If your home is more than 30 years old chances are it harbors some galvanized pipe. While this type of pipe was used primarily for residential water systems, it also was employed in the construction of residential drain, waste and vent systems.

Actually, galvanized pipe is iron that has been coated with zinc to protect it from rust and extend its life. Unfortunately, nothing is forever or at least not with galvanized pipe, as many folks no doubt have discovered.

Copper pipe has been widely used in the last three decades for residential water systems and is by far the leading type nationwide. Various types of plastic have replaced iron pipe for the drain, waste and vent systems in most modern homes. Although not widely, plastic pipe is also being used in lieu of galvanized and copper for residential water systems.

Non-galvanized iron pipe or "black" iron pipe continues to be popularly used for residential natural gas and propane gas systems.

Still, with all of the modern alternatives to iron pipe, a majority of homes in this country still house galvanized pipe. Whereas many people have opted to replace galvanized water piping with modern alternatives, due to the often disruptive process, many wait to combine the task with impending remodeling projects. Others don't have the budget or see the value in replacing the pipe and simply prefer repairing an occasional leak. It is to the latter that we direct today's discussion.

Copper pipe is joined by "sweating" or soldering the connections. Plastic pipe is either glued or clamped, depending on the specific material being used. Both of these methods are in sharp contrast to iron pipe wherein the connections are made via threaded ends and fittings.

Replacing a section of threaded pipe is not nearly as difficult as one might imagine thanks to the wide assortment of threaded sections that are now standard inventory at most hardware stores or home improvement centers. This material is offered pre-fab in various diameters and lengths. Furthermore, many stores will custom cut and thread a section of pipe in the event a stock item is not available. This saves the do-it-yourselfer from having to rent or purchase a costly set of iron pipe cutting and threading tools.

The first step in replacing a section of damaged water pipe is to turn off the water and open a faucet at the lowest point in the home to allow the line to empty. Next, cut through the damaged section using a hacksaw or a sawzall. This will allow each of the two pieces that remain to be unscrewed from its adjacent fitting.

That brings us to the single most difficult aspect of replacing a section of threaded pipe, the removal of the existing pipe from the fittings to which it is attached. Over time these connections can become frozen ö making them virtually impossible to separate. Using two medium pipe wrenches in opposing directions (one gripping the pipe and the other the fitting) will provide the leverage needed to break the connection.

If at first you don't succeed in loosening the connection, spray the area with a penetrating oil or lubricant such as WD-40. This will act to break down some of the rust and corrosion that is likely preventing the pipe from budging. Once the pipes have been removed, spray the threads within the fittings with more of the penetrating oil. Allow the oil to sit for approximately 15 minutes, then use a small wire bottle brush to remove any residue that might remain and prepare the area for a new leak-free connection.

In order to put things back together, two sections of pipe and a union will be needed. The total length of the two pieces of pipe and the union must be equal in length to the damaged pipe. When calculating the overall length of material needed, measure from the face of one fitting to the face of the opposite fitting and add one inch. This accounts for one half inch of threads at either end that will overlap into the fittings.

The union is a fitting consisting of three components; two union nuts and a ring nut. The union nuts attach to the replacement sections of pipe at the location where they are to be joined. The ring nut is inserted over one of the sections of pipe and acts to join the two pieces.

Prior to assembling the pipes, apply a pipe-joint compound to the threaded ends and the threads located within the fittings. Press the compound into the threads with your fingertip. Just as in the removal process, using two pipe wrenches will make reassembly easier and safer.

Complete the process by turning the main water supply on and checking for leaks.