatter the soft filler, contaminating materials and blocking pipelines.
Application under harsh conditions: Under high-temperature, cryogenic, frequent hot-cold cycles, high vibration, or strong corrosive media conditions, gaskets used on flat-face and protruding flanges should be equipped with appropriately material inner rings. Low-grade material gaskets must not replace high-grade ones.
Metal corrugated composite gaskets, with their unique structural design and excellent sealing performance, have become high-performance options in industrial sealing. These gaskets perform well under traditional conditions and demonstrate extraordinary advantages under high-temperature, high-pressure, and complex working conditions.
Metal corrugated composite gaskets consist of a metal skeleton with multiple concentric corrugations combined with flexible graphite. Their structural types include basic, positioning ring, and spacer bar types. The metal corrugated skeleton can have “V”-shaped, trapezoidal, or arcuate grooves, and the corrugations can be aligned or staggered, providing significant sealing advantages:
Basic type: Suitable for general conditions, simple structure, and low cost.
Positioning ring type: The positioning ring ensures the gasket remains correctly positioned during installation, preventing offset; suitable for applications with high installation accuracy requirements.
Spacer bar type: The spacer bar increases gasket rigidity and prevents deformation under high pressure; suitable for high-pressure conditions.
The main performance advantages of metal corrugated composite gaskets are their multi-layer sealing structure and excellent compressibility and recovery:
Multi-layer sealing: The metal skeleton provides primary support. When bolt preloading is applied, flexible graphite is pressed into the grooves of the skeleton and flange, and the metal teeth contact the flange. Further compression causes elastic deformation of the metal skeleton and additional compression of graphite, sealing the annular space between metal and flange. This forms a combined metal and graphite multi-layer seal.
Good compressibility and recovery: The corrugated composite gasket maintains excellent sealing even under relatively low compressive force. This makes it particularly suitable for high-temperature, high-pressure, and fluctuating conditions, serving as an ideal alternative to traditional metal spiral wound and metal-jacketed gaskets.
Wide applicability: Metal corrugated composite gaskets can be used in low and high temperatures (-200°C to +700°C) and low to high pressures (vacuum to 25 MPa). With appropriate metal skeleton materials, they can handle most corrosive fluids.
Metal corrugated composite gaskets are widely used under special conditions. For extremely high temperature or strongly corrosive environments, gaskets can be made of stainless steel 304L, 321, 316Ti, 309, 347, 410, duplex steel (2205, 31803), MONEL 400, INCONEL 600/625, INCOLOY 800/825, HASTELLOY B2/C276, titanium (T2). These specialized materials meet sealing requirements under extreme conditions.
Do not damage sealing surfaces; the gaskets are easy to remove, simplifying maintenance and replacement.
The metal corrugated part can be reused for larger or specially material gaskets, such as heat exchanger gaskets, reducing costs.
Metal contact graphite gaskets, with their excellent sealing performance and adaptability to extreme conditions, have become premium solutions in industrial sealing. They are not just gaskets but provide assurance of safety and reliability under demanding environments.
Metal contact graphite gaskets are composite gaskets with high-performance flexible graphite as the core, representing the latest structural form among flexible graphite composite gaskets. The flexible graphite ring is formed in a specially designed raised-recessed mold and then embedded between two stainless steel rings. The design relies on metal-to-metal contact, with one or both metal rings serving as limit rings.
The main advantages are exceptional sealing and adaptability to temperature and pressure fluctuations:
Excellent sealing: Under the specified bolt preload, the metal rings contact the flanges, restricting further compression of graphite. The metal rings absorb mechanical stresses from pipes and thermal shocks, ensuring the sealing performance, making it suitable for conditions with temperature and pressure fluctuations.
Strong adaptability: This gasket provides reliable sealing and safety, especially in applications with extremely high sealing requirements, such as nuclear power plant reactor systems.
Due to the high cost, metal contact graphite gaskets are typically used only in high-end applications. Ensuring gasket quality and proper installation is necessary to fully leverage performance advantages.
From the analysis of the three types of flexible graphite composite gaskets, the following conclusions can be drawn:
Metal-graphite spiral wound gaskets: Suitable for various conditions, with multi-seal structure and good compressibility and recovery. Attention should be paid to sealing element width and limitations of basic-type gaskets.
Metal corrugated composite gaskets: High-performance, suitable for high-temperature, high-pressure, and fluctuating conditions, with excellent compressibility and wide applicability. Care should be taken to protect sealing surfaces and consider reuse of metal corrugated parts.
Metal contact graphite gaskets: Exceptional sealing, particularly suitable for applications with extremely high sealing requirements, such as nuclear power plants. However, they are expensive and require correct installation.
When selecting a gasket, factors such as operating conditions, media characteristics, temperature, and pressure range should be comprehensively considered, balancing performance and cost. This analysis aims to help you better understand and choose the appropriate flexible graphite composite gasket, ensuring safe and reliable operation of industrial equipment.