| Size | Thickness | No. threads per inch |
|---|---|---|
| 11⁄4 | 0.140 | 111⁄2 |
| 11⁄2 | 0.145 | 111⁄2 |
| 2 | 0.154 | 111⁄2 |
| 21⁄2 | 0.204 | 8 |
| 3 | 0.217 | 8 |
| 31⁄2 | 0.226 | 8 |
| 4 | 0.237 | 8 |
| 5 | 0.259 | 8 |
| 6 | 0.280 | 8 |
Screw pipe work came into common use with the advance of modern steel structures. Some difficulty had been experienced in getting the cast-iron pipe joints tight and to keep the pipe so anchored that it would not crack. The screw pipe was found to answer all of the requirements of modern structures and therefore has been used extensively. The life of screw pipe is not as long as extra heavy cast-iron pipe. This is the only serious objection to screw pipe, which must be renewed after a term of years, while extra heavy cast iron lasts indefinitely. Screw pipe is never used underground. When piping is required underground, extra heavy cast-iron pipe is used.
PIPING
The pipe used in Durham work is galvanized extra heavy, or standard wrought-iron, or steel pipe. It is almost impossible to recognize wrought-iron from steel pipe without the aid of a chemical or a magnifying glass. To test the pipe to distinguish its base, take a sharp file and file through the surface of the pipe that is to be tested. If the pipe is steel, under a magnifying glass the texture of the filed surface will appear to be smooth and have small irregular-shaped grains, and there will also be an appearance of compactness. If the pipe is iron, the texture will have the appearance of being ragged and will show streaks of slag or black. When screw pipe is cut there is always left a large burr on the inside of the pipe. This burr greatly reduces the bore of the pipe and is a source of stoppage in waste pipes. After the pipe is cut this burr should be reamed out thoroughly. One of the strong points of screw pipe is the strength of each joint. Care should therefore be taken to see that perfect threads are cut on the pipe and that the threads of the fittings are perfect. The dies should be set right and not varied on each joint. There should be plenty of oil used when threads are cut so that the thread will be clean and sharp. The follower or guide on stocks should be the same size as the pipe that is being threaded, otherwise a crooked thread will result. If a pipe-threading machine is used, the pipe is set squarely between the jaws of the vise that holds the pipe in place. When cutting a thread on a long length of pipe, the end sticking out from the machine must be supported firmly so that no strain will come on the machine as the pipe turns. It is necessary to cut crooked threads sometimes on the pipe to allow the pipe pitch for drainage or to bring the pipe into alignment where fitting would take up too much room. To cut a crooked thread on a piece of pipe, simply leave the follower out of the stock or put in the size larger. The dies not having a guide will cut a crooked thread. Piping should be run with as few threads as possible. With a thorough knowledge of and the intelligent use of fittings, a minimum number of threads will result.
The pipes in a building are run in compact parallel lines in chases designed especially for them. The tendency is to confine the pipes to certain localities as much as possible. This makes a very neat job and in case repairs are needed, the work and trouble incurred will be confined to one section.
FITTINGS
The fittings used in screw pipe work are cast-iron recess type (see [Fig. 54]). The fittings are so made that the inside bores of the pipe and the fittings come in direct line with each other, thus making a smooth inside surface at all bends. The fittings are all heavily galvanized. All fittings should be examined on the inside for any lumps of metal of sufficient size to catch solid waste matter, and these must be removed or the fitting discarded. All 90° bends, whether Ts or elbows, are tapped to give the pipe that connects with them a pitch of at least 1⁄4 inch to the foot. Except where obligatory, 90° fittings should not be used. To make a bend of 90° a Y-branch, a nipple and a 45° bend should be used, or two 45° bends will make a long easy sweep of the drainage pipes and reduce the possibility of stoppage.
Y-branches are inserted every 30 feet at least to allow for a clean-out which can be placed in the branch of the fitting. When a clean-out is placed an iron plug should not be used. These plugs are not removed very often and an iron plug will rust in and be almost impossible to get out. Brass clean-out plugs are used and are easily taken out.
At times it is necessary to connect cast iron and wrought iron, or in a line where a union could be used if the pipe were not a waste pipe, a tucker fitting is used. This fitting is threaded on one end and has a socket on the other to allow for caulking. To get a good idea of all the fittings in general use, the reader should get a catalogue from one of the fitting manufacturers and a survey of it will give the names and sizes of the fittings. However, I show a few common ones. In the writer's opinion, the studying of the catalogue would be of more benefit than a description of fittings at this point. The sizes used and the methods employed to vent the waste-pipe systems are the same as in cast-iron work.