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Difficulties in corrosion protection of flanges

Anti-corrosion of pipeline flange has always been a technical problem. Pipeline and equipment in the open air layout and ground installation and painted for anti-corrosion, so it should have good adhesion with the metal surface, waterproof and anti-atmospheric corrosion, ultraviolet aging and weather resistance.

The coating composition of process pipeline is: Epoxy zinc-rich primer (bottom layer, thickness ≥80 m), epoxy-iron anti-rust paint (middle layer, thickness ≥140 m), fluorocarbon topcoat (top layer, thickness ≥100 m), total coating thickness ≥320 m.

In accordance with the requirements of anti-corrosion construction norms, anti-corrosion coating before coating, derusting quality reach Sa2.5 level, but in the flange connection, especially the group of flange clearance, due to the fitting surface and gaps grease dirt cleaning difficulty, derusting quality is often difficult to meet the standard requirements, so the coating anti-corrosion paint falls off easily, can’t have anti-corrosion effect.

The problem of anti-corrosion for flange
The direct external cause of flange and bolt corrosion is the existence of corrosive media between the flange gap, in the absence of corrosion protection coating, the flange metal surface and bolts directly with water and air after the corrosion will soon occur.

We have taken the measure of wrapping adhesive tape or plastic pipe around the joint of two flanges to try to prevent external moisture and debris from entering the gap of flanges. This method can prevent debris from entering the gap of flanges to a certain extent, but it has little anti-corrosion effect on flange parts. Three problems were found after use:

  1. Due to the failure to achieve complete sealing, condensate still accumulates in the gap of the flange due to the difference in temperature in the humid environment. Failure to eliminate it in time will accelerate the corrosion.
  2. After the gap of a pair of flanges is closed from the outside, once the flange gasket leaks, it is easy to produce natural gas accumulation, which is not conducive to safe production.
  3. After being used for a period of time, the adhesive tapes and plastic pipes need to be replaced regularly due to aging of the materials.

Therefore, the use of adhesive tape or plastic pipe from the outside of the clearance of the closed flange anti-corrosion treatment, the actual effect is not ideal, we need to find a new pipeline flange anti-corrosion treatment technology and methods.

After several years of exploration and experiments, there is a kind of anti-corrosion technology of viscoelastic body material flange in gas pipeline. The viscoelastic body used in this new anti-corrosion technology is a kind of polymer material, between liquid and solid, in the temperature range of -50-85℃, neither flows at will, nor solidifies, can maintain good air tightness and water tightness.