mmm last ersa I had the iron lasted a week....

But that was long ago.
Indeed I suspec ttips is big bussiness, many 'long life' tips start corroding
rather fast at the not prepared end it seems.
Yes I use them to weld plastics too ;-)
It has to do with tip temp, and the water in one's sponge, and the
oxidizing effect of the flux.
Tip temp is the biggest. A really hot tip wiped on the sponge will
corrode far worse than a cooler tip. It depends on the number of
layers that are attached to the via for thru hole and SMD can always
be soldered at proper, cooler temps. Almost every production line I
have ever walked down that had adjustable temp irons, they were set to
nearly 850 degrees F, chugging away in their stand... Corroding very
quickly.
I like my Metcall, which I turn off when I am not using. The tip
heats in 6 seconds flat, and lasts for years.
For heavier work, I do like an adjustable type iron, and a real good
one, cheap tips and all, is a nice Edsyn. Great, high value
production line quality, constant duty cycle (per shift) irons and
tips. Instead of turning it off, I just reach over and turn it down,
and then back up right before I use it. Works great to extend tip
life. Big blobs of solder on it while in use doesn't do much for it
because with the big blob of solder came big gobs of flux.
Ny tip is wiped very clean. I turn off the iron, and right as it is
cooling toward 500, I add a small drop to my tip
faces/nose/whateveryouwannacallit. The temp drops even lower, the
solder solidifies, and the flux quits acting on the metal. Now that
it is cool and solid, I can wipe the excess flux off of that solder
drop, while it is still hot on the sponge, further cooling the tip for
the night's rest. My tips have always lasted for months longer than
anyone else's. It's all about chemistry and heat.
Now, get the flux out! ;-]