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The Navy builds its ships with steel, and the grades of steel used in the construction can experience rust. Solutions: Switch to 100% stainless steel. Stainle

The Navy builds its ships with steel, and the grades of steel used in the construction can experience rust. Solutions: Switch to 100% stainless steel. Stainless steel is an alloy and contains a minimum of 11% chromium. This allows the formation of a protective film of chromium oxide which acts as a shield against rust. The protective film will re-form if damaged. Corrosion resistance can be further enhanced with the addition of nickel. Use a weathering steel, also known as “COR-TEN” steel which contains up to 21% of alloying elements such as chromium, copper, nickel, and phosphorous. The alloys form a protective rust patina which reduces the corrosion rate with time. COR-TEN steel tends to be cheaper than stainless steel. Galvanized steel. Galvanizing is a method of rust prevention. This is accomplished through hot-dip galvanizing or electroplating. The iron or steel object is coated in a thin layer of zinc. This stops oxygen and water from reaching the metal underneath but the zinc also acts as a sacrificial metal. Zinc is more reactive than iron, so it oxidizes in preference to the iron object. The zinc oxide layer prevents the formation of iron oxide, thus eliminating the possibility of rust forming.

GekkePrutser 4y ago
That's a good idea. Everyone knows chromium does not contain any Rust. Joking aside: There are many ways to prevent rust, though I think environmental concerns are also an issue. Galvanising might leak heavy metals into the sea? And chrome is also a pollutant. Iron is not.
incompatible 4y ago
Stainless steel is pretty expensive, but I suppose it would be no big deal for the US Navy. I thought they used sacrificial anodes to stop rust.
- GekkePrutser 4y ago
  I don't think those anodes are 100% effective though? I've seen many ships that have them and still have signs of rusting.
- wiredfool 4y ago
  I think that the sacrificial anodes work for places where it’s a hull in electrolyte, it wouldn’t necessarily work for salt spray in the superstructure.
- jhgb 4y ago
  Is it mechanically a 100% replacement for traditional steel used in naval construction? I recall specialty alloys like Wotan steel being used in WW2 warships. Perhaps such kinds of armor are not in vogue anymore, but corrosion resistance surely isn't the only requirement for naval construction, even if it's an important one. I'm not a metallurgist though, so I have no idea of all the implications of using stainless steel pervasively in naval construction.
qchris 4y ago
I don't know if there's a name for this phenomenon, but it's sort of like an invisible Chesterton's fence. "Just make them out of a different steel" feels like a idea that is elegant, but even as someone that's never built a ship, I have to imagine there's some good reason why they're built out the materials they are, and why a simple material change is unlikely to be a solution. Maybe I'm wrong (it's not like organizations haven't done dumb things before despite a having a good simple solution), but it really feels like that's probably not the case here.
- wiredfool 4y ago
  Stainless doesn’t really hold up in saltwater, with the exception of a few grades. The material properties (toughness, ductility, brittleness, weldability) can also be significantly different than non stainless. Corten can work in less aggressive environments, but it has been known to fail to provide the expected protection in places with more acidic rain than was expected. Salt water is really aggressive. Hot dip galvanizing does work, and is common for small boats, dock fittings, and other smaller items. There are also likely sacrificial anodes on the ship made of zinc.
  - rwmurrayVT 4y ago
    There are many sacrificial zincs on ships, including in tanks.
- blagie 4y ago
  I don't know about modern ships -- I suspect a lot of this is classified -- but as an example, the WWII Bismark had a hull which was around a foot thick, as armor. (1) Rust wouldn't go all the way through. Surface rust isn't a problem. (2) You want high-quality armor; toughness is key. Steel composition should be primarily chosen for toughness-to-weight (3) And cost, of course. Stainless would have been expensive, and given little upside, and potentially a lot of downside in terms of less effective armor plating. Obviously, modern ships are entirely different (much less armor, actually, instead relying on active defenses), but I assume there are sensible reasons for materials choices.
wiredfool 4y ago
You’re not a marine engineer, are you?
- Victerius 4y ago
  ... I'm not.
robbiep 4y ago
So surprising no one involved in a multi billion dollar industry hasn’t tried to consider the solutions you propose
smiley1437 4y ago
> Use a weathering steel, also known as “COR-TEN” steel which contains up to 21% of alloying elements such as chromium, copper, nickel, and phosphorous. The alloys form a protective rust patina which reduces the corrosion rate with time. COR-TEN steel tends to be cheaper than stainless steel. If the point is for the ship to look 'not-rusty', Cor-Ten is probably about as far from that goal as one can get
lazide 4y ago
Stainless steel is prone to stress cracking corrosion (SCC) in saltwater environments which causes catastrophic sudden failure when under load. You REALLY don’t want that in a ship. Galvanizing basically works like anodic protection. Already used, but a galvanized coating will disappear (even a very thick one) in just a few years at sea, and can’t be reapplied in the field effectively. Paint works better. Cor-ten works best where the rusting surface isn’t exposed to wear directly (like a ship hull). Something like a bridge span member or a shipping container side, or a side of a building. It has to rust for it to work. If exposed to a particularly corrosive environment it still rusts through pretty quickly. A lot of Corten products (like shipping containers) still get painted to slow the process down. Ships have desired operational lives of 20+ years. Painting and rust removal is the only way that works.
- msrenee 4y ago
  I honestly don't know too much about the maintenance that goes on when a ship is underway, but I do know that stainless releases hexavalent chromium when you're welding on it and requires a number of extra considerations for safety. So any sailor doing any kind of patching or repair to whatever part of the hull is stainless needs extra education and extra PPE. As well as monitoring for blood levels and other health issues. Nothing insane, but an added inconvenience in an already inconvenient job.
Eddy_Viscosity2 4y ago
Wood is also corrosion resistant, maybe they could make the ships out of wood. /s
- nradov 4y ago
  The US Navy literally built some ships out of wood up through 1994. Those were minesweepers where minimizing the magnetic signature was more important than strength or corrosion resistance.
rland 4y ago
You can’t just replace a material like that in something as large as a ship. You need to have the right toughness, ductility, fatigue, etc. Steel varies a lot. You can buy a 1000 page book that just lists different steels, along with their material properties. Saying “just use stainless” is kinda like saying “just 3d print it” or “just make it out of carbon fiber”

GekkePrutser 4y ago

That's a good idea. Everyone knows chromium does not contain any Rust. Joking aside: There are many ways to prevent rust, though I think environmental concerns are also an issue. Galvanising might leak heavy metals into the sea? And chrome is also a pollutant. Iron is not.

incompatible 4y ago

Stainless steel is pretty expensive, but I suppose it would be no big deal for the US Navy. I thought they used sacrificial anodes to stop rust.

GekkePrutser 4y ago
I don't think those anodes are 100% effective though? I've seen many ships that have them and still have signs of rusting.
wiredfool 4y ago
I think that the sacrificial anodes work for places where it’s a hull in electrolyte, it wouldn’t necessarily work for salt spray in the superstructure.
jhgb 4y ago
Is it mechanically a 100% replacement for traditional steel used in naval construction? I recall specialty alloys like Wotan steel being used in WW2 warships. Perhaps such kinds of armor are not in vogue anymore, but corrosion resistance surely isn't the only requirement for naval construction, even if it's an important one. I'm not a metallurgist though, so I have no idea of all the implications of using stainless steel pervasively in naval construction.

qchris 4y ago

I don't know if there's a name for this phenomenon, but it's sort of like an invisible Chesterton's fence. "Just make them out of a different steel" feels like a idea that is elegant, but even as someone that's never built a ship, I have to imagine there's some good reason why they're built out the materials they are, and why a simple material change is unlikely to be a solution. Maybe I'm wrong (it's not like organizations haven't done dumb things before despite a having a good simple solution), but it really feels like that's probably not the case here.

wiredfool 4y ago
Stainless doesn’t really hold up in saltwater, with the exception of a few grades. The material properties (toughness, ductility, brittleness, weldability) can also be significantly different than non stainless. Corten can work in less aggressive environments, but it has been known to fail to provide the expected protection in places with more acidic rain than was expected. Salt water is really aggressive. Hot dip galvanizing does work, and is common for small boats, dock fittings, and other smaller items. There are also likely sacrificial anodes on the ship made of zinc.
- rwmurrayVT 4y ago
  There are many sacrificial zincs on ships, including in tanks.
blagie 4y ago
I don't know about modern ships -- I suspect a lot of this is classified -- but as an example, the WWII Bismark had a hull which was around a foot thick, as armor. (1) Rust wouldn't go all the way through. Surface rust isn't a problem. (2) You want high-quality armor; toughness is key. Steel composition should be primarily chosen for toughness-to-weight (3) And cost, of course. Stainless would have been expensive, and given little upside, and potentially a lot of downside in terms of less effective armor plating. Obviously, modern ships are entirely different (much less armor, actually, instead relying on active defenses), but I assume there are sensible reasons for materials choices.

wiredfool 4y ago

You’re not a marine engineer, are you?

Victerius 4y ago
... I'm not.

robbiep 4y ago

So surprising no one involved in a multi billion dollar industry hasn’t tried to consider the solutions you propose

smiley1437 4y ago

> Use a weathering steel, also known as “COR-TEN” steel which contains up to 21% of alloying elements such as chromium, copper, nickel, and phosphorous. The alloys form a protective rust patina which reduces the corrosion rate with time. COR-TEN steel tends to be cheaper than stainless steel. If the point is for the ship to look 'not-rusty', Cor-Ten is probably about as far from that goal as one can get

lazide 4y ago

Stainless steel is prone to stress cracking corrosion (SCC) in saltwater environments which causes catastrophic sudden failure when under load. You REALLY don’t want that in a ship. Galvanizing basically works like anodic protection. Already used, but a galvanized coating will disappear (even a very thick one) in just a few years at sea, and can’t be reapplied in the field effectively. Paint works better. Cor-ten works best where the rusting surface isn’t exposed to wear directly (like a ship hull). Something like a bridge span member or a shipping container side, or a side of a building. It has to rust for it to work. If exposed to a particularly corrosive environment it still rusts through pretty quickly. A lot of Corten products (like shipping containers) still get painted to slow the process down. Ships have desired operational lives of 20+ years. Painting and rust removal is the only way that works.

msrenee 4y ago
I honestly don't know too much about the maintenance that goes on when a ship is underway, but I do know that stainless releases hexavalent chromium when you're welding on it and requires a number of extra considerations for safety. So any sailor doing any kind of patching or repair to whatever part of the hull is stainless needs extra education and extra PPE. As well as monitoring for blood levels and other health issues. Nothing insane, but an added inconvenience in an already inconvenient job.

Eddy_Viscosity2 4y ago

Wood is also corrosion resistant, maybe they could make the ships out of wood. /s

nradov 4y ago
The US Navy literally built some ships out of wood up through 1994. Those were minesweepers where minimizing the magnetic signature was more important than strength or corrosion resistance.

rland 4y ago

You can’t just replace a material like that in something as large as a ship. You need to have the right toughness, ductility, fatigue, etc. Steel varies a lot. You can buy a 1000 page book that just lists different steels, along with their material properties. Saying “just use stainless” is kinda like saying “just 3d print it” or “just make it out of carbon fiber”