Good start! - Bit too monochrome (especially the pipe) add some more soft colour variation in there with a low opacity layer in your PSD - The undersurface on the pipe is too similar to the pipe texture. Would be something else. More worn down. Needs more transition from pipe to under surface. - occlusion (black lines) are…
You should check out the Polycount wiki. There's a metal texture tutorial listed there that looks like it's the sort of thing you're going for: http://forums.cgsociety.org/showthread.php?f=46&t=373024 Basically you'll need to look at actual reference and pay attention where things like rust/scratches and wear naturally…