Anaerobic flange sealant or preformed gasket?
Anaerobic flange sealants cure gap-filling between two rigid metal flanges and replace preformed paper or rubber gaskets. This guide shows when the liquid option seals better, which gap size is allowed and how curing works with and without an activator.
View flange sealantsWhy do anaerobic sealants seal rigid flanges better?
An anaerobic flange sealant is a single-component resin that cures in the absence of air and in contact with metal ions. Applied to a rigid flange it fills every surface irregularity completely and forms a form-fitting seal with no set.
Preformed gaskets made of paper, cork or rubber have a fixed thickness and relax under load. After a few operating cycles the bolt preload drops, the gasket takes a set and the flange starts to weep. The liquid option has no such creep because the cured resin stays dimensionally stable.
- No set and no re-torque of the bolts after assembly.
- Full metal-to-metal contact increases the stiffness of the joint.
- No need to stock many gasket sizes, one cartridge covers many flanges.
- Resistant to oils, fuels, water-glycol and many solvents.
Which gap size and strength are acceptable?
The gap between the assembled flanges is decisive. Depending on the type, anaerobic sealants fill 0.05 to about 0.50 mm reliably. Larger gaps can only be bridged with high-viscosity thixotropic products or an additional sealing tape.
For gearboxes, pump housings and oil pans a medium-strength, removable type is chosen. It withstands operating pressure and vibration yet can be separated again for service. High-strength types are reserved for joints that stay permanently closed.
How does curing work and when do you need an activator?
Curing starts as soon as the flange is closed and atmospheric oxygen is displaced. Active metals such as steel, cast iron and brass accelerate the reaction. At 22 °C handling strength is usually reached after 10 to 30 minutes and full strength after about 24 hours.
- Inactive materials such as stainless steel, aluminium or anodised surfaces cure more slowly.
- An activator based on copper or iron compounds shortens the cure time significantly.
- Large gaps cure more slowly because there is less metal contact per volume.
- Cold slows the reaction, warmth up to about 40 °C speeds it up.
For tapered threads and fittings there are matching anaerobic sealing systems.
Read the guideFrequently asked questions
How large may the gap be for an anaerobic flange sealant?
Standard products reliably fill 0.05 to about 0.25 mm, high-viscosity thixotropic types up to around 0.50 mm. The real gap must be measured in the bolted state.
When is an activator needed?
On inactive materials such as stainless steel, aluminium or anodised surfaces, and at low temperatures or large gaps. The activator shortens the cure time significantly.
Can I disassemble the flange later?
Yes, if you choose a medium-strength, removable type. Heating to about 150 °C lowers the break-loose torque. High-strength types are only meant for permanently closed joints.
Do I have to re-torque the bolts after assembly?
No. The cured resin is dimensionally stable and does not take a set, unlike paper or rubber gaskets. Re-torquing as with preformed gaskets is not required.
Looking for the right anaerobic flange sealant?
We supply liquid flange sealants and matching activators for rigid metal flanges - matched to gap size, temperature and removability.
Gap-filling
Dimensionally stable seal with no set or re-torque.
Temperature-proof
Continuous use from -55 to +150 °C by type.
Media-resistant
Resistant to oils, fuels and water-glycol.
Expert advice
We match strength and activator to your application.