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Comment by lbrindze | Hacker News Reader

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...

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I worked for a sailmaker in the Netherlands who also did rigging. You really get to appreciate the difference if you see saltwater exposed rigging after a year or two from slightly different steel formulations, one still pristine, the other looking as though someone is pulling a bad joke on your with rust colored paint. Also: maintenance made all the difference, people that would immediately fix a small issue were often able to arrest it without further damage. But ignore it for a while and one thing leads to another.

edit: as to your point regarding crevice corrosion: yes, that is very nasty indeed, especially because a visual inspection will typically turn up nothing out of the order, all it takes is a bit of trapped moisture and some time.

What would u use for a floating scaffolding or buoy that you want to last in sea water?

(Yes, we can tow it to shore for inspections, but would rather not)

> that you want to last in sea water?

How long?

Under what kind of load?

Well, the payload has a 20 year life time.

Solar panels, navigational lights, etc. Hopefully very little physical contact with other man made objects.

A decade of sea life before some sort of land refurbishment would be a nice value for the excel.

Is aluminum an option for your structural loads? If so I would pick that before I'd even look at steel. Check out 6061 if that will work for you.

Here is a nice little article comparing two common marine grade aluminum alloys:

https://www.marinealu.com/a/marine-grade-aluminium-5083-vs-6...

thanks!!

So many helpful responses here.

most objects like this I have passed in the water seem to be made of some sort of painted steel. I think this is a good combination of durability vs economical. I suspect your electronics will go long before anything corrodes away to nothing, since in my experience its always the electronics that fail first (even when properly sealed for marine use).

Note that the main issue with any barrier coating (assuming there are no collisions) is going to be due to sea life living on/underneath your object and slowly breaking down the material. A copper based metal (read bronze) could be interesting (but expensive) since it tends to stand up fairly well in marine environments and has biocidal properties that prevent fouling/growth. Also very clear to visually inspect since green means good and red means bad which I always thought was very easy to remember.

edit: re-reading your initial comment it looks like you are describing an autonomous vessel of some sort. I used to work at a company that produced such devices and they were made out of composite plastics (which have their own issues that cause them to break down eventually in the water as well).

> autonomous vessel of some sort.

Actually just a large floating shed to support all those panels.

But yeah, there are multiple moving pieces (floating?!) involved.

Would love to chat in the future and brain storm, if u want to leave your details in my profile puppet mail.

are you constructing a floating tower to mount microwave panels for HFT?

I'd look at the nickel alloys, Inconel 625 and Hastelloy C22 would be a good start. They should be orders of magnitude more corrosion resistant than stainless steel and still have respectable strength. Of course they are more expensive and harder to fabricate.

The tooling alone will cost a small fortune though.

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