Galvanic corrosion testing

Vanadium is resistant to attack by hydrochloric or dilute sulfuric acid and to alkali solutions. It is also quite resistant to corrosion by seawater but is reactive toward nitric, hydrofluoric, or concentrated sulfuric acids. Galvanic corrosion tests mn in simulated seawater indicate that vanadium is anodic with respect to stainless steel and copper but cathodic to aluminum and magnesium. Vanadium exhibits corrosion resistance to Hquid metals, eg, bismuth and low oxygen sodium. 

For galvanic corrosion tests it is important to maintain the same ratio of anode to cathode in the test sample as in the service environment. 

Guidance on conducting and evaluating galvanic corrosion tests in electrolytes is given in ASTM G71 1981 (R1986). 

Galvanic corrosion testing under atmospheric exposures has been standardized and bears the titles ISO 7441-84, ASTMG 104-89 for plate tests and ASTM G116-93 for wire-on-bolt tests.21,34,35 A form of test assembly for galvanic corrosion testing is shown in Figure 2.5. 

H.P. Hack, Galvanic Corrosion Testing Methods, NACE International, Houston, TX, 1993. 

ASTM G71-81, Standard Guide for Conducting and Evaluating Galvanic Corrosion Tests in Electrolytes, Philadelphia, PA, 1981. 

H.P. Hack, Galvanic, Corrosion Tests and Standards, R. Baboian, Ed., ASTM, 1995... 

Several specimen were tested for each of the coating types listed in Table 7.3. In this sub-section, however, the term SPECIMEN No. X is also used for COATING TYPE No, X and should be so interpreted according to the context. The material used for the coated steel specimens were unalloyed steel St 37, Crevice and pitting corrosion testst and galvanic corrosion tests with copper as a contact matcrialj were performed on all specimens supplied,... 

Galvanic corrosion test (DIN 50 919) and galvanic current measurement... 

The galvanic corrosion tests showed a very differentiated response by the different specimens, and this also applied to the changes in the test media. The specimens are documented in the Figures 11.85(a)-(i). 

Generally speaking, the (improved) coating types 8 and 9 supplied later, lie, with the exception of visual assessment after the galvanic corrosion test with short-circuit, in the upper region of the rating scale. The best corrosion resistance is displayed by specimen No. 9. 

Figure 11.86. Specimens after end of galvanic corrosion test (DIN 50 919) with short-circuit (a)-(c) show specimens 1-3 [120],...

Table 11.11. Concentration of iron, copper and zinc in the test solution after the end of the galvanic corrosion test [120]...

Fig. 6. 27 SEM analysis of anode coating top surfaces after the 20 h galvanic corrosion test (a) Ni8o-Al2o (b) Nigs-Ahs (c) Nigo-Aho (d) Ni/graphite coupled to Nigs-Alos [80].

In order to be able to properly design and interpret the results from galvanic corrosion tests, it is necessary to have some appreciation of the electrochemical theory behind galvanic corrosion. Metal corrosion consists of at least two reactions. The first is the metal going into solution in the electrolyte... 

---