September 15, 2025
The Flange Bell Mouth is a key component in pipeline systems for connecting pipelines and equipment to enable medium transportation. Characterized by a bell-shaped flared design at the flange end, it is widely used in industrial fields such as petrochemical engineering, natural gas transmission, water treatment, and energy. Seal failure can easily lead to safety accidents and economic losses; therefore, clarifying its sealing principle and mastering prevention and control technologies are crucial for the stable operation of pipelines.
The sealing of the Flange Bell Mouth essentially relies on "contact pressure sealing", which blocks the penetration path of the medium from the inside to the outside of the pipeline through the tight fit between the sealing element and the flange sealing surface. Its sealing process involves three core elements: sealing surface structure, sealing element characteristics, and pre-tightening force effect. The specific principle can be broken down into the following three aspects:
The sealing surface of the Flange Bell Mouth usually adopts a Raised Face (RF), Male-Female Face (MFM), or Tongue and Groove (TG) design. Different sealing surfaces need to be matched with corresponding sealing elements to form an initial sealing interface through "surface-element matching":
· Raised Face (RF) + Flexible Gasket: Suitable for medium and low-pressure scenarios. Under the action of pre-tightening force, the flexible gasket undergoes elastic deformation to fill tiny scratches and depressions on the smooth sealing surface, forming a continuous sealing contact layer and blocking the medium penetration path.
· Male-Female Face (MFM)/Tongue and Groove (TG) + Metal-Clad Gasket: Ideal for high-pressure and high-temperature applications, the MFM or TG design offers "positional constraint" on the sealing element through its mechanical structure, which prevents gasket displacement under extreme conditions. The metal-clad gasket, such as a stainless steel-clad graphite gasket, utilizes the rigidity of metal to ensure a secure fit on the sealing surface. Meanwhile, the internal flexible filler, like graphite, helps fill small gaps, achieving a combination of "rigid support and flexible sealing."
Pre-tightening force is the key driving force for sealing. It transmits external force to the flange sealing surface and sealing element through bolt connection, with the specific process as follows:
1. Bolt Pre-Tightening: Apply pre-tightening force to the flange connecting bolts using a torque wrench or hydraulic tensioner, causing elastic elongation of the bolts and driving the flange sealing surfaces to approach each other.
2. Sealing Element Deformation: The extrusion force from the flange sealing surface acts on the sealing element, causing it to undergo elastic or elasto-plastic deformation. Elastic deformation can automatically restore the fitting state when pressure fluctuates, while elasto-plastic deformation can form a "permanent sealing contour" to adapt to the micro-irregularities of the sealing surface.
3. Contact Pressure Formation: When the sealing element is deformed, it creates a "contact pressure" in the area where it touches the sealing surface. If this contact pressure exceeds the internal pressure of the medium in the pipeline, the medium cannot escape through the sealing interface, effectively preventing leakage. However, if the initial tightening force is inadequate, the contact pressure will be lower than the medium pressure. In this case, the medium can seep through the gaps in the sealing surface, resulting in leakage.
The sealing effect is also related to the physical and chemical properties of the transported medium, and the selection and matching of sealing elements are required to achieve "anti-penetration":
· Medium Viscosity: High-viscosity media have poor molecular fluidity and weak penetration ability, requiring lower flatness of the sealing surface. Low-viscosity media have highly permeable molecules, so high-density sealing elements must be used to reduce molecular penetration paths.
· Medium Corrosiveness: Corrosive media can erode the sealing surface and sealing elements. Corrosion-resistant materials should be selected to prevent gaps in the sealing interface caused by corrosion.
The sealing principle of the Flange Bell Mouth is centered on "contact pressure sealing", relying on the synergy of the sealing surface, sealing element, and pre-tightening force, while being affected by medium characteristics and operating conditions. A closed-loop management system should be established to effectively reduce the risk of leakage.
