A leak at a flange connection is more than a nuisance. It drives downtime, wasted fluid, safety exposure, and quality escapes. Flange joints in fluid and gas systems need dependable sealing, and modern anaerobic flange sealants offer a durable alternative to cut gaskets when the flanges are rigid and machined. Anaerobic Flange Sealants Versus Cut Gaskets Cut gaskets seal by compressing between two flange faces. Over time they relax, can extrude under pressure, and often fail to fill fine surface imperfections, which leads to slow leaks under thermal cycling or vibration. Anaerobic flange sealants behave differently: Formed-in-place sealing: they fill every microscopic void between rigid metal flanges, giving full surface-to-surface contact and closing leak paths a gasket leaves open. No relaxation or shrinkage: once cured to a thermoset plastic, they hold clamp load without creep. Added joint strength: they resist vibration, shock, and thermal movement. Corrosion control: by displacing air and moisture, they limit fretting and galvanic corrosion at the interface. Simplified inventory: one product replaces many pre-cut gasket sizes. Serviceability: many grades still allow disassembly with standard tools. Step 1: Surface Preparation This step decides the outcome. Anaerobic adhesives need clean, active metal. Remove all old gasket material, previous sealant including RTV silicone, paint, oil, grease, dirt, and rust with a residue-free solvent cleaner. Avoid razor blades and aggressive wire wheels that gouge the flange face and create new leak paths. Use plastic scrapers or dedicated gasket removers. Inspect for nicks, burrs, and warping. Anaerobic sealants bridge minor imperfections; severe damage needs machining. Typical gap-filling capability is up to 0.5 mm. Larger or irregular gaps call for an RTV silicone instead. Confirm both faces are fully dry before application. Step 2: Activate If Needed Anaerobic sealants cure readily on active metals such as steel, brass, and copper. On passive metals such as aluminum, stainless steel, or plated surfaces, or in a cold shop, apply a thin, even coat of activator to one flange face and let the solvent flash off completely before sealing. Good surface preparation and activation choices are where most flange leaks are won or lost. Email Us to review your substrates and shop conditions with Incure's technical team. Step 3: Apply the Sealant Dispense a continuous bead onto one prepared flange face, placed near the inner rim and encircling every bolt hole. On large flanges or automated lines, a dispensing head or roller gives a consistent bead. Apply enough to fill surface imperfections without heavy excess, which only squeezes out and has to be wiped away. Step 4: Assemble Promptly Bring the flanges together as soon as possible so the sealant is confined and the cure begins. Avoid lateral sliding, which smears the bead. Torque the bolts to specification in a cross pattern for even pressure. Some grades give an instant low-pressure seal, but full strength follows the specified cure, typically 24 hours at room temperature. Step 5: Cure and Test Allow the full data sheet cure before putting the joint into service. Wipe away uncured…

Anaerobic sealants stay stable as liquids in the bottle, then turn into durable, leak-proof solids once applied and assembled. That change is a precisely engineered chemical reaction, not a drying step, and understanding it helps you control quality and cycle time. Two Conditions Drive the Cure The word anaerobic means without air, and oxygen exclusion is the defining trait of these sealants. Unlike adhesives that cure by reacting with oxygen or evaporating solvent, anaerobic sealants are formulated to stay liquid while oxygen is present. Two conditions must both be met for cure to start: Absence of oxygen: once the sealant is confined between mating surfaces, dissolved oxygen is consumed or displaced, removing the inhibitor that keeps it liquid. Contact with active metal ions: active metals such as iron, copper, brass, and steel carry trace surface ions that act as catalysts, initiating the reaction that converts the liquid resin into a solid polymer. The Chain Reaction, Step by Step The cure is a free-radical polymerization: Initiation: the sealant contains methacrylate monomers, initiators such as peroxides, and accelerators. With metal ions present and oxygen absent, the initiators break down into reactive free radicals. Propagation: those free radicals attack the monomers, linking them into long chains that branch and cross-link into a dense polymer network. Termination: the reaction continues until the free radicals are consumed or the entire confined volume has polymerized. Any sealant that squeezes out of the joint and stays exposed to air remains liquid and can simply be wiped away. Factors That Change Cure Speed and Quality Metal activity: copper and brass promote a fast cure, steel is moderate, and passive metals such as stainless steel, aluminum, and plated surfaces are slow and often need an activator. Bondline gap: anaerobic sealants are built for tight tolerances, typically up to 0.5 mm. Larger gaps leave trapped oxygen that inhibits cure in the center of the joint. Temperature: higher temperatures speed the reaction; cold parts and surroundings slow it, and below about 5 degrees C cure can stall without an activator or applied heat. Surface cleanliness: oil, grease, dirt, and some cleaner residues interfere with the metal's catalytic action and cause slow or incomplete cure. Activator use: for passive metals, cold conditions, or fast fixture requirements, an activator applied to one surface adds catalytic components and secures a reliable cure. Cure control is a process-engineering problem as much as a chemistry one. Email Us to review your metals, gap, and line conditions with Incure's technical team. Why the Cure Stays Stable in the Bottle Anaerobic sealants are shipped in permeable containers that are deliberately underfilled, because dissolved and headspace oxygen is what keeps the product liquid during storage. The polyethylene bottle wall lets oxygen diffuse in slowly to replace what is consumed by trace side reactions. This is why decanting anaerobic sealant into a sealed glass jar or a full, airtight container shortens its shelf life: the oxygen supply is cut off and slow gelling begins. It also explains why the nozzle…

Anaerobic sealants seal rigid metal-to-metal flanges. Gaskets bridge larger gaps and dissimilar materials. That raises a practical question in assembly planning: can you use an anaerobic sealant together with a conventional gasket? In most cases the two are alternatives, not partners, and combining them creates problems. What Each Method Is Designed to Do Anaerobic sealants: liquid or gel adhesives that cure in the absence of air and the presence of metal ions, forming a rigid thermoset seal that fills microscopic imperfections between close-fitting metal surfaces. They act as a formed-in-place gasket and add structural stiffness to the joint. They suit precision-machined, metal-to-metal flanges. Traditional gaskets: pre-formed compressible materials such as fiber, rubber, or cork that fill larger, less precise gaps by compressing under bolt load and conforming to surface irregularities. They suit dissimilar materials, wider clearances, and joints that are opened frequently. The General Rule: Anaerobics Replace Gaskets On rigid machined metal flanges, anaerobic flange sealants are used instead of cut gaskets. As a gasket eliminator they: Prevent the relaxation and re-torquing that compressible gaskets need over time. Improve joint rigidity by filling the entire void between flanges. Reduce inventory, since one product replaces many pre-cut gasket sizes. Seal microscopic leak paths that a solid gasket can miss. Why Combining Them Usually Fails Putting an anaerobic sealant and a compressible gasket in the same joint is generally counterproductive: Inhibited cure: the anaerobic sealant needs metal-to-metal contact and oxygen exclusion. A non-metallic gasket between the flanges blocks the metal ion contact and can trap air, leaving the sealant partly or fully uncured. Compromised gasket function: a rigid cured film interferes with the designed compressibility of the gasket, so the gasket cannot seat and seal as intended. Disassembly damage: uneven partial adhesion can tear the gasket and mar the mating faces during future service. Redundancy: you spend on two solutions for a job one is designed to do, adding cost and assembly steps with no benefit. If you are using an anaerobic liquid gasket, you are replacing the pre-cut gasket, not supplementing it. What Happens Inside a Combined Joint Picture a compressible fiber gasket coated on both faces with anaerobic liquid, then bolted between two cast flanges. The gasket holds the flange faces roughly a millimeter apart, so almost none of the anaerobic material sees metal contact. Air trapped in the fiber keeps the inhibitor active. When the joint is torqued, the gasket compresses unevenly because pockets of gelled adhesive resist where the material happened to touch metal at a bolt boss. The finished joint has neither the full clamp stability of a formed-in-place seal nor the even compression the gasket was designed for. Under thermal cycling it tends to weep at the low-contact zones first. The Rare Exception A very thin, non-curing anaerobic liquid used as a gasket dressing is occasionally applied with a rigid, non-compressible gasket in specialized static applications where fluid resistance on the gasket surface is critical. This is outside standard practice and requires material compatibility checks and…

Anaerobic sealants create reliable, leak-proof seals in metal-to-metal assemblies because they cure only in the absence of air and the presence of metal ions. A recurring question on the production floor is whether an activator is always required. The answer depends on the metal, the gap, the temperature, and the cycle time you need. The Anaerobic Cure, Briefly Anaerobic sealants contain initiators that react with metal surfaces once oxygen is excluded. That reaction generates free radicals, which polymerize the liquid resin into a solid. Cure speed and completeness depend on: Metal type: some metals catalyze the cure far more actively than others. Bondline gap: tighter gaps exclude oxygen more effectively and cure faster. Temperature: warmer parts and surroundings accelerate the reaction. When an Activator Becomes Necessary Many anaerobic sealants cure adequately on their own. An activator becomes important in specific situations: Passive metals: stainless steel, anodized aluminum, zinc-plated surfaces, cadmium, chrome, and titanium carry few active surface ions and slow or inhibit the cure. An activator deposits the catalytic species the reaction needs. Larger gaps: anaerobic sealants target close-fitting parts, typically up to 0.5 mm. Wider gaps trap oxygen and interfere with cure; an activator helps overcome that inhibition. Low temperatures: in a cool workshop or on cold parts, cure slows markedly. An activator restores a workable cure time. Faster cycle times: even on active metals, an activator can sharply reduce fixture time in high-volume assembly. Marginal surface condition: an activator can help overcome minor residual contamination, though it never replaces proper cleaning. The Cost of Skipping an Activator When One Is Needed When a passive substrate or cold part slows the cure, the visible symptom is a joint that has not fixtured by the time it reaches the next station. Less visible is partial cure: the sealant near the metal reacts while material in the center of a wider gap stays soft. That joint may pass a quick handling check and still leak under pressure or vibration weeks later. On plated fasteners and stainless flanges, an untreated surface can extend fixture time from minutes to hours, which is rarely compatible with a moving line. An activator removes that variability, giving a predictable fixture time regardless of incoming part passivation. What an Activator Does Anaerobic activators are usually solvent-based solutions carrying a catalyst, often a copper compound or similar accelerator. Sprayed or wiped onto the metal, they leave a microscopic film of active material that promotes polymerization, allowing the sealant to cure on otherwise slow surfaces or in less favorable conditions. The solvent must flash off fully before the sealant is applied. Applying an Activator Correctly Apply a thin, even coat to one mating surface only. Allow the solvent to evaporate completely, following the data sheet dwell time. Assemble within the activator's open time; effectiveness declines after prolonged exposure. Avoid heavy application, which can leave residue that weakens the bond. Getting activator use right is often the difference between a consistent line rate and unpredictable fixture times. Email Us to…

Two sealing chemistries handle most industrial leak-prevention work: room temperature vulcanizing (RTV) silicones and anaerobic sealants. They cure by different mechanisms and suit different joints, and choosing the wrong one is a common cause of persistent leaks. How Each Sealant Cures Anaerobic Sealants Anaerobic sealants are single-component liquids that stay fluid while exposed to air. They cure only when confined between close-fitting metal surfaces, starved of oxygen, and in contact with active metal ions such as iron or copper. The result is a rigid thermoset plastic that fills microscopic surface imperfections and creates full surface-to-surface contact. Key characteristics: Cures in the absence of air, in contact with metal. Designed for small, close-fitting gaps, typically up to 0.5 mm. Primarily a metal-to-metal technology. Cures rigid and adds shear strength to the joint. Strong resistance to oils, fuels, and coolants. Heat resistance generally 150 to 200 degrees C for standard grades. Disassembly can require localized heat. RTV Silicone Sealants RTV silicones cure by reacting with atmospheric moisture at room temperature, releasing a byproduct such as acetic acid or alcohol, and forming a flexible elastomer. Key characteristics: Cures on exposure to humidity. Fills larger, uneven gaps, often 6 mm or more. Adheres to metals, many plastics, glass, ceramics, and painted surfaces. Cures to a flexible, rubber-like film. High flexibility suits thermal movement, vibration, and dynamic joints. Some formulations withstand over 300 degrees C. Generally easier to peel or scrape away during service. Cure Byproducts and Corrosion RTV silicone chemistry matters when electronics or sensitive metals are nearby. Acetoxy-cure grades release acetic acid, which can corrode copper, brass, and some coatings and irritate operators in enclosed areas. Neutral-cure grades, using oxime or alkoxy chemistry, release milder byproducts and are the safer choice around electrical contacts, bare copper, and enclosed housings. Anaerobic sealants release no atmospheric byproduct, since they cure only in the confined joint, but the rigid cured film means a joint sealed this way is harder to open later. Dispensing and Application Anaerobic sealants are applied as a continuous bead to one clean, dry flange face, encircling all bolt holes, then assembled promptly so the joint closes before the surface film can begin to set. RTV silicones are applied as a bead sized to the gap, with parts brought together within the skin-over time, typically a few minutes. Both benefit from automated dispensing on higher-volume lines for consistent bead placement and volume, which reduces both squeeze-out waste and thin spots that leak. A Direct Comparison Feature Anaerobic Sealants RTV Silicone Sealants Curing trigger Absence of air plus metal contact Atmospheric moisture Best gap range Small, precise, machined flanges Large or irregular, stamped sheet metal Material compatibility Primarily metal-to-metal Wide range of materials Cured state Rigid thermoset plastic Flexible elastomer Structural contribution Adds rigidity and shear strength Provides flexibility and vibration damping High-temperature limit Good, 150 to 200 degrees C typical Excellent, often over 250 degrees C Disassembly Can require heat Generally easier When to Choose Which Choose an anaerobic sealant when you have…

Two machined metal surfaces that look perfectly flat to the naked eye are, under magnification, a landscape of microscopic peaks and valleys — and that gap is exactly where anaerobic flange sealant does its work. The Basic Chemistry Behind the Name An anaerobic flange sealant is a single-component adhesive that cures in the absence of air and in the presence of metal ions — hence "anaerobic," meaning without air. Applied as a liquid or gel to a flange face, it stays liquid as long as it's exposed to atmospheric oxygen. Once the two mating surfaces are brought together and oxygen is excluded from the joint, the metal ions at the surface catalyze a rapid polymerization reaction that converts the liquid into a durable, solvent-resistant thermoset plastic filling every void in the joint. Why Traditional Gaskets Leave Gaps Anaerobics Don't Traditional pre-cut gaskets can bridge some surface irregularities under clamping pressure, but they can't conform to every microscopic imperfection on a machined flange — and those unfilled voids are where leaks eventually start. Because anaerobic sealant is applied as a liquid before it cures, it flows into gaps a solid gasket simply can't reach, producing full surface-to-surface contact rather than a series of point contacts under compression. Characteristics That Explain Why They're Widely Used No shrinkage or creep: curing happens without solvent loss, so the seal doesn't relax or loosen the way compressed gaskets can over time. High strength and durability: the cured bond resists vibration, thermal cycling, and shock without losing joint integrity. Chemical resistance: most formulations tolerate oils, fuels, coolants, and hydraulic fluids without degrading. Gap-filling range: typically effective up to roughly 0.5 mm, depending on the specific product, which covers the vast majority of machined-flange tolerances. Even stress distribution: full surface contact spreads load evenly across the joint rather than concentrating it at a few high points. Where Anaerobic Flange Sealants Are Used Engine and transmission housings, pump and compressor assemblies, hydraulic and pneumatic system connections, machined flanges, and bearing caps all rely on this class of sealant to hold pressure and exclude contaminants without the bulk or replacement cost of a traditional gasket. In each case, the deciding factor is the same: a rigid, close-fitting metal-to-metal joint that needs a seal capable of filling microscopic surface variation rather than bridging a larger, more flexible gap. How Cure Time Interacts With Assembly Scheduling Anaerobic sealants typically reach handling strength well before they reach full chemical cure, and confusing the two is a common source of premature seal failure. A joint may be stable enough to move to the next station within minutes, but full cure — the point at which the sealant reaches its rated chemical and pressure resistance — can take considerably longer, particularly at lower ambient temperatures or on passive metal surfaces without an activator. Pressurizing or loading a joint before full cure is reached can permanently compromise the seal even though it appeared solid when handled. Production schedules should build in the manufacturer's specified full-cure…

A leaking flange rarely means the anaerobic sealant chemistry was wrong for the job — in most cases it means something in the assembly process undermined a perfectly good product, and the fastest path to a permanent fix is matching the actual symptom to its real cause. For background on how anaerobic chemistry cures and where it fits against gasket alternatives, see our overview of anaerobic flange sealants for industrial metal-to-metal sealing. Symptom: Weeping Appears Within the First Few Days of Startup An early leak, showing up before the assembly has accumulated meaningful service hours, points to an incomplete cure rather than a sealant selection problem. Anaerobic chemistry cures in the absence of air and in the presence of metal ions at the mating surfaces, and disturbing the joint — pressurizing it, running the equipment, or even revisiting the torque — before the manufacturer's specified cure window has elapsed removes the polymer's chance to reach full cross-link density. Checking the cure-time log against the actual time the assembly went into service is the first thing to verify before questioning the product itself. Symptom: The Leak Only Appears on One Side of the Flange A leak concentrated at one section of an otherwise sealed flange face is a strong signal of an uneven clamping pattern rather than a sealant failure. Tightening bolts in a random order instead of a specified crossing sequence leaves one part of the flange face under-compressed while the sealant is still curing, so that section never achieves full surface contact even though the rest of the joint looks perfectly sealed. Re-torquing the assembly in the correct sequence on the next rebuild — rather than switching sealant formulations — resolves this failure mode in most cases. Symptom: Lubricant or Process Fluid Shows Contamination After Assembly Particles or a film in the lubricant or process fluid downstream of a newly sealed flange, misdiagnosed as a sealant chemistry problem, is frequently a squeeze-out issue instead. Excess sealant applied beyond what the joint's gap-filling requirement calls for gets pushed into the bore of a pump or gearbox housing during assembly, where it can break off after cure and travel downstream. Reducing bead size to match the actual gap, rather than applying a generous margin "to be safe," prevents this without needing a different product. Symptom: A Seal That Held for Years Suddenly Starts Leaking A joint that performed reliably for an extended period before failing usually points to accumulated thermal-cycling stress rather than a sudden chemistry breakdown, particularly on assemblies where dissimilar metals expand at different rates across repeated heating and cooling. Each cycle adds a small amount of stress at the flange interface, and a rigid sealant chemistry that seemed adequate at installation can eventually reach its fatigue limit years into service, especially on equipment that runs through frequent startup-shutdown cycles rather than staying at a stable operating temperature. Symptom: The Same Flange Keeps Leaking After Repeated Rebuilds If a specific flange location fails repeatedly despite reapplying sealant correctly each…