I received some images of unusual corrosion failure. Can anyone identify what might have happened here?

How did this happen?
One manifold but many pieces.

Yes, it's cracked alright.

Jack,
I just noticed this...oh well, betterlate than never. Someone has done a clevver job of whittling a manifold out of a pine log.
Jokes aside, this is not actually corrosion, but a high temperature failure in which the material grain boudaries have separated by a creep-rupture mechanism. More so is the case if the material (steel presumably) has an unusually high sulfur content.
John