Do steel rebar not need to be anticorrosive in sewage tanks?
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I’ve seen that in the wastewater tanks of some chemical plants, composite fillers supported by rebar are used (with all the rebar submerged in water). Although their surface is a bit rusty, they still function properly. Why haven’t they corroded much after being in use for over a year?
Steel structures only rust under certain environmental conditions, and the composition as well as the acidity and alkalinity of the wastewater tanks in chemical plants vary. In an alkaline environment, carbon steel doesn’t necessarily corrode, right? If it’s an organic solvent, it probably won’t cause corrosion, right?
I agree with the view above: in alkaline environments, carbon steel develops a dense protective film on its surface, which results in a very slow rate of corrosion; therefore, it can be used for a long time without any anti-corrosion treatment； Most organic solvents do not undergo chemical reactions with metals; therefore, carbon steel does not require anti-corrosion treatment unless there are specific requirements.
Is the rebar exposed to sewage? The answer above is correct – alkaline environments facilitate the formation of a passivation layer that provides good protection. I wonder if there is anything else covering the rebar, and whether the rebar is black; if it is black, that indicates that the passivation layer is providing effective protection
The rebar is black; it seems to be well passivated
It seems that’s an alkaline solution; a passivation film forms on the surface, so no anti-corrosion coating is needed. Hehe, I’ve learned something new
I guess the main reason for using rebar is that its corrosion resistance is better than that of galvanized steel pipes, etc.; it may also be related to the environment.
However, the substances in wastewater often change; depending on their source, their acidity or alkalinity can vary. It is best to analyze its components first before deciding whether anti-corrosion treatment is necessary.
It is estimated that it contains alkaline wastewater, which is why it has an anti-corrosive effect.
It is the passivated film layer that forms; if a margin is taken into account in the design of the rebar, anti-corrosion treatment may not be necessary, but otherwise it is required, otherwise the properties of the rebar will be affected. The strength will be affected
In an acidic environment, it’s not enough to consider only the excess amount!
It’s also unknown whether the wastewater is acidic or alkaline. Judging from the comments of the experts upstairs, it is likely that passivation has occurred.
Even in corrosive media, rebar does not get completely corroded and disappear immediately; chemical corrosion is not chemical dissolution. In neutral and mildly corrosive media, a layer of corrosion products forms on the surface of carbon steel, and this black layer of corrosion products provides some protection for the carbon steel as well. Rebar can be used for a year without a protective coating without any problems.
The material properties do not cause corrosion; even if any occurs, it is only slight electrochemical corrosion
The original poster might as well add some acidic liquid to see what happens; haha, any iron will get corroded, and it mainly depends on the pH level of the medium
I think one reason is the passivation film; most importantly, it is inside the dielectric and in a non-pressurized state