Are anodes always wired back to the steel in the case of passive cathodic protection? 4

[T2ioTD]

My question if for galvanic systems only (not immersed).
Pardon my ignorance, but in the first image, the theory dictates an insulated wire back from the sacrificial anode to the tank, while in the second image, the anodes seems directly welded to the tank, visibly by a conducting metal, and finally in the bottom image, clearly an impressed system, we see the wiring.

What is the correct method? Am I missing anything?

 

[SJones]

What is the difference between a “metallic connection” and the steel core strap of the anodes in picture 2 ?

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.

 

[TugboatEng]

Also, you are comparing an impressed current system that uses a power supply to a passive system.

 

[LittleInch]

They are all the same.

For sacrificial anodes, so long as the current travels between cathode and anode it matters not how this happens. The above usually needs to be fairly close to the cathode.

Not quite sure what S1 is in the last photo. If that is a power supply then tug is correct.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[T2ioTD]

OP here.

I think I got from your answers that the metallic connection in picture 1 plays the same role as the metal that connects the sacrificial metal to the steel in picture 2. However, the course I read clearly states that the connection should be "isolated", and I fail to understand why is that, and why in the 2nd picture the insulation is clearly not respected.

This is how I first learned about the insulated wire:

 

[SJones]

In picture 2, the insulation is "not respected" because it is unnecessary; the sacrificial anode will protect the minimal surface of the anode strap AND a much larger surface of the item to which it is attached. The strap serves to hold the anode material together as it dissolves, and to facilitate connection by welding - it wouldn't be good to weld the aluminium, zinc, magnesium, etc to the steel.

For sure, in systems where current is conducted via cables and wires, the conductors need to be insulated from the external environment (and from people). If they were bare wire, firstly they would possibly divert protection current; if not, they may corrode (definitely will corrode if they are the positive anode cable in impressed current). It's all about simply maintaining current from the anode to the cathode through the electrolyte without any extraneous bare metal in the circuit. In some instances, owners' specs will require the steel anode straps to be painted.

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.

 

[EdStainless]

And in your photo either the middle anode is new and just installed or it is not actually connected to the tabs and the shell.
It has done no work.
I am guessing that it is new, because these alloys are reactive enough to be corroding and protecting an area even without a connection.


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P.E. Metallurgy, consulting work welcomed

 

[SJones]

If the old anode in 2 had a strap in the same location as the others, it probably fell off when the anode material had disintegrated around it. The doubler plate has also gone walkies somewhere.

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.

 

[Gr8blu]

To answer the question about S1: it's a simple switch. Presumably the resistance path through whatever is in the tank is higher than the resistance path through the short wire connecting the ammeter (A) to the circuit. Since we don't really want gobs of current to be flowing, we only close the switch (just the way it's shown in the image) when we want to measure the current. Otherwise, the switch stays open.

Converting energy to motion for more than half a century

 

[LittleInch]

If you leave S1 open then no current = no protection.

You won't get "gobs" of current - you will get a steady current showing that the circuit is working as the anode slowly dissolves.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.