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showed that the CHC impregnated nitrite, on the other hand, has not WO vapour-phase corrosion in paper provided almost complete pro been found to arrest further rusting, hibitors which have attracted tection up to a 'distance of 2 in. for considerable attention recently are once some corrosion has begun. mild steel and also incidentally reduced dicyclohexylamine nitrite which is the corrosion of copper in normal available commercially; and cyclo- Test results humid air containing the usual indus hexylamine carbonate (CHC) which trial pollution. has recently been developed and can The table below shows the losses be supplied in trial quantities by the sustained by various metals after 14 Vapour-phase inhibitors are only sole manufacturers, Howards of Ilford recommended for use where vapour days exposure at 40°C. to a water- Ltd., Ilford, Essex. loss can be reduced to the lowest vapour-saturated atmosphere. It will be seen that CHC reduces corrosion in practicable proportions by using (and CHC is a white solid smelling faintly most cases and in some cases almost storing) the inhibitor in a closed of ammonia. It is soluble in water completely prevents it. Copper, package and, as has already been noted, and in alcohols. Tests have shown copper alloys and magnesium, how laboratory tests indicate that the that CHC volatilises rather more present inhibitors are not anti-corrosive ever, are liable to be attacked by CHC slowly than camphor but more quickly agents for some non-ferrous metals if droplets of water are allowed to than dicyclohexylamine nitrite. The condense on the metal, as happened and alloys under all conditions. protective CHC vapour is produced in this case. immediately the solid is introduced into a package and it diffuses rapidly In actual everyday conditions, atmo Possible futur e developments throughout the whole of the space. spheric pollution is a major controlling CHC vapour inhibits corrosion even factor in corrosion problems. To Experience of CHC is at present in the presence of water, water vapour check the effect of these conditions, limited to laboratory scale trials and or salt water and arrests corrosion of mild steel and cast iron was tested in firm recommendations cannot at this already partially rusted iron and steel. open tubes made of CHC-impregnated stage be made with certainty. Never wrapping paper. The test pieces were theless the tests which have been Extensive laboratory investigations exposed outdoors for 49 days, the paper carried out indicate that CHC may have shown that, while no single known being changed every three days to prove on further large scale trials to inhibitor will protect all metals and compensate for the loss of the CHC be a considerable step forward in the alloys under all conditions, CHC from the open tubes, a loss which field of corrosion prevention. For reduces corrosion in most cases and would not occur under service con packing cases or for the insides of gives almost complete protection to ditions in closed packages. In closed metal vessels, pellets, impregnated many materials. A high degree of packages, atmospheric pollution would porous blocks or powder in porous protection is given by the CHC vapour generally also be less. The results bags appear to be convenient ways of to mild steel, cast iron, aluminium, showed CHC to have strikingly good introducing CHC. The loss of CHC chromium-plated steel, tinplate, zinc, protective power. during the storage life will be mainly and solder even when exposed in a determined by the rate of vapour water-saturated atmosphere for two In a series of tests to determine the leakage and therefore a reasonably weeks at 40°C. Under some conditions effect of distance, test pieces of mild strong and air-tight package would be CHC has some corroding action on steel were suspended at various dis desirable. Packages such as steel copper, brass and magnesium. tances from 5% aqueous solutions of drums and other air-tight metal the inhibitors. The results after six Solid CHC does exert an inhibiting containers lend themselves admirably months exposure proved that CHC was effect in contact with metal surfaces, to the vapour-phase inhibitor tech effective up to a distance of 30 in. but tests have shown that in almost all nique. Protection of the insides of Exposure tests at various distances cases the vapour is more effective. empty boilers and storage tanks is between the test pieces and sheets of Comparisons of CHC-impregnated practicable by these methods. impregnated wrapping paper(1g./sq.ft.) paper (ig./sq.ft. of paper) with paper similarly impregnated with dicyclo hexylamine nitrite have shown CHC Figures Given are Losses in Weigh t (milligrams) to be generally superior, particularly where the inhibitor is a foot or more Metal panels exposed in vapour of from the object to be protected. The Metals superiority of CHC is still more Controls Dicyclohexylamine CHC marked when compared in the vapour no inhibitor nitrite phase under the stringent conditions Ferrous : of salt-water-contaminated moist air Mil d steel .. .. .. .. 19.0 0.1 27.5 at 40°C. for 18 days. 1.4 Cast iron .. .. .. .. 161.3 146.2 Non-ferrous : Where rust has already formed on 1.8 0. 8 Aluminium .. .. .. .. 3.9 metal surfaces, and particularly where Brass (60/40) .. .. .. 1.3 0. 5 8.8 salt spray has also come into contact 10. 2 Cadmiu m (massive metal) .. 9.5 9.5 with the rusted surface, CHC provides 0. 4 0. 4 Chromiu m plate on brass .. 0. 2 efficient inhibiting action and effec Chromiu m plate on steel .. .. 4.4 4. 0 Coppe r .. .. .. .. 2. 4 16.7 tively arrests the progress of the cor 4. 2 Magnesiu m .. .. .. 18.9 5.0 rosion. This protection can be given 1. 1 10. 0 0. 5 Solder on brass .. .. .. by contact with the solid, but again Tinplat e (hot-dip) .. .. .. 11.3 1.2 the vapour has been shown to provide 0. 9 Tinplat e (electrolytic) .. .. 16.9 3. 2 Zinc .. .. .. .. 21.4 14.5 the best results. Dicyclohexylamine 8 CORROSION TECHNOLOGY, January 1955
Anti-Corrosion Methods and Materials – Emerald Publishing
Published: Jan 1, 1955
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