Corrosion testing continued alloys

Specification for electroplated coatings of 65/35 tin/nickel alloy Method for the evaluation of results of accelerated corrosion tests on metallic coatings Methods of test for paints Cross-cut test Pull-off test for adhesion Resistance to artificial weathering (enclosed carbon arc) and Addendum No. 1 Resistance to continuous salt spray Notes for guidance on the conduct of natural weathering test... 

A dense and electronically insulating layer of LiA102 is not suitable for providing corrosion resistance to the cell current collectors because these components must remain electrically conductive. The typical materials used for this application are 316 stainless steel and chromium plated stainless steels. However, materials with better corrosion resistance are required for longterm operation of MCFCs. Research is continuing to understand the corrosion processes of chromium in molten carbonate salts under both fuel gas and oxidizing gas environments (23,25) and to identify improved alloys (29) for MCFCs. Stainless steels such as Type 310 and 446 have demonstrated better corrosion resistance than Type 316 in corrosion tests (29). 

A summary of the test results, subsequent to those reported in ANL-5260, is given in Table XVIII. Typical plates are shown in Fig. 76. Two of the plates have not been further tested since the last report and one niobium-5 % zirconium plate has been added. Nine other binary alloy plates, apparently without defects, are being continued in corrosion testing and have shown no indication of failure in as much as 2000 hr. (Some are now being tested dynamically at 500F and others statically at 550F.)... 

Figure 12.11 Preferentiai attack of the continuous austenite phase in an autogenous GTA weld in Ferral-ium Alloy 255. Crevice corrosion test was performed in synthetic seawater according to ASTM D 1141 at 100°C (212 °F). Etched with 50% FINO (xt 00). (Reproduced with permission from Daubert Cromwell.)...

Corrosion tests in uranyl fluoride solutions. In contrast to uranyl carbonate solutions, uranyl fluoride solutions are acid, and in general the corrosivity of the fluoride solutions is much greater than that of the carbonate solutions. To determine the relative corrosion resistances of many different metals and alloys, a 0.17 m UO2F2 solution was used. Te.sts were performed at 100 and 250°C in static systems and at 250°C in loops. The static tests were continued for periods up to 1000 and 2000 hr. The dynamic tests lasted for 200 hr, and the flow rate of the solution past the specimens was 10 to 15 fps. The results of the dynamic tests are shown in Table 5-4. 

Tantalum-Molybdenum Schumb, Radtke and Bever studied the corrosion resistance of tantalum-molybdenum alloys that form a continuous series of solid solutions. The results of tests of up to 500 hours duration (Table 5.26) indicate the corrosion resistance of the alloy to be substantially that of tantalum, provided its concentration exceeds 50%. 

To ensure maximum continuity of the tin-iron compound layer between tin and steel. This layer is itself corrosion resistant and appears to act as a nearly inert screen limiting the area of steel exposed as tin is removed by corrosion. Its effectiveness is measured by the Alloy-Tin Couple (A.T.C.) test, in which the current flowing is measured between a sample of tinplate from which the unalloyed tin layer has been removed, and a relatively large tin electrode immersed in an anaerobic fruit juice. ... 

A similar method of test was used at the International Nickel Company s Corrosion Laboratory at North Carolina. The specimen discs are mounted on insulated vertical spindles and submerged in sea-water, which is supplied continuously to the tank in which the specimens are immersed. The maximum peripheral speed of the spinning disc is about 760cms , and the characteristic pattern of attack is shown in Fig. 19.3a. Studies of variation of depth of attack with velocity indicate that at low velocities (up to about 450 cm s ) alloys such as Admiralty brass, Cu-lONi and cupro-nickel alloys containing iron maintain their protective film with a consequent small and similar depth of attack for the diflferent alloys. At higher velocities the rate increases due to breakdown of the film. 

Predictions of the corrosion performance should be obtained from published data and through testing.The essential requirements of accelerated testing are that the acceleration should produce the same mode of failure and reflect at least a known order of resistance of some alloys in service media.168 The most common approaches employed to achieve testing objectives in SCC are the use of high stresses, slow continuous straining, precracked specimens, higher concentration of species in the test environment than in the service environment, increased temperature, and electrochemical stimulation.169 For electrochemical corrosion, the properties of the medium at the interface should be considered in accelerated tests. 

Corrosion of the glass-making melters must be maintained at an absolute minimum to increase the lifespan of the melter. Laboratory-measured corrosion rates indicate that melter lifetimes of several years can be achieved with high chrome oxide or zircon refractories metallic melters may have lifetimes of several months if alloys such as Inconel 690 are used. These conclusions have been reached on the basis of extrapolation of laboratory tests. Long-term tests, particularly with waste glasses in engineering-scale continuous melters, have not yet been made. 

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