Document NGMKebK8o1d7MoyNq2ewLGrDV

American Society of Heating and Ventilating Engineers Guide, 1924-25 distinct corrosive influence on the materials of engineering. The affinity of iron for oxygen,'which may be looked upon as the chief factor of cor rosion, is apparent to the most casual observer in the rust developed, which is evident on every hand. That this activity of corrosion is greatly accelerated by an elevation in temperature, is readily seen in the black smith shop, where iron oxidizes to form a heavy scale in the short time that elapses between the forge and the hammer. Not so with brass. Its oxidation is slow and years of exposure are re quired to effect a noticable corrosion. Metals may be subjected to air, water, sulphurous fumes, nitrogen, hydrogen and free carbon dioxide, The nitrogen is inert, but the oxygen and free or half-bound carbon dioxide in the presence of moisture exercise a distinct corrosive influence, the latter exhibiting, with water, the corroding effects of a weak acid. Iron or steel under these exposures are incomparably more subject to attack than brass, a fact demonstrated by daily experience and extensive research in the laboratory. Internal corrosion, accelerated by higher temperatures is -most to be feared and is often the determining factor in endurance. We often see an old iron pipe that is pitted completely through at certain points, due to this action. The proof of this assertion is shown in the more rapid cor rosion of hot-water piping than cold. In cold water piping the tempera ture of the water restrains the chemical interaction, but gases released at points where a partial vacuum obtains, still exercise a corrosive effect. The iron oxides have a much greater volume than the metallic iron from which they were originally derived. A 1%In. pipe, would be entirely closed up when only 1/27 of the thickness of its wall would have been converted into oxides, and in a 1 in. pipe only 1/40. This results in " wire drawing " and .greatly reduces the volume of the stream at outlets and leads to complaints that the pressure is abnormally low, whereas the real source of trouble is in excessive interior corrosion. Brass piping is immune to this type of corrosion, and always delivers water free from discoloration or rust. Due to its maintenance of a smooth, unrusted interior, full flow and pressure are continued throughout the life of the system, and piping friction losses are kept reduced to the minimum. Under conditions usually obtaining,- good quality brass piping and fittings will satisfy all requirements. The architect engineer or contractor should by all means require that piping , and fittings be supplied by a reputable dealer, the product of a reputable manufacturer. Certain known special conditions of corrosion may require special mixtures, in order to obtain for the piping system the longest life. Among such instances might be. mentioned salt water service, for which a uni- , versal recommendation is "admiralty", mixture (70 per cent copper, 29 per cent zinc, and 1 per cent tin.) Where unusual factors of corrosion are present, the engineer or'contractor should heed the recommendations of the pipe manufacturer; In alt cases, pipe fittings should have approxi mately the same composition as the metal of the pipe itself. 158 159