1.Turn off the water or gas system so that nothing is running through the pipe where you will be installing the union. 2.Mark the steel pipe at the point where the union needs to be installed using a felt-tip pen. 3.Measure the length of the union, when all three parts are installed together. Subtract from this figure the amount that the steel pipe's threads will enter both ends of the union. For example, if the union's length is 3 inches and the pipe will enter each end of the union by 3/4 inch, you would calculate 1 1/2 inches. Make a second mark along the pipe at a distance from the first mark that equals this calculated measurement. 4.Place a rotary pipe cutter around the pipe, tightening the cutter blade onto one of the marks. Lubricate the pipe and the cutter blade with cutting oil. Rotate the cutter once 360 degrees, and tighten it again. Rotate again. Repeat this process until the pipe is cut through. Follow the same steps to cut through the pipe at the second mark. 5.Remove the pipes on each side of the cuts by placing a pipe wrench around the pipes at a point close to the nearest couplings. Turn the pipe wrench counterclockwise to remove the pipes. 6.Take both pipes to a major DIY store to have the cut pipe ends threaded. 7.Apply threading compound around the older threads on both pipes. Thread both pipes by hand into the couplings that they were removed from. Tighten the pipes into place with the wrench. 8.Apply threading compound to both newly threaded pipe ends. Remove the female end of the union from the male end -- the female end will have the central nut. Thread the female end of the union onto one of the pipe threads. Tighten it in place with the wrench. Thread the male end of the union onto the remaining pipe end. Tighten it with the wrench. Thread the central nut onto the male end of the union by hand. Tighten the two together with one wrench on the central nut and another on the male end.
