7 ms·

Why aren't bridges and ships made out of stainless steel? Is it too expensive, or not as strong as regular steel?

denimnerd42 4y ago
There is a steel called Corten where the rust develops a protective layer similar to aluminum and won't rust all the way through. The only issue is it isn't good when exposed to constant water as the rust will wash off and not protect.
- Arrath 4y ago
  Some may also find the rusted patina look less than ideal. Personally I don't mind it at all.
  - denimnerd42 4y ago
    some people use it as an architectural element. they'll build planters, roofs, siding, fences...
- kibwen 4y ago
  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.
denimnerd42 4y ago
Probably just insanely expensive. Just the welding process for stainless alone would add so much.
apatil 4y ago
According to http://www.kastenmarine.com/metalboats.htm http://www.kastenmarine.com/metalboats.htm, mostly cost plus other drawbacks that sound like they would not be blockers if the cost were lower. That author thinks monel would be even better than stainless, but it's even more expensive.
Arrath 4y ago
Cost, primarily. I'm not certain but I believe joins and welds also need further attention to ensure the corrosion protection isn't impaired. Anyway, O&M is the problem for the guy trying to get the next decade's budget approved so if the upkeep is more expensive, hey at least I got this thing built.
- jacquesm 4y ago
  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.
- JohnBooty 4y ago
  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)
  - jopsen 4y ago
    > ...democracy... It's a system explicitly designed to be short-sighted. It's not explicitly designed for that. It's designed to avoid concentration and abuse of power, peaceful transition of power, and to create some level of fairness. Democracy wasn't designed to produce the best society or the most wealthy society. Democracy was designed to avoid dictators/kings and other really bad things :) That said, we often seem to think that we can optimize for something beyond the short term. It's a seductive thought. But experience with communism/central-planning, suggests that maybe it's best to optimize for the short term. At least that works, and produces results in the meantime. It's the same with waterfall software development vs agile software development. Optimizing for the short term and iterating is usually better than to try and plan the future top-down.
HPsquared 4y ago
Cost, basically. Even if it was built, you'd also probably see people stealing parts of the structure for scrap value... Not a good thing to have happen.
alex_young 4y ago
IIRC stainless isn't actually rust proof, especially in applications where there is a lot of interaction with odd chemicals and things like sea water, so bridges may not be an ideal use for the product.
- Ekaros 4y ago
  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?
  - ortusdux 4y ago
    IIRC, Coated rebar can actually fail faster or in less predictable and therefore worse ways. The coating is often damaged during install, but even perfectly coated bar forms cracks eventually. The entire system's galvanic potential is focused on these small exposed areas, causing extremely fast rusting. The coating tends to fail in higher stress areas, which means that not only does the bar fail, it fails in the worst possible locations.
    - dijonman2 4y ago
      Fiberglass rebar is the future: high strength and won’t rust. You can also add glass fiber to cement to increase strength but it’s not nearly as strong as rebar.
    - avar 4y ago
      Don't confuse stainless steel with galvanized steel. The latter is just normal steel dipped in melted zinc, once you're past that thin coating it'll rust just like normal steel does. Stainless steel is an is an alloy, you can saw apart a beam made of stainless 316 and the inside will be just as stainless as the outside.
jacquesm 4y ago
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. The more chromium, the better the rust resistant properties. https://www.pennstainless.com/resources/product-information/stainless-grades/400-series/420-stainless-steel/ https://www.pennstainless.com/resources/product-information/... Is pretty good stuff and https://www.cralloys.com/alloys/17-chrome/ https://www.cralloys.com/alloys/17-chrome/ is possibly better still. If you want (much) better rust resistance than that you are going to be into coatings or active protection such as cathodic protection using a sacrificial material. https://en.wikipedia.org/wiki/Cathodic_protection https://en.wikipedia.org/wiki/Cathodic_protection Coatings work well as long as there is no mechanical abrasion of the coating, cathodic protection works very well until you run out of sacrificial material.
- lbrindze 4y ago
  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...
  - jacquesm 4y ago
    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.
bliteben 4y ago
Almost all metals oxidize. You could build something out of gold or maybe platinum and avoid oxidation, but it would obviously be expensive. The U.S. navy does have some very large aluminum ships such as the Independence Class[1]. These ships are apparently having some teething issues, but it is quite the feat to have a 414 ft long aluminum ship that can go upwards of 50 knots. [1] : https://en.wikipedia.org/wiki/Independence-class_littoral_combat_ship https://en.wikipedia.org/wiki/Independence-class_littoral_co...
- ElectricalUnion 4y ago
  > 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.
  - red369 4y ago
    Very interesting - I’ve always been confused by why aluminium is often stated as being rust-proof, but doesn’t appear to be as useful in the real world. Aren’t there quite a few aluminium engine blocks in cars though? For example, the LS small block is now aluminium. Or do you mean used in marine applications, where rust is an issue? That would probably make more sense (and may actually be implied by the context).
  - bliteben 4y ago
    sorry I annoyed you. I thought I covered both in my post. Feels like you have to walk on egg shells around here least someone correct you.
    - 4y ago
elil17 4y ago
Yes and yes. Stainless is expensive. It's stronger than some types of steel but not as strong as others. It's also difficult to weld. Plus, it's not 100% corrosion resistant - it only offers partial protection.
- scrumbledober 4y ago
  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.
dexwiz 4y ago
In addition to other comments, it's also difficult to weld. Stainless steel retains heat, so prolong welding can warp it. Also unless careful, welding can destroy the Chromium coating, so the area are the weld will rust quicker than the bulk material. When choosing a metal material, it's important to consider not just its innate properties, but it properties during join. Welding can melt the metal surrounding the weld, which can undo many heat treatment or mechanical processes previously used to get the material to the desired specs.
- xyzzy123 4y ago
  Stainless can also be a pig to machine due to work hardening.
kansface 4y ago
Stainless steel is ~5x the cost.
bobthepanda 4y ago
For a plane you want to reduce weight as much as possible, and steel isn’t particularly lightweight. A lot of commercial aircraft have switch to composite materials to reduce weight even further than would be possible with just metals, though that approach has its own drawbacks.

There is a steel called Corten where the rust develops a protective layer similar to aluminum and won't rust all the way through. The only issue is it isn't good when exposed to constant water as the rust will wash off and not protect.

Arrath 4y ago
Some may also find the rusted patina look less than ideal. Personally I don't mind it at all.
- denimnerd42 4y ago
  some people use it as an architectural element. they'll build planters, roofs, siding, fences...
kibwen 4y ago
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.

denimnerd42 4y ago

Probably just insanely expensive. Just the welding process for stainless alone would add so much.

apatil 4y ago

According to http://www.kastenmarine.com/metalboats.htm http://www.kastenmarine.com/metalboats.htm, mostly cost plus other drawbacks that sound like they would not be blockers if the cost were lower. That author thinks monel would be even better than stainless, but it's even more expensive.

Arrath 4y ago

Cost, primarily. I'm not certain but I believe joins and welds also need further attention to ensure the corrosion protection isn't impaired. Anyway, O&M is the problem for the guy trying to get the next decade's budget approved so if the upkeep is more expensive, hey at least I got this thing built.

jacquesm 4y ago
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.
JohnBooty 4y ago
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)
- jopsen 4y ago
  > ...democracy... It's a system explicitly designed to be short-sighted. It's not explicitly designed for that. It's designed to avoid concentration and abuse of power, peaceful transition of power, and to create some level of fairness. Democracy wasn't designed to produce the best society or the most wealthy society. Democracy was designed to avoid dictators/kings and other really bad things :) That said, we often seem to think that we can optimize for something beyond the short term. It's a seductive thought. But experience with communism/central-planning, suggests that maybe it's best to optimize for the short term. At least that works, and produces results in the meantime. It's the same with waterfall software development vs agile software development. Optimizing for the short term and iterating is usually better than to try and plan the future top-down.

HPsquared 4y ago

Cost, basically. Even if it was built, you'd also probably see people stealing parts of the structure for scrap value... Not a good thing to have happen.

alex_young 4y ago

IIRC stainless isn't actually rust proof, especially in applications where there is a lot of interaction with odd chemicals and things like sea water, so bridges may not be an ideal use for the product.

Ekaros 4y ago
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?
- ortusdux 4y ago
  IIRC, Coated rebar can actually fail faster or in less predictable and therefore worse ways. The coating is often damaged during install, but even perfectly coated bar forms cracks eventually. The entire system's galvanic potential is focused on these small exposed areas, causing extremely fast rusting. The coating tends to fail in higher stress areas, which means that not only does the bar fail, it fails in the worst possible locations.
  - dijonman2 4y ago
    Fiberglass rebar is the future: high strength and won’t rust. You can also add glass fiber to cement to increase strength but it’s not nearly as strong as rebar.
  - avar 4y ago
    Don't confuse stainless steel with galvanized steel. The latter is just normal steel dipped in melted zinc, once you're past that thin coating it'll rust just like normal steel does. Stainless steel is an is an alloy, you can saw apart a beam made of stainless 316 and the inside will be just as stainless as the outside.

jacquesm 4y ago

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. The more chromium, the better the rust resistant properties. https://www.pennstainless.com/resources/product-information/stainless-grades/400-series/420-stainless-steel/ https://www.pennstainless.com/resources/product-information/... Is pretty good stuff and https://www.cralloys.com/alloys/17-chrome/ https://www.cralloys.com/alloys/17-chrome/ is possibly better still. If you want (much) better rust resistance than that you are going to be into coatings or active protection such as cathodic protection using a sacrificial material. https://en.wikipedia.org/wiki/Cathodic_protection https://en.wikipedia.org/wiki/Cathodic_protection Coatings work well as long as there is no mechanical abrasion of the coating, cathodic protection works very well until you run out of sacrificial material.

lbrindze 4y ago
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...
- jacquesm 4y ago
  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.

bliteben 4y ago

Almost all metals oxidize. You could build something out of gold or maybe platinum and avoid oxidation, but it would obviously be expensive. The U.S. navy does have some very large aluminum ships such as the Independence Class[1]. These ships are apparently having some teething issues, but it is quite the feat to have a 414 ft long aluminum ship that can go upwards of 50 knots. [1] : https://en.wikipedia.org/wiki/Independence-class_littoral_combat_ship https://en.wikipedia.org/wiki/Independence-class_littoral_co...

ElectricalUnion 4y ago
> 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.
- red369 4y ago
  Very interesting - I’ve always been confused by why aluminium is often stated as being rust-proof, but doesn’t appear to be as useful in the real world. Aren’t there quite a few aluminium engine blocks in cars though? For example, the LS small block is now aluminium. Or do you mean used in marine applications, where rust is an issue? That would probably make more sense (and may actually be implied by the context).
- bliteben 4y ago
  sorry I annoyed you. I thought I covered both in my post. Feels like you have to walk on egg shells around here least someone correct you.
  - 4y ago

elil17 4y ago

Yes and yes. Stainless is expensive. It's stronger than some types of steel but not as strong as others. It's also difficult to weld. Plus, it's not 100% corrosion resistant - it only offers partial protection.

scrumbledober 4y ago
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.

dexwiz 4y ago

In addition to other comments, it's also difficult to weld. Stainless steel retains heat, so prolong welding can warp it. Also unless careful, welding can destroy the Chromium coating, so the area are the weld will rust quicker than the bulk material. When choosing a metal material, it's important to consider not just its innate properties, but it properties during join. Welding can melt the metal surrounding the weld, which can undo many heat treatment or mechanical processes previously used to get the material to the desired specs.

xyzzy123 4y ago
Stainless can also be a pig to machine due to work hardening.

kansface 4y ago

Stainless steel is ~5x the cost.

bobthepanda 4y ago

For a plane you want to reduce weight as much as possible, and steel isn’t particularly lightweight. A lot of commercial aircraft have switch to composite materials to reduce weight even further than would be possible with just metals, though that approach has its own drawbacks.