Molybdenum disulfide anti-seize compounds are specially formulated assembly lubricants for threaded connections operating under high-temperature, heavy-load, and galling-prone conditions. With high-purity molybdenum disulfide (MoS₂) solid lubricant as the core active ingredient, combined with high-temperature-resistant carriers and metal powders, they form a stable and durable lubricating isolation layer during bolt tightening and disassembly. In flange, valve, turbine, and steam-turbine bolted connections across the power, petrochemical, metallurgy, marine, and wind-power industries, ordinary greases fail quickly as their base oils volatilize and oxidize at elevated temperatures, causing cold welding, rust adhesion, and thread seizure on mating surfaces—bolts can no longer be tightened to the specified torque, and disassembly during maintenance becomes difficult or even results in bolt fracture. Owing to their chemical stability at high temperatures, extremely low friction coefficient, and outstanding extreme-pressure anti-wear performance, molybdenum disulfide anti-seize compounds have become the standard industrial solution to the "high-temperature sintering" problem of bolted connections.

Failure Mechanisms of High-Temperature Bolted Connections

### Galling and Cold Welding

When bolted connections operate at elevated temperatures, the thread pairs are subjected to extremely high contact stresses. As tightening torque is applied, the normal pressure on thread flank surfaces can reach several hundred megapascals. In the absence of an effective lubricating film, micro-asperities on the thread surfaces come into direct contact, producing intense metallic adhesion. During relative sliding, adhesion points are torn apart with material transfer, forming local cold welds and groove-like tearing—this process is known as "galling." Once galling occurs, the effective friction coefficient of the thread pair rises sharply, the actual preload deviates severely from the set torque, and disassembly often requires cutting or destructive methods.

### Effect of High Temperature on Lubricants

Conventional greases typically have an upper operating temperature limit of 120–180°C; their base oils undergo evaporation, oxidation, and thermal decomposition at elevated temperatures, forming carbon deposits and gum. Mineral oils oxidize at significantly accelerated rates above 150°C, and synthetic hydrocarbon oils also face volatile losses at 200–250°C. Once the base oil is depleted, only the soap thickener and additive residues remain, losing lubricating capability. By contrast, molybdenum disulfide is an inorganic solid lubricant that provides lubrication without relying on a liquid carrier; its layered crystal structure ensures sustained lubricating performance even after carrier depletion.

Lubrication Mechanism of Molybdenum Disulfide Anti-Seize Compounds

### Layered Crystal Structure and Low-Friction Nature

Molybdenum disulfide has a typical hexagonal layered crystal structure (space group P6₃/mmc). Each MoS₂ molecular layer consists of an S-Mo-S sandwich: two sulfur layers on the outside and one molybdenum layer in the middle. Atoms within each layer are joined by strong covalent bonds, while adjacent layers are held together by weak van der Waals forces. Under shear stress, interlayer sliding occurs, converting macroscopic sliding into microscopic slip between molecular layers, thereby significantly reducing the friction coefficient.

### Physicochemical Stability at High Temperature

Molybdenum disulfide begins to oxidize in air at approximately 350°C and is fully oxidized at 450–500°C; in vacuum or inert atmospheres it remains stable up to 1100°C. This means that within the vast majority of industrial high-temperature bolting applications (200–600°C), MoS₂ retains its complete layered structure and lubrication function. Even if slight surface oxidation occurs, the resulting MoO₃ still provides a certain friction-reducing effect below 795°C, so lubrication does not fail instantaneously.

Moreover, MoS₂ exhibits natural affinity for metal substrates (carbon steel, alloy steel, stainless steel, titanium alloys, etc.). Under fastening pressure it forms a dense transfer film, converting metal-to-metal contact into MoS₂-to-MoS₂ interlayer sliding and fundamentally blocking the path of galling initiation.

### Synergy of Carrier and Composite Components

Commercial molybdenum disulfide anti-seize compounds typically comprise three parts: the solid lubrication core (MoS₂ micropowder, usually 20–65% by weight), a high-temperature-resistant carrier (synthetic oil, silicone oil, or inorganic binder systems), and auxiliary solid components (copper powder, nickel powder, graphite, mica, etc.). The carrier provides workability and initial lubrication at ambient temperature; the solid components continue to provide lubrication and isolation after carrier volatilization; copper, nickel, and other soft metal powders fill micro-depressions on thread surfaces through their own ductility, further enhancing extreme-pressure load-bearing capacity. This "solid–liquid–metal" synergistic system enables anti-seize compounds to cover the entire process from ambient-temperature assembly to high-temperature service.

Key Performance Indicators and Testing Standards

The performance evaluation of anti-seize compounds relies on a series of international and Chinese national standards. The following indicators should be emphasized during engineering selection:

Among these, ISO 16047 specifies a unified method for measuring friction coefficients during the tightening of fasteners and is the core standard for evaluating the influence of anti-seize compounds on preload; DIN 946 provides the standard procedure for measuring thread friction coefficients; GB/T 16823.2 corresponds technically to ISO 16047, facilitating direct reference in domestic engineering practice. ASTM F606 specifies, from the perspective of fastener mechanical properties, that anti-seize compounds must not weaken bolt strength.

Typical Application Scenarios

### Steam Turbines and Power Generation Equipment

The flange bolts of intermediate- and high-pressure steam turbine casings can serve at 500–600°C, with bolt specifications typically ranging from M30 to M100 large studs. These bolts require extremely high preload consistency—excessive preload deviation can lead to flange sealing failure or bolt fatigue fracture. Molybdenum disulfide anti-seize compounds keep the friction coefficient stable within the 0.10–0.12 range, making the preload applied by hydraulic tensioners and torque wrenches repeatable and predictable, while ensuring smooth bolt removal during major overhauls.

### Petrochemical and Refining Plants

Flanges of catalytic cracking units, hydroprocessing reactors, and heat exchangers operate long-term at 300–450°C, with media often containing sulfides, chlorides, and other corrosive components. Flange bolts face not only high-temperature galling risk but also the dual threat of sulfur corrosion and chloride stress corrosion. The composite film formed by MoS₂ and soft metal powders in anti-seize compounds effectively blocks direct contact between corrosive media and the thread substrate, significantly extending bolt service life.

### Wind Power and Transmission Equipment

Tower flange and nacelle connecting bolts of wind turbines endure alternating loads and vibration, with preload decay being the primary cause of bolt loosening and fracture. Anti-seize compounds reduce tightening scatter by stabilizing the friction coefficient; combined with anti-loosening designs, they significantly reduce fretting wear, while their weatherability maintains reliable connections in outdoor humid and salt-spray environments.

### Metallurgical and Heat-Treatment Equipment

Bolts on furnace doors and platforms of rolling mills, heating furnaces, and heat-treatment furnaces operate long-term in high-temperature oxidizing atmospheres, where threads readily seize due to oxide scale and rust adhesion. Regular application of molybdenum disulfide anti-seize compounds significantly reduces removal torque during disassembly, minimizing downtime losses caused by forced destructive cutting.

Comparison Between Anti-Seize Compounds and Ordinary Greases

Selection Recommendations

1. **Select by temperature**: For long-term service below 350°C, conventional MoS₂ anti-seize compounds are sufficient; for 450°C and above or corrosive media, formulations with high MoS₂ content (≥40%) containing nickel/copper powder are recommended; for extreme conditions above 600°C, special ceramic-based or composite solid lubrication solutions should be evaluated.

2. **Select by bolt material**: Carbon steel and alloy steel bolts can safely use copper-containing anti-seize compounds; austenitic stainless steel bolts should avoid copper-containing formulations to prevent copper embrittlement and intergranular corrosion—nickel-based or copper-free formulations are recommended; titanium alloy bolts require dedicated formulations with strictly controlled chloride content.

3. **Select by preload control requirements**: For critical connections with high preload consistency requirements (steam turbines, pressure vessel flanges), choose products whose friction coefficient has been calibrated per ISO 16047 or DIN 946 with good batch-to-batch stability, and control coating thickness and coverage per standards during application.

4. **Consider environmental and occupational health factors**: Prefer lead-free, antimony-free, low-VOC formulations to meet increasingly stringent occupational exposure limits; some formulations may contain nitrites, so verify compliance with local regulations.

5. **Coating process essentials**: Clean threads and remove old coatings and rust before application; coating thickness should fully cover the thread profile without overflowing; for critical connections, verify coverage after trial assembly and tighten per the manufacturer's recommended torque factor.

Conclusion

Molybdenum disulfide anti-seize compounds take the low-shear characteristic of the MoS₂ layered crystal as the lubrication core and, through the synergistic design of "solid lubrication + soft metal isolation + high-temperature-resistant carrier," systematically solve the problems of galling, adhesion, preload loss of control, and difficult disassembly in high-temperature bolted connections. Their performance can be quantitatively evaluated and quality-controlled by the standard system of GB/T 16823.2, ISO 16047, DIN 946, and ASTM F606. In high-temperature heavy-load fields such as power, petrochemical, wind power, and metallurgy, correctly selecting and properly applying molybdenum disulfide anti-seize compounds is a critical engineering measure to ensure connection reliability, reduce maintenance costs, and enhance full life-cycle safety.

Tags: Molybdenum disulfide anti-seize | High-temperature bolts | Anti-seize compound | Bolt lubrication | MoS₂ | High-temperature lubrication | Thread galling | Preload | ISO 16047 | GB/T 16823.2 | DIN 946 | ASTM F606 | Anti-seize | High-temperature fasteners | Anti-rust lubrication