1. Inadequate Preparatory Work: Rust and burrs on the flange contact surfaces were not cleaned before installation; thread integrity was not checked; mismatched gasket sizes were selected; old gaskets were reused; and even non-standard flanges were used, resulting in inherently unsuitable foundation conditions.
2. Improper Tightening Operations: Tightening was not performed in a diagonally staggered sequence; during manual tightening, force deviations at various points were significant; insufficient torque failed to compress the gasket, while excessive torque directly crushed the gasket or broke the bolts, ultimately causing severe uneven stress on the flange surface.
3. Misalignment and Positioning: The axes of the two flanges were not aligned; the end faces were not perpendicular to the pipe axis; small-diameter bolts were forcibly inserted after misalignment of the bolt holes, resulting in a significant decrease in connection strength and incomplete flange fit.
4. Neglected Detail Control: Bolts of different specifications were not used; the exposed length of the nuts was too long or too short; rust prevention treatment was not performed as required; no temperature difference compensation space was provided under high and low temperature conditions; after operation, the gaskets experienced creep and loosening, ultimately leading to seal failure.
