I was not familiar with these grades, very interesting reading and finding out about them. The most common grades of stainless I have encountered in the marine industry is either 316 (best) or 304 (budget, requires regular cleaning to keep rust free). Both have issues with crevice corrosion and are also very expensive compared to zinc-plated equivalents (which I would never use on a boat since they will effectively disintegrate over a few months). Marine grade stainless often suffers from crevice corrosion and hard to detect failures which is sort of terrifying when you really think about it (things look OK until one day they break without clear visible warning).

For bridges or large-scale industrial applications where you dont care how the metal itself appears, I agree that coatings (especially galvanization) is the best bang for the buck. All of my insights are purely anecdotal though, as a hobbyist...

"Stainless steel is not 'rust proof' it is mostly rust retardant, it has a chromium coating that reduces oxidization but does not stop it completely."

Just to be clear ... you can indeed coat things with stainless steel.

However, most stainless steel objects (like screws or bolts or tools, etc.) are stainless throughout - you cannot abrade or scratch into a non-stainless inner core.

This is unlike, for instance, galvanized hardware which is merely steel with a coating over the top. Galvanized items can, indeed, be mechanically altered to reveal non-galvanized material underneath.

As for my grandparents question:

You can, indeed, buy stainless steel beams, rebar[1], etc. They have all the fantastic properties you imagine and are, again, not merely coated like (for instance) galvanized rebar. They are also extremely expensive.

[1] https://www.stainlesssteelrebar.org/

more difficult than most steel, but still easier to weld than aluminum... also less rust resistant than aluminum... I'm not sure what my point is.

> Almost all metals oxidize.

> The U.S. navy does have some very large aluminum ships

Unfortunately aluminum also rusts, it just happens to be a chemically stable and resistant rusting - but not in a stable enough manner to be mechanically/abrasive resistant, that's why you don't see them deployed in widespread use at stressing conditions like internal combustion engine blocks or fast ship hulls.

From said cited Wikipedia article:

> In February 2020 it was announced that the Navy plans to retire the first four LCS ships. On 20 June 2020, the US Navy announced that all four would be taken out of commission in March 2021, and will be placed in inactive reserve, because it would be too expensive to upgrade them to match the later ships in the class.

Those large aluminum ships crack because aluminum has poor fatigue performance when subjected to repeated cycling. Small aluminum boat? You're probably fine for a lifetime. 400ft aluminum boat? Good luck with that.

Stainless can also be a pig to machine due to work hardening.

Some may also find the rusted patina look less than ideal. Personally I don't mind it at all.

The USX Tower ("The Steel Building") in Pittsburgh is made entirely of Corten, designed to showcase the material when it was first developed. Other than turning all the sidewalks black when it was first weathering it seems to work great, as long as you're into the industrial aesthetic.

I have heard the same. Actually making rusting proof stuff is very hard. Specially if there is any chance of things like acids being involved. Coatings could help, but even then why not just paint regular steel.

Now other thing I wonder is how structurally sound some of the stainless alloys are? Do they have similar characteristics to steels now used?

Yes, this is called electrochemical cleaning. If you don't do that then the weld will be more vulnerable to oxidization because the protective layer that forms on stainless steel will be damaged and upset by the welding process leaving some of the iron in the steel directly exposed to the environment. This then can cause pitting of the surface, which is the beginning of the end.

For such a process to be effective it has to be done immediately after welding. You can use it to try to repair something that is already rust damaged but in my experience the gain from that is mostly a stay of execution, not a perfect solution.

    Anyway, O&M is the problem for the guy trying to get 
    the next decade's budget approved

This is why democracy, while far better than the alternatives, still absolutely sucks.

It's a system explicitly designed to be short-sighted. There is massive disincentive to produce systems and infrastructure that will actually work some distance into the future. The only incentive for politicians is either (a) merely look like they're doing something (b) produce the fastest, cheapest possible thing that they can take credit for when they're up for re-election.

Democracy would only really thrive if the public valued the future, and had some reliable way of judging how our politicians' solutions actually benefit the future. (ex: I value the future, but if we build a bridge today I have no way of judging if it's built to last for 5 years or 500 years)