CATHODIC PROTECTION AND ELECTRICAL RACK GROUNDING

[pristava]

Cathodic Protection and Electrical Distrubution Grounding

Our package provides an installation of the Electrical Rack for feeding a pipeline controls and instrumentation.
Electrical Rack plus the part of Pipeline ( above ground level) will be protected with a fence and grounded.

We are informed that galvanized steel ground rods have to be used in lieu of copper ground rods because of future cathodic protection systems in that area, what has to reduce a potential difference.

Is it true ? Please, comments !

 

[ScottyUK]

If copper and steel are in close proximity to an area where an impressed current cathodic protection system is to operate, the copper will tend to hog the current. This is a result of the relative potential of copper with respect to the ground. The problem can be overcome by imposing large current to overcome the presence of the copper, but this is not always possible.



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If we learn from our mistakes,
I'm getting a great education!

 

[RalphChristie]

Galvanic corrosion

Principle: Galvanic corrosion occurs when a burried electrode of one kind of metal is connected to another kind of buried metal (connection above or below ground) and the soil contains electrodes in a moist enviroment.

The table gives a restricted list of metals which are used in electrical contacts in one form or another. The aluminium end of the series is known as the "active" end and the gold end of the series as the "noble' end.

Metal Standard electrode potential at 25°C
Aluminium -1.67
Zinc -0.76
Mild Steel -0.44
Cadmium -0.40
Stainless Steel(active) -0.30
Nickel -0.25
Tin -0.14
Lead -0.13
Copper +0.34
Stainless Steel(passive) +0.50
Silver +0.80
Carbon +0.81
Mercury +0.85
Platinum +1.20
Gold +1.70

The less noble of the two metals will become the anode and will corrode. For instance, in a sell using zinc and copper, negative ions in the soil will flow from the copper (cathode) towards the zinc (anode), and the latter will corrode

Hence if metal of the earth electrode is more noble than other metals buried in the ground (e.g. copper-plated earth rods in the vicinity of steel foundations, steel reinforcing in concrete foundations, cast iron pipes, zinc coatings on galvanized pipes or steel armouring of cables), galvanic corrosion of the steel and zinc can occur.

The wider apart the metals are in series, the higher the potential difference and hence the greater the galvanic corrosion.

Loss of some typical metals when they are anodic is:

Lead :33 kg/ampere-year
Zinc :11 kg/ampere-year
Iron (steel) :9.1 kg/ampere-year


Regards

Ralph

 

[peebee]

I'd consider a concrete-encased electrode, a stainless-steel electrode, or other similar systems to avoid any problems with corrosion of your ground rods.

 

[Sargardani]

Normally Zinc anode bed is used for cathodic protection (CP) of steel pipelines. The CP system further boosts the natural potential/voltage between the anode and cathode making sure that no metal is lost from the Cathode i.e the pipe. A current is established in this way ... positive ions flowing from the anode towards the pipe underground and electrons flowing from the pipe towards the anode in the external CP circuitary, comprising of transformer, rectifier and cables.

If you have Cu ground rods and by some chance its potential is higher than the anode bed, either due to location or physical conditiions, then the Cu rod will start decaying.

On a side note any metal in between the anode and cathode shall decay because it would act as a cathode for the anode bed but at the same time would also act as anode for the pipeline. I know this isn't the case here with the Cu rod.

In nut shell its recommended to have steel electrodes for the grounding system.




Sarg