PIPE AND PIPE THREADS

BRIGGS STANDARD PIPE THREADS

THE particulars in the following paragraph regarding this system of pipe standards are from a paper by the late Robert Briggs, C.E., read in 1882, before the Institution of Civil Engineers of Great Britain.

The taper employed has an inclination to 1 in 32 to the axis. The thread employed has an angle of 60 degrees; it is slightly rounded off, both at the top and at the bottom, so that the hight or depth of the thread, instead of being exactly equal to the pitch X .866 is only four-fifths of the pitch, or equal to 0.81, if n be the number of

I

n'

X

I

n'

n=Number of Threads per In.

FIG. 1. Longitudinal Section of Briggs Pipe Thread

threads per inch. For the length of tube-end throughout which the screw-thread continues perfect, the formula used is (0.8 D + 4.8) where D is the actual external diameter of the tube throughout its parallel length, and is expressed in inches. Further back, beyond the perfect threads, come two having the same taper at the bottom, but imperfect at the top. The remaining imperfect portion of the screw-thread, furthest back from the extremity of the tube, is not essential in any way to this system of joint; and its imperfection is simply incidental to the process of cutting the thread at a single operation.

Thread Section

The threads as produced at the pipe end in the Briggs system are represented clearly in the longitudinal section, Fig. 1.

Here the threads that are perfect at top and bottom are shown at F, the depth being indicated at E. Back of the perfect threads

are represented the two threads with perfect bottom and flat tops and behind these are the imperfect threads produced by the chamfer or bell mouth of the threading die. A table giving the general dimensions of wrought iron tubes in the Briggs system will be found on page 40, while complete data pertaining to the thread depths, lengths of perfect and imperfect portions, allowances for making the joint in screwing the pipe into the fitting, gaging allowances, etc., are contained in the tables on pages 43 and 44.

In cutting pipe threads with a lathe tool as in threading taper work in general, the tool should be set at right angles to the axis of the piece and not square with the conical surface.

* By the action of the manufacturers of wrought-iron pipe and boiler tubes, at a meeting held in New York, May 9, 1899, a change in size of actual outside diameter of 9-inch pipe was adopted, making the latter 9.625 instead of 9.688 inches, as given in the table of Briggs standard pipe diameters.

WHITWORTH PIPE THREADS

THE table below shows the practice in Great Britain in regard to pipe and pipe threads. The Whitworth pipe thread, which is the standard, is cut both straight and taper, the Engineering Standards Committee recommending, for taper threads, inch per foot as in the Briggs standard.

The sizes of Twist Drills to be used in boring holes, to be reamed with Pipe Reamers, and Threaded with Pipe Taps, are as follows:

THE PIPE JOINT IN THE BRIGGS SYSTEM

THE illustrations below and the tables on pages 43 and 44, represent the relation of the reamer, tap, die and testing gages in the preparation of the Briggs pipe end and fitting preliminary to making up the joint.

FIG. 2. - Reamer, Tap, Die and Gages for Briggs Pipe Standard

The illustrations to the left in Fig. 2 show the relative distances that the pipe reamer, tap, testing plug and pipe end are run into the fitting in making the joint; while at the right are shown the die and ring gage on the pipe end, and the relative diameters of the standard ring gage and the testing plug for the fittings.

In pipe fitting the end of the pipe should always be cut to fit the Briggs standard pipe gage. The fitting should be tapped small in order to insure a tight joint. Theoretically the joint should be tight when the pipe end has been screwed into the fitting a distance represented at H in the diagrams, Fig. 2 and following tables. However, to allow for errors the thread on the pipe is actually cut two threads beyond H. Similarly the fitting should be tapped two threads deeper than distance H.

The following table used in conjunction with the illustrations in Fig. 2, contains information as to length and number of perfect and imperfect threads; distance and number of turns the pipe screws into fitting by hand and with wrench, or the total length and number of threads of joint; ring and plug gage data for testing tools; besides general pipe dimensions, drill and reamer sizes, etc.