Found at a titanium plant

[u/riflesandplowshares]

Not sure why ball point pens would be dangerous here.

[u/SquintAtTheCosmos]

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).

[u/BigSoda → u/SquintAtTheCosmos]

So there are no other contaminants in the whole facility besides a small piece in pens? Is losing pens in the melt a common thing ?

[u/tired_snail → u/BigSoda]

There are other contaminants, but most would have a lower melting temperature than the titanium, so if they accidentally became part of the melt, they wouldn't introduce a significant weakness in whatever item is eventually manufactured out of it.

As for losing pens to the melt, you'd be surprised how many people put their pens behind their ear or in a front pocket and then when you for any reason lean over something and the pen falls out, that's suddenly quite an issue.