Cathodic corrosion protection with platinised or mixed oxide anodes

Cathodic corrosion protection of steel is a well known method for protecting steel against corrosion. It started with sacrificial anodes 80 years ago - modern installations use full-dimension-stable anodes made of titanium an niobium, activated with a very thin layer of platinum or of mixed oxides. These anodes offer longer lifetimes, save contact of the cable to the anode, an easy and safe to install and transport.

For all impressed current systems, the anodes are the sensitive element. They have to be selected for each application, depending on the current and the specific electric resistance of the soil or the water.

In the field of platinised anodes, platinised niobium has been introduced over the last 20 years for critical purpose. However, only few suppliers offered these anodes as a high quality. The columbium (niobium) is highly corrosion resistant - it’s breakdown voltage is 10 times higher than that of titanium, so the advantage of this metal should be very high compared to titanium. But the electrochemical behaviour of this metal was not completely understood for a long time. Only a few companies were able to deliver platinised columbium of the highest quality. The platinised niobium allows very high impressing voltages and installations with few anodes. For hydrocarbon industries, impressed current protection systems are used for pipelines, oil rigs, harbour and off-shore constructions, oil tankers, gas as well as oil drilling casings and deep well beds.

All these systems use more and more titanium and niobium anodes. They are activated with platinum or mixed oxides. Mixed oxides means depending on the mixtures of ruthenium, iridium, sometimes rhodium with titanium and tantalum oxides.

These anodes offer a remarkable advantage compared with all other semi-dimension-stable anodes like silicon-iron, magnetite, graphite. The impressed current system is easily controlled, but lifetime of the anode reflects the lifetime of the installation. The cable contact to the anode can corrode and the anode itself can be broken or damaged during transport or installation like silicon-iron or magnetite. Titanium and niobium are highly corrosion protected themselves and can be greatly manipulated. This allows very secure contacts from the cable to the anode. Titanium and niobium anodes are dimension-stable. Their lifetime depends on the lifetime of the activating layer.

For off-shore and harbour constructions, platinised or mixed oxide anodes are used. Steel pilings on oil-rigs and platforms are protected with rod or wire anodes. If high currents (anodic current-densities) are demanded or high voltages are applied, niobium anodes offer higher security than titanium anodes. The breakdown potential of columbium ( niobium) is 10 times higher than that of titanium.

Cathodic protection of pipelines uses coal-coke-bed anodes. Mixed oxide activated titanium metal mesh gives a secure contact from the cable to the coke. The metal mesh can not break while transported or installed. The contact to the current leading cable can be performed easily. The titanium metal mesh is light, easily transported and installed. The metal-mesh gives a good current distribution over the coke bed.

Tankers and other kind of ships use cathodic protection by impressed current systems. The anodes are recessed from the out side body. And preferably platinised niobium anodes are used.

There is a wide range of used for DSA-anodes, from protecting steel constructions in the field of oil and gas exploration, to transport and production installations. They are also widely used in oil and gas drilling applications.