1953/54 Annual Report-Corrosion Aspects HE corrosion of metals group of gear teeth become pitted and may Metal coatings the Chemical Research Labora cause complete breakdown. A new method of hot-dip coating of tory has recently been concerned with Tests carried out on steel spheres steel with aluminium, which is acid cheaper and more easily operated under artifically produced conditions resisting, is likely to prove exceedingly methods of testing the corrosion resis of loading show that soft steel is de useful for locomotive sheds and also tance of metals and the protective formed by brinelling but does not for industrial plant where high tem value of different types of coating. In crack. Hard steel cracks first on the peratures are required, as the coating this connection the 'C.R.L. beaker- outside and the cracks then work will withstand temperatures of up to test apparatus' has been extensively inward. The Laboratory is continuing 600°C. The bonding of aluminium- used, and the Institute of Petroleum with these tests to determine whether coated body members to aluminium has approved it as a means of evaluat the metal always behaves in this way body sheets in vehicles should reduce ing protective grease preparations and under fluctuating compressive loads. corrosion and give much longer life. the temporary protection afforded by Until recently the alloyed aluminium light oils. The apparatus has also been Pulverised fuel-fired boilers and iron did not produce a soft and modified to test the extent of attack In collaboration with the Boiler easily manipulated coating, but the by marine and industrial atmospheres. Availability Committee the British British Iron and Steel Research As The Laboratory is investigating the Coal Utilisation Research Association sociation has developed a method of cause of 'filiform' corrosion, which has performed a number of tests in re careful preparation of the steel surface, disfigures the coating on steel pro lation to die deposits from pulverised followed by the application of a film tected by paint, lacquer or metal, and fuel fired boilers. Air-cooled metal of glycerol. The metal to be coated it has produced examples of this form probes were inserted in the gas passes enters the bath through a protective of corrosion by introducing a variety between the primary and secondary box in which the glycerol burns gently, of salts in a steel panel and exposing it superheaters of six boilers, in tempera thus preventing oxidation of the steel, to high-humidity atmospheres. To tures varying from 650 to 950°F., and and owing to the temperature of gether with the British Shipbuilding it was found that deposits were all dipping, heavily cold-worked steel can Research Association, tests are being loosely adherent and similar in com be annealed and coated at the same carried out on four boilers to investi position, although the sulphur con time. gate means of prolonging the life of tents and sulphur/chlorine ratios in the A second coating method is the mild steel, which has so far proved different coals fired varied consider electrolytic deposition of iron and zinc gready inferior to the wrought iron ably. The largest deposit of alkali on steel sheet. These coatings are previously used in the manufacture salts on steel surfaces occurred when hard, adhere to the steel base and give of boiler tubes. the carbon dioxide content of flue an even surface to the metal. They gases was 12.5% and, when the flue The corrosion section has given will be particularly useful when used gas contains alkali salts and sulphur valuable assistance in the field of as undercoatings for chromium plate, oxides, scaling is further increased by cathodic protection, and the discovery or on goods normally galvanised. the presence of alkali chlorides. It of the toxicity of tannic acid towards B.I.S.R.A. is now directing research has also been found that the corrosion sulphate-reducing bacteria is likely to towards combining the brightness to of steel is particularly severe when have far-reaching results. In the same be found when the alloy has a low films of dilute hydrochloric acid con field the British Cast Iron Research zinc content, and the corrosion resis dense at temperatures near the water Association has continued its work on tance which increases with higher zinc dewpoint. cast-iron ship propellers, particularly content. with regard to prolonging the fife of In the course of investigations the anode used in cathodic protection. carried out as a result of requests for Tar distilling equipment advice, the Association has found that Fretting corrosion the presence of powdered dolomite in In a study of the corrosive effect on mild steel by inorganic salts or higher- Regarding corrosion in machinery, oil-fired boilers does not change the boiling phenolic compounds, the Coal tests carried out in the Mechanical condition of economisers, nor was Tar Research Association discovered Engineering Research Laboratory have there any noticeable effect, as a result that, whereas alkali injection limited shown that fretting corrosion between of treating the surface of superheater attack by the former, it increased the pin and tongue is the chief cause of the tubes with carbon and using alumi- low fatigue strength of joints of nised tubes, on the acid dewpoint possibility of corrosion by the latter. Mechanical dehydration also mini aluminium alloys, and much has been characteristics of the gases in a stoker- mised the effects of inorganic salts, done towards alleviating this con fired boiler burning coke breeze-coal but without affecting the phenols; these dition. The corrosion occurs between mixtures. By decreasing the air-fuel could be neutralised by large quan closely fitting surfaces which vibration ratio to values approaching stoichio tities of iron oxide, or by high-boiling causes to rub together, and measure metric, and by passing some of the ments were taken showing that, after oil through auxiliary, thus producing tar acids increased above 275°C. and a very short period, hard-steel speci a coarser spray, the acid dewpoint steam or vacuum distillation. Inconel and aluminium resisted corrosion by mens became coated with ferric oxide, characteristics benefited considerably. inorganic salts and phenolic com which has high electrical resistivity A much greater acid concentration pounds ; stainless steel and un- and acts as an abrasive, producing resulted when a glass-melting tank machined cast iron gave good resis furrows in the steel. Where gears are was fired with fuel oil than when fired running for any length of time, the with producer gas. tance. 106 CORROSION TECHNOLOGY, April 1955
Anti-Corrosion Methods and Materials – Emerald Publishing
Published: Apr 1, 1955
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