The Correct Installation of a Stainless Steel Pipe Union


Both stainless steel and gas pipe comes in various lengths, with threads at both ends. However, pipes of any size can be cut and threaded at major DIY stores. Union joints are installed into pipelines so that pieces of pipe in the middle of the line can be removed if desired. A union joint has a central nut, a female end and a male end. Installing the union requires cutting the pipeline and threading the pipe ends on each side of the cut.

Things You'll Need

  • Felt-tip pen
  • Tape measure
  • Rotary cutter
  • Cutting oil
  • 2 pipe wrenches
  • Threading compound
  • Turn off the water or gas system so that nothing is running through the pipe where you will be installing the union.

  • Mark the steel pipe at the point where the union needs to be installed using a felt-tip pen.

  • 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.

  • 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.

  • 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.

  • Take both pipes to a major DIY store to have the cut pipe ends threaded.

  • 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.

  • 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.

Tips & Warnings

  • Though rotary cutters can have large handles, smaller cutters are available to get into confined spaces. If one cannot be found, use a hacksaw to cut through the pipe and have the DIY store cut the pipe ends properly and to length when the ends are threaded.
  • If you have a die and a pipe vise, you can thread the pipes yourself, but most home improvement stores charge very little to thread pipes.
  • If cutting gas pipes, make sure that the gas is off, and that no gas is left in the pipeline.

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