07-19-17, 11:22 AM
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#1989
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Gefallen Engel U-666
Join Date: Jul 2013
Location: On a tilted, overheated, overpopulated spinning mudball on Collision course with Andromeda Galaxy
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The components of failure...and success tests our mettel
1989: United Flight 232 crash-lands after suffering catastrophic failure of its tail-mounted engine, which led to the loss of all flight controls.  < a cracked titanium fan rotor=cause)The flight was en route from Denver to Chicago. Of the 296 passengers and crew on board, 111 died in the accident and 185 survived in total.
Quote:
Post-crash analysis of the crack surfaces showed the presence of a penetrating fluorescent dye used to detect cracks during maintenance. The presence of the dye indicated that the crack was present and should have been detected at a prior inspection. The detection failure arose from poor attention to human factors in United Airlines' maintenance procedures...
Investigators discovered an impurity and fatigue crack in the disk. Titanium reacts with air when melted, which creates impurities which can initiate fatigue cracks like that found in the crash disk. To prevent this, the ingot that would become the fan disk was formed using a "double vacuum" process: the raw materials were melted together in a vacuum, allowed to cool and solidify, then melted in a vacuum once more. After the double vacuum process, the ingot was shaped into a billet, a sausage-like form about 16 inches in diameter, and tested using ultrasound to look for defects. Defects were located and the ingot was further processed to remove them, but some contamination remained. (GE later changed to an improved triple-vacuum process because of their investigation into failing rotating titanium engine parts.)
The contamination caused what is known as a hard alpha inclusion, a brittle part of the metal, which cracked during forging and then fell out during final machining. This formed a cavity with microscopic cracks at the edges. For the next 18 years, the crack grew slightly each time the engine was powered up and brought to operating temperature....
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Ever since, my own impurity and fatigue notwithstanding, I've always wondered about my hard alpha inclusion solidifying in in a vacuum whenever I get on any airliner....or a rented Cessna 172 while 'learning to fly'...and what overworked 'poor human factors' may have inspected my ride?!
...But perhaps I'm just being...Petty
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"Only two things are infinite; The Universe and human squirrelyness; and I'm not too sure about the Universe"
Last edited by Aktungbby; 07-19-17 at 11:43 AM.
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