Ahoy Sailingdog,
We've only anchored about 2 dozen times since this past May! In the last four years the longest we've left our anchor in the mud may have been for a few nights before we raised the anchor and moved, even when we were in Norfork, VA anchored off Hosiptal Point for just over a week. So I suspect the opportunity for crevice corrosion to acumulate is minimal.
David,
Crevice corrosion begins nearly immediately once stainless is devoid of oxygen and in salt water. These effects are cumulative. A number of yeas ago I dropped a $350.00 stainless Schaefer genny car over board one day while washing my boat. I dove but could not see nor find it without a dive light. It was three weeks before I could get a diver to retrieve it. The block was destroyed and heavily pitted in a very short amount of time sitting in the very silty soft mud. I tired to polish it but it was to no avail as the surface was so pitted.
An important point about stainless chain is that the welds on stainless chain have usually not been relieved or passivated from the welding process as it is quite expensive to do this, even for quality anchor chain companies like Acco, Peerless etc. who sell 5/16" ss chain for $20+ per foot.. These welds may develop crevice corrosion relatively quickly, within days, under water and cannot easily be inspected. They can also develop galvanic corrosion because the weld stick is not always the same composition as the extruded chain stock.
The main point is that stainless can be destroyed when buried in oxygen-starved bottoms in SALT water. This is part of the reason the alloy in prop shafts is not 316L though at the surface the oxygen content in the water may be hing enough to prevent crevice corrosion & micro stress cracking.
These photos of stainless chain were posted on another forum by a member for RI.
And a stainless shackle used with galvanized chain. This photo and the quote below were by Alain Poiraud the author of "The COmplete Anchoring Handbook" and also the inventor of may anchors such as the Spade:
Well the following photo is not exactly chain.. but shackle.
this shackle was not used on a mooring line but between a galavanised chain and anchor..
I will NEVER use a stainless steel anchor on my own boat..
You'll probably never have a problem with your size boat but do be aware that stainless can fail with little warning while still looking fine and that any crevice corrosion or micro stress cracking is cumulative. It's just good info to know.
The thing that scares me most about your chain is the dubious lack of information on the vendors web site. It's certainly a good thing that you over sized it.
I see no certifications for that chain, no country of origin not even NACM specs or a statement that the chain meets NACM specs..? You've put your trust into something that lists no certifications, nor country of origin, and sells for far less than comparable chain from well respected & highly reputable manufacturers. For example 5/16 US made G4 grade 316 stainless chain sells for about $20.50 per foot while the chain you bought sells for $6.25 per foot. As Craig said the quality of stainless you'll want to use in any anchoring system is VERY expensive.
The maker of my mooring pendants, a Maine based cordage supplier, has to test each lot of stainless thimbles they receive into stock because the manufacturing and quality control has totally gone to pot with their foreign supplier. They can no longer even source these thimbles in the US so are forced to run lots through batch metallurgy testing because the quality of the stainless is so erratic.