DEFENDER FS™ Sealing/Isolating Gaskets
and Flange Isolation Kits

General Description

DEFENDER FS Gasket Manunfactured by 3-Flow, Inc., 
an engineered equal to the Picotek VCFS-Line-Seal gasket

Patent Pending

The DEFENDER FS™ sealing/isolating gasket is designed to withstand the rigorous API standard 6FB (Third Edition) test and therefore provides a solution for those who want to electrically isolate their flange while also requiring protection against the introduction of fire in and around the flange.
The objective of the test is to monitor the total leakage for the duration of the burn/cool-down cycle and during re-pressurization. Leakage was determined by the total water level drop through a visual sight gauge during the burn/cool-down cycles, by manually catching the water in a calibrated container during re-pressurization.
The results concluded that the Defender FS Gasket was able to maintain its fire safe characteristics throughout the entirety of the test. During the 30 minute burn and 30 minute cool down period, the measured leakage was 0 ml/min versus the allowable rate of 22.765 ml/min. The leakage rate during the re-pressurization cycle was 5 ml/min versus the allowable rate of 22.765 ml/min.
Based on years of technological experience, the DEFENDER FS™ sealing/isolating gasket not only meets but exceeds the pressure-containing capabilities in standard 6FB (Third Edition) as outlined by API.

  • Tested and Certified to API 6FB (Third Edition).
  • Two integral robust sealing elements for sealing and isolating in an engineered Fire Safe design.
  • Serves as a sealing/isolation for Fire Safe Applications.
  • Incorporates industry proven Kammpro®: sealing technology.
  • Patent Pending Design

  • DEFENDER FS gaskets are engineered for Fire Safe, extreme, high reliability sealing and electrical isolation critical service applications High Pressure Flanges: 2500#, API 10K or PN420.
  • Critical/Extreme service
  • High Ph service.
  • H2S/CO2 service.
  • Locations where end users prefer an integral seal element and high volatile fluids are present.

  • 1/2" through 48" diameter (and corresponding API and DN diameters)
  • Available as "E" or "F" Type Gasket.

Industries (Oil, Gas, Offshore)
  • Production Fields
  • Petroleum Marketing Facilities
  • LNG/SNG Systems
  • Pipeline and Distribution Piping
  • Refineries
  • Tank Farms
  • Offshore Platforms

Before Tightening
The flange face makes initial contact with the sealing elements which protrude above the gasket retainer surface (isolation material) laminated on both sides of the stainless steel core.

After Tightening
The sealing elements are compressed into the serrations of the stainless steel retainer.

Retainer Materials (G10S6, G11S6)

Note: Consider G10S Material for applications of Nominal Pipe Size 12-inch and larger and ANSI pressure class 600# and higher.

Gasket/Retainer Material Specifications






Dielectric Strength Volts/Mil Short Time




Compressive Strength (psi)




Water Absorption (%)




Flexural Strength (psi)




IZOD Impact Strength (Ft-lbs/Inch




Tensile Strength (psi)




Shear Strength (lb)




Bond Strength (lb.)




Temperature - Operating

Cryogenic -238°F (-150°C) to +302°F (+150°C)

-100°F (-73°C) to +392°F (+200°C)

NOTE: Operating Temperature for Gaskets and Flange Isolation Kits is based off the Gasket Retainer Temperature. Seal element temperature does not dictate the Min. and max. gasket operating temperature. Performance suitability and material compatibility shall be determined by the user. The DEFENDER FS is an engineered fire safe gasket that has passed API 6FB fire test (Third Edition). No other claims regarding suitability/compatibility for a particular application or performance in a fire are made.

Seal Element Materials

Sealing Element

Temperature - Operating

Mica (Hi-Temp)

+1,832°F (+1,000°C)

Biaxial Oriented PTFE

-450°F (-268°C) to +500°F (+260°C)

Kammprofile PTFE Coating

-58°F (-50°C) to +350°F (+176°C)

Configurations for Gasket Type and Sleeve and Washer Sets

Type "E" Gasket
Fits over the bolt holes and extends to the O.D. of the flange to assist contractors as the bolt holes automatically center the gasket. Provides excellent protection against shorting out of the corrosion mitigation hardware.

Type "F" Gasket
Fits within the bolt hole circle of the flange and extends to the I.D. of the bolt circle providing good protection against shorting out of the corrosion mitigation hardware.

Double Washer Set
One isolation sleeve, two steel washers and two insulating washers for each stud/bolt.

Suggested Sleeve/Washer Set

FD = G10 Sleeves, Steel HC Washers and Steel HC Washers - Double Washer Set

TF = Nomex Sleeves, Steel HC Washers and Steel HC Washers