A bolted flange looks simple, but it leaks, corrodes, and loosens in ways a gasket and torque wrench alone cannot prevent. Applied correctly, industrial sealants and threadlockers close the microscopic gaps, block corrosion at the joint face, and hold clamp load under vibration.

Where Mechanical Sealing Alone Falls Short

Even a well-machined, correctly torqued flange develops problems over time:

• Micro-leaks. Vibration, thermal cycling, and fastener relaxation open leak paths that a compressed gasket cannot follow. Gaskets also creep and can be nicked during installation.
• Joint-face corrosion. Moisture and process media wick into the flange interface, causing crevice corrosion, galvanic attack between dissimilar metals, and pitting that damages both flange and fasteners.
• Bolt loosening. Vibration and thermal movement reduce clamp load, which lowers gasket stress and starts the leak cycle again.
• Fretting. Micro-movement between mating faces or between bolts and holes generates wear debris and surface damage.

A sealant fills surface irregularities the gasket bridges over, and by displacing air and moisture it stops corrosion at the source. Because flange faces and fasteners often involve dissimilar metals, understanding how expansion mismatch drives bond and seal failure helps set realistic expectations for a rigid seal on a joint that runs hot and cold.

Choosing the Right Chemistry

There is no single product for flange protection. Match the chemistry to the joint:

Anaerobic Flange Sealants

Cure in the absence of air and in contact with metal, forming a co-cured seal that fills all surface imperfections. Best for rigid metal-to-metal flanges in pumps, gearboxes, compressors, and hydraulic systems, often replacing a cut gasket. Typical gap capability is up to about 0.5 mm, and passive metals such as stainless steel may need an activator.

RTV Silicone Sealants

Cure at room temperature into a flexible, resilient rubber that accommodates thermal movement, vibration, and dissimilar materials. Best for flexible or stamped flanges, irregular surfaces, and applications that need a conformable seal. Pressure resistance is lower than an anaerobic and cure is slower. An Incure Pyra-Sil RTV silicone suits joints where movement is expected.

Anaerobic Threadlockers

Fill the clearance in bolt threads and cure into a solid that resists self-loosening from vibration and shock, maintaining clamp load across the flange. Select strength by disassembly need: medium strength where the joint will be serviced, high strength where it will not.

Matching Selection to Service Conditions

Work through the joint parameters before choosing a chemistry:

1. Rigidity. Machined, bolted metal-to-metal faces suit an anaerobic. Stamped, flexible, or dissimilar-material flanges suit an RTV silicone.
2. Gap. Anaerobics are designed for close-fitting faces, generally up to about 0.5 mm. Larger or uneven gaps need a silicone or a solid gasket dressed with sealant.
3. Pressure. Anaerobic seals resist high internal pressure once cured. Silicone seals are better suited to lower-pressure service.
4. Temperature. Confirm the product’s continuous rating covers the peak joint temperature, and account for thermal cycling that works a rigid seal harder than a steady temperature.
5. Media. Verify chemical compatibility with the specific process fluid, not a generic resistance claim.
6. Disassembly. If the flange is serviced on a schedule, avoid a high-strength threadlocker on the bolts and choose a sealant that releases with normal joint separation.

Common Mistakes

• Applying sealant to a contaminated face. Old cured product and light corrosion both prevent a fresh seal from wetting the metal.
• Over-torquing to compensate for a marginal seal. Excess clamp load can crush a gasket or distort a thin flange, opening a new leak path.
• Pressurizing before cure. An anaerobic needs time in contact with metal to develop strength; testing too early disturbs the partially cured film.

Application Practice

Clean both flange faces and the fasteners to bright metal, removing oil, old sealant, and corrosion. Apply an even film of sealant across the full face, or run threadlocker into the engaged threads. Assemble and torque to specification within the product working time. Allow the stated cure before pressurizing. If you need help selecting between an anaerobic and a flexible seal for a specific joint, Email Us with the flange type, media, pressure, and temperature.

Retrofitting an Existing Leaking Joint

A flange that has leaked once will usually leak again unless the interface is addressed. When a joint is opened for service, inspect the faces for erosion, corrosion pitting, and warpage. Light imperfections can be sealed with an anaerobic dressing over a new gasket; deep pitting or a face that is out of flat needs machining or a flexible silicone that can bridge the profile. Remove every trace of the previous gasket and cured product, since a partial old layer holds the new seal off the metal. Re-torque in the correct crossing pattern and in stages, and record the sealant and torque values so the next service interval starts from a known baseline.

How Incure Supports Flange Reliability

Incure supplies anaerobic sealants, RTV silicones, and anaerobic threadlockers formulated for defined flange types, media, pressures, and temperatures, along with activators for passive metals. Our team reviews the joint design and operating conditions, then advises on surface preparation, application method, and cure so the seal performs across maintenance intervals. The same discipline of rating the thermal environment first applies here as it does when specifying compounds for heavy-duty, high-stress service.

To match a sealing approach to your flange connections, Contact Our Team with your application details.

Visit www.incurelab.com for more information.