quiet_2008 know his stuff. Yes, the delta function, is what kills the equipment. Humans do not naturally realize, that the metal does not care that it is hotter than the temperature we perceive as normal. Technically speaking, the whole "temperature" think is misunderstood. There is no such thing as warm and cold.

But, anyway, back to the metal. As long as it is within it stable temperature range, the only thing that metal cares for, is that there is no delta, i.e. that there is no changes.

Electronic components, care that there is no delta in current or voltage.

As to which is cheaper to fix, the parts that wear out of use, are generally cheaper and less significant (with exceptions).

And the parts that will fail because of delta, are generally more expensive and critical.