Sounds like arrogance.
Given that there hasn't been any known issues with the steel provided, perhaps she's correct that the requirements of the test were stupid. But still not right.
I'm not a metallurgist, but I did take a class at MIT on the subject and worked in a metallurgy lab for a couple of summers. The temperature of steel has an effect on the nature of fractures that can occur. Ductile fractures start at a crack and the steel deforms as the crack widens. This is the way most everyday metals under everyday circumstances act. The deformation absorbs energy and dissipates the forces acting on the metal. If this occurred in a beam, it might be observed to be deformed before a catastrophic failure happens.
Brittle fracture is different. A crack forms and it travels rapidly like breaking glass. Such fractures travel through the metal at the speed of sound through the metal (over 2000 ft/sec for steel). Pipelines in Alaska can experience such fractures. Such a fracture could travel thousands of feet because at the point of fracture there is no pressure drop at all (since that drop in pressure would travel at the slower speed of sound though natural gas).
This is a concern in Alaska because a piece of steel can exhibit ductile fracture behavior at ordinary temperature but transition to brittle fracture at lower temperatures. This transition point depends on the steel composition and its history. The history of the steel includes heat and mechanical treatments during it's production, but also the stresses put on it during its use such as welding, shaping and forming, vibration, and even exposure to radiation (which will occur in some parts of a submarine since they contain nuclear reactors). I have no idea how the steel was intended to be used, but conceivably there could be good reasons for the -100F requirement even if the steel was never going to come close to this temperature. (For example, I know nothing of the relationship of radiation embrittlement and the ductile-brittle fracture temperature transition.) So while the testing requirement sounds "stupid" it is perhaps even stupider to ignore it.
1) Just because the testing requirements say -100 °F but the temperatures will "never" get there is false.
2) There is a direct correlation between fracture toughness at various temperatures and impact testing, but testing may need to be at a different temperature than operation conditions to successfully validate the material.
Regarding 1, rapid release of a compressed gas can reach cryogenic temperatures shockingly fast, even if the surrounding environment will never reach those temperatures. This principle is widely used[0] and the correct conditions can occur in everyday situations. For example, vessels meant for operation on the Texas coast are routinely designed to withstand -20°F temperatures despite the fact that the lowest temperature ever recorded in the area is 10°F.
Regarding 2, there has been nearly a century of intense research into fracture toughness and how it correlates with low temperatures. The American Society of Mechanical Engineers (ASME) and American Petroleum Institute (API) have published gobs of (paywalled) articles about correlating minimum design metal temperatures and fracture toughness, although here's[1] an older U.S. DOD document from 1981 outlining their findings in guns, specifically.
[0]: https://www.nexflow.com/blog/vortex-tubes-use-compressed-air...
I'm not even a metallurgist, and yet I know metals and other materials[1] can lose their strength at low temperatures.
[1] https://en.wikipedia.org/wiki/Space_Shuttle_Challenger_disas...
I'm not defending her actions, but isn't the coldest ocean water possible still going to be warmer that 24°F? How would a submarine ever get to the top of a mountain at the South Pole (where the -100°F temps are)?
Evaporative cooling by definition cannot cool below the wet-bulb temperature.
Right. The absolute value is related to the evaporation process, which is affected by wind.
> Evaporative cooling by definition cannot cool below the wet-bulb temperature.
Wet bulb temperature is not “the true temperature of the environment”. Besides, that is true for humans as well, so again not any different between living and non-living things.
The main point is that a thing left in a given environment can end up at temperatures lower than that of their local environment. This process depends on the atmosphere in contact with the thing, which depends on winds.
Wind chill is explicitly and only the experienced subjective temperature caused by cold air being continuously replaced by the wind.
For example, take the US National Weather Service's wind chill formula, which only uses wind speed and tempurature as inputs and provides the wind chill in W/m².
Source: https://www.weather.gov/media/epz/wxcalc/windChill.pdf
> Wet bulb temperature is not “the true temperature of the environment”. Besides, that is true for humans as well, so again not any different between living and non-living things.
Wind chill and evaporative cooling are independent mechanisms, and the wind chill value and wet bulb temperature are separate values.
My reply was to your original comment, which said:
> For second the coldest wind chill recorded in the US was -100°F at McGrath, Alaska in 1989.
That value is not the temperature that an object could have reach at that time and place. It is the wind chill, an approximation of how cold it would have to have been on a windless day to make a person subjectively feel equally cold.
That’s just good engineering, and someone doing tests who does not understand that is clearly in the wrong industry.
But it is not possible for sea water, anywhere in the oceans, to be much colder than freezing, nor does the air temperature at sea level begin to approach the coldest temperatures recorded on Earth, which are always recorded at elevation. I can't seem to find the record lowest temperature recorded at sea level, but I can't imagine it could be much lower than a few dozen degrees below 0°F.
The question that comes to me is, why is that -100°F metal test even a standard? On the one hand, it is vanishingly unlikely a watercraft could ever experience temperatures that low or even 50°F above that, and on the other hand, temperature measure goes down all the way to -459.67°F. So why aren't they stress testing at -559.67°F? And if tests at those literally impossible temperatures were required, could we at least agree that that would be objectively stupid? And if so, there must be a way to determine what test temperatures are stupid to test at in a sliding scale diminishing towards test temperatures that are less stupid to test.
Though other comments are intolerant of the metallurgists' actions, fundamentally, she was correct, although it is clearly unethical she faked tests results, her reasons for doing so are not entirely irrational. The more intelligent and the more expert an individual is, the less tolerant they will be when asked to do things they know could never matter. Though the military is famous for requiring irrational actions, such as constantly digging a ditch to only fill it in again (which I believe has something to do with proving compliance and following orders, maybe testing the command structure), the woman was not in the military. While I do not condone faking tests, I have some empathy for her, as it is difficult for intelligent individuals to intentionally do stupid things, especially when they are required to do so by less intelligent individuals. I could only guess that most of HN members are a lot like her, and less tolerant of objectively stupid requirements.
She falsified tests and produced parts that were not up to the specs required by the customer. That is very much wrong, regardless of how justified the specs are.
If the navy is overly pessimistic, the discussion needs to happen with them. Second guessing and assuming that they won’t really need that anyway is what I’d expect from a cut-throat Chinese factory selling in AliExpress, not a supplier for a major western power’s navy.
It also can be useful if these extreme test are better at revealing manufacturing defects. Maybe you literally only want the most perfect 1% of steel coming out of the foundry to actually be used, because you believe that will make a better submarine. In that case, sure maybe -100f is overkill for the specific application but you have to remember these objects are literally designed to have explosives near them. Being EXTREMELY GOOD at resisting brittleness literally will save sailors lives when it comes to close calls from depth charges.
That’s why we test over the operating range for the different parameters, not just at the limits.
> It's one thing for the purposes of science, to know, but my understanding is that engineering and material specifications for an actual thing needs to be more practical, especially for something that already costs $3.5B.
You need to be pessimistic about operating conditions if you don’t want it to fail unexpectedly. That is absolutely critical in engineering. Now, you set the boundary differently depending on the field and the importance of the widget you engineer (tolerances are quite different for a phone than for an aircraft), but the concept itself is part of engineering.
There are cases where practicality is less important than reliability. Things like space probes and a lot of things related to national security. That is one of the reason why they cost billions in the first place.
All metals have a ductile-to-brittle transition temperature. Ductile failures are generally preferred to brittle (think bend/dent vs shatter). Some steels have a D2B temp around 0°C, which makes them basically untrustworthy in colder environments.
The D2B Temp can be lowered by altering the elemental makeup of the metal, controlling the crystal structure, and other various metallurgical techniques. These same techniques are utilized to produce metals with other desirable properties, like increased ductility, higher tensile strength, corrosion resistance, etc.
Casting, especially large complex castings of custom tailored alloys, are temperamental. Controlling the elemental makeup is relatively easy, but controlling the crystal structure is difficult.
My guess is that they were paying for a specific alloy & temper of metal because it had their desired properties, and successfully cast samples would have a D2B below -70°C.
It is a standard & easy test to perform, but I could see how the tech running it would not connect the dots above. That being said, they don't need to know why the test was ordered & paid for, they just need to run it.