how do you prevent items from breaking or failing? it seems a bit of a stretch that someone can upgrade armor to 12+ and not break

I don't think there's a way to prevent armor from breaking unless you're incredibly lucky and manage to get to 12+ without breaking it.

I tried to upgrade +5 item, with blue stone ~ 6 times and got 2 broken and 4 FAILED ;D
As you can see u need to be Lucky,for successful upgrade

I wonder if i upgrade +5 with "blue", can I upgrade +9with a purple stone with no risk, or only +8?

whats exactly what i mean, it dosent seam feasible that someone will take a +20% physical crit damage weapon that costs 30-60mil, and tossing purple stones at it risking destroying the item. especially when purple U50-U55's are 10-80mil a pop and not guaranteed to go up more than one rank. but still see +12 or so weapons and gear

for the chest, the left side and middle usually don't brake they switch back and forth randomly between success and failed

the right side is usually break?

Nope. It's completely random.