Stainless steels galvanic coupling

Figure 10. Visual comparison of stainless steel/painted auto-body steel galvanic couples, one season exposure. Right to left Boston, Dallas, Detroit, Montreal.

Note also that a galvanic couple can be established between passive regions and active regions of the same stainless steel component. For... 

The specimen design used in the study by Rostoker et al. was such that it simulated both galvanic coupling and crevice conditions. Specimens were immersed in a 1% saline solution at 37 C, and examined by optical microscopy after exposures of a few to 100 days. No corrosion was observed on Ti-6A1-4V when the alloy was either uncoupled, coupled with itself (simple crevice). Or coupled with type 316L stainless steel, cast Co-Cr-Mo... 

Contact of brass, bronze, copper or the more resistant stainless steels with the 13% Cr steels in sea-water can lead to accelerated corrosion of the latter. Galvanic contact effects on metals coupled to the austenitic types are only slight with brass, bronze and copper, but with cadmium, zinc, aluminium and magnesium alloys, insulation or protective measures are necessary to avoid serious attack on the non-ferrous material. Mild steel and the 13% chromium types are also liable to accelerated attack from contact with the chromium-nickel grades. The austenitic materials do not themselves suffer anodic attack in sea-water from contact with any of the usual materials of construction. 

Galvanic couples of stainless steel trim with painted auto-body steel produced very dramatic differences in cosmetic corrosion between cities, as seen in Figure 10. Numerical corrosion ratings are listed in Table IV. The decreasing order of aggressiveness is ... 

Presence of different metals. Rebars of carbon steel in certain cases can be connected to rebars or facilities made of stainless steel or copper. This type of coupling, which in other electrolytes would provoke a considerable degree of corrosion in carbon steel by galvanic attack, does not cause problems in the case of concrete any different from those provoked by coupling with normal passive steel. In fact, the corrosion potential of passive carbon steel in concrete is not much different... 

L. Bertolini, M. Gastaldi, T. Pastore, MP. Pedeferri, P. Pedeferri, Effects of galvanic coupling between carbon steel and stainless-sted reinforcement in concrete , Int. Conf. on Corrosion and Rehabilitation of Reinforced Concrete Structures, Federal Highway Administration, Orlando, 7-11 December 1998 (CD-ROM). 

AUoy galvanic corrosion has been measured in alcohol fuel [27]. The corrosive effects of the alcohol fuels on different galvanic couples Zamak 5, low-carbon steel AISI 1010, stainless steel ABNT 420, and Al-Si alloy-4000 series were studied. Zamak was used as a permanent anode for these tests. Samples were immersion tested for three weeks at 50 °C. The alcohol fuel-water content was varied in this study and the corrosion product effect was investigated. Results indicated that higher ethanol fuel-water content was more corrosive regardless of the galvanic couples. 

E6.1. Predict the possibihty of galvanic corrosion in sea water for the following coupled pairs of alloys and metals (i) aluminum alloys and aluminum brass, (ii) cadmium and manganese bronze, (iii) zinc and tin, (iv) low alloy steel and stainless steel 410, (v) low alloy steel and stainless steel 430, (vi) nickel 200 and Ni-Cr-Mo-Cu-Si... 

Table 7.3 shows an example of galvanic corrosion rates of aluminium alloys in 3.5% NaCl solution when coupled to different materials. For instance, it is seen that the contact with low-alloy steel gives considerably higher galvanic corrosion rates on aluminium than does contact with the - from a practical point of view - more noble stainless steels as well as Ni- and Ti-based alloys (regarding material descriptions, see Section 10.1). The table reflects the cathodic efficiency of the various materials coupled to aluminium (with the exception of cadmium, zinc and aluminium alloys) in the actual environment. 

Figure 7.8 Effect of the area ratio between the cathode and the anode in a galvanic couple of carbon steel and stainless steel in two different environments.

The reservoir of carbon steel plated with stainless steel, with the latter in contact with seawater, would be quite probably the most rapidly perforated. Indeed, the localized corrosion on stainless steel, once it reaches the carbon steel, would allow the galvanic coupling between the cathodic high surface area of stainless steel and the anodic small surface area of carbon steel, exposed through the holes in the stainless steel layer, with consequent rapid perforation. 

To avoid the galvanic coupling between different materials, especially when the electrical conductivity of the solutions is high. A higher conductivity corresponds to a higher extent of the cathodic area related to the same anodic area or vice versa. Sometimes, because of differences in degradability, it may be appropriate to use bolts and/or weld material more noble in comparison to the materials that are connected, but we must keep in mind that the electrochemical scale of nobility is not always that of seawater but depends on the environment and the pollutants. Copper is normally more noble than iron, but in the presence of sulfides, the practical nobility of the two materials can be virtually coincident, while in the presence of ammonia, the nobility of copper may be lower than that of iron. Stainless steel is usually more noble than carbon steel, but in aerated alkaline enviromnents, the order of nobility can be inverted. 

One of the earliest applications of carbon as an implant material was in restorative dentistry. The first devices were bulky posts fabricated from glassy carbon that were implanted in the maxilla or mandible to serve as artificial tooth roots. Because of the inherent lack of strength of glassy carbon, they were bulky and poorly accepted. As a further complication, the stainless steel post on which a crown was cemented formed a galvanic couple in vivo leading to complications caused by accelerated corrosion of the stainless steel. 

Fracture fixation devices that are fabricated from stainless steel are unsuitable for coating or coupling with carbon because of galvanic effects (Haubold et ai, 1986). Carbon composite devices have been used reportedly with good results but such usage has not become widespread presumably because of an unaccepted cost/benefit ratio. 

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