Impressed current anodes tubes

The first anode installation for the cathodic protection of gas pipelines in New Orleans consisted of a 5-m-long horizontal cast-iron tube. Later old tramway lines were used. Since in downtown New Orleans there was no suitable place to install impressed current anodes and to avoid detrimental effects on other pipelines, Kuhn recommended the use of deep anodes which were first installed in 1952 at a depth... 

In the cathodic protection of storage tanks, potentials should be measured in at least three places, i.e., at each end and at the top of the cover [16]. Widely different polarized areas arise due to the small distance which is normally the case between the impressed current anodes and the tank. Since such tanks are often buried under asphalt, it is recommended that permanent reference electrodes or fixed measuring points (plastic tubes under valve boxes) be installed. These should be located in areas not easily accessible to the cathodic protection current, for example between two tanks or between the tank wall and foundations. Since storage tanks usually have several anodes located near the tank, equalizing currents can flow between the differently loaded anodes on switching off the protection system and thus falsify the potential measurement. In such cases the anodes should be separated. 

Fig. 16-8 Impressed current anodes for protecting tube supports of a loading bridge.

Figure 20-9 shows the negative effect of uninsulated heating elements on corrosion protection. In a 250-liter tank, an electric tube heating element with a 0.05-m surface area was screwed into the upper third without electrical separation, and in the lower third a tinned copper tube heat exchanger with a 0.61 -m surface area was built in. The Cu heat exchanger was short-circuited for measurements, as required. For cathodic protection, a potential-controlled protection system with impressed current anodes was installed between the two heating elements. The measurements were carried out with two different samples of water with different conductivities. 

Impressed current anodic protection is of Little importance in comparison to cathodic protection. It has been applied successfully to the protection of stainless steel and titanium alloys in the presence of acidic electrolytes. As in the case of impressed current cathodic protection, it is essential to control the electrode potential within suitable limits. Figure 10.35 indicates the application of anodic protection to a simple tank and to a more complex tube-and-shell heat exchanger. When anodic protection is commissioned, the current must be large enough to exceed icurr order to passivate the surface. The current then falls to fpAss current is increasingly deflected to more remote parts of the structure which passivate in turn. Once established, the current drain is minimal and is approximately equal to ipASs ... 

Fig. 1DJ5 The application of (impressed current) anodic protection, (a) Protection of a steel tank storing add using a reference electrode and potentiosiatic control (b) Pro tection of a tube-and-shell heat-exchanger, (after West (1980).)...

Niobium is used as a substrate for platinum in impressed-current cathodic protection anodes because of its high anodic breakdown potential (100 V in seawater), good mechanical properties, good electrical conductivity, and the formation of an adherent passive oxide film when it is anodized. Other uses for niobium metal are in vacuum tubes, high pressure sodium vapor lamps, and in the manufacture of catalysts. 

A higher content of AI2O3 and SiOj is critical for the composition of the protective films in the tubing, assuming the water contains silicates or silicic acid. The protective films have a maximum thickness of 1.5 mm and cannot grow further. The corrosion process can be stopped even in copper pipe networks with type I pitting [21] by providing a reaction tank with impressed current aluminum anodes. 

Consumable Anodes. Scrap steel and iron have often been used in the form of abandoned pipes, railroad, or well casings, as well as any other scrap steel beams or tubes. These anodes found application particularly in the early years of impressed current CP installations. Because the dominant anode reaction is iron dissolution, gas... 

---