Chainplates are typically hidden in at least some areas. Being hidden and in areas with poor air contact, they are frequently subject to crevice corrosion
which attacks stainless rapidly and invisibly. Pulling them for inspection
is a chore that often gets skipped. I think I read somewhere that 40% of dismastings are due to chainplate failures, and crevice corrosion
is a leading cause of that.
Take your existing chain plates and inspect them with a magnifying glass in areas that are not exposed to fresh air - so look where they pass through the deck
or lie against a surface. And if they are painted, beware that paint
off creating perfect crevice corrosion sites (never paint
stainless). Look for small pits, 1mm or less in diameter. Especially look for clusters of these. Then, take a dremel tool and start digging like a dentist. You'll find these pits just go on and on, often changing course, and often exploding out creating planes of failed material. Dig them all out and see how much you have to remove to stop the rot
. You can remove a few percent of the cross sectional area of your chainplates without worrying much about loss of strength. I suspect after you do this you'll reconsider Titanium as it does not suffer from this.
So, I'm planning on replacing our chainplates with Ti when the time comes. My machinist friends tell me it's not hard to weld (not that I'd want to rely on a weld to fix a crack....) and is easy to machine.
FWIW, Brion Toss - a rigger here in the PNW who's written a nice book called the Rigger's Apprentice - also suggests Titanium. The cost of materials is not much higher than SS and anyway, most of the cost is likely to be labor.