The corrosion prevention at pipeline flange connections has always been a technical challenge. The process pipelines and equipment at gas transmission stations are generally arranged outdoors and installed on the ground, using coatings for corrosion prevention. These coatings are required to have good adhesion to metal surfaces, be waterproof, resist atmospheric corrosion, and have good UV aging resistance and weatherability. The typical composition of the process pipeline coating includes: epoxy zinc-rich primer (base layer, thickness ≥ 80μm) —— epoxy iron oxide anti-rust paint (intermediate layer, thickness ≥ 140μm) ——- fluorocarbon topcoat (top layer, thickness ≥ 100μm), with a total coating thickness of ≥ 320μm. According to the requirements for corrosion prevention construction, the rust removal quality must reach Sa2.5 level before applying the anti-corrosion coating. However, at flange connections, especially in the gaps of assembled flanges, due to the difficulty in cleaning grease and dirt from the surfaces and gaps of the connecting parts, the rust removal quality often fails to meet standard specifications. As a result, the applied anti-corrosion coating is prone to peeling off, failing to provide effective corrosion protection. The direct external cause of corrosion on flanges and bolts is the presence of corrosive media in the flange gaps. Without the protection of anti-corrosion coatings, the metal surfaces of the flanges and bolts quickly come into contact with water and air, leading to rapid corrosion. Measures have been taken in the past to wrap adhesive tape or plastic tubes around the connection points of two flanges to prevent external moisture and debris from entering the flange gaps. This method can somewhat prevent debris from entering the flange gaps, but it has limited effectiveness in protecting the flange components from corrosion. After use, three issues were identified:
(1) Due to the inability to achieve complete sealing, in humid environments, condensation can still accumulate in the flange gaps due to temperature changes. If not promptly drained, this can accelerate corrosion.
(2) Once the gaps between a pair of flanges are sealed from the outside, if the flange gasket leaks, it can easily lead to the accumulation of natural gas, which is detrimental to safe production.
(3) New adhesive tape and plastic tubes need to be replaced regularly due to material aging after a period of use.
Therefore, using adhesive tape or plastic tubes to seal the flange gaps from the outside for corrosion treatment is not ideal, and there is a need to find a new technology and method for corrosion prevention treatment of pipeline flanges.