How do I rust-proof a metal pole?
DA01 is correct about direct contact with concrete to a point. If the steel and concrete are above ground grade and the concrete is beveled enough for any water to run off or not collect around the pipe, then serious rusting will take a very long time. As far as rust proofing the steel pipe, clean the metal very well. Sand off any paint or other materials. Prime the steel with a zinc chromate primer. This is available in spray cans from Krylon.  After 24 hours, coat the surfaces with truck bed liner.  You can buy truck bed liner in either brush on or spray on cans. Use a couple of thin coats and overlap the bed liner down and over the concrete. This will give you a great water/moisture proof covering.  Good luck