West Coast Corrosion Prevention Ltd.

CATHODIC PROTECTION HISTORY

Sir Humphrey Davy was commissioned (in 1823) to investigate the corrosion of the copper sheathing of the hulls of wooden naval ships, the Admiralty were the first users of cathodic protection. Davy experimented with the anodes of tin, iron and zinc to protect the copper. The last two metals were used and in a later paper (1824) he favoured the use of cast iron because it lasted longer and remained electrically more active than zinc. Zinc remained in use, however, and no doubt gave considerable protection to the copper sheathing. When wooden hulls were superseded by iron and steel, zinc anodes or protectors were still fitted. Though there was every reason to believe that zinc would successfully protect steel, its continued use seems to have rested more on tradition. The zincs were placed close to the stern gear and "yellow" metal parts, such as circulating pipe inlets, as these areas proved to the most susceptible to corrosion. The practice became universal in shipping circles and protectors were even placed in boilers, though it is doubtful whether any complete protection resulted. Zincs were reported as being in sound order, that is uncorroded, and this was often regarded as good practice.

Edison tried to achieve cathodic protection of a ship at sea from trailing impressed current anodes but the materials and techniques available to him in the eighteen nineties proved to be inadequate. Most early users of impressed current in seawater were concerned with attempts to effect antifouling or to prevent the scaling that would occur in boilers which were replenished with seawater. The polarity of this current was often considered unimportant and anticipation of the present cathodic protection trends can hardly be claimed.

Since the beginning of the present century liquid and gaseous fuels have been pumped through underground pipeline made of steel or iron. The extensive networks of oil pipelines that were installed in America in the nineteen twenties presented a vast corrosion problem. To an oil company a single leak from a pipeline can cause numerous losses and may include: loss of commodity, property damage including fire, expensive repairs, service interruptions, contamination of water supplies and loss of livestock, all of which leads to a deterioration of public relations.

By the late twenties leaks were few and could have been tolerated had not the leak frequency curve begun to rise alarmingly. In the early thirties all the major pipeline owners were applying anti-corrosive measures to the external protection of their pipes, including various coatings and cathodic protection. The earliest schemes were applied to the worst sections where the pipes had been laid in corrosive soils, and great success was achieved. The cathodic protection was derived from zinc anodes or form impressed current supplied by d c wind generators or by transformers and copper oxide rectifiers from a c power supplies.

In 1936 the mid-continent Cathodic Protection Association was formed to discuss and exchange information on cathodic protection. This association later became the foundation of the National Association of Corrosion Engineers.

The other area where oil pipeline were used extensively was the Middle East, the first cathodic installation protected a group of seawater loading pipelines in Bahrain in 1939.

There are a great number of patents on methods of preventing the corrosion of buried metals, particularly pipelines and cable sheaths. Seventy or so years ago a major cause of corrosion of buried metal pipes was the electrolysis effect, or interference, caused by stray currents from the electric traction systems. The first patents describe the connection of the pipes to the negative pole of the station generator; this method was universally adopted and is still used. The introduction of a further d c generator between the negative return of the electric traction and the structure was claimed to give superior results. In 1911 a German, Herman Geppert, obtained letters patent on ‘a method of protecting articles from earth currents’ and substantially described cathodic protection. Since then patents have applied to more specific devices such as reverse current switches, anodes, boosters, etc.

From these early beginnings cathodic protection has developed rapidly and its use has become widespread. New materials such as sacrificial alloys of magnesium, zinc, aluminium and superior impressed current anodes together with developments in electrical and electronic engineering have allowed great advances in the techniques. Cathodic protection is now established as an essential engineering service with a sound and comprehensive scientific background.

Copyright © 2001 WEST COAST CORROSION PREVENTION LTD.