Steels, corrosion testing

Haynie, F. H., Spence, J. W., et al. (1990). Evaluation of an atmospheric damage function for galvanized steel. Corrosion Testing and Evaluation Silver Anniversary volume. ASTM STP 1000. ASTM, Philadelphia, pp. 225-240. 

Kane, R. D., Wilhelm, S. M., and McIntyre, D. R., Application of the Critical Pitting Temperature Test to the Evaluation of Duplex Stainless Steel, Corrosion Testing and Evaluation Silver Anniversary Volume. ASTM STP 1000, R. Baboian and S. W. Dean, Eds., ASTM International, West Conshohocken, PA, 1990, pp. 289-302. 

Austenitic Stainless Steels—Determination of resistance to intergranular corrosion of stainless steels— Part 1 Austenitic and ferritic-austenitic (duplex) stainless steels—Corrosion test in nitric acid medium by measurement of loss in mass (Huey test)... 

The rdle of chlorides in the presence of sulphates has already been mentioned, but these can also have a serious effect in the absence of other contaminants. The presence of chloride not only leads to considerable acceleration of oxidation rate but can also give substantial subsurface intergranular penetration of the steel. Corrosion test results for several steels are shown in Table 7.13. The attack noted on the calcium sulphate + calcium chloride mixtures indicated in Table 7.12 can possibly be attributed solely to the presence of chloride. Very small amounts of chloride are sufficient to cause serious acceleration, as illustrated in Fig. 7.34. Samples of 347S31 steel were heated in air to 650 C for 20 h cycles. Between cycles the samples were cooled to room temperature and weighed together with any loose scale. 

AFNOR (1998) NF EN ISO 3651-1 1998. Determination of Resistance to Intergranular Corrosion of Stainless Steels. Part 1 Austenitic and Ferritic-Austenitic (Duplex) Stainless Steels. Corrosion Test in Nitric Acid Medium by Measurement of Loss in Mass (Huey Test), AFNOR, Paris. 

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. 

Sa.lt Spray Tests. One of the older accelerated corrosion tests is the salt spray test (40). Several modifications of this imperfect test have been proposed, some of which are even specified for particular appHcations. The neutral salt spray test persists, however, especially for coatings that are anodic to the substrate and for coatings that are dissolved or attacked by neutral salt fog. For cathodic coatings, such as nickel on steel, the test becomes a porosity test, because nickel is not attacked by neutral salt fog. Production specifications that call for 1000 hours salt spray resistance are not practical for quahty acceptance tests. In these cases, the neutral salt spray does not qualify as an accelerated test, and faster results from different test methods should be sought. 

The information in Sections 2.2, 2.4 and 3.3 is relevant for protection criteria. Investigations [43] with steel-concrete test bodies have shown that even in unfavorable conditions with aerated large-area cathodes and small-area damp anodes in Cl -rich alkaline environments, or in decalcified (neutral) surroundings with additions of CU at test potentials of (/f.y.cuso4 = -0.75 and -0.85 V, cell formation is suppressed. After the experiments had proceeded for 6 months, the demounted specimens showed no recognizable corrosive attack. 

France, W. D. and Greene, N. D., Some Effects of Ex(>erimental Procedures on Controlled Potential Corrosion Tests of Sensitised Austenitic Stainless Steel , Corros. Sci., 10,379(1970) Tedmon, C. S. (Jr.), Intergranular Corrosion of Austenitic Stainless Steel , J. Electrochem. Soc., 118, 192(1971)... 

Figure 4.17 illustrates the corrosion occurring on high-purity AZ31 and ZW3 in contact with steel bolts. Tested alone in sea-water, the corrosion rate of the former is much the lower. It is evident from the illustration, however, that the governing factor in galvanic corrosion is the type of electrolyte present rather than the composition of the alloy. 

The data on which Fig. 8.74 is based are for tests carried out in carbonate well-water. McAdam made the further interesting discovery that if mild steel were tested in condenser water and a similar graph constructed, the set of contours corresponded more closely to the right-hand side of Fig. 8.74, i.e. the behaviour of mild steel in condenser water was similar to that of Monel in carbonate water. The apparent universality of this diagram is an interesting observation, but it has not provoked a basic theory of corrosion fatigue. 

It is hardly surprising that the preparation of surfaces of plain specimens for stress-corrosion tests can sometimes exert a marked influence upon results. Heat treatments carried out on specimens after their preparation is otherwise completed can produce barely perceptible changes in surface composition, e.g. decarburisation of steels or dezincification of brasses, that promote quite dramatic changes in stress-corrosion resistance. Similarly, oxide films, especially if formed at high temperatures during heat treatment or working, may influence results, especially through their effects upon the corrosion potential. 

Selective corrosion in the heat-affected zone of a weld occurs most commonly when unstabilised stainless steels are used in certain environments. The obvious answer is to use an extra-low-carbon grade of stainless steel, e.g. types 304L, 316L or a stabilised grade of steel, e.g. types 321 and 347. Knifeline attack at the edge of a weld is not commonly encountered and is seldom predictable, and it must be hoped that it is revealed during preliminary corrosion testing. 

Galvanised steel provides increased corrosion resistance in carbonated concrete. In concrete with more than 0.4% chloride ion with respect to the cement content, there is an increased risk of corrosion and at high chloride contents the rate of corrosion approaches that of plain carbon steel. In test conditions the rate of corrosion is greater in the presence of sodium chloride than calcium chloride. Fusion-bonded epoxy-coated steel performs well in chloride-contaminated concrete up to about 3.9% chloride ion in content. 

Corrosion Tests of Flame Sprayed Coated Steel-19 Year Report, American Welding Society. Miami (1974)... 

The extent of pitting is estimated by a special microscopical technique, or by the attack on the substrate using an appropriate indicator. Thus in the case of steel 1,10-phenanthroline hydrochloride is added to the electrolyte (solution B) to detect the formation of Fe ions. Alternatively, the specimens can be removed from the corrosion test solution and placed in an indicator solution, i.e. solution C for zinc-base die castings and solution D for steels. 

Practice for making and using U-bend stress corrosion test specimens Recommended practice for laboratory immersion corrosion testing of metals Method for vibratory cavitation erosion test Practice for recording data from atmospheric corrosion tests of metallic-coated steel specimens... 

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