What Is a Metal Gasket?

Quick Answer: A metal gasket is a sealing element made entirely or predominantly of metal, designed for flanged joints operating at high pressures, high temperatures, or in critical services where soft gaskets and semi-metallic gaskets cannot maintain a reliable seal. Metal gaskets require high bolt loads and precision-machined flange faces.

Types of Metal Gaskets

Type	Construction	Typical Application	Standard
Ring Type Joint (RTJ)	Solid metal ring (oval or octagonal cross-section) seated in machined grooves	High-pressure, high-temperature: wellheads, Christmas trees, Class 600-2500 flanges	ASME B16.20, API 6A
Solid flat metal	Flat ring cut from sheet metal (no filler)	Heat exchangers (shell-and-tube pass partition), high-temp exhaust systems	ASME B16.20
Corrugated metal	Thin metal sheet formed with concentric corrugations	Low-to-moderate pressure, large-diameter flanges, heat exchangers	ASME B16.20
Corrugated metal with filler	Corrugated metal with graphite or PTFE in the grooves	Moderate pressure/temperature; improved sealing over bare corrugated	ASME B16.20
Kammprofile (grooved metal)	Solid metal core with concentric serrated grooves, coated with graphite or PTFE	High-pressure, high-temperature; excellent recovery and re-usability	EN 1514-6, DIN 2697
Metal-jacketed	Soft filler (graphite, ceramic) wrapped in a thin metal jacket	Heat exchangers, irregular flange faces	ASME B16.20
Lens ring	Spherical-profile solid metal ring	Very high pressure (up to 1500 bar+), reactor closures	DIN 2696

Material Selection

The gasket material must be softer than the flange face material to deform and create a seal without damaging the flange:

Gasket Material	Hardness (HB)	Max Temp	Typical Service
Soft iron	~90 HB	450 degC	Steam, general hydrocarbons
Low carbon steel	~120 HB	450 degC	Standard carbon steel flanges
SS 304	~160 HB	600 degC	Stainless steel flanges, corrosive service
SS 316	~160 HB	600 degC	Marine, chloride-containing environments
Inconel 625	~180 HB	980 degC	High-temperature, corrosive (H2S, CO2)
Monel 400	~130 HB	480 degC	Seawater, HF alkylation
Titanium	~200 HB	315 degC	Highly corrosive chemicals

RTJ Gaskets: Oval vs. Octagonal

Ring Type Joint gaskets are the most common metal gaskets in oil and gas. They are available in two cross-section profiles:

Feature	Oval (R-type)	Octagonal (RX/BX-type)
Contact	Line contact (tangent point)	Face contact (flat surfaces)
Sealing	Slightly lower bolt load needed	Better seal; higher bolt load required
Interchangeability	Fits both oval and octagonal grooves	Fits only octagonal grooves
Reuse	Not recommended (deforms permanently)	Not recommended
Cost	Lower	Higher (tighter tolerances)

Common Mistake

Installing an octagonal RTJ gasket in an oval groove. While an oval gasket can seat in an octagonal groove (line contact), an octagonal gasket will not seat properly in an oval groove—it will bridge the corners and fail to seal. Always match the gasket profile to the flange groove type.

When to Use Metal Gaskets vs. Other Types

Gasket Category	Pressure Range	Temperature Range	Bolt Load Required
Soft gaskets (PTFE, rubber, fiber)	Low (Class 150)	-50 to 200 degC	Low
Semi-metallic (spiral wound)	Medium-high (Class 150-2500)	-200 to 600 degC	Moderate
Metal gaskets (RTJ, Kammprofile, solid)	High (Class 600-2500+)	-200 to 1000 degC	High

Metal gaskets are specified whenever ASME B16.5 or B16.47 flanges are furnished with RTJ faces, or when the service conditions exceed the capability of semi-metallic gaskets.

Read the full guide to gasket types