I know that. I wasn't saying that 316 isn't a stainless steel, just that Monel isn't.

BTW, getting back to 304 as a spoke material, there are two grades of 304, standard 304 and 304L with the "L" meaning low carbon. The L grade is more corrosion resistant, particularly when welded as the lack of carbon won't allow it to form carbide inclusions in the weld or body of the metal. That makes 304L more resistant to intergranular corrosion and may be the difference between vulnerable and more durable spokes in Cl- environments.

I just had a Specialized Allez with two broken rear spokes. They seemed strange to me. The failures were near the nipples, but still in the mid-section of the spokes. I looked at the failed ends and they were very ragged. Black straight gauge spokes.

After measuring and inspecting the spokes, I do what I usually do: bend them in half so they'll go into the garbage more easily and not poke holes in the garbage bag. Which is when the spokes "cracked" when I bent them. Huh? Never saw that before.

Bike had signs of some significant rust. Tiagra brake springs REALLY rusted. Other areas as well. Then I looked more closely at the spokes. Sure enough there were "lines of rust" running perpendicular to the length of the spokes in several places.

Ironically, I had watched a YouTube video from Practical Engineering about the tragic failure of a concrete swimming pool ceiling in Switzerland. The stainless steel rods holding the ceiling up failed due to chlorine corrosion, falling on swimmers below, killing several. What are the chances I JUST watched this video?

So I suspected the same phenomenon here. Without a doubt!

So thanks to the OP and everyone who replied about this issue.

Interesting.

an aside: Is it just me who never puts steel in landfill? No matter how small. Everything metal goes in a container and gets taken to the recycling centre every so often.

Don't remember any strange spoke breakages with rear wheels. Just normal breakage.

But I've owned two new bikes with a pattern of spoke failures.

The first was a Bianchi Eco Pista, their early-'80's affordable track bike. The rear wheel was fine. The front wheel spokes were the problem.

I suspect that those spokes were under-tensioned from the factory. Replaced the ones that broke and re-tensioned the rest. It was fine after that.

The second was a Specialized Langster, their aluminum road-geometry fixed-gear bike, which I bought the year it came out.

That one had black spokes, too. Pretty sure they figured that by painting them black, they could get away with using cheap galvanized spokes. I broke so many of those spokes that I ended up just buying a replacement set of wheels.