How to Select a Flange Gasket

Gasket selection starts with the flange face type. The flange face dictates which gasket families are physically compatible. From there, operating pressure, temperature, fluid chemistry, and project specifications narrow the choice to a single gasket type and material.

Step 1: Match Gasket to Flange Face

The flange face is the first constraint. Using the wrong gasket on a given face type causes leaks or flange damage.

Flange Face	Compatible Gasket Types	Notes
Raised Face (RF)	Spiral wound (SWG), soft gaskets (ring type)	Most common face in process piping
Flat Face (FF)	Full-face soft gaskets only	Used with cast iron (ASME B16.1) flanges; never use SWG on FF
Ring Type Joint (RTJ)	RTJ metallic rings (R, RX, BX)	Groove-machined flanges; metal-to-metal seal
Tongue & Groove (T&G)	SWG (without outer ring) or flat gaskets	Confined gasket; self-centering
Male & Female (M&F)	SWG (without outer ring) or flat gaskets	Confined gasket design

Step 2: Check Pressure Class and Temperature

Service Condition	Recommended Gasket	Standard
Class 150-300, ambient to 200 degC	Soft gasket (graphite, PTFE, CAF)	ASME B16.21
Class 150-600, up to 450 degC	Spiral wound gasket (flexible graphite filler)	ASME B16.20
Class 600-2500, high pressure/temp	RTJ gasket (oval or octagonal)	ASME B16.20
Vacuum service	SWG with inner ring	ASME B16.20
Cryogenic (below -46 degC)	SWG with PTFE filler, or RTJ	Project-specific

Step 3: Consider the Process Fluid

The fluid determines the gasket material, not just the type. A chemically incompatible gasket degrades rapidly and leaks.

Fluid Category	Gasket Material	Avoid
Hydrocarbons (oil, gas, refined products)	SWG with SS 316 winding + flexible graphite	Rubber, PTFE in high-temp hydrocarbon
Steam	SWG with SS 321 winding + graphite	PTFE (limited to 260 degC)
Strong acids (HCl, H2SO4)	SWG with Hastelloy winding + PTFE or graphite	Carbon steel rings
Oxidizing acids (HNO3)	PTFE envelope or virgin PTFE gasket	Graphite (oxidizes)
Caustic (NaOH)	SWG with Monel winding + graphite	Stainless steel windings (caustic cracking)
Water / utilities	Compressed graphite sheet or EPDM rubber	NBR in hot water
Toxic / lethal service	SWG-CGI (with inner ring) or RTJ	Soft gaskets (blowout risk)

Step 4: Verify Against Project Specifications

Most EPC projects define gasket types in the piping class or piping material specification. The pipe class datasheet specifies gasket type, material, and applicable standard for each service. Always cross-check the project specification before ordering.

Key documents that govern gasket selection:

• Piping class / piping material specification
• Line list (fluid, pressure, temperature per line)
• Gasket datasheet (material, dimensions, standard)

Pro Tip

Never downgrade gaskets to save costs on critical services. A spiral wound gasket costs a few dollars more than a sheet gasket but prevents leaks that can shut down an entire unit. The gasket is always the cheapest component in the flanged joint; the stud bolts and flanges cost far more.

Quick Decision Matrix

Priority	Low P/T, non-hazardous	Moderate P/T	High P/T or hazardous	Extreme P/T
Gasket type	Soft (sheet)	SWG (CG)	SWG (CGI) or RTJ	RTJ (BX)
Flange face	RF or FF	RF	RF or RTJ	RTJ
Bolt load	Low	Medium	High	Very high
Cost	Low	Medium	Medium-High	High

Read the full guide to gasket selection