Salvaging weapon upgrades

Has anyone written a guide on this? Like, how does the game decide which upgrade to take off the item if it has two on it? Or, why sometimes it decides to give me steel ignots instead of the uprage that is on the item?

I tried taking my runes off of my old armour to put onto my new armour, and all of them worked except my superior absorption rune (which were sold out of the trader at the time, Murphy's law).

It's frustrating, as my brother almost consistently gets salvage materials instead of the item upgrades on the weapons he finds.

http://gw.gamewikis.org/wiki/Salvage

Should answer all your questions,

~Salad

Thanks.