Anti-seizure methods for stainless steel bolts and nuts

For the stainless steel bolts used to connect pressure pipelines, it is required that the surface of these fasteners be hardened. You can check to see if the technical requirements have been met. There are hardening heat treatment processes for stainless steel surfaces. The best ones are the stainless steel instrument connection sleeves, and the surface hardening methods for them are all their own patents.

Stainless steel bolts and nuts are prone to galling (i.e., \"cold welding\") during tightening due to material properties such as adhesive tendency and similar coefficients of thermal expansion, which makes them difficult to remove. Here are the common methods for preventing metal interlocking along with relevant precautions: 1. Use anti-interlocking lubricants. Anti-interlocking pastes/agents: Specialized lubricating pastes (containing components such as copper, nickel, molybdenum, or graphite) can reduce friction and prevent direct contact between metals. Common brands: Loctite LB 8008, Molykote 1000, Permatex Anti-Seize. Applicable scenarios: high-temperature, highly corrosive environments (such as in the chemical industry and at sea). Lubricating grease: Ordinary lubricating grease can prevent galling in the short term, but it tends to lose its effectiveness at high temperatures. 2. Choose different material combinations: Use different stainless steel grades for bolts and nuts (e.g., 316 for bolts and 304 for nuts) to reduce the risk of adhesion between metals of the same type. Coating: Bolts are galvanized, nickel-plated, or treated with Dacromet to increase surface hardness and lubricity. 3. Mechanical isolation measures: Use of gaskets – stainless steel flat gaskets or polytetrafluoroethylene (PTFE) gaskets to isolate the contact surfaces. Threaded sleeve/insert: A copper alloy threaded sleeve is inserted into the nut to prevent direct contact between stainless steel. 4. Optimize the assembly process and control torque: Use a torque wrench to prevent thread deformation caused by over-tightening. Low-speed assembly: High-speed tightening generates high temperatures, increasing the risk of seizure. Step-by-step tightening: Tighten in stages (e.g., 50% torque → 100%) to evenly distribute stress. 5. Surface treatment: Passivation treatment: Improves the density of the stainless steel oxide film and reduces adhesion. Polished threads: reduce surface roughness and minimize friction. 6. Other precautions: Avoid reusing them – the risk of damage increases with the number of times they are removed; in high-temperature environments, it is recommended to replace them with new ones. Clean the threads: Remove metal shavings and dirt before assembly to prevent particles from exacerbating wear. Corrosion protection: Galling and corrosion can occur simultaneously, so rust prevention measures must be selected based on the environment. Common mistake ❌ Using regular butter as a substitute for specialized anti-chafing agents (it becomes ineffective after carbonization at high temperatures). ❌ Over-reliance on forceful removal (may cause thread stripping). By comprehensively applying the above methods (such as lubricants + dissimilar materials + torque control), the risk of galling in stainless steel threads can be effectively reduced, especially in high-temperature, humid environments or during frequent disassembly.

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