Selection of Sealing Gaskets
(1) Sealing Rubber Sheets
Natural rubber sheets are ideal for applications involving water, seawater, air, inert gases, alkaline solutions, and saltwater. However, they lack resistance to mineral oils and non-polar solvents. The maximum long-term operating temperature is around 90°C, with excellent low-temperature performance that allows usage down to -60°C.
Nitrile rubber is well-suited for petroleum-based products like oil, lubricants, and fuels. It can operate safely at 120°C over the long term. Withstanding temperatures up to 150°C in hot oil environments is possible, though the low-temperature limit drops to around -10 to -20°C.
Neoprene rubber works well with seawater, weak acids, weak bases, and saline solutions. It shows great resistance to ozone and oxidation, outperforming nitrile rubber in these areas but falling short compared to other specialty rubbers. Its operating temperature ranges from -50 to 90°C, with a maximum use temperature of 130°C.
Fluorocarbon elastomers come in various types, each offering excellent resistance to acids, oxidants, oils, and solvents. They are suitable for nearly all acidic media, certain oils, and solvents, with a long-term operating temperature below 200°C.
Rubber sheets are commonly used as gaskets in frequently dismantled pipe connections or manholes/handholes, typically at pressures not exceeding 1.568 MPa. Among all gasket types, rubber gaskets are soft and adaptable, providing effective seals with minimal preload forces. However, this flexibility makes them prone to extrusion under high pressure or with thicker gaskets.
When exposed to organic solvents like benzene, ketones, or ethers, rubber sheets tend to swell, increase in weight, soften, and become sticky, leading to seal failure. Swelling rates exceeding 30% make them unsuitable for such applications.
At low pressures (especially below 0.6 MPa) and in vacuum conditions, rubber gaskets are preferable due to their good density and low permeability. Fluorocarbon elastomers, for instance, are ideal for sealing vacuum vessels, maintaining vacuum levels up to 1.3×10â»â· Pa. At ultra-high vacuum levels (10â»Â¹ to 10â»â· Pa), rubber gaskets need to be pre-baked and degassed before use.
Asbestos rubber sheets are economical and easy to handle but have limitations. Despite adding rubber and fillers, tiny pores remain unfilled, allowing for minor seepage. This makes them unsuitable for highly contaminating media, even at moderate pressures and temperatures. Over time, in high-temperature oil environments, the rubber and filler materials may degrade, leading to leaks, coking, and smoke. Additionally, asbestos rubber gaskets tend to bond to flange surfaces at high temperatures, complicating replacement.
(2) Synthetic Fiber Rubber Sheets
Synthetic fiber rubber sheets are eco-friendly, heat-resistant, and pressure-resistant, offering broad media compatibility. Bode’s synthetic fiberboard can withstand pressures up to 120 bar and temperatures ranging from -200°C to 800°C. Custom sealing solutions can be tailored to specific applications, making it a leading product in the sealing market.
(3) Polytetrafluoroethylene (PTFE)
PTFE tends to deform under high pressure and temperature due to cold flow and creep, so it is best suited for low-pressure, medium-temperature applications involving strong corrosion or media that must remain uncontaminated (e.g., strong acids, alkalis, halogens). The safe operating temperature is 150°C, with pressures below 1 MPa. Filled PTFE offers higher strength but cannot exceed 200°C in operation, with reduced corrosion resistance. Maximum pressure ratings for PTFE gaskets rarely surpass 2 MPa.
(4) Other Materials
Asbestos-resin composite gaskets and non-asbestos impregnated gaskets are primarily used in acidic media applications, such as pipelines, pumps, valves, and flanges. Operating temperatures max out at 80°C, with pressures below 0.6 MPa.
(5) Metal-Clad Asbestos Gaskets
These gaskets feature an asbestos board or asbestos rubber sheet coated with a thin metal layer, preventing direct contact with the medium. This improves strength retention and reduces leakage risks, expanding the applicability of asbestos rubber sheets. Metal-clad asbestos gaskets typically operate up to 450°C (some models reach 600–700°C in environments like flue gas at pressures up to 0.16 MPa), with pressures up to 4 MPa and a maximum of 6 MPa. Higher pressures lead to cross-flow and extrusion of the core material. Due to the high bolt tightening requirements, flanges rated below PG 25 kg/cm² cannot be used at pressures below 2.45 MPa without risking flange and bolt deformation. Changing the core material to elastic synthetic rubber doesn’t reduce tightening forces, as the core absorbs much of the load, leaving insufficient force for proper sealing. Furthermore, in chloride-rich or acidic media, the overlap between stainless steel and iron cores can lead to crevice corrosion.
(6) Metal Gaskets
Metal flat gaskets and corrugated gaskets are typically used on medium- and high-pressure valves, pipes, and small-diameter equipment flanges. Usage pressure depends on temperature: flat gaskets operate at 1.568–31.36 MPa, while corrugated gaskets work at 1.568–3.92 MPa. Material selection depends on the medium and temperature.
(7) Octagonal and Elliptical Gaskets
Octagonal gaskets and elliptical gaskets excel in trapezoidal groove flanges and elliptical groove flanges (referred to as “earth rings†in oil refining). Octagonal gaskets provide surface contact, while elliptical gaskets offer line contact. Elliptical gaskets seal well under low tightening forces but require double tightening, whereas octagonal gaskets generally prevent leaks after a single tightening. Both require significant bolt tightening forces. Low-pressure, high-temperature applications demand flange levels above PG 25 kg/cm².
Overall, selecting the right gasket depends on factors like temperature, pressure, medium type, and frequency of disassembly. Each material brings unique advantages and limitations, requiring careful consideration for optimal performance.
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