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Pipe Threads.

the taper is too great or the die has been run over it two or three times, reducing the end of the thread, and though the pipe may be screwed in the full length of thread, it actually holds only by the imperfect threads at the bottom, and all others are soon corroded.

The short and imperfect thread on pipes is usually
Standard Pipe and Pipe Threads.

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Standard Pipe Tables.

made when piping is cut where the work is put up and the men have hand machines. The dies are usually dull, and the men stop as soon as they have a thread long enough to screw up and make a tight joint.

The thread and taper for pipes that have been generally adopted are known as the "Briggs standard."

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The threads have an angle of 60 degrees, but are rounded off slightly at top and bottom, so that the depth of the thread is only four-fifths as great as it would be if the threads were sharp. The outside surface of the pipe is tapered to a certain distance from the end, the standard taper being such that the surface inclines towards the axis of the pipe by 1 in 32.

This makes the

total taper, as measured by the variations in outside diameter, equal to I in 16, or 34 inch to the foot. The total length of the tapered part is given in the table.

High Pressure Piping.

For some reason it has become the custom to list pipe above 12 inches inside diameter as O. D., or outside diameter. At the present writing there is a movement on foot to list 10-inch pipe and above as O. D.

Fig. 19 shows a section of 5-inch pipe reproduced from The Locomotive. The taper is slightly exaggerated for greater clearness. Two threads, it will be seen, are · perfect at the bottom but flat on top, and four are imperfect at both top and bottom.

Standard weight pipe will withstand any steam pressure that will ever be put upon it if the weld is good and the threads perfect.

For hydraulic work up to 1,000 to 1,200 pounds pressure, use ordinary pipe and fittings up to 3/4 inch.

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Above that, extra heavy is safer. For those high pressures, cast-iron fittings are unsafe and brass should be used.

For high pressures, it is better to use flanges rather than couplings, or sockets, as the end of the pipe in a flange can be expanded or peened in. This should be the case in all work 5 inches and over. The standard flanges for heavy work are safe for pressures up to 130 pounds, but for larger work the flanges should be steel castings, or, what is still better, drop-forged steel. Ordinary cast iron is too weak and even iron in which there is sufficient charcoal iron or steel to bring the tensile strength up to 26,000 to 28,000 pounds is liable to crack. For cold water at high pressures the tongue and

Flanged Joints.

groove joint, where the tongue fits the groove accurately, with a thin rubber gasket at the bottom makes the best joint. If the tongue does not fit the groove this joint is but little better than an ordinary faced joint.

For steam, the use of rubber for packing is inadmissible. For large work and high pressures, the making up of large pipe mains requires close and accurate mechanical work. It is a machinist's job throughout. The flanges require to be fitted as closely as engine work, and after the pipe is put in the flanges and expanded, the ends

Fig. 20. Rabetted Joint.

Fig. 21.

Peened Joint,

still must be faced off. A rabbetted joint is shown in Fig. 20, in which a corrugated copper gasket painted with black lead is used. This copper gasket packs the flange joint and also the end of the thread on the pipe. If accurately done, this makes a tight and durable joint, but is very expensive.

Another joint is shown in Fig. 21, but this joint is not trimmed after peening. The end of the pipe is peened in the form of a round corner down on to the thread. Where a pipe does not pulsate it will make a good joint, but should there be pulsations so as to strain the thread and

Joints Without Threads.

get it loose, it will eventually leak, and it is a bad joint to tighten once it leaks at the thread.

Riveted joints on piping are apt to leak. Some jobs of this kind are put up where the joints are all tight, so it is claimed. The engineer never saw one of these jobs.

Fig. 22. Van Stone

Pipe Joint.

Fig. 23. Mitchell Pipe Joint.

All that he had seen, that had rivetted joints, leaked more or less. Of course they can be caulked, but his observatios led him to think that caulking a leaky joint that was pulsating was not a thing to look forward to with pleasure.

Fig. 22 is the Van Stone joint, made by the Walworth

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