Corrosion Protection - Offshore Structures: Design, Construction and Maintenance - page 419

TABLE 6.13 Recommended Compositional Limits for

Al-Based and Zn-Based Anode Materials

Alloying/Impurity Element Zn-Based Al-Based

Zn NA * 2.5 - 5.75

Al 0.10 - 0.50 rem

In NA * 0.015 - 0.040

Cd ≤ 0.07 ≤ 0.002

Si NA ≤ 0.12

Fe ≤ 0.005 ≤ 0.09

Cu ≤ 0.005 ≤ 0.003

Pb ≤ 0.006 NA

*NA is not available

TABLE 6.14 Recommended Design Electrochemical Capacity and Design

Closed-Circuit Potential for Anode Materials at Seawater Ambient
Temperatures

Electrochemical
Capacity (Ah/kg)

Closed-Circuit
Potential (V)

Anode Material Environment

Al-based Seawater 2000 − 1.05

Sediments 1500 − 0.95

Zn-based

Seawater 780 − 1.00

Sediments 700 − 0.95

theoretical limit (e.g., 2,500 Ah/kg for Al-Zn-In material). Such data do not

replace the recommended design values for electrochemical capacity. The use of
electrochemical capacity greater than the default values based on DNV RP
B401 (2005) in Table 6.14 should be justified by long-term testing. Even such test-
ing will tend to result in slightly non-conservative values, as the testing time is still
relatively short and the anodic current density is relatively high compared to the
working conditions for real anodes. The design values for closed-circuit anode
potential, E oa (V), in Table 6.14 are used for design. The data are applicable for
all seawater temperatures with a yearly average of max 30

≥

° C.