sacrificial anode

[GaryP]

I have a question that I need help finding the answer to so here goes.

When I did chemistry at school back in the early 80's, we were taught about using sacrificial anodes on pipelines etc and as an experiment, I volunteered to take a strip of zinc home and crudely soldered it to a 6" steel nail via a short length of wire and was asked to bury it in the ground for a period of time. When I dug it up some months later, the obvious had happened and I took it back to class to show everyone and much their amazement, the nail showed no sign of rust.

Now, I've just installed a steel universal beam as part of an extension to my kitchen and being over enthusiastic, didn't use a galvanised beam (which apparently is a requirement of building regs...oops!)

I was told by a structural engineer that if I primed it with zinc phosphate primer and gave it 2 coats of bitumen paint, the officer from the council should accept it (hopefully...) and now comes the question...

If I were to attach a length of copper wire to the steel and attach the other end of the wire to a zinc anode and then, bury the anode in almost permanently wet soil close by, would the anode do it's job and protect the steel as if it were galvanised?

Any help with the answer to this would be much appreciated, thank you.

[chenbeier]

Theroetically it will work, but what happen at the connection of copper with the steel? You would have steel-Cu-Zn. Zink will corrode, but are you sure steel will not?. The copper is the noblest element in this row.

[John Cuthber]

You can make sure the copper/ steel connection is somewhere dry.

 

But that's not the point.

The "man from the council" probably won't accept it.

It doesn't agree with the standards, there's no guarantee that the wire won't get broken, and eventually, the  zinc will all corrode away, and then you have no protection.

It's no use saying " but I will look after it".

The council knows that you will die (and you may well move house before that).

The new owner of the property may not understand how your system works.

[GaryP]

21 hours ago, John Cuthber said:

You can make sure the copper/ steel connection is somewhere dry.

 

But that's not the point.

The "man from the council" probably won't accept it.

It doesn't agree with the standards, there's no guarantee that the wire won't get broken, and eventually, the  zinc will all corrode away, and then you have no protection.

It's no use saying " but I will look after it".

The council knows that you will die (and you may well move house before that).

The new owner of the property may not understand how your system works.

thanks for the reply.

The steel itself is very substantial and the only part of it that "could" get wet is where it enters the fabric of the building (it is primed with zinc phosphate primer and will be painted with bitumen paint). I would try to compare it to a galvanised steel's lifespan.... surely a decent sized block of zinc will be comparable to the amount of zinc used in the plating process and it has the advantage of being able to be renewed?

As for new owners, I'd write up what I've done in the house files. I've got a huge file on all the work I've done so far and this could go in the maintenance section, along with an explanation of how it works. As long as it does work, that is the main point.

22 hours ago, chenbeier said:

Theroetically it will work, but what happen at the connection of copper with the steel? You would have steel-Cu-Zn. Zink will corrode, but are you sure steel will not?. The copper is the noblest element in this row.

thanks for the reply.

If I was to substitute the copper wire for stainless steel, something like rigging wire from a yacht, would that be a better solution?

[Endy0816]

Should ask or check with an official to see if the exception would be allowed first. Don't want to spend even more money if you end up needing to redo it all anyways.

May work but the possibility of corrosion would put me on edge. Metals can rust fast and furious in the right circumstances.

[GaryP]

4 hours ago, Endy0816 said:

Should ask or check with an official to see if the exception would be allowed first. Don't want to spend even more money if you end up needing to redo it all anyways.

May work but the possibility of corrosion would put me on edge. Metals can rust fast and furious in the right circumstances.

I think it would be acceptable because some information I sourced online talks about cathodic protection of steel in concrete and for older buildings which have steel or iron components rusting away inside walls eg https://metallisation.com/applications/cathodic-protection-of-steel-in-concrete/

I think in my circumstance the steel is well protected from the elements anyway and it is really only the 350mm of the beam that inserts into the fabric of the building that is susceptible to possible corrosion. It will be filled over with render and the wall will be re-painted with masonry paint. The render that I removed was bone dry and this was after some very heavy spells of rain so the paint is doing it's job.

If what I've proposed will actually work, then I will incoporate it as a belt and braces approach in addition to the zinc primer and bitumen paint.