# Measuring corrosion between copper and steel

#### jegjessing

Joined Feb 22, 2019
3
Hi
I can, easily measure resistance and loop in district heating pipes. But how do I measure the corrosion?
I've seen some examples using a ZRA (how ever that design would be) and a voltmeter. But all of these schematics have 3 connections one to each electrode and then a plane between the two.

But here we only have a copper wire and the steel pipe, where the copper wire is separated from the steel pipe using a non conductive foam.

So how can I in fact measure the actual corrosion? I've read that the voltage between copper and steel would be around 0.3V, but I guess that depends on the purity of the water?
Also if I try to convert the current using a I/V converter between the two "wires" (steel and copper) I measure something in the order of 2mV but if I measure with a voltmeter I measure something like 200mV

On another set I measure i.e. 0mV using the ZRA but 400mV with the voltmeter.. What gives?

#### wayneh

Joined Sep 9, 2010
17,405
So how can I in fact measure the actual corrosion? I've read that the voltage between copper and steel would be around 0.3V, but I guess that depends on the purity of the water?
I don't think the cell voltage depends on the water purity.
Also if I try to convert the current using a I/V converter between the two "wires" (steel and copper) I measure something in the order of 2mV but if I measure with a voltmeter I measure something like 200mV

On another set I measure i.e. 0mV using the ZRA but 400mV with the voltmeter.. What gives?
It's hard to tell what you're doing - a drawing might help - but I think your "probe" has a high impedance, and any load you place on it is affecting the measurement.

For the benefit of others here, a manual for a commercial ZRA device:
https://www.alspi.com/manuals/ms1000manual.pdf

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#### jegjessing

Joined Feb 22, 2019
3
I don't think the cell voltage depends on the water purity.
Well, in district heating we use water that are completely purified. If the water is not completely pure, it could have a "acid" like effect depending on how sour the water is. (Sorry for the lack of words. English is not my primary language)
Of course, if the water contains element from dirt, it can have elements in it that breaks down steel quicker than water that is completely pure.
Also if the elements from the dirty water breaks down the galvanic protection it will get trough to the raw steel and therefore make a quicker corrosion than if the water are just in contact with the outer surface of the pipes.

It's hard to tell what you're doing - a drawing might help - but I think your "probe" has a high impedance, and any load you place on it is affecting the measurement.
Yes, that is exactly what I mean. Any probe would affect the result, and since the copper wire is just "dangling" there with the only potential being the galvanic effect.

I will try to make or find some drawing that would indicate how this is done

#### wayneh

Joined Sep 9, 2010
17,405
My understanding is that you need to measure a very tiny current (proportional to corrosion that has occurred) at the galvanic voltage, roughly 0.3V.

#### jegjessing

Joined Feb 22, 2019
3
Yes, that is exactly what I mean. Any probe would affect the result, and since the copper wire is just "dangling" there with the only potential being the galvanic effect.

I will try to make or find some drawing that would indicate how this is done
True, but any instrument I use for measuring will result in changes to the voltage. The impedance of what I'm trying to measure the voltage on is, in principle infinite.

#### sparky 1

Joined Nov 3, 2018
734
The boundary conditions create lattice structure that grows over time.
This video highlights corrosive boundary conditions using preventative science not the circuit's electrical impedance.

The nature of electricity tends to cause materials to return to an oxidative elemental form.
But not always, so we can disolve some corrosion to see what is going on.
A sacrificial material like zinc can absorb what would otherwise be charge movement between cooper and Iron. (called cathodic protection)
A mosfet's internal field can be sensitive to small changes at the gate. The high impedance can be less electrically invasive to the specimen under test.

I made the mistake of using a chemical to brighten copper which changed the Cu surface, I should have used procedures like ph meter.
The influence from current in copper trace creates a dissimularity of surface conditions in pcbs on top of Cu Fe being dissimular metals.
Some pcbs are complex with a long list of design specifications. A desription of a really great circuit board of that order described just for controlled impedance routing as an example of what a proffesional discussion might sound like between designer and pcb manufacturing engineers.

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