Galvanic compatibility

For inlet or outlet end erosion-corrosion, either extend tube ends 3 or 4 inches into the water box or install sleeves, inserts, or ferrules into the tube ends. These should be a minimum of 5 inches long. The ferrules may be nonmetallic or erosion-resistant metals, such as stainless steel, if galvanically compatible. The end of the ferrule should be feathered to prevent turbulence. 

Galvanic compatibility is an important consideration for choosing materials for hydrogen systems. It is based on the relative position of metals in what is called the electrochemical series, galvanic series or electromotive series. 

Galvanic compatibility is of most concern in electrolyzer design where a conductive KOH solution is used, and a variety of metals are used as electrodes, fasteners and containment vessels. It is also a concern for coupling I dissimilar metal fittings. 

D. L. Hawke and T. Ruden, Galvanic compatibility of coated steel fasteners with magnesium, paper no. 950429, International Congress and Exposition, Detroit, Michigan, SAE International, Warrendale, PA, 1995. 

The corrosion potential of titanium vmder normally passive conditions is quite noble, but similar to stainless steel or nickel-base alloys in the passive condition. The small potential differences between these passive engineeiing alloys generally mean negligible galvanic interactions and good galvanic compatibility as long as passive conditions prevail for the alloys involved. 

Ion vapor deposition of aluminum is attractive because it avoids the environmental and toxicological problems associated with cadmium. It does not cause hydrogen embrittlement of steel or solid metal embrittlement of steel or titanium, and it should be more galvanically compatible with aluminum alloy structure and avoid the exfoliation corrosion of sensitive alumimun alloy structme. However, views on the ability of alumimun to protect steel fasteners appear to vary. A view is that the presently available pure aluminum coatings are not able to provide adequate sacrificial protection to steel in a chloride ion environment, and for this reason a recommendation is made for the development of alruninrun coatings containing small amounts of zinc or other elements for improved protection. 

The vessel, as weU as the wick, must be compatible with the working fluid. Where possible, the wick and vessel are made of the same material to avoid the formation of galvanic corrosion ceUs in which the working fluid can serve as the electrolyte. In addition to its role within the heat pipe, the vessel also serves as the interface with the heat source and the heat sink. 

For ethylene glycol systems copper tubing is often used (up to 3 in), while pumps, cooler tubes, or coils are made of iron, steel, brass, copper, or aluminum. Galvanized tubes should not be used in ethylene glycol systems because of reac tion of the inhibitor with the zinc. Methanol water solutions are compatible with most materials but in sufficient concentration will badly corrode aluminum. 

Initially, knowledge of the process is required. It is assumed that the component is free m defects, e.g. porosity, as this will affect surface integrity, and free from residual stresses caused by any previous manufacturing process. There is also a risk in the reduction of component fatigue life associated with some surface coating processes. The compatibility between mating surfaces in service must also be addressed because of possible galvanic corrosion failure... 

Galvanic corrosion reports have emerged from two sources. In the first , the chemical compatibility of uranium carbides and Cr-Fe-Ni alloys was discussed. Evaluation was by thermodynamic modelling and experimental... 

Material used for reinforcement may differ from that of the run pipe, provided it is compatible with run and branch pipes with respect to weldability, heat treatment requirements, galvanic corrosion, thermal expansion, etc. 

For previously painted and fireproofed surfaces, the mastic manufacturer should be consulted to assure compatibility with the existing surface, proposed paint primer, and mastic. New galvanized surfaces should be mechanically abraded to ensure adherence of the prime coating. 

Galvanized (zinc-coated) steel compatibility Poor Poor... 

The zinc, cadmium or tin plating reduces the galvanic corrosion of magnesium, as seen in Figure 4.6. The compatibility of various fasteners shown in the figure leads to the order of effectiveness tin > cadmium > zinc. 

As mentioned above, the environment has a significant effect on whether or not galvanic corrosion will be a problem. For example, carbon steel will corrode rapidly if equal or larger areas of Monel 400 are coupled with it in seawater. Conversely, carbon steel is compatible with Monel 400 in concentrated caustic solutions. Even freshwater can be sufficiently different from seawater couples incompatible in seawater work well in freshwater. For example, copper-steel and aluminum-steet couples are satisfactory for handling... 

Coupling of dissimilar metals in the atmosphere may also result in galvanic corrosion. Figure 1.22 can be used to determine the compatibility of metals when exposed to atmospheric conditions that cause corrosion (i.e., when the relative humidity exceeds -50%). 

Conduct-O-Fil PI-1040 - aluminum compatible particles which do not cause galvanic corrosion in gaskets contacted with aluminum The PQ Corporation, Valley Forge, PA, USA... 

Potters Industries, Ine. developed a new aluminum compatible particles which can be used in gaskets in contact with aluminum. If silver in the gasket were to come in contact with the aluminum of the enclosure, galvanic corrosion may result. The aluminum compatible grade was found to pass 3000 hours in a salt spray chamber without loss of shielding effectiveness. 

Glass electrochemical cell. A microscope FTO-glass was chemically etched7 to produce a standard three-electrodes cell. Quasi-reference electrode was prepared by flash galvanic deposition directly on the FTO electrode. Electrochemical activity was monitored by cyclic voltammetry using a Fc-MeOH 10 4 mol/L solution in PBS 0.1 mol/L (pH 7.5). Electrodes shapes and distances have been optimized to obtain the configuration shown in Fig. 1, which produced experimental curves compatible with the E1/2 expected for first oxidation (+0.2-0.3 V vs. Ag). 

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