I have a CB500-4,
I fitted my 4 pipes in around 1991.they cost a princely sum of £250 c/w brackets,
during their life,I try never to ride less than 10mls.
make sure they get very hot !!
also make sure the drain holes are clear,
most of my corrosion was/is caused by salty roads,
after over 20yrs,they are not "as new" surface damage,but hell,the bike gets ridden,
my thoughts are that the exhausts last much longer now,because of unleaded fuel,
check also on car exhausts,
the lead additive cause a chemical reaction with the mild steel,now its not there to do so,
keep them clean,externally,and hot internally,
and you could have them for years and years
check these pics