Re: Cracked Forestay Chainplate
This kind of failure is not unusual with stainless steel, and can be seen on many stainless parts in saltwater service, especially those under cyclical loads just like your headstay chainplate.
We had this happen with one of our jib cars, and if I zoom in close on your photo, I am pretty sure the same scenario presents itself. https://fetchinketch.net/2019/07/26/failure-analysis/
The other place I have seen this happen on our boat is in the shackles on the boom outhaul cars. The usual assumption is they break because of overloading, when they actually have been greatly weakened by nearly invisible crevice corrosion before the failure.
The shape of this piece and its location on your boat means that it is very hard to actually give it a really effective visual inspection, even if it was removed from the boat and in hand.
The best way to prevent it is to be sure than any welding is first class, by somebody who really knows stainless steel, and it is fully electropolished afterwards so there are no pits or cracks for corrosion to get started. Then careful inspection on a regular basis with a magnifier looking for incipient cracks.
Charleston, SC, USA