Background: I worked in the pressure vessel manufacturing industry as a design engineer and have pretty deep experience with designing around brittle fracture.

Background: I worked in the pressure vessel manufacturing industry as a design engineer and have pretty deep experience with designing around brittle fracture. 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-generate-cold-hot-air-simultaneously/ https://www.nexflow.com/blog/vortex-tubes-use-compressed-air... [1]: https://apps.dtic.mil/sti/citations/ADA099736 https://apps.dtic.mil/sti/citations/ADA099736