Having lived on small yachts for many years I have had to buy new chain a few times.
Because chain and anchors are a yachts insurance policy I have tried to do the right thing and buy the best and that has been recognized as being pwb chain which happens to be also Australian made.
No cheap Chinese chain for me, but to my amazement the chain was lucky to get 6 months before it was totally rusted I didn't even get to end for end it .
I know I am not the only one who has had this happen as a mate bought his at the same time and his has done the same thing as well.
What happened to chain lasting for years and then being able to have it regalvanised ? , this stuff is not cheap are we supposed to except 12 months as the standard and change it every year as we do with the antfouling .?
A few questions,
PWB chain is marked as such on every link from memory, was yours?
Where did you buy it from? Know of places selling chain as PWB when it's not
And finally, even if it's rusty you can get it re galvanized.
Wow, unusual.
Contact PWB direct, reckon they might help you out. May of been a bad batch
Bought the same in 8mm from Whitworths five years ago. Didn't last much longer.
Went to 10 mm in the other "quality" chain they keep. Idea was at least there is a bit more steel? Gal has lasted a bit better. Still not nearly as long as you might hope for the price.
Not sure how true it is, but have been told even the good chain is sent to China to be galvanised?
Whether you anchor on sand or mud and how often the boat swings can make a big difference? Still, that 8mm PWB I bought was ****! 
