[Kamog]

I think it's because one piece of crystalline armor has a damage resistance of 150 kT, so a hit that does more than 149 kT of damage would destroy it.

EDIT:
Hmm, that's only if your ship has 0 shields left, and then it gets hit by 150 or more damage, right?

If your ship has 10 crystalline armor and say, 100 shields, what would happen?
A 150 damage hit will use up 100 shield points and 50 will get through to the armor, which is not enough to destroy a piece. Then the shield will regenerate by 150 so next turn you would have no damage and 150 shields.

But then if you get hit again, 150 shields will be gone so you would have no shields left, and you get hit a third time by 150 damage, one of your armor would be destroyed.

This doesn't seem to make sense: you are better off to start off with 100 shields than it is to start with 150 shields, because 150 shields would be exactly cancelled out and there will be no regeneration. If you have 100 shields, part of the damage will get through and trigger regeneration, so you end up with more shields at the end of the turn.

But what happens to the 50 damage that got through? Is it carried over to the damage for the next hit?

Also, if you had 20 pieces of crystalline armor, would a hit that reaches the armor cause the shields to regenerate by 300 points? Then it seems that the more crystalline armor you have, the much better it would be, because any hit that doesn't destroy a full piece of armor gives you more shields back. ...or am I misunderstanding something?