With this mid pipe, the rust was mostly only around the flanges and welds, so I gently soaked this for days while I was away, in CLR / coca cola mix. That got rid of most of the rust, but gave this a final session in muriatic also for around the steel hangars and there is a curved support rod welded between the resonators that was hard to get at by soaking. I was careful not to get acid inside anywhere.