Zinc anodes

[Tony Wilding]

MODERN SHIPS HAVE ZINC ANODES ON THERE HULLS UNDERWATER, TO STOP CORROSION, I THINK CAUSED BY DIS- SIMILAR METALS, CALLED ELECTROLOCIS, ? WHAT DID OLDER SHIPS USE, OR DID THEY JUST LET IT HAPPEN, ?

[robpage]

The first work was done on this by Sir Humphrey Davey in 1823 on the copper plating fitted to wooden hulled ships . there are German Patents pre World War one on this , and it has been used in the oil industry pre workld war two . So I would suggest that its popularity rose in the nineteen fifties . Some Cathodic Protedtion used Anodes supplied with an Electric DC current . It has been around a long time .

[Pat Marshall]

Oriana ( the old one) had a trailing Anode which had to be wound out once Full Away had been rung then wound back in again at the next Standby. If the Lecky on the aft mooring deck was a bit slow in winding it in it was quite easy to loose 50 or 60 feet...a tad awkward.
It was of the impressed current variety but what the settings were I cannot recall.

[robpage]

You might ! , but I used History of Cathodic Protection much better detail than Wikipedia , also more likley to be accurate as Wikipedia can be notoriously unreliable

I had left it as a simple answer as I thought that is what would satisfy Tony's question , But as people have an eye for detail , and users of Wikipedia can supply inaccurate information , here is a bit more detail . It is used a lot in construction to safeguard steel reinforcement as well as on pipeline systems , especially those in a corrosive atmosphere




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History of Cathodic Protection
The first application of cathodic protection (CP) can be traced back to 1824, when Sir Humphry Davy, in a project financed by the British Navy, succeeded in protecting copper sheathing against corrosion from seawater by the use of iron anodes. (reference)

About 1820 the Navy Board was anxious to find the reason why copper sometimes got fouled, whilst iron was dissolving, and at other times the copper was dissolving rather too quickly. A Committee was formed with the Royal Society, of which Sir Humphry Davy was President. Davy had already in 1806 advanced the hypothesis that chemical and electrical charges may be identical, and later convinced Berzelius of this idea. Now, assisted by Michael Faraday, he began to experiment with copper and other metals, such as iron and zinc in various saline solutions, and found the electrochemical reactions he had expected. Sir Humphry Davy advocated a small quantity of zinc, or of even cheaper malleable iron, should be placed in contact with copper, and thereby prevent its corrosion.

Electrochemical Corrosion Protection

In 1825 Davy was able to move away from the laboratory tests and continue his research aboard a naval vessel. Davy found that small "protectors" of malleable iron preserved the copper by the iron gradually dissolving in a galvanic process. (Source: "On the corrosion of copper sheeting by seawater, and on methods of preventing this effect, and on their application to ships of war and other ships". Philosophical Transactions of the Royal Society, 114 (1824), pp 151-246 and 115 (1825), pp 328-346.) Here is a detailed account of the events surrounding this important work from a recent biography written by Sir Harold Hartley:

"In 1823 the Commissioners of the Navy Board consulted Davy about the rapid decay of the copper sheathing of his Majesty's ships of war. A Committee of the Royal Society was appointed to consider the problem and Davy started to investigate it experimentally. He first showed that the corrosion was independent of small impurities in the copper and then, after examining the products of corrosion, he decided that it must depend on the oxygen dissolved in the sea water. Experiments having verified this conclusion, it occurred to him, in the light of his early researches, that he might prevent the oxidation of the copper by changing its electrical condition so as to make it slightly negative. It was not possible to do this in ships with a voltaic battery but it might be done by contact with zinc, tin or iron. Laboratory experiments with zinc and iron in sea water gave perfect protection and large-scale trials gave similar results, so that the problem seemed to be solved. Davy then went on a voyage in the North Sea to measure the wastage of copper plates armed with zinc and iron protectors and some trials with oceangoing ships seemed to be successful. Unfortunately, it was then found that while the corrosion of the copper was prevented, the ship's bottom became so foul, from the adhesion of shells and weed, that her speed was greatly reduced. The Admiralty ordered the protectors to be removed just after Davy had read a paper to the Royal Society announcing the complete success of his plan."

This limited use of CP on copper sheathing has endured and when wooden hulls were replaced by steel the fitting of zinc protector blocks on the sterns of naval vessels became traditional. These zinc slabs, although they offered some protection to steel hulls against local galvanic effects due to the presence of the bronze propellers, were generally not deemed to be effective. (reference)

This lack of efficiency was mainly due to the use of unsuitable zinc alloys and other factors such as insufficient appreciation of the technology of cathodic protection and the tendency to reduce the efficiency of the zinc material to zero by painting their surfaces. From that early beginning, CP has grown to have many uses in marine and underground structures, water storage tanks, gas pipelines, oil platform supports, and many other facilities exposed to corrosive environments. More recently, CP has been proved to be an effective method for protecting reinforcing steel from chloride-induced corrosion.

The CP effectiveness at protecting steel in soils has been demonstrated in the early 1940’s when CP was applied to an old natural gas piping network that had been developing leaks at a rapidly increasing rate, enough so that abandonment was seriously considered. The observed reduction in the number of leaks immediately after the CP installation was impressive. A similarly impressive reduction in the frequency of leaks on a cast iron water main was achieved at about the same period.

Modern specifications for the cathodic protection of active ocean-going ships were first described in 1950. Since that time progress has been rapid. Considerable advances in cathodic protection technology have been made, better sacrificial anode materials have been developed, and circuits for the use of controlled applied current systems, using inert anodes, have been perfected.

The first reinforced concrete impressed current CP system was an experimental system installed on a bridge support beam in 1959. A more advanced system was subsequently installed on a bridge deck in 1972. The anode system used in both applications was based on a conventional impressed current CP system for pipelines, but ‘spread out’ over a bridge deck. CP has since then become one of the few techniques that can be applied to control corrosion on existing structures.


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Source: "On the corrosion of copper sheeting by seawater, and on methods of preventing this effect, and on their application to ships of war and other ships". Proceedings of the Royal Society, 114 (1824), pp 151-246 and 115 (1825), pp 328-346.

[Ivan Cloherty]

[QUOTE=robpage;60822]You might ! , but I used History of Cathodic Protection much better detail than Wikipedia , also more likley to be accurate as Wikipedia can be notoriously unreliable

Rob

It seems that our Michael has had his week of being nice, it would seem that it has just been too much for him to bear therefore he now needs to get back on the path of downing people.

Michael,

why do you do it, people were just starting to respond to your sensible postings, be nice to your fellow shipmates, there is enough trouble in the world without adding to it. As I've said before we have less time left than that already used, use it wisely and to the benefit of your fellow men

Ivan Dross

[Ivan Cloherty]

[QUOTE=Michael Hughes;60848]

Ivan the Dross

Noted!

Can't help yourself can you Michael

[Tony Wilding]

IN WW2 WHEN SHIPS WERE DE-GAUSSED TO COMBAT MAGNETIC MINES, WOULD THIS HAVE SAME EFFECT AS ANODES, OR MAKE IT WORSE, ? ? TONY WILDING.

[robpage]

Entierly diferent applications . we had a thread on here a few months ago about Degaussing . One basically demagnetises the ship the other electro- chemically wastes zinc instead of steel . so as distant from each other as pork chops and Kosher barbeques

[Des Taff Jenkins]

Hi Tony.
I worked up untill 2002 on the Old Sydney Ferry; South Steyne, we had zinc anodes hung on wires over the side around the hull, Being built in 32 and having had quite a few jobs done on her she had iron and steel in her hull, the engineer said it was the only way to keep the electoloses from corroding her.
Cheers Des

[john sutton]

anyone who has lifted his boat and seen pink propellers knows the value of anodes.its happened to me,once,both props also bronze skin fittings.the marinas in spain are full of boats plugged into the electrics
and electrolysis is rife.many boats hang an anode over the side in the marina especially if berthed near a steel boat
john sutton