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Inconel is used in chemical plants for its extreme resistance to harsh chemicals which quickly corrode even the highest-quality stainless steels. Inconel (and i
by reaperman 3y ago
Inconel is used in chemical plants for its extreme resistance to harsh chemicals which quickly corrode even the highest-quality stainless steels. Inconel (and its cousin, Monel) is primarily made from nickel (>70% for Inconel-X, >63% for monel). Stainless steel also incorporates about 10% nickel and 20% chromium. Nickel is very expensive, so if you can get away with using something with less nickel, you'd really prefer to! There are "recent" advances in corrosion-resistant steel with smaller amounts of nickel, like "duplex steel" - duplex 2204 is just slightly less corrosion resistant than 316 stainless, but contains 4% nickel instead of 10%.
You only use inconel when you absolutely cannot use anything less. It costs $2.50/lb compared to $0.80 for 316 and $0.40/lb for mild steel (standard run-of-the-mill steel). Not sure what 2204 costs these days, but will be somewhere between 316 and mild steel. No one wants to pay three times more for material if they don't have to, and also pay extra for specialized machinists who are confident working with a somewhat rare material.
Materials scientists are working hard to create new, cheaper alloys with high corrosion resistance, and it drives a lot of really cool new science! Over the past 1-4 years I've seen some super interesting articles here on HN about new science being discovered around this, but I can't find them at the moment.
That said, Inconel is only 4% denser than run-of-the-mill steel, so it's not going to make a difference which of these alloys fall from space onto your house or head.
- MobiusHorizons 3y agoI think it will make difference which alloy falls from space, because much more of the inconel will be left after the fall. After all, they use it in spacecraft because of how well it handles high temperatures like reentry.
- adrian_b 3y agoIt handles better high temperatures than steel in the sense that it retains its strength at high temperatures, but which are still much lower than its melting point. This does not imply that Inconel is more resistant at vaporisation than steel. It is possible and even probable that it is less resistant (Inconel X has less chromium than many stainless steels and pure nickel has higher vapor pressure than pure iron, so it evaporates more quickly, but the behavior of alloys may be different from their components). Therefore it is not certain that more of the inconel will be left after the fall, it is quite likely that less will be left than from stainless steels with high chromium content.
- MobiusHorizons 3y agoInteresting, I had assumed breakup happened because of structural failures related to aerodynamic pressure and weakened material properties as the material approaches melting. But of course vaporization would account for most of the “burning up” during reentry
- auspiv 3y agoAlso used in oil/gas downhole in corrosive environments (primarily CO2/H2S). Typical tubing size is 2-7/8", which is ~10.4 lb/ft x thousands of feet. Not cheap. https://super-metals.com/news/inconel-alloy-718-and-725-in-oil-and-gas-industry/ https://super-metals.com/news/inconel-alloy-718-and-725-in-o...
- reaperman 3y agoOh my gosh. I did some downhole work analyzing the corrosion of casing and tubing. It boggles my mind that some wells produce enough to justify that. I should have known - it's "only" 5-10x more in material cost; just belies my typical rule-of-thumb intuition.