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How to Replace a Section of Threaded Pipe

Galvanized pipe is notorious for rust, corrosion, and leaks. When this happens, the most prudent solution for a permanent repair is to remove the damaged section and replace it with a new section of threaded pipe.

Replacing a section of threaded pipe is not nearly as difficult as you might imagine, thanks to the wide assortment of threaded sections of pipe that are now standard inventory at most hardware stores and home-improvement centers. These prefab sections come in various diameters and lengths. Many stores will custom-cut and thread a section of pipe if a stock item is not available.

Before you begin the process here, turn off the main water shut-off valve so that no water flows into your home. Then open a faucet at the lowest point in the home to allow the line to empty.

  1. Cut through the damaged section using a hacksaw or a reciprocating saw so that the two pieces that remain can be unscrewed from the adjacent fittings.

    You will need two sections of replacement pipe and a union. The total length of the two pieces of pipe and the union, when fully assembled, must equal the length of 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 1 inch. This accounts for 1/2 inch of threads at either end, which overlap into the fittings.

  2. Remove the existing pipe, using two medium pipe wrenches, one gripping the pipe and the other gripping the fitting, and then pry in opposite directions.

    Removing the old pipe from the fittings may prove difficult. Prying the two wrenches in opposite directions enhances 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, to break down some of the rust and corrosion that prevents the pipe from budging.

  3. Spray the threads within the fittings with more of the penetrating oil.

    Allow the oil to sit for approximately 15 minutes before continuing.

  4. Remove any residue to prepare the area for a new leak-free connection.

    A small wire bottle brush is perfect for this task.

  5. Apply a pipe joint compound to the threaded ends and the threads in the fittings, pressing the compound into the threads with a fingertip.

  6. Insert the ring nut over one of the sections of pipe.

    The union is a fitting that consists of three components: two union nuts and a ring nut. The union nuts attach to the replacement sections of pipe where they join together. The ring nut acts to join the two pieces.

  7. Screw both sections of pipe into their respective fittings.

  8. Tighten both sections of pipe and then the ring nut.

    Just as with the removal process, using two pipe wrenches makes reassembly easier and safer.

After the section is replaced, complete the process by turning the main water supply on and checking for leaks.

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