The impact of bolt corrosion

Direct consequences of bolt rusting
1. Effective cross-sectional area loss
Corrosion will erode the surface of bolts, reduce their cross-sectional area, and directly lower their tensile strength.
2. Increased stress concentration
A rust pit with a depth of 0.1mm can achieve a stress concentration factor of 2.5, significantly accelerating the propagation rate of fatigue cracks.
3. Risk of hydrogen embrittlement fracture
In humid outdoor environments, corrosion reactions can precipitate hydrogen atoms into the metal lattice, causing an average decrease of 20% in bolt fracture toughness.
4. Uncontrolled preload force
Slight visible rust can cause a fluctuation of ± 30% in the bolt torque coefficient, directly leading to connection failure.
In highly corrosive environments such as seaside and industrial areas, the slight rust spots on bolts in the early stages are by no means a minor issue that can be ignored. If not dealt with in a timely manner, the subsequent losses will be several times higher than the initial maintenance investment.
II Temporary repair and long-term rust prevention measures for rusted bolts
A scientific and precise comprehensive response strategy must be adopted to address rust spots on bolts. Effective measures must be taken promptly in the early stages of rust development, when slight rust spots or localized corrosion points appear; Moreover, temporary emergency repair measures can only serve as short-term emergency response measures, and long-term anti-corrosion treatment measures must be carried out in a timely manner to truly ensure the long-term safety of the connecting structure.
01. Temporary repairs
Quickly stop local rust and prevent its spread.
Without dismantling or replacing the bolts, the existing rust layer on the surface of the bolts can be quickly removed through on-site construction, restoring the local anti-corrosion barrier and temporarily isolating it from corrosive media in the environment, in order to obtain buffer time for subsequent long-term anti-corrosion treatment or replacement construction. Mainly suitable for: equipment that cannot be stopped temporarily, limited construction space, and situations where immediate replacement is not possible.
Step 1: Surface cleaning and rust removal
Only by thoroughly removing all rust products and pollutants on the surface of the bolt can the adhesion and protective effect of the subsequent anti-corrosion coating be ensured. During the polishing process, excessive polishing should be avoided as much as possible. Remove visible rust on the surface of the bolt, but retain local cross-sectional defects and stress concentration defects.
Step 2: Passivation or phosphating treatment
Form a stable chemical conversion film on the surface of the bolt to enhance the adhesion and short-term protective performance of subsequent coatings.
Step 3: Apply temporary protective coating
The selection of coating is comprehensively determined based on the material of the bolt, the corrosion strength of the operating environment, and the subsequent construction requirements, to ensure the protective effect of emergency repair and the buffering time requirements of subsequent construction. Common temporary protective coatings include rust proof oil or wax, cold galvanized coatings, and epoxy resin adhesive coatings.
02. Long term rust prevention measures
Resolve from three aspects: material, process, and operation and maintenance.
Material upgrade: Select high corrosion resistant bolts that match the working conditions. In the actual engineering design and construction phase, it is necessary to select the appropriate type of bolt material based on the environmental corrosion level of the project. If there is a deviation in material selection, any subsequent anti-corrosion measures cannot guarantee the long-term performance of the bolts.
Process optimization: In highly corrosive environments, regardless of the grade of bolt material, it must be accompanied by professional surface anti-corrosion treatment processes. Without professional surface treatment processes as support, corrosive media can penetrate through pores and invade the surface of the bolt substrate, causing localized corrosion.
Operation and maintenance management: Regular inspections to promptly identify potential hazards. A scientific operation and maintenance management system is the ultimate guarantee for connecting structural security. Differentiated regular inspection plans can be developed based on the corrosion intensity of the environment; And carry out effective maintenance and treatment work as soon as local rust defects are discovered.
III On site disposal steps
1. Rapid detection and judgment
Measure the remaining diameter of the bolt with an ultrasonic thickness gauge. If the diameter loss exceeds 5%, replace it directly.
2. Emergency treatment for mild corrosion
Bolts with only surface rust can be cleaned with a wire brush and rust remover, and then reapplied with anti rust grease to reduce the subsequent rusting rate.
3. Moderate corrosion forced replacement
Bolts with obvious rust pits should be scrapped and replaced with new bolts.