How do you install a steel pipe union?

Answer 1

Start with one of the pipes you are connecting together. I usually start with the female half of the union. The half that has the nut on it. Slide the nut over the pipe first so you don't forget it. Use pipe dope or Teflon tape on the threads of the pipe. Screw on the female half of the union and tighten it with two pipe wrenches, holding the pipe with one of them. Put the other half of the union on the second piece of pipe you are connecting and tighten it. Now bring the two halves of the union together and screw on the union nut. Do not put any pipe dope or tape on the union itself. It is a dry fit. Tighten the nut while holding the male half of the union. The second half of the union.

-- I always put pipe dope on the union, it helps the union tighten more and it helps keep the threads from corroding together over time, making taking it appart easier.

Answer 2

Either by welding or threading the piping