I got lost way before the end.
The main point I picked up is that the presence of rust makes the remaining iron rust even faster. Minor points is this there are at least two types of iron oxide, FE2-O3 and FE3-O4.
The FE2-O3 is the red rust, the FE3-O4 is the black rust usually underneath the red rust. The red rust takes more space than the black rust, and once formed, is will lift paint enough to allow more moisture to get under the paint, and now the paint just keeps the steel wet longer, so more rust forms.
I have found phosphoric acid solutions remove the red rust pretty easily, but not so much the black rust. I have had pretty good luck with using electrolysis to remove both types of rust. the process is explained in detail here.
ELECTROLYTIC RUST REMOVAL (ELECTROLYSIS)
Iron rusting is a pain for us working with steel. But in the grand scheme of things, it is the affinity that iron has for oxygen that allows red blood cells to transfer oxygen from our lungs, to our cells, and the CO2 back to our lungs, so we can live.