Cathodic protection 1

[ysohail78]

Dear,
We have jetty at out plant site which is in operation more than 35 years old. We want to protect the rebar in existing concrete slab with impressed current cathodic protection system. Please advise on design and its implementation. How anodes to be fixed in concrete.

 

[ScottyUK]

The anodes (groundbeds) need to be remote from the protected structure. Speak to a CP specialist for advice, design is not a simple task and even the experts sometimes get it wrong.

 

[crshears]

What ScottyUK said.

More than that, though, you might be wise to have the specialist you engage perform an as-found examination of the existing structure to determine its soundness; looking to apply CP thirty-five years after commissioning could be a bit like closing the stable doors years after the mare got away...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[SilverfoxUK]

Does the 35 year concrete slab forming your jetty still have re-bars or have they long since oxidized and gone to the great place in the sky where many oxidized re-bars that used to be part of motorway bridges have gone?

As one of the op's has stated 35 years is a long time to start looking to CP.

 

[vreijb]

I have worked on current impression systems for oil storage tanks to protect the bottom.
there are 2 ways that I have worked with.
one method is you use deep-well anode away from the concrete. You install anodes in the deep well, usually there will be anodes at different levels through a chain. The anodes will be terminated to anode junction box close-by to deep well. From anode JB you will connect to rectifier transformer +Ve terminal. The impressed currentwill be adjustable based on the size of the unit from 10A - 500A.
You will have a cathode JB next to transformer and connected to the transformer.
you will get cathode Junction Box close to the transformer and connected to rectifier -Ve terminal. from cathode JB you can get several cathod cables connected to the items to protect at various locations.
The current will travel through the ground to the structure to complete the circuit.
you will need test electrodes under the structure you want to protect, probably in this case close to the structure. Test electrodes will be connected to JB for measurement at regular intervals during the year. The measurement will be between the electrodes and the structure you want to protect, and you'll get some 100-120mV (not sure exact figure but in that range)voltage shift when you apply or don't apply current, which gives good indication that your system is protected.

You can have horizontal bed of anode as well away from the structure you want to support.


The second method is having Mg based anode strips in grid form under the structure, spot welded at grid points.
The rest of the system similar with sand bed between anode and the steel to complete the circuit. This is more suitable to New Construction Tanks.