Stray current corrosion testing

[Willem19]

Dear People,

I am working on a project on which there is a possibility that stray current will occur. I know what stray current corrosion is in general, but I don't know why and when it occurs. Therefore I've made 3 setups which I may test to see if i can make a representation of my project. In my project a leakage current will flow directly on to reinforced concrete, and the current will flow away through lightning rods connected to the reinforced concrete. The lightning rods are made up of 1 ohm and are therefore not drawen in the setups. I am wondering if somebody knows beforehand in which of my 3 experimental setups corrosion will occure, and why. And if my setups are correct.
I am looking forward to a respone.

Kind regards,
Willem

 

[Dhurjati Sen]

Have you tested the set-ups yet?
Maximum corrosion i.e icorr in Set-up 1, followed by Set-up 2.

DHURJATI SEN
Kolkata, India

 

[EdStainless]

What will the electrolyte be?
How will it be delivered?


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P.E. Metallurgy, consulting work welcomed

 

[SJones]

The current is shown flowing directly through the metallic elements, not “onto the concrete.”. The current appears to be confined completely to a metallic circuit, and thus, should not ‘stray’.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[Willem19]

@Dhurjati Sen, I've made the setup but the concrete is still drying out. I will try start testing before christmas.
@EdStainless, the electrolyte will be concrete.
@Sjones, So because the current will be completely confined to a metallic circuit, I should expect that no corrosion will occur?

 

[EdStainless]

You want to wire it so that the rebar is the anode, and the return path is through your 'ground' line.
And you will want to keep the concrete damp.

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P.E. Metallurgy, consulting work welcomed

 

[stevenal]

I see three short circuits with positive and negative poles of a battery connected together by rebar. Are we looking to kill batteries?

 

[Willem19]

@EDStainless, Why is the rebar not the anode in the figures i showed?
@stevenal, The voltage scource has an internal resistance that prevents this.
Sorry for my late responses, I was on a holiday.

 

[EdStainless]

You just show the rebar as a conductor.
There are a couple of ways to do this.
You could connect one side of your power supply to one bar and the other side to the other bar.
This would make one anode and the other cathode.
A second option would be to connect both bars to be anodes, and then use a pin driven into the concrete as the other terminal.
You will need to keep this damp (like rain fall damp) or this will take decades to corrode.
The low pH of the concrete is a powerful inhibitor.
Until you carbonation raises the pH and/or you get enough Cl leaching you will not see any corrosion.
Don't use too high of potential or you will just make hydrogen (1.24V I think).

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P.E. Metallurgy, consulting work welcomed

 

[Willem19]

@EdStainless, Thank you for your response. So what you are saying is that in figure 1 I should only connect the negative side of my power supply to the bottom rebar? If so, can i expect much corrosion if I put power on the rebars, one day after pouring mortar around the reabrs? The resistance of the mortar should be low compared to when it is in a dry state.

 

[EdStainless]

Unless you have used seawater or sand with high Cl in your mix, I would still expect it to take many months to show any signs of corrosion. And that would be if you kept it wet with salt water.
Any potential over 1V will not speed it up.
And as long as the pH is above 9 or so there will not be any corrosion.


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P.E. Metallurgy, consulting work welcomed

 

[Willem19]

@EdStainless, will a high current make a difference or will there still be no corrosion seen in short term? And how does pH prevent corrosion? I thought it only de-accelerates when the pH increases and accelerates when the pH decreases.

 

[EdStainless]

The current will depend on conductivity, you can't independently control it.
And if it is too high you may induce corrosion modes that would never happen in nature.
All aqueous corrosion is electrochemical.
You can't move metal ions unless you also move hydrogen ions.
At high pH the H ions are consumed by the environment.

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P.E. Metallurgy, consulting work welcomed

 

[Willem19]

@EdStainless, What are the ranges of current that induce corrosion modes that would never happen in nature? I was thinking of using a current between 0,5 and 2 amps. Thank you for your explanation about the pH value.

 

[EdStainless]

To reach 1A at 1V infers a resistance of 1ohm.
That low of resistance is highly unlikely.
More likely is thousands (or tens of thousands) of ohms and currents of 2-50 mA.

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P.E. Metallurgy, consulting work welcomed

 

[Willem19]

@EdStainless, thank you for your responses. They have been very helpful. I think im just going to pour the concrete, put power on the rebars and measure the current to see what current I will get and after some time will check if corrosion occured on the rebar.

 

[WKTaylor]

Corrosion protection and electrical grounding of reinforced concrete structures is already established with good practices...

NACE SP0187 Design for Corrosion Control of Reinforcing Steel in Concrete

NACE 01110 Stray-Current Corrosion in Reinforced and Prestressed Concrete Structures

etc...

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[Willem19]

@WKTaylor, I would love to get a look at both of these. But as a student unfortunately I can't afford to take a look at it.

 

[SJones]

Right - so this is a student project

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.

 

[WKTaylor]

Willem19... this forum is for working professionals... there is a forum dedicated for students to ask these type questions. Please use it.

MOST company and technical college libraries... and some public libraries, especially those supporting technical colleges/businesses... have access to a wide range of industry publications and standards.

Even though my company is aerospace, it is also heavily involved with civil engineering simply because that infrastructure supports efficient aircraft manufacturing.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov