Please tell me about the anti-corrosion issues of underground pipelines for storage and transportation.
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A raw material line goes underground. After anti-corrosion was done, the journey went smoothly and the operation was good. However, after 3 years, problems continued to arise in one area, which was the tank area. In other words, why do our raw material lines always leak around the tank area, but there are no problems in other areas?
Is the electric field strength here too large?
Could it be that there is a lightning rod in the irrigation area, and the insulation layer of the underground pipeline was broken down due to induced lightning? If this is the case, a zinc oxide arrester can be added
If construction quality problems and regional geological problems are excluded, generally first consider whether there is cathodic protection in the tank area, that is, stray current interference. For details on the method of determining whether there is stray current and the method of eliminating interference, please see: Huang Chunfang or Zhong Cathodic Protection Chapter.
Initially, I also suspected that the lightning rod or grounding had broken down the anti-corrosion layer, but if you want to find the breakdown point, it is easy in theory, but in fact you have to dig a long way. Can the brother about electrochemical corrosion explain it in more detail?
Cathodic protection can be adopted. Each metal has a certain potential when immersed in a certain medium, which is called the corrosion potential (natural potential) of the metal. Corrosion potential indicates the relative ease with which a metal loses electrons. The more negative the corrosion potential is, the easier it is to lose electrons. We call the area where electrons are lost the anode area, and the area where electrons are gained is the cathode area. The anode area is corroded due to the loss of electrons (for example, iron atoms lose electrons and become iron ions that dissolve into the soil), while the cathode area is protected by electrons. Corrosion potential (V) of different metals in soil relative to saturated copper sulfate reference electrode (CSE) Metal potential (CSE) High purity magnesium -1.75 Magnesium alloy (6%Al, 3%Zn, 0.15%Mn) -1.60 Zinc -1.10 Aluminum alloy (5%Zn) -1.05 Pure aluminum -0.80 Low carbon steel (bright surface) -0.50to-0.80 Mild steel (surface corrosion) -0.20to-0.50 Cast iron -0.50 Mild steel in concrete -0.20
My understanding is that the storage tank constitutes the anode of the electrolytic cell, and the weak part of the pipeline constitutes the cathode of the electrolytic cell.； The normal electrode potential is that the pipe is higher than the storage tank, and electrochemical corrosion occurs at one end of the storage tank. ； However, since current often passes through the storage tank itself, the tank itself is polarized and the electrode potential increases. ； Weak links in buried pipelines depolarize and cause corrosion. . . Just my humble opinion for reference