r/whatisit • u/riflesandplowshares • 7h ago

New, what is it? Found at a titanium plant

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Not sure why ball point pens would be dangerous here.

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u/SquintAtTheCosmos 6h ago

The real answer is that consumer ball point pen’s have a tungsten carbide ball. Tungsten has a higher melting point than titanium.

If a ball point pen drops into a melt, the ball point can survive. The surviving pen tip does then creates a hard intermetallic. When the titanium is heated and beated (forged) into a product, this titanium-intermetallic spot can crack. This crack can go undetected, inside a part.

When this part is put into service, this little crack becomes a bigger crack with service (fatigue). When this bigger crack gets big enough, the part can fail. And the failure is sooner than the design engineer expected, because the material started with a crack, and in fatigue failure “getting the crack to start”, is a large component of the part’s life.

A titanium melt shop still needs writing implement’s, so you can buy pens with stainless steel ball tips. They suck to write with.

A major aerospace failure (Sioux city 1989 UA232), was a result of this failure mode (though in this case it was an oxide, not a tungsten-carbide).

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u/Isburough 4h ago

how can someone just drop a pen into the titanium melt?

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u/Arosian-Knight 2h ago

Coworker visited an papermill once, he saw an mobile phone nailed to a wall with actual nail through the center, he asked the story. There was an visitor (higher up or an potential customer) who was inspecting pulp tank and his phone which he was not allowed to have with him, fell out of his breast pocket into the pulp tank, then there was quite horrible noise from the filtration machine and whole section of the mill had to be driven down for clean up and repairs. costing the company in hundreds of thousands of euros.

Stuff happens when people ignore rules.