illuminating gas, and our fuel in those favored regions supplied with natural gas. I believe the day is not far distant when it will be found more economical to pipe all our fuel, as gas, to the place of consumption, rather than to carry it there in the form of coal; or at least to effect its distribution within the cities in this manner. Already, in some of our cities, steam for both heat and power is thus distributed. I wish to call your attention to-night, as engineers, to an interesting departure in the manufacture of this useful article. I refer to the steel pressure pipe manufactured by The Spiral Weld Tube Co., of East Orange, N. J., of which you have a specimen before you. These pipes are made by winding a ribbon of steel or iron spirally, and hammer-welding the overlapping edges. They are of any desired weight of metal, from No. 29 B. W. G. up to No. 8 B. W. G.; are hammer-welded along the entire length of the helical seam, and are probably the strongest pipes in proportion to weight ever made. The advantages of winding the stock spirally in the case of iron pipe are evident, as it is well known that the greatest strength of rolled iron lies in the direction of the grain. Lapwelded boiler tubes, for example, are often "safe ended" to prevent splitting of the tubes in setting, the safe ends being merely short pieces of tube made with the grain running around the pipe, which are welded on to the tube proper. Steel, being homogeneous, is as strong one way as the other; but with either metal the helical weld acts as a strengthening band, instead of forming a line of structural weakness as in all butt-welded and most lapwelded pipe. Spirally welded tubes, however, are hardly to be classed as competitors with lap-welded tubes, as they are not made at all in the smaller diameters, their inferior limit being practically 6 inches. On the other hand, lap-welded pipes above 6 or 8 inches diameter increase rapidly in cost and difficulty of manufacture, as the stock used must be proportioned, not to the required strength of the pipe, but to the necessities of the process. Since the entire body of the pipe in the lap-welded process must be heated to a welding heat, light stock could not be used at all, as it would collapse and prove unmanageable. Consequently, pipes intended to carry large volumes of fluids at light pressures often present the anomaly of say 75 lbs. of metal introduced solely to enable the pipe to be made at all, while 25 lbs. of metal do all the work. The new pipes may hence be said to cover a hitherto unoccupied or imperfectly occupied field. The manufacture of spirally welded pipe is accomplished by automatic machinery. The skelp is passed into the machine, cold, from a guide table set at the desired angle. It is then fed forward to the "former," which bends it to the desired curvature. On its way to the forming jaws the anterior edge passes through a blow-pipe flame of fuel gas and air, meeting at the focus of the flame and overlapping the posterior edge of the preceding spiral. The edges are here united by the action of a light hammer striking about 160 blows per minute, the metal being sustained by an anvil block within the pipe. The normal product of a machine is about one foot of pipe per minute, receiving the stock cold and delivering its product cold. For long pipes it is necessary to cross-weld the skelp into continuous bands. This is done by automatic machines which unite the ends of the metal by straight lap-welds. The only limit to the length of a pipe, without joint, that may be thus made is that imposed by the conditions of economical transportation. As evidencing at once the length of pipe that can be made and the remarkable stiffness of the product, I have seen a single piece of 10-inch pipe, 40 feet long, supported on trestles near the ends and bearing the weight of three men without perceptible deflection. The stock used was No. 14 B. W. G. The question as to the durability of this pipe, that is, its ability to withstand corrosion, will at once occur to the engineer. As to this, much will depend upon the character of the protective coating applied to the pipe, and upon the conditions under which it is used. We have not had sufficient experience in the East with light riveted pipes to determine this question, but upon the Pacific coast they have been largely used, and apparently have given little trouble upon this score. Mr. Hamilton Smith, Jr., in a paper read before the British Iron and Steel Institute, says: "So far as rust is concerned, in my extensive experience I have only seen one notable instance where an asphaltum coating properly applied did not protect the iron, and that was with a pipe over which a stream of water highly charged with sulphate of iron passed. For a period of twenty years an asphaltum coating has prevented rust and also the formation of interior tubercles where soft water flows through the pipe." After a section of the required length has been formed and welded on the machine, the ends are cut square and the pipe is tested by hydraulic pressure. Diameters under 16 inches are tested to 300 lbs. per square inch, larger diameters to 200 lbs. per square inch. The pipes never fail under this test, even in the case of light gauges and large diameters, the chief value of the trial being to develop leaks due to imperfect welding or defective spots in the stock. The couplings usually employed are the flange coupling with bolts, the cast-iron hub and spigot, and a locking sleeve, though a number of special couplings for special uses have been devised. In the first-named coupling, a cast or wrought-iron flanged collar, provided with the proper bolt holes, is passed over the pipe. The pipe end is then expanded and laid flat against the face of the flange. The joint is made by bringing pipe to pipe, with the intervention of a gasket suited to the use to which the pipe is to be put, and is entirely independent of the fit of the flange collars, whose sole office is to hold the flanged ends of the pipes together. Flanges are also attached to the pipe ends, rigidly. The following tables, taken from the company's catalogues, indicate (table 1) the sizes of pipe manufactured, the theoretical strength for internal pressures, and (table 2) the comparative weights of spirally welded steel, lap-welded iron, and cast iron pipes, of equal diameters. I have not verified the figures, but have no doubt of their correctness : |