Ahoy! So you have some pipe that needs to be bent but you don't have a pipe bender. Well no problem! This instructable will show you how to do it using sand and some creativity.
The pipe shown here is 4130 steel - 3/4" in diameter with a wall thickness of 0.035".
The point of using sand is to support the pipe (keep it round) so that it does not buckle when bent. It worked for me!
Plan ahead - the end closest to the bend will likely have to be cut off and discarded.
Step 1: Pack your pipe
The first thing to do is to plug one end of the pipe. I used a small carriage bolt that fit snugly in the end. The next step is to fill the pipe with sand. I used beach sand. The sand should be nice and compact to stop the pipe from buckling. I used a rod to tamp the sand but what really packed it in was tapping (bouncing) the pipe on a concrete paving stone.
Step 2: Bend!
Clamp one end to a form. Here I used a wine barrel planter and then added a rounded block (that just happened to be in my workshop) to get a tighter radius. You will likely need a lot of leverage to bend the pipe. This piece was 4 feet long and it took some muscle to get the bend.
Step 3: Finish it up
Cut the deformed end off. Clean out the sand. I used a piece of string with a rag on the end to get all the sand out.
The picture below shows the slight dimple in the center of the bend. Unfortunately the method is not perfect but I am very happy with how this turned out (the pipe is a new steerer arm for my bamboo box bike http://www.instructables.com/id/Intro-How-to-Design-and-Build-a-Bamboo-Cargo-Bik/ )
One last thing - you can heat up the pipe with a torch before bending to soften the metal and get a cleaner bend. I did not want to mess with the temper of the pipe so I did not do this.