Fastener maintenance

Fasteners are the "skeletal joints" of industrial equipment. The stable state of basic connecting components such as bolts, screws, nuts, and anchor bolts directly determines the operational accuracy, structural safety, and overall service life of the equipment. Standardized maintenance can be used in production activities to reduce equipment failure rates, extend machine service life, ensure production continuity, and reduce operation and maintenance costs.
 I  Failure type
All fastener failures follow the laws of fixed mechanics and materials science, and precise maintenance can only be achieved by mastering the principles to avoid blind operation.
1. Loose failure
The vibration and temperature fluctuations during equipment operation can gradually weaken the pre tightening force of fasteners. Long term failure to tighten can cause gaps, vibrations, and offsets, ultimately leading to loose and ineffective connections. Under long-term alternating loads, ordinary spring washers are prone to stress relaxation and cannot continuously compensate for the loss of preload force.
2. Fracture failure
Overload fracture: Excessive pre tightening force during assembly, mismatched thread size, or external forces exceeding the load-bearing limit of fasteners during equipment operation can all cause ductile or brittle overload fracture.
Fatigue fracture: The most common form of failure is the alternating stress generated by long-term vibration and frequent start stop of equipment, which causes cracks to form in the threaded area and gradually propagate, ultimately leading to fracture.
Hydrogen embrittlement fracture: High strength fasteners absorb hydrogen atoms during electroplating, acid washing, and other processes. Hydrogen atoms aggregate under stress to form hydrogen embrittlement, which can suddenly fracture within tens of minutes to several months after assembly.
3. Corrosion failure
In a humid, dusty, and corrosive environment, the surface of fasteners will gradually rust, which not only reduces the mechanical properties of fasteners, but also causes thread jamming, making it impossible to disassemble and tighten normally.
4. Thread wear and bite failure
During installation, impurities in the threads, uneven tightening torque, and repeated disassembly and assembly wear can damage the accuracy of thread engagement, resulting in insufficient effective engagement area, sliding teeth, locking, and fastening failure, and complete loss of connection ability.
II Installation phase (key foundation)
80% of the lifespan hazards of fasteners are formed during the first installation, and standardized installation can directly avoid most of the later failures, which is the core foundation of long-term maintenance.
1. Precise torque tightening (to prevent over tightening/over loosening)
Bolts have elastic fastening intervals, and a small torque can lead to insufficient pre tightening force and easy loosening; Excessive torque can exceed the elastic limit, causing plastic deformation and tensile damage to bolts, losing their load-bearing capacity, and significantly shortening their service life. Using a calibrated torque wrench to tighten the connectors in a standardized manner improves connection stability.
2. Thread pretreatment and cleaning protection
Thoroughly clean the thread oil stains, rust, and impurities before installation. Impurities can cause excessive thread engagement clearance, uneven stress, and rapid wear and loosening during operation
3. Scientific selection of anti loosening structures (suitable for working conditions)
Based on the scientific selection of vibration intensity and in accordance with the principle of mechanical anti loosening: equipment with slight vibration can use flat pads+spring pads, nylon anti loosening nuts; Medium vibration equipment uses detachable thread locking adhesive and double nuts for locking; For heavy-duty, high-frequency vibration, and high-altitude safety areas, wedge-shaped anti loosening washers and mechanical stop structures must be used to eliminate the risk of loosening. When connecting dissimilar metals, install insulation gaskets and anti-corrosion gaskets.
III Scientific inspection, maintenance, and upkeep
1. Daily inspection and scrapping standards
Accurate detection and timely scrapping are key to avoiding major equipment failures and extending the lifespan of the entire machine. It is strictly prohibited to use fasteners beyond their expiration date or with defects.
Daily inspection (timely detection of hidden dangers): visually inspect for rust, deformation, thread damage, gasket aging, looseness and displacement before starting up; Key part inspection: Maintenance personnel use torque wrenches to check whether the pre tightening force of the fasteners at the connection parts of key equipment meets the requirements of the equipment manual every week.
Scrap criteria (meeting any one of them): thread wear, slipping teeth, excessive meshing clearance, unable to guarantee fastening accuracy; The bolt rod shows elongation, bending, surface pits, and cracks due to stretching; Corrosion depth exceeding 10% of wall thickness, severe localized pitting corrosion; High strength bolts have been disassembled and assembled more than 3 times (with accumulated fatigue damage and decreased elastic performance); The anti loosening structure has failed and cannot be repaired; Stress relaxation and failure to meet tightening torque standards occur under high-temperature impact conditions.
2. Periodic maintenance in different scenarios (adapted to the working environment)
The damage rate of fasteners varies under different working conditions, and it is necessary to follow differentiated maintenance cycles, conform to environmental damage laws, and balance efficiency and safety.
a. Normal temperature and dry indoor working conditions
No strong corrosion, mild vibration, mainly caused by long-term stress relaxation and slight dust accumulation wear. It can be inspected every 6 months to clean the surface dust, apply anti rust oil to slightly corroded areas, check the gaskets for aging and collapse, and conduct a comprehensive inspection of fastening.
b. Wet/outdoor/salt spray conditions (outdoor equipment, coastal units)
High humidity accelerates oxidation, salt spray accelerates electrochemical corrosion, coating is prone to peeling, and threads are prone to rusting. Special inspections can be conducted every three months; Perform comprehensive rust prevention maintenance before and after the rainy season. Focus on checking the integrity of the fastener coating, and promptly apply anti-corrosion coating to the detached parts; Clean up accumulated water and salt on the threads, apply waterproof and rust proof grease, and prevent moisture retention and corrosion.
c. High temperature and high pressure working conditions (boilers, thermal pipelines)
High temperature leads to stress relaxation of bolts, rapid attenuation of pre tightening force, and material is prone to high-temperature fatigue deformation. Hot re tightening can be performed every 3 months, and non-destructive testing can be performed every 6 months. Prohibit excessive tightening in cold state to avoid stress overload after high-temperature expansion; Select high-temperature resistant special lubricating grease to prevent thread from biting due to high temperature and reduce disassembly wear.
d. Strong vibration/impact conditions (vibration equipment, production line transmission end)
The continuous consumption of pre tightening force by alternating loads results in repeated slight displacement of the threads, making them highly susceptible to loosening and fatigue cracking. Conduct monthly inspections and comprehensively tighten and verify torque every three months. Key review of the integrity of the anti loosening structure, timely replacement of failed anti loosening washers and locking adhesives; Eliminate long-term vibration operation and avoid cumulative fatigue damage to bolts.
3. Special maintenance based on material (to avoid exclusive damage)
The corrosion resistance, wear resistance, and fatigue resistance of fasteners made of different materials vary significantly, requiring targeted maintenance to avoid blind maintenance and accelerated damage.