Flange connections in piping, machinery, and pressure vessels contain fluids and gases under load. A compromised seal can mean production loss, safety exposure, and environmental release. Knowing the range of flange sealing methods, and where each fits, is essential for building leak-free systems.

From Gaskets to Formed-in-Place Sealants

Gaskets have long been the default: a deformable material compressed between mating surfaces to fill irregularities. Rising demands on pressure, temperature, and reliability have added specialized options alongside them.

Traditional Gaskets

Gaskets are physical barriers between flange faces. Their performance depends on material, design, and correct bolt load.

Non-Metallic (Soft) Gaskets

Made from rubber such as EPDM or nitrile, compressed non-asbestos fiber, PTFE, or graphite. They are compressible and conform to uneven surfaces, and suit lower pressure and temperature service. Full-face types cover the whole flange including bolt holes; ring types fit inside the bolt circle. Their main limitation is creep and relaxation over time, which loses bolt load and allows leaks.

Semi-Metallic (Composite) Gaskets

A combination of metal and soft filler, such as spiral-wound gaskets with graphite or PTFE filler, or metal-jacketed designs. They offer better resilience and pressure and temperature capability than soft gaskets and are common on steam, oil, and gas lines. They still rely on compression and can be damaged during handling.

Metallic (Hard) Gaskets

Solid metal, such as ring type joint gaskets with oval or octagonal sections. They seal by deforming into machined grooves and serve very high pressure and temperature service in oil, gas, and petrochemical plants. They require precise flange machining and are less forgiving of misalignment.

Liquid Gasketing (Formed-in-Place Sealants)

Liquid or semi-liquid materials that cure in place, filling the joint completely.

Anaerobic Flange Sealants

Single-component liquids that cure rapidly when confined between close-fitting metal surfaces without air. They give full surface contact and close microscopic leak paths, do not shrink or relax, resist fretting and galvanic corrosion, and can add shear strength to the joint. They suit rigid metal-to-metal flanges on gearboxes, pumps, compressors, engine sumps, and hydraulic systems, with gaps typically up to 0.5 mm.

RTV Silicone Sealants

Single or two-component systems that cure with atmospheric moisture or a catalyst to a flexible elastomer. They accommodate movement and thermal expansion, adhere to many substrates including some plastics, and offer good temperature resistance. They suit flexible or stamped flanges, larger gaps, and joints needing a conformable seal, such as valve covers and enclosures. Pressure resistance is generally lower than anaerobics.

Selecting among these methods is a matching exercise between joint design and service conditions. Email Us to review your flange type, gap, and operating envelope with Incure’s technical team.

Choosing a Method

Weigh these factors together:

• Operating conditions: pressure, temperature range, and chemical exposure.
• Flange type and material: rigid machined metal favors anaerobics; flexible or stamped flanges favor RTV silicones or gaskets.
• Gap tolerance: the measured gap dictates which sealant can cure and seal reliably.
• Disassembly needs: how often the joint must be opened, and how easily.
• Cost and efficiency: material, labor, inventory, and rework from leaks. Liquid gasketing often reduces labor and waste.
• Vibration and dynamic load: joints under vibration benefit from a sealant that adds stiffness and helps keep fasteners tight.

Bolt Load and Joint Assembly

No sealing method compensates for poor bolted-joint practice. Whatever the seal, the flange leaks if clamp load is uneven or lost. Torque the bolts in a cross pattern in two or three passes, stepping up to the final value, so the flange faces pull together in parallel. Use calibrated tools, and specify a torque value based on the fastener grade, thread condition, and the friction of any threadlocker or anti-seize used, not a generic number. On joints exposed to vibration or thermal cycling, an anaerobic threadlocker on the flange bolts prevents the slow loss of preload that opens a seal over time. Re-torquing soft gaskets after a heat soak is often required; formed-in-place anaerobic seals do not need it because the cured film does not relax.

Surface Finish Requirements

Each method has a target flange finish. Soft gaskets tolerate a rougher, 3 to 6 micrometer Ra face because the material conforms. Spiral-wound gaskets need a controlled serrated finish for the filler to grip. Anaerobic sealants want a clean, machined face with no deep gouges, since they bridge only microscopic voids. Metallic ring joints demand a smooth, accurately machined groove. Confirm the incoming flange finish matches the method before assembly rather than discovering the mismatch as a field leak.

How Incure Supports Flange Sealing

Incure supplies anaerobic flange sealants formulated for a range of industrial demands, along with anaerobic threadlockers for flange bolts, and provides technical support on selecting and applying the right method for each joint. Every product is manufactured under defined quality controls for consistent, repeatable performance.

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

The right flange sealing method depends on pressure, temperature, flange rigidity, gap, and serviceability. Traditional gaskets, anaerobic formed-in-place sealants, and RTV silicones each have a defined window. Match the method to the joint and validate with leak testing.

Contact Our Team to discuss your flange sealing requirements.

Visit www.incurelab.com for more information.