Corrosion problem of bottom plate of normal pressure storage tank
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The lower chapter of API651 - Cathodic Protection of Above-ground Atmospheric Storage Tanks explains the failure mechanism of the tank bottom plate, among which oxygen concentration difference is one. The details are as follows: My question is, what are the similarities and differences in this mechanism between carbon steel and stainless steel? Thanks!
This post was last edited by Shutong on 2022-4-8 15:57 to explain the principles of carbon steel corrosion based on surface corrosion of oil tank bottom plates.: Since the center and edge ring beams of the tank bottom are high and the middle is low, all the water deposited from the crude oil cannot be discharged through the large tank. There must be some water in the lower part. In addition, the salt in the crude oil dissolves in the water, forming an electrolyte solution. And because there are many small-scale anode areas and large cathode areas within the same metal structure, once the structure is in an electrolyte environment, the corrosion battery will start to work. Most of the reactions that corrode batteries are anode processes.: Fe Fe2++2e cathode process: O2+4e+2H2O 4HO total reaction: 2Fe+O2+2H2O 2Fe(OH)2 Since the potential of Fe3C and other small impurities in the carbon steel of its base plate is higher than that of the metal body, it becomes many micro cathodes, which contact the electrolyte solution to form many short-circuited micro batteries. ； In addition, since the anode area is dispersed and small-scale, the structure shows pitting corrosion at this time. The bottom plate of the oil storage tank is corroded mainly in this way. Therefore, a certain number of new plates need to be replaced for each overhaul. In severe cases, the entire bottom plate needs to be replaced. Stainless steel corrosion please other brothers add more
Did I misunderstand? You are talking about the corrosion of the inner wall of the tank bottom?
Our company now requires that the bottom of the pipe be specially waterproofed before being insulated.
Carbon steel and stainless steel are mainly oxygen-driven corrosion. For stainless steel, the influence of chloride ions in the soil must be considered. In addition, bacterial corrosion also needs to be considered.
That is to say, if there are no chloride ions, the corrosion of stainless steel can be slightly reduced. Is this correct?
The poster is asking about the corrosion principle outside the bottom tank, and it is an area with stones.