Maintenance and Inspection Scheme for Flange Fitting Systems

Regular maintenance and systematic inspection extend the service life of flange pipe fittings and prevent unexpected pipeline leakage accidents. Enterprises should build targeted inspection plans according to pipeline medium characteristics, operating pressure and temperature. Inspection work is divided into daily visual patrol, periodic offline inspection and emergency special inspection. Daily patrol mainly focuses on visible flange joints. Inspectors observe traces of medium leakage, rust accumulation, bolt corrosion and obvious flange deformation. For flammable, toxic and volatile media, leakage detection instruments can be used to discover invisible micro leakage that cannot be identified by naked eyes. Periodic comprehensive inspection needs scheduled shutdown of pipeline systems. Workers loosen flange connections to check aging degree of sealing gaskets, corrosion status of flange inner surfaces and bolt thread wear. Gaskets with hardening, cracking and deformation must be replaced completely. Bolt threads need cleaning and anti-rust lubrication treatment. Corroded bolts with reduced bearing capacity should be updated to avoid bolt fracture under load. Flange surface corrosion detection is essential. Local pitting corrosion reduces effective wall thickness, lowering pressure bearing capacity. Ultrasonic thickness measurement equipment detects residual thickness of flange bodies to judge whether replacement is required. Thermal cycling pipelines experience frequent temperature changes. Thermal expansion and contraction cause repeated stress changes on flange connections, leading to bolt stress relaxation. During maintenance, re-tightening bolt torque according to standard specifications is necessary. Many factories ignore this point and face leakage after seasonal temperature variation. Special maintenance schemes are required for flanges used in outdoor open-air environments. Wind, rain, frost and atmospheric humidity accelerate bolt rust. Coating anti-rust paint or installing flange protection covers can slow corrosion speed. For flanges contacting seawater and acid media, inspection cycles should be shortened compared with conventional pipelines. Records of each inspection should be documented, including inspection time, flange position, existing defects, maintenance measures and replaced components. Historical data helps technicians predict failure trends and arrange advance spare parts procurement. When leakage happens during pipeline operation, blind maintenance without shutdown is risky. If the medium is toxic, high-temperature or flammable, operators must shut down the system and release internal pressure before disassembling flanges. It is forbidden to directly tighten bolts under operating pressure to deal with leakage. Temporary bolt tightening may stop leakage temporarily, yet it will accelerate bolt fatigue and trigger sudden large-scale leakage. After maintenance and assembly, pressure testing must be carried out again to confirm sealing performance before pipeline recovery.