New water supply lines are usually copper or plastic, but if you need to repair or extend a galvanized pipe system, it makes sense to use the same material. Working with steel isn't difficult, but there are a few things you need to know before tackling a pipe project.
First, almost all gas lines are black threaded pipe, which is installed the same way as galvanized pipe. Make sure you know the difference when working.
It's also crucial to measure carefully, keeping in mind that 1/2- and 3/4-inch pipe goes about 1/2 inch into each fitting. Have a home center or hardware store employee cut and thread pieces to these exact measurements. A more flexible strategy is to estimate your pipe and fitting needs. Then you can buy long pipes as well as a variety of nipples—short lengths of threaded pipe ranging from 1 to 12 inches. Also buy extra couplings. When you come close to the end of a run, you probably can create the correct length simply by combining nipples and couplings.
It'll take about an hour to cut into a line and install several fittings and pipes. Prepare for the project by shutting off water. Also know that threaded pipe must be installed consecutively, meaning you cannot break into a line unless you use a special fitting called a union. If there is a nearby union fitting, you may be able to avoid cutting a pipe.
Shut off water to the line. To tap into the middle of a line when there is no nearby union fitting, cut through a pipe with a reciprocating saw equipped with a metal-cutting blade or with a hacksaw. Unscrew the pipe on both sides of the cut.
Before threading a pipe into a fitting, wrap the threads with several windings of pipe-thread tape. With the pipe end facing you, wrap clockwise. Or brush pipe joint compound onto the threads of the pipe end and the inside of the fitting.
Twist on a pipe or fitting by hand. If it does not turn easily, the joint is not straight and the threads are crossed. Back up and try again. Then firmly tighten each pipe or fitting using a 14-inch pipe wrench. You may need a second wrench to hold the adjacent piece steady.
Once the tee-fitting for the new line is installed, add a nipple and slip on the nut for the union, checking that the threads are toward the joint. Apply tape and install half of the union. Set the second half of the union in place and measure for the final section of pipe.
Attach the second half of the union to the final piece and install. The union halves should line up so they can set against each other. Slip the union nut up and hand-tighten. Then fully tighten the nut with a pipe wrench to complete the union.
To install a dielectric union, screw the threaded part onto the steel pipe. Before sweating the brass fitting of the copper pipe, slip on the nut and sleeve and push them well away from the heat of the torch. Once the fitting is sweated and cools, join the two parts. Use only groove-joint pliers to tighten the nut.