In pressure vessels and piping across petrochemical, metallurgy, and nuclear plants, bolted flange connections depend on gaskets to prevent leaks. Under high-temperature and high-pressure conditions, sealing performance and reliability must be exceptional. Any gasket leakage at these joints wastes resources, pollutes the environment, and at worst, can lead to fires or explosions, risking personnel safety and causing major economic loss.
A key root cause of leakage in such duties is the thermo-mechanical instability of some gasket constructions: their properties vary significantly with temperature and pressure, undermining sealing integrity. Designing a gasket with stable high-temperature sealing behavior is therefore essential for dependable bolted-flange service.
To address this, we present a high-temperature, high-pressure metal jacketed flat gasket (MJG) and its manufacturing method. The design improves heat/pressure resistance, corrosion and oxidation resistance, and delivers stable performance, long service life, and the potential for multiple reuses—making it suitable for broad industrial adoption.
Construction and materials (industry formulation, by weight)
The gasket comprises a filler encapsulated in a metal jacket. The filler is formulated as follows (parts by weight):
Flexible graphite: 100
Tannic acid: 3–7
Methyl acrylate: 0.5–1
Composite fibers: 3.5–15
Polyvinylidene fluoride (PVDF): 1.5–5
Composite polyhedral oligomeric silsesquioxane (POSS): 6–15
Metal jacket: 316 or 316L stainless steel thin sheet.
Functional additives and synergy
1)Composite POSS (synergistic flame-retardant/anti-oxidation system).
First, octachloropropyl-POSS is prepared via hydrolysis. It is then ionized by reaction with an N-alkyl tertiary amine. Subsequent anion exchange with salts bearing different anions—e.g., sodium tetrafluoroborate (NaBF₄), potassium hexafluorophosphate (KPF₆), or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)—yields POSS microspheres with various counter-anions, achieving POSS/ionic-liquid synergy for flame retardancy.
2)Composite POSS definition.
A 1:1 mass mixture of octavinyl-POSS and ionic-liquid-containing octaphenyl-POSS.
In octavinyl-POSS, all eight cage vertices carry vinyl groups.
In octaphenyl-POSS, all eight vertices carry 4-(chloromethyl)phenyl substituents.
3)Fiber and matrix modification.
Silicon carbide fibers and ceramic fibers are surface-modified and combined with flexible graphite to deliver high temperature/pressure resistance. PVDF is graft-modified using octavinyl-POSS to enhance inorganic–organic interfacial adhesion, suppress particle agglomeration, and strengthen the two-phase interface—raising allowable service temperature and pressure.
Ionic-liquid functionalized octaphenyl-POSS further elevates oxidation and corrosion resistance and increases thermal stability via POSS/ionic-liquid cooperation.
Composite fiber blend: 3–12 parts SiC fibers + 0.5–3 parts ceramic fibers (within the 3.5–15 parts total fiber window).
Preparation of ionic-liquid-containing octaphenyl-POSS (process S1–S5)
1). Charge methanol to a reactor; under magnetic stirring, add 4-(chloromethyl)phenyltrimethoxysilane and hydrochloric acid.
2) Heat to 80 °C and reflux 24 h.
3). After reaction, add tetrahydrofuran (THF) for recrystallization.
4). Wash with methanol and vacuum-dry at 50 °C for 24 h to obtain octaphenyl-POSS.
5). Add the product from S4 to a mixed solution of ammonium tetrafluoroborate, 1-(3-chlorophenyl)-3-methyl-piperazine, and toluene; stir at 70 °C for 12 h (isothermal, magnetic). Vacuum filter to obtain the ionic-liquid-containing octaphenyl-POSS.
Ratios and conditions:
Methanol: 4-(chloromethyl)phenyltrimethoxysilane: HCl (volume) = 100 : 3–15: 1–10.
Ammonium tetrafluoroborate: 1-(3-chlorophenyl)-3-methyl-piperazine: octaphenyl-POSS (molar) = 1.1–1.3: 1.1–1.3: 1.
Toluene: octaphenyl-POSS (volume: mass) = 5–20: 1 ml/g.
Manufacturing method for the high-temperature, high-pressure metal-jacketed flat gasket
1). Fiber modification via supercritical CO₂.
Charge 3.5–15 parts composite fibers to a reactor. Introduce CO₂ and raise temperature/pressure to supercritical conditions for 1–15 min to swell the fibers. Depressurize; add 2–5 parts composite POSS; re-introduce CO₂ and hold supercritical for 5–10 min to obtain modified composite fibers. Supercritical CO₂ enhances swelling and penetration, ensuring POSS uniformly permeates the fiber interior.
2). Filler mixing (high-shear dispersion).
By weight, combine flexible graphite (100), tannic acid (3–7), methyl acrylate (0.5–1), PVDF (1.5–5), composite POSS (4–10), and the modified composite fibers from S1. High-speed mechanical mixing improves inorganic/organic dispersion and bonding, elevating high-temperature/high-pressure performance. (Note: the overall formulation window also allows composite POSS at 6–15 parts, as specified above.)
3) Jacket forming and encapsulation.
Place a punched, flanged, roughened stainless 316/316L thin sheet into a mold. Lay the filler onto the metal sheet, then press, roll, and hem the jacket edges to obtain the metal-jacketed flat gasket.
Preferred pressing conditions: 50–60 °C, 15–20 MPa, 5–10 min.
What this design delivers
High-temperature & high-pressure capability. Flexible graphite + modified SiC/ceramic fibers, reinforced by POSS-grafted PVDF, provide a filler with excellent strength at temperature and under load.
Anti-oxidation & corrosion resistance. The ionic-liquid-containing POSS system cooperates with the graphite matrix to improve oxidation resistance and chemical durability.
Stable properties & long life. Strong chemical bonding among organic and inorganic components yields a stable, reusable filler system with extended service life in severe duty.
316/316L stainless jacket. Corrosion-resistant, oxidation-resistant metal cladding protects the filler, spreads load, and safeguards flange faces.
Typical use cases
Designed for high-temperature, high-pressure, and corrosive flange joints in refining, petrochemical, chemical processing, metallurgy, and nuclear services—where leakage control, uptime, and safety are paramount.
Conclusion
By combining a 316/316L stainless jacket with a graphite-based, POSS-reinforced filler—modified via supercritical CO₂ processing and ionic-liquid chemistry—this metal jacketed flat gasket provides reliable sealing under severe temperature and pressure, with enhanced oxidation/corrosion resistance, stable performance, and extended service life suitable for large-scale industrial deployment.
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