Corrosion meter

[nibola]

Hi
I have a corrosion meter, a 9030 Plus corrater instrument that measures the corrosion of a copper probe in mils per year. This corrosion meter is connected to a Web Master Water Controller, that reads the 4-20mA signal.
So there are two displays, one for the corrater on the other one for the controller
On the configuration panel of the corrator, I can change the “Probe rate 4-20 LOOP F/S”. This value defines the full scale for the 4-20mA. By default is 20MPY.
If I change this value to 1 for instance, the reading in the corrater stays the same but the reading in the controller is multiplied by 20.
I guess that this is changing the scale of the 4-20 signal. My questions are:
What is this value for? I mean, how do I know which is the correct value? The corrater determines the corrosion rate measuring the current between the two electrodes. Why should that current be multiplied by a factor?
It is confusing also that when I change this value (Probe rate 4-20 LOOP F/S), the readings on the corrator stays the same and the readings on the controller change.
As far as I know, the only way I have to check that corrator is working fine is replacing the copper probes and checking that the value is going to near zero.

Any help regarding corrosion meters will be highly appreciated

Best regards

 

[cloa]

For starter here is the manual.

http://www.cosasco.com/documents/9030_Plus_Corrosion_Rate_Instrument_Manual.pdf

and as I suspected its Linear Polarisation device which means

http://www.caproco.com/catalog/pdf/...zation-Resistance/LPR-General-Information.pdf

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[cloa]

http://events.nace.org/library/corrosion/Electrochem/LPR.asp

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[nibola]

Hi Cloa

Thank you for your answer.
Yes, it is a Linear Polarization Resistance measurement. But still I don’t know why the resistance value can differ depending on the settings.
For instance, if you take a look at the manual (first link you attached), on page 16, on the “PROBE RATE 4-20 LOOP F/S”, the settings can be chosen from a value of 1 up to 1000. Which is the correct value ?
This is important, because the readings will be multiplied by a factor depending on this value.
And if I change this value, why the readings in the 9030Plus remain the same and the values on the Data Log changes?

Thanks

 

[cloa]

What is the actual environment in which you are measuring corrosion- what is the piping metal, what is the fluid, its velocity, temperature, pressure, does it vary in normal operation, what is geometry of the piping?
The reading on 9030 are the raw values so you can see the effect that scaling and other corrections has on the result that the Datalogging so you can confidence that its doing its job right during calibration. To know the right setting you need to understand the system- the values you get are not the "real"- they seem to based on factory setting or someone who set it up but obviously didn't document their work so you can't understand why they did what they did.

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[nibola]

Conditions are:
pH is about 6.8. Conductivity is about 2mSiemens/cm, level of oxygen is about 4ppm. The velocity of the fluid where the probes are installed is about 0.2m/s. The fluid is water and the pipe where the meter is installed is PVC. But all the circuit is made of PVC, stainless steel and copper
We have low conductivity and we are going to lower it, so that might be a problem when doing the measurements.
Right now we are measuring the copper corrosion rate and iron corrosion rate. I am still working on the signals but my guess is that copper rate is about 0.55MPY and iron rate is about 0.1MPY.
I also have another corrosion meter installed in another place but in the same cooling circuit. The results for both meters don’t really match, that is another question I need to solve. And for one of the meters there are many ups and downs in the values while the other one is quite stable.
This system was installed many years ago and nobody from that time is at work anymore, so many questions that I have cannot be answered.

Thanks

 

[cloa]

Can you draw a diagram of the piping and the connections of the meter to the piping? It sounds like you (company) have connected the meter to PVC which won't measure anything- hopefully all you mean is the the probe is within a PVC piping section and the meter is connected to metal but that is increasing the electrolytic resistivity by physical separation.

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[nibola]

Almost all the cooling circuit is made of stainless steel, plus the components that are made of copper. Only a few meters are connected to a PVC pipe. The principle of the corrator is through oxidation of the probes, so it shouldn't make a difference whether the meter is installed in a PVC pipe or a different type of pipe. The probes that we use to measure corrosion are made of copper, iron and aluminum.

 

[cloa]

Draw the diagrams if you want real answers. It only matters with the part of piping system that the corrator is connected to and near to. The probes are not to be corroded themselves- they are references(help the computer determine voltage or temperature) or connectors. You want the corrosion rate of the pipe not of some piece of metal (which only nominally the same but could have difference metallurgy and surface condition)- that metal will have totally different corrosion rate and corrosion behavior (e.g. pitting is statistical so it may not pit (hole corrosion) on the sample but its pitting somewhere on the pipe).



As an aside corrosion engineers do use coupons (pieces of metal as close to the original pipe as possible placed in corrosive fluid) to measure corrosion but it is difficult as its hard to exactly the same metal condition, there are edge effects, the greater area of the pipe has an effect on the corrosion of a small section of it and the coupon affects the flow so its not the same. They generally don't do coupon corrosion measurement online rather weight and assess it periodically.

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