Anti-corrosion epoxy powder coating play a protective function
The joint application of cathodic protection and corrosion protection layer, allows underground or underwater metal structure to obtain the most economical and effective protection. Usually coated with a protective coating before use, to the metal and dielectric environment electrical insulation isolation, a good coating can protect more than 99% of the structures of the outer surface from corrosion. The pipe coating in the production, transportation and construction, can not absolutely guarantee against any damage to (fill the mouth coating, the coating density, coating pinhole, etc.), it is not possible to pipeline corrosion environment is completely isolated. But also for anti-corrosion insulation layer of various materials, in varying degrees, absorbent and breathable, and will gradually buried absorbent. To maintain an effective anti-corrosion, it is necessary to take the cathodic protection that is, joint protection. Thick coatings (thickness> 1mm), pipeline joint protection should be selected protection potential of -1.10 to-1.15V (CSE), the thin coating (thickness ≤ 1mm) take the protection potential of -1.05 to-1.10V (CSE), Taking into account the soil composition, humidity, temperature, coating types, coating quality, as well as microorganisms, appropriate adjustments to the protection potential, both to protect the pipeline without destroying the anti-corrosion coating. The corrosion of the polarization current evaluation environment is more effective. “Protection” is an important concept here, which anti-corrosion epoxy powder coating in place, “protection”?
The coated cathode stripping of the coating, destructive effects, the actual buried steel pipeline to run the best protection potential selected cathodic protection coating (3PE coating, the underlying fusion bonded epoxy powder) off the reasons worth exploring. About the best protection potential. Current-potential curve in the foreign scholars study corrosion and cathodic protection situations, intense hydrogen desorption reaction potential of-1.15V. According to the investigation Malaysia, Lloyd’s Register, Shell provide maximum protection potential of-1.1V limit take-1.15V; German standard DIN30676-19853.1 reads as follows: in the thin coating (<1mm) thick was used for corrosion protection the case, due to the polarization will have the opposite impact such as blisters formed, in order to minimize the impact, should limit the scope of the protection potential as a function of the coating, such as maximum protection potential of -1.00 ~~-1.20V (relative CSE) . Abroad, specifically mentioned the potential cause of failure of the coating by a number of factors, including soil composition, humidity, temperature, coating types, coating quality and microbial, the industry generally considered to avoid potential power outages lost -1.05 ~ – 1.10V (CSE) (Note: the widespread use of fusion bonded epoxy powder coating). Cathodic protection lead coating (3PE coating the bottom off the mechanism of fusion bonded epoxy powder coating).
Coating type, humidity, temperature determines the coating of water absorption, resistance to penetration ability into a function of coating thickness and coating under the same conditions. Research has shown that cross-linked epoxy resin will form a certain amount of pore and pore channels for the water molecules into the epoxy resin. Solution reach the coating / metal interface, from the tunnel into the corrosion product film generated at the interface with the metal reaction, this layer of corrosion product film to prevent the reaction of the metal and the solution, the coating resistance decreases gradually. With more and more corrosive ions reach the interface, this layer of corrosion product film is destroyed gradually, corrosion intensified, and ultimately result in the epoxy coating stripped from the drum. Fusion bonded epoxy powder coatings cured is still rich in ether and hydroxyl groups, these active groups and the pipe surface firmly bonded together by chemical bonds to form anti-corrosion coating. Fill the mouth of the coating, dense, pinhole reasons, the coating are different degrees of water absorption and permeability, if the cathodic protection is excessive, resulting in the cathodic hydrogen evolution, with the active hydrogen atoms of the accumulated, to a certain extent, hydrogen will ether and hydroxyl reaction, thereby undermining the bond strength of the coating and the steel pipe, resulting in the disappearance of bond strength. The result is that the coating off from the steel pipe.
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