Ensuring a leak-proof flange connection is a constant priority in manufacturing and maintenance. Pre-cut gaskets have long been the standard. Anaerobic flange sealants offer a different approach, and the common question is whether they supplement a gasket or replace it. In practice they replace it.

The Anaerobic Cure Principle

Anaerobic sealants cure under two conditions that must both be present:

1. Absence of oxygen: the sealant must be confined between mating surfaces.
2. Contact with active metal: metal ions catalyze the curing reaction.

This mechanism is the reason anaerobic sealants and traditional gaskets do not work together.

Why You Should Not Combine Them

Anaerobic sealants are generally not designed for use with pre-cut gaskets made of cork, paper, rubber, or most semi-metallic materials. Combining them tends to produce a worse seal, for several reasons:

• Oxygen exclusion is defeated: a fibrous or porous gasket traps air in the joint, so the anaerobic sealant stays liquid or forms a weak partial gel.
• Metal contact is blocked: the gasket sits between the flange faces, keeping the sealant from touching metal, so the catalytic reaction never fully initiates.
• Gap mismatch: anaerobic flange sealants are formulated for tight, rigid, machined joints up to about 0.5 mm. A gasket creates a larger, compressible gap the sealant cannot cure across.
• Material incompatibility: some gasket rubbers and plastics are not chemically compatible with anaerobic formulations and can degrade.

If you use an anaerobic liquid gasket, sometimes called a formed-in-place gasket, you are replacing the pre-cut gasket, not adding to it.

When Anaerobic Sealants Replace Gaskets

Anaerobic flange sealants are engineered to take the place of cut gaskets on rigid metal flanges, and offer real advantages there:

• Full-contact sealing: they fill every microscopic void between machined faces, giving a continuous seal that resists leaks better than many gaskets.
• No relaxation or creep: the cured thermoset holds clamp load, unlike compressible gaskets that lose bolt tension over time.
• Unitized assembly: the joint resists vibration and shock that loosen gasketed joints and fasteners.
• Corrosion protection: sealing out moisture limits fretting and galvanic corrosion.
• Simplified inventory: one product covers many flange sizes.

Ideal applications include gearbox housings, engine sumps with rigid machined flanges, pump housings, compressor casings, and rigid hydraulic and pneumatic connections.

Choosing between a formed-in-place sealant and a gasket is a decision about flange rigidity, gap, and materials. Email Us to review your joint with Incure’s technical team.

When Gaskets or Other Sealants Remain Right

Traditional gaskets, or an RTV silicone, stay appropriate when:

• Flanges are flexible or stamped rather than rigid machined castings, so the faces move or are uneven.
• Gaps are large or irregular, where a flexible RTV silicone that cures with atmospheric moisture is more suitable.
• Surfaces are dissimilar, such as plastic to metal, where an anaerobic sealant will not cure.
• Frequent, easy disassembly is required, favoring a reusable gasket or a non-hardening paste.
• The equipment maker specifies a gasket or a particular RTV for warranty or performance reasons.

Cost and Lifecycle Comparison

The purchase price of a tube of sealant versus a box of gaskets is only part of the picture. A gasketed joint carries the cost of stocking many sizes, the labor of cutting or fitting, scrap from damaged gaskets, and the re-torque step after thermal soak. Over the life of the equipment it may also carry repeat leaks as the gasket relaxes. A formed-in-place anaerobic seal removes the gasket inventory, applies in one dispensing step, does not need re-torque, and typically lasts the service interval of the joint. Against that, disassembly of a high-strength anaerobic seal takes more effort, and the method only works on rigid machined metal. Run the comparison on your own joint, including warranty and field-service exposure, not just the shelf cost.

Disassembly and Rework

A gasketed joint opens by removing bolts and scraping the old gasket, and a fresh gasket goes back in. An anaerobic joint opens the same way for low- and medium-strength grades; high-strength grades may need localized heat to soften the cured film. In both cases, the flange faces must be cleaned back to bare metal before resealing. Plan the maintenance procedure and tool list around the grade you specify, and document it in the service manual so field technicians do not damage the flange trying to pry a heat-softenable seal cold.

How Incure Supports Sealing Decisions

Incure offers a range of anaerobic flange sealants for rigid metal-to-metal assemblies, along with technical consultation to assess your flange application, materials, operating conditions, and gap sizes, and determine whether an anaerobic sealant or an alternative is the better fit. We also advise on surface preparation, application technique, and cure.

For related guidance, see how thermal expansion mismatch causes seal failure, our comparison of adhesive strength for heavy-duty repairs, and how cure speed varies across chemistries.

Summary

For rigid, machined metal-to-metal flanges, anaerobic flange sealants are designed to replace pre-cut gaskets, not to be layered with them. For flexible flanges, large gaps, or dissimilar materials, a gasket or RTV silicone remains the correct choice. Match the method to the joint and confirm with a leak test.

Contact Our Team to identify the right sealing strategy for your assemblies.

Visit www.incurelab.com for more information.