SHEET-IRON WATER PIPE.
IN the far West, says The Metal Worker, where water is conveyed long distances for irrigating and other purposes, it is a frequent practice to make use of thin sheet-iron pipes. It is not at all remarkable that pipes of light weight should be used, for the saving in cost thus effected is an all-important item in a new and sparsely settled country. But what is not so easily accounted for is the durability of water pipes of such material. Practically they are nothing more than sheet-iron, and are run over the surface of the ground without covering or protection of any sort. Nevertheless these water mains are said to last an extraordinary length of time. The only explanation offered of their endurance is the fact that they are not moved or subjected to shocks and rough usage. A pipe is run over the ground and there it remains undisturbed until it becomes useless, while water pipes in cities and towns are constantly being tampered with, displaced by the settling of the earth if underground, or, if exposed, subject too often to rough usage and not infrequently to shiftings. Such rough usage, it is urged, rapidly hastens the destruction of a pipe, which, if left untouched, would last a much longer time. According to the advocates of this theory, it would appear that a water pipe is like a steam boiler in some respects. A boiler may be almost rusted through in spots, and yet under the hydraulic test will show no evidence of being worn out. The same boiler, on the other hand, if submitted to test with the hammer, will immediately discover its weakness. So it is claimed to be with the thin iron pipe which, though pitted and rusted in many places, will yet continue to carry water until it finally collapses or is made to leak by some sudden shock.
While speaking of water pipes, attention may properly be drawn to the comparatively little success that has attended all efforts to coat iron pipe with a thin surface of some non-corrosive metal. Galvanized iron pipe is often used for water service, but it is far from being an ideal pipe of its kind. In the first place, zinc is more or less corrodible, and in some drinking waters it is rapidly dissolved. That zinc salts are poisonous when taken into the human system will be generally admitted, so if it is proven that a galvanzed iron pipe loses its internal zinc coating this fact is sufficient to condemn it. Furthermore, as soon as the zinc lining is stripped from the pipe the iron will quickly corrode, and in a small pipe entirely fill up the bore. It is this objection that makes it inadvisable to put in small wrought-iron pipe, as experience has shown that such pipe will usually become choked with rust after a few years of use. Apart from the unhealthfulness of 2inc, it is impossible to perfectly coat the inside of a pi, e, since it cannot be adequately cleaned before applying the zinc. The simple process of tinning has also been tried, but unsuccessfully, presumably because of the impossibility of thoroughly cleaning the inside of the black pipe. Another application of tin to this purpose consisted in making a thin tin shell or core of a size to slip in the iron pipe. After being thus inserted, the tin was expanded by hydraulic pressure until it fitted the encasing pipe closely. The linings were also applied to elbows and couplings, so that the pipe would practically be a pure tin conduit. This pipe apparently had everything to recommend it, as far as quality was concerned, but a too high cost or some other reason has prevented its use. As coatings for sheet-iron, tin and zinc have given the best results, but their application to iron service pipe, for one reason or another, has not been successful.