Valve seal lubrication is a key guarantee for long-term reliable operation of high-temperature valves. In thermal power steam systems, petrochemical refining, metallurgy, and nuclear power plants, valve stems, gates and packing boxes operate under high-temperature media of 200–600°C for extended periods, where ordinary greases drip, coke and even carbonize at high temperature, leading to seal failure and stem galling. Molybdenum disulfide (MoS2), with its excellent thermal stability and low friction characteristics, has become an important choice for high-temperature valve seal lubrication. From the perspective of thermal stability, this article analyzes the application mechanism and verification standards of MoS2 in high-temperature valves.

Operating Conditions and Challenges of High-Temperature Valve Seal Lubrication

High-temperature valves impose stringent requirements on lubricating materials. The stems of steam valves, quick-closing valves and blow-off valves pass through the sealing packing box, where the medium temperature is high and the opening/closing frequency is high, and the sealing pair operates under boundary lubrication conditions. Frequent reciprocating motion intensifies fretting wear on the stem surface, and stainless steel and nickel-based alloy mating surfaces are prone to adhesive galling at high temperature. Ordinary mineral greases have limited drop points: under high temperature they rapidly volatilize, oxidize and coke, and the carbonized deposits adhere to sealing surfaces and packing, aggravating wear while destroying sealing integrity. In addition, high-temperature media may cause softening and aging of sealing materials, requiring lubricants to be chemically inert and not react with steam, hydrogen sulfide and other media.

Thermal Stability and Lubrication Mechanism of MoS2

The thermal stability of molybdenum disulfide is the key to its application in high-temperature valves. MoS2 has a melting point above 1000°C and can work stably up to 1100°C in vacuum or inert atmospheres without volatilization; in atmospheric environments it begins to slowly oxidize to molybdenum trioxide at about 350–400°C, but still maintains its layered structure in most engineering atmospheres such as nitrogen and steam. Within the layer, atoms are bonded by strong covalent bonds while adjacent layers interact through weak van der Waals forces, resulting in low shear strength and a friction coefficient as low as 0.03–0.06; its Mohs hardness is only 1.0–1.5, causing minimal wear to valve stems and sealing surfaces. Owing to its solid lubrication characteristics, MoS2 neither drips nor cokes, providing continuous friction-reduction protection in the high-temperature range where greases fail, which is well suited to long-term lubrication of valve stem guides and sealing surfaces.

Application Forms in High-Temperature Valves

In high-temperature valves, MoS2 is mainly applied in three forms. First, as a molybdenum disulfide dry film sprayed or brushed onto valve stems, valve seat sealing surfaces and gate surfaces; a transfer film is formed during assembly and initial operation to prevent high-temperature galling. Second, as an extreme-pressure anti-wear additive added at 3%–10% by mass to high-temperature greases or heat-resistant synthetic oils for maintenance lubrication of packing boxes and stem threads. Third, blended directly into sealing packings (such as braided graphite/aramid packings), which release solid lubricant microparticles during compression and deformation, reducing opening/closing torque and extending packing life. For special valves in the nuclear and petrochemical fields, composite solid lubricating films can also be prepared by physical vapor deposition.

Performance Verification and Standard System

The evaluation of high-temperature valve lubricants relies on verifiable standards. At the product level, the purity and chemical composition of MoS2 are tested in accordance with GB/T 23271-2009 "Molybdenum disulfide" and GB/T 23274-2009 "Methods for chemical analysis of molybdenum disulfide", ensuring batch-to-batch quality stability of the solid lubricant. At the performance level, ASTM D2596 (corresponding to GB/T 12583) determines the four-ball weld load to evaluate extreme-pressure load-carrying capacity under high temperature and pressure; ASTM D4172 (corresponding to GB/T 3142) determines the wear scar diameter to quantify anti-wear performance. The overall sealing reliability of the valve can be verified by shell and sealing surface pressure tests in accordance with GB/T 13927 "Industrial valves - Pressure testing". This combination of standards provides an objective basis for the selection, acceptance and failure analysis of high-temperature valve seal lubrication.

Conclusion

The seal lubrication of high-temperature valves directly affects equipment safety and maintenance intervals. With its outstanding thermal stability and solid-state friction-reduction characteristics, MoS2 provides a reliable lubrication solution in the high-temperature range where ordinary greases fail, effectively suppressing stem galling and sealing surface wear. Relying on verifiable standards such as GB/T 23271, GB/T 23274, ASTM D2596, ASTM D4172 and GB/T 13927 for verification helps promote its scientific selection and large-scale application in the high-temperature valve field.

Tags: Valve Seal Lubrication | Molybdenum Disulfide | MoS2 | High-Temperature Valves | Thermal Stability | Solid Lubrication | Stem Anti-Galling | GB/T 23271 | ASTM D2596 | 阀门密封润滑 | 二硫化钼

*（内容由AI生成，仅供参考）*

*（内容由AI生成，仅供参考）*