You can weld a cap on one end of the pipe and pound it full of really dry sand and then weld a cap on the other end but make sure that there is a hole in each end to let moisture escape if there is any in the sand. Heat up the pipe to a red color and bend away. The sand supports the pipe so that it won't collapse. You could also fill the pipe with lead and cold bend it after it solidifies and then melt it out. Practice on a scrap and be carefull. Good luck.
