A flange gasket is used to create a static seal between the two mating flanges of a flanged connection. The gasket fills the spaces and the irregularities existing on the flange faces to ensure a leak-free connection (hence, gaskets installation is mandatory, and not an optional, requirement for flanged joints). The three types of gaskets are: soft (non-asbestos die cut, mainly for flat flanges), semi-metallic (spiral wound, Kammprofile, and jacketed for FF and RF flanges), and metallic (ring joint gaskets for RTJ flanges).

 

FLANGE GASKET TYPES

Flange gaskets can be classified in multiple ways. The most common taxonomy is based on the gasket material type:

  • non-metallic gaskets or soft gaskets (flat, soft, sheet and die-cut gaskets)
  • semi-metallic gaskets (Kammprofile, Spiral Wound, and Metal Jacketed gaskets)
  • metallic gaskets (Ring Joint gaskets, type R, RX, and BX)

ASME B16.21 covers types, sizes, materials, dimensions, tolerances, and markings for nonmetallic flat gaskets for pipe flanges. ASME B16.20 covers metallic and semi-metallic gaskets for pipeline flanges.

Flange gasket
Flange gasket

 

THE 5 GASKETS SELECTION FACTORS

Flange gasket shall be selected based on multiple process parameters, such as operating temperature/pressure, type of fluid conveyed by the pipeline, flange type, size, pressure rating, material grade, and specifications. The key factors to consider to select proper gaskets are:

1 – TYPE OF FLUID CONVEYED BY THE PIPELINE

The flange gasket should not be affected by the fluid conveyed by the pipeline over the whole range of operating conditions (pipeline operating temperature and pressure). The chemical resistance chart shows how different flange gasket materials resist specific temperatures, pressures, and fluids.

Gaskets Chemical Resistance Chart

Gasket Material Max temperature (F) Max Pressure (psi) Gasket Thickness Gasket Service Recommended
Butyl -40 to 225 150 1/16 to 1/4 Gases, inorganic acids & alkalis. Excellent weather/abrasion resistance.
EPDM -40 to 212 150 1/16 to 1/4 Water, steam, animal/vegetable oils, oxygenated solvents. Excellent weather resistance.
Natural (Pure Gum) -20 to 140 100 1/32 to 1 Acids, organic salts & alkalis. Non-toxic. Abrasion resistant. Soft.
Neoprene -20 to 170 150 1/32 to 2 Oil/gasoline. Excellent weather resistance.
Neoprene – Cloth Inserted -20 to 170 150 1/32 to 1/4 Oil/gasoline. Excellent weather resistance. Handles movement. High tensile strength.
Nitrile (NBR, Buna-N) -25 to 170 150 1/32 to 2 Oil/Aromatic fuels, mineral, animal and vegetable oils, solvents and hydraulic fluid. Available in commercial, premium and FDA grades.
SBR (Red Rubber) -20 to 170 150 1/32 to 1/4 Air, hot/cold water.
SBR – Cloth Inserted -20 to 170 150 1/16 to 1/4 Air, hot/cold water, saturated/ low-pressure steam. Excellent for high compression loads. Handles movement.
Silicone to 400 150 1/32 to 1/4 High-temperature air or water (not oil or steam). Soft. Available in FDA grade.
Vinyl 20 to 160 150 1/16 to 1/4 Water, oxidizing agents. Excellent weather/abrasion resistance
Viton to 400 150 1/32 to 1/4 Oil/Aromatic fuels, mineral, animal and vegetable oils, solvents and hydraulic fluid.

 

Gasket Material Max temperature (F) Max Pressure (psi) Creep
Relaxation
(%)
Gasket Service Recommended
Non-Asbestos/EPDM 800 1200 15 Steam/oxygenated solvents/
mild organic acids/alkalis. Excellent aging properties.
Non-Asbestos/Hypalon 400 900 40 Strong organic & inorganic acids/oils/aromatic hydrocarbons, powerful oxidizing agents.
Non-Asbestos/Neoprene 800 1200 15 Fuel/oils. Good general purpose material.
Non-Asbestos/Nitrile 800 1500 15 Steam/oil/fuel/solvent. Excellent general purpose material with wide chemical resistance.
Non-Asbestos/Nitrile
(with metal insertion)
850 2500 15 Hot gases. High load/stress environments. Available with galvanized low carbon steel foil or mesh insert.
Non-Asbestos/SBR 800 1500 15 Steam/industrial gases.
Low pressure/temperature.

 

Gasket Material Max temperature (F) Max Pressure (psi) Creep
Relaxation
(%)
Gasket Service Recommended
Pure PTFE 500 800 35 – 55 Excellent chemical resistance.
Filled PTFE 500 1200 11 – 40 Excellent chemical resistance.
Filled PTFE – Metal Inserted 500 2500 20 Excellent chemical resistance. 316 SS perforated core.
Expanded PTFE 600 3000 30 Excellent chemical resistance. Highly compressible.

 

 

Gasket Material Max temperature (F) Max Pressure (psi) Creep
Relaxation
(%)
Gasket Service Recommended
Carbon or Graphite/Nitrile 840 1900 20 Excellent for steam. Excellent chemical resistance except for powerful oxidizing agents.
Carbon or Graphite/SBR 900 2000 14 Excellent for steam. Excellent chemical resistance except for powerful oxidizing agents.
Pure Flexible Graphite 950 2100 5 Excellent chemical resistance except for powerful oxidizing agents. Available laminated or homogeneous.
Pure Flexible Graphite – Metal Inserted 950 2800 7 Excellent chemical resistance except for powerful oxidizing agents. Available with 316 SS Foil, Mesh or Tang Core. Available laminated or homogeneous.
Gasket Material Max temperature (F) Gasket Service Recommended
Copper 600 Excellent for steam. Excellent chemical resistance except for powerful oxidizing agents.
Brass 500 Excellent for steam. Excellent chemical resistance except for powerful oxidizing agents.
GHL 212 Excellent chemical resistance except for powerful oxidizing agents. Available laminated or homogeneous.
Grafoil ® 800 Excellent chemical resistance except for powerful oxidizing agents. Available with 316 SS Foil, Mesh or Tang Core. Available laminated or homogeneous.
Titanium 1000 Similar strength to 300 series stainless, but tougher and much less dense. Excellent resistance to chloride solutions (sea water) and bleaching solutions.
Soft Iron, Low Carbon Steel 1000 Soft. Will corrode in water. Mostly used where immersed in liquid hydrocarbons.
Stainless Steel,

Type 304

1000 A general-purpose, soft, corrosion-resistant, non-magnetic stainless that will not harden under heat.
Stainless Steel,

Type 316

1000 Not as strong as 304, but more corrosion-resistant in chemical solutions (except for a limited range of oxidizing acids)
Stainless Steel,

Type 321

1600 Stronger than 304. Used when similar performance to 304 is needed at higher temperatures.
Stainless Steel,

Type 347

1600 More corrosion-resistant and harder than 321.
Stainless Steel,

Type 410

1200 Commonly referred to as “Chrome”. This stainless will harden when heat-treated. It is highly magnetic, hard and strong, but not very corrosion-resistant.
Stainless Steel,

Type 430

1400 More corrosion-resistant than 410, but will not harden when heat-treated. This stainless is soft and no stronger than 300 series stainless.
Nickel 1400 Exhibits good corrosion and erosion resistance at moderate temperatures.
Monel® 1500 A family of nickel/copper alloys that offer greater corrosion and erosion resistance than nickel alone. Particularly useful in seawater applications.
Inconel® 2000 A family of nickel/chromium alloys that are non-magnetic and take corrosion resistance to elevated temperatures.
Hastelloy® 2000 A family of Nickel/chromium/molybdenum alloys for use in highly aggressive chemical environments at elevated temperatures

 

2 – PROCESS TEMPERATURE

The selected flange gasket should have a reasonable service life expectancy considering the most demanding conditions that the pipeline may experience (highest expected temperature-pressure conditions for high-temperature applications, and lowest temperatures for low-temperature applications).

The temperature-pressure ratings of the common gasket materials are shown in the image below as a general reference.

Gaskets and temperature
Gaskets and temperature

Gasket materials are designed to compress under load to seal the flanges. However, to retain such seal, the gasket should be able to keep a proper sealing surface and not creep significantly (an adverse phenomenon that may be activated by temperature).

 

3 – PROCESS PRESSURE

The flange gasket should be able to withstand the maximum pressure expected in the pipeline; this is often the test pressure, which can be at least 2 times the flange rating at ambient temperature.

 

4 – FUGITIVE EMISSIONS LEGISLATIVE CONSTRAINTS

More and more stringent procedures and legislation are coming about in the field of allowed fugitive emissions, and such constraints shall be duly considered during the design of a pipeline and its flanged joints.

 

5 – OTHER ASPECTS

The other key factors to consider for a proper gasket selection are listed below:

a) Pipeline vibration and oscillation: the gasket shall withstand the oscillations and the vibrations that may affect the pipeline

b) Fluid erosion: a properly selected flange gasket shall withstand the erosion and the corrosion coming from the fluid conveyed by the pipeline. This aspect impacts either the gasket mat, rial, type and size

c) Fluid contamination risk: For some applications, it is important to select flange gaskets materials that do not contaminate the fluid conveyed by the pipeline (for example; pharmaceutical and food applications, or gas pipelines)

d) Flanges corrosion: Some flange materials, such as austenitic stainless steel, are subject to stress corrosion cracking. Therefore, the flange gasket selection should consider the possible impurities that may induce corrosion of the flange’s metal

e) Integrity: When the integrity of a gasket is of prime importance (e.g. when sealing a highly toxic chemical), the choice of the gasket may be influenced by the requirement for a larger safety margin. As an example, a spirally wound gasket with an outer retaining ring may be selected in place of a compressed asbestos fiber gasket.

f) Potential financial impact of gaskets failures: Although a gasket is a relatively inexpensive item in the overall pipeline cost, due care should be given to the proper selection of gaskets to prevent leakages and failures that may generate way larger financial impact

As a general reference, the following table shows the recommended types of gaskets by service, pipeline temperature and pressure rating, and flange facing types:

Gasket selection guideline