Document yrwak36J6vRmZm69y78y4G2ZE

American Society of Heating and Ventilating Engineers Giuide, 1935 Distinction should be made between corrosion in heating systems Dr and in the condensate discharge lines from other apparatus using stea^ such as water heaters, kitchen equipment, and sterilizers. Experie m' has shown that in heating systems the partial pressures of the gases'^ not reach such magnitudes as to cause harmful amounts of gas to beco a dissolved in the condensate when steam supplies are of reasonable puritvf In other kinds of steam-using apparatus which are not ordinarily well vented, the gases tend to accumulate in the steam space and to become dissolved in the condensate in appreciable concentrations. Consequently corrosion is frequently observed in the condensate discharege. lines from such apparatus, but this does not necessarily indicate that equally serious corrosion is taking place in the heating system supplied with steam from the same source. Table 11. Standard Roughing-in Dimensions Angle Type Valves' Connecting ends shall be threaded and gaged as to threading according to the American (Taper) Pipe Thread Standard, A.S.A. No. B2--1919. The standardization of the Roughing-in Dimensions of Angle Steam and Hot Water, and Modulating Radiator Valves was made possible by the cooperation of the Manufacturers Standardization Society of the Valves and Fittings Industry. When corrosive conditions are believed to exist, their seriousness should be determined by actual measurement, rather than by inference from isolated instances of pipe failures. The National District Heating Associa tion has perfected a corrosion tester for measuring the inherent corrosive ness of existing conditions. This corrosion tester consists of a frame sup porting three coils of wire which are carefully weighed. After the tester has been inserted in the pipe line for a definite length of time, the loss of 596 Chapter 34--Pipe, Fittings, Welding . , t 0f the coils, referred to an established scale, indicates the relative W rrosiveness of the condensate. Accompanying such corrosion measure00 nts a careful chemical analysis should be made of the condensate, and the findings will' serve as a basis for an intelligent study of the problem. Corrosion, if found to exist, can be lessened or overcome by several means If the steam supply is found to be definitely contaminated, per chemical treatment of the water, followed by deaeration, is an obvious remedy- The leaks in the piping system, particularly in vacuum systems, should be stopped so far as is practicable. ____ Some success has been reixirted with the use of inhibitors; chief among which are oil, sodium silicate, and ammonia. Oil may be fed into the main steam-supply pipe by means of a sight-feed lubricator. The type of oil known as 600-W is usually recommended. In the present state of knowledge on this point, the quantity to be fed can best be determined by trial. The use of sodium silicate, fed in a similar manner, is reported ter be successful but it has not been widely used. The effect of ammonia is to increase the pH value of the condensate above the point where corrosion is likely to take place. Speller4 reports having injected small quantities of ammonia into a small closed heating system (the entire amount of condensate being returned to the boiler) and finding the pH value maintained at a high point for several months without further additions of ammonia.. The concentration of ammonia must be kept low to avoid corrosion of brass parts of the system. The use of ammonia is not to be recommended where steam may come in contact with food or other materials. In view of the fact that corrosion is most frequently found in the return lines from special equipment, which constitute a relatively small part of the total piping in a building, a simple solution of the corrosion problem may be to use non-corroding materials in those certain portions of the piping system, since the higher cost will usually be an unappreciable portion of the total. Brass and copper are undoubtedly less subject to this type of corrosion than the ferrous metals, and considerable attention is now being given to corrosion-resistant linings for ferrous pipe. Castiron pipe, sometimes alloyed with other metals, also deserves con sideration. `Corrosion in Steam Heating Systems, by F. N. Speller (A.S.H.V.E. Transactions. Vol. 34, 1928). PROBLEMS Ii\T PRACTICE 1 What materials are used for pipes of heating systems? Steel pipe is generally used for steam piping and for return lines where corrosion is not particularly active. Where corrosion is an important factor, it is good practice to use special corrosion-resistant ferrous alloys, or brass or copper pipe. 2 Why is thin-walled copper pipe made up with.sweated joints? If the pipe were threaded it would be necessary to use at least standard-weight wall thickness on account of the metal removed in threading. Flared ends with coupling nuts may be used, but this construction is expensive and hard to keep tight. 597