What Is a Double-Jacketed Gasket?

Quick Answer

A double-jacketed gasket is a semi-metallic gasket made by enclosing a soft filler material inside a metal jacket that wraps around both the inner and outer diameters. The metal jacket provides structural integrity and blowout resistance, while the internal filler (typically flexible graphite, ceramic fiber, or vermiculite) creates the sealing surface. Double-jacketed gaskets are widely used on heat exchangers, pressure vessels, and large-diameter flanged joints.

The metal jacket is formed from thin sheet metal (0.3-0.5 mm) folded around the filler to create a smooth, uniform sealing surface on both faces. Under bolt load, the jacket deforms slightly to conform to the flange face while the filler compresses to fill surface imperfections. This combination delivers reliable sealing across various temperatures and pressures.

Gasket Construction

Component	Options	Function
Outer jacket	Soft iron, SS 304, 316, 321, Monel 400	Protects filler from process fluid; provides blowout resistance
Inner jacket	Same as outer jacket	Seals inner diameter; prevents filler extrusion into bore
Filler material	Flexible graphite, ceramic fiber, vermiculite, PTFE	Compressible sealing medium
Jacket thickness	0.3-0.5 mm per side	Thin enough to deform; thick enough to contain filler
Standard	ASME B16.20 Type D	Dimensions and tolerances

Double-jacketed gaskets differ from single-jacketed types (where only the outer edge is jacketed) by providing metal containment on all exposed surfaces. This prevents filler degradation from process fluid contact and eliminates filler extrusion paths.

Filler and Temperature Selection

Filler Material	Min Temp	Max Temp	Typical Application
Flexible graphite	-200 degC (-328 degF)	550 degC (1,022 degF)	Steam, hydrocarbons, general refinery
Ceramic fiber	0 degC	1,000 degC (1,832 degF)	Furnace, exhaust, extreme high-temperature
Vermiculite	0 degC	900 degC (1,652 degF)	Exhaust manifolds, boiler joints
PTFE	-200 degC (-328 degF)	260 degC (500 degF)	Chemical, food-grade, oxidizing service
Mica	0 degC	900 degC (1,652 degF)	High-temperature, fire-safe

The jacket metal must resist corrosion from the process fluid. For sour gas service, use Incoloy 825 or Inconel 625 jackets per NACE MR0175. For standard hydrocarbon service, SS 316 jackets with flexible graphite filler cover most applications.

Typical Applications

Double-jacketed gaskets are preferred over spiral wound gaskets in these situations:

• Shell-and-tube heat exchanger channel flanges: large diameters with uneven bolt loading
• Manway covers on pressure vessels and storage tanks
• Boiler and HRSG connections at elevated temperatures
• Catalyst bed flanges where gasket removal and reinstallation is frequent
• Custom and non-standard flange sizes where spiral wound gaskets are not available off the shelf

Comparison with Other Gasket Types

Feature	Double-Jacketed	Spiral Wound	Kammprofile	Soft
Max pressure	Class 600	Class 2500	Class 2500	Class 300
Max temperature	1,000 degC (ceramic filler)	1,000 degC	550 degC	450 degC
Bolt load required	Low to moderate	Medium	Medium to high	Low
Custom sizes	Easy to manufacture	Limited stock sizes	Specialty	Easy to cut
Cost	Moderate	Low to moderate	High	Low

Pro Tip

For heat exchanger re-tubing projects, order double-jacketed gaskets with the exact OD and ID matching the channel flange; not the pipe size. Heat exchanger flanges frequently use non-standard dimensions that do not match ASME B16.5 tables. Provide a gasket drawing or template to the manufacturer.

Pair double-jacketed gaskets with stud bolts torqued per ASME PCC-1 guidelines using the correct bolt torque chart.

Read the full guide to gasket selection