Galvanic series, metals seawater

Figure 30 Partial list of galvanic series in seawater. (From H.P. Hack, Metals Handbook, Vol. 13, Corrosion, 9lh ed ASM, Metals Park, OH, p. 234, 1987.)...

The galvanic series in seawater is often used to estimate the risk of galvanic corrosion in other media, for which the series may not be available. The risk of galvanic corrosion depends as much on the corrosivity and conductivity of the medium as on the separation of the two metals in the galvanic series. Fresh waters generally have neither the corrosivity nor the conductivity to support galvanic activity. 

Figure 2 shows two bars made of zinc and copper immersed in an electrolyte (seawater). Needless to say, after some time, the zinc bar shows signs of corrosion. In this situation an electrical potential difference is established between the two metals which can be measured and is in agreement with the table of galvanic series in seawater. Here, the zinc and copper bars acts as an anode and a cathode, respectively. The simple experiment demonstrates the basic idea behind the concept of cathodic protection. The zinc bar (anode) is being sacrificed to protect the copper bar (cathode). This method of cathodic protection is known as the sacrificial anodic method. 

The galvanic series of metals and alloys in seawater has been given in Figure 1.6 whenever dissimilar metals are used, it is pmdent to select a pair of metals with minimum difference in potential, in the particular environment and temperature of exposure. 

Figure 6.11 Galvanic series for some metals in seawater (Hack)5...

The galvanic series of metals and alloys in seawater is given in Table 7.20. From this series it is clear that steel and 2024 aluminum are in close proximity. From their positions it is inferred that steel is cathodic and aluminum is anodic in seawater. The corrosion potentials of iron and aluminum measured after immersion in various media for 24 h are given in Table 7.21. It is seen from these data that the corrosion potentials of iron and aluminum are very nearly the same in 0.1M sodium chloride. Some studies on the galvanic action of the steel-aluminum couple in fresh waters such as pure, river, lake and underground water and salt solutions are noted in Table 7.22. In one of the studies, the... 

Fie. 4.20 Galvanic series of various metals in flowing seawater at 2.4 to 4.0 m/sat 5 " to 30 °C (volts vs. saturated calomel reference electrode). Note Dark boxes indicate active behavior of active-passive alloys. Source Ref 12 and 1 3... 

Figure 1.7 Galvanic series of metals in seawater. (Reproduced by permission. National Association of Corrosion Engineers International (11).)...

Cathodic protection from sacrificial anodes is based on the principle of galvanic corrosion. This means that a less noble material is connected to the structure (metal) to be protected. To select the right saeriflcial anode material, the galvanic series is important. Table 19.1 shows the galvanic series for seleeted materials in seawater. The table indicates that magnesium, zinc, and alnminum alloys are well suited as sacrificial anodes when protecting steel. 

The following list shows a practical galvanic series for metals and alloys exposed to seawater. 

Table 9.25. Galvanic series of metals and alloys in seawater Metal or alloy...

FIG. 2—Galvanic series of various metals In flowing seawater at 2.4-4.0 m/s for 5-15 days at 5- 0°C (redrawn from original In Ref 21 taken from ASTM G 82). 

FIG. 3—Galvanic series of various metals exposed to seawater (taken from ASTM G 82). 

Base metals and alloys used in medical and dental devices are corrosion-resistant due to the presence of an oxide film on the surface that is protective [49]. These materials are not corrosion-resistant initially as is evident from their positions in the electromotive force series. The galvanic series, a listing of electrode potentials measured in seawater, indicates the changes in the noble and active tendencies of these materials in practical use for this given environment. Passivity is dependent on environmental factors such as solution pH, temperature, ions, oxygen, etc. Some ways of minimizing corrosion of these materials follow. Others are given in the discussion of the types of corrosion that can occur. 

FIGURE 5.176 Galvanic series of metals and alloys in seawater. Metals and alloys are listed in the order of their corrosion potential in seawater. When two metals are coupled, those close together in the list are less susceptible to galvanic corrosion than those widely separated in list. 

The galvanic series of aluminum alloys and other metals representative of their electrochemical behavior in seawater and in most natural waters and atmospheres is shown in Table 19.6. The effect of alloying elements in determining the position of aluminum alloys in the series is shown in Figure 19.4. These elements, primarily copper and zinc, affect electrode potential only when they are in solid solution. 

Figure 6.31 Galvanic series of some commercial metals and alloys in seawater.

Any two metals can be used to make a galvanic cell. Whether a metal will behave as an anode or a cathode in combination with another metal in the same environment can usually be determined by its relative position on a galvanic series. Figure 7.18 shows the galvanic series of many metals and alloys in slow-moving seawater and Table 7.5 presents the galvanic series which was constructed for metals exposed to neutral soils and water [15]. 

Using sacrificial anodes (Fig. 13.2) that have a corrosion potential lower than the metal to be protected. This ranking can be obtained by consulting the seawater galvanic series. 

The galvanic series is an arrangement of metals and alloys in order of their corrosion potentials in the environment. The potentials of the metals and alloys are measured in the desired environments, with the most noble (positive) at the top and the most active at the bottom. Table 2.5 shows a galvanic series of some commercial metals and alloys in seawater. The potentials are measured in seawater by means of a saturated calomel electrode and all potentials... 

Referring to the galvanic series of some commercial metals and alloys in seawater, mark the condition which would lead to minimum corrosion by galvanic coupling. 

Galvanic series It is a list of metal and alloys based on their relative potentials in a specified environment. The environment generally used is seawater. 

A galvanic series of metals and alloys in flowing seawater is shown in Table 9.50. It is observed that titanium would be a cathodic member of the couple, and hence it would not imdergo galvanic... 

The galvanic series in Table 17.2 indicates the relative reactivities in seawater of a number of metals and alloys. When two alloys are conpled in seawater, the one lower in the series experiences corrosion. Some of the alloys in the table are grouped in brackets. Generally the base metal is the same for these bracketed alloys, and there is little danger of corrosion if alloys within a single bracket are conpled. It is also worth noting from this series that some alloys are hsted twice (e.g., nickel and the stainless steels), in both active and passive states. 

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