Shadow pierce question

Hello I have a question about shadow pierce upgrade gouging rush (the first) it says: each hit of the shadow piercer has a 15% chance of reducing your target's armor by 10%. This effect lasts after some seconds or it's permanent? The 15% means that if I have the last upgrade (atm not plan to use it but who knows)that allows me to target 3 times when charged I will have 15% chance 3 times to get the enemy armor reduced? For example in a situation where there is a boss with a mob and the pierce attacks boss-mob-boss I will have 2 chances to reduce the boss armor of 10%? The 10% reduction stacks? If yes how many times? The 10% is calculated on actual armor not on the armor previous the first debuff right?Do you suggest to me to put this upgrade or not? I want to play both in elite maps and pvp and I think I will use theese skills : pierce, razor, aimed and nox for pve and heal pack instead of razor in pvp or boss fight.
Thanks in advance for your replies.

i think its permenant.

i think its permenant.

it's impossible to be permanent. no debuff in this game are permanent, it would be too stronger. if you hit the same enemie 2 times you have 15% chance for all 2 your attack. the skill you want to use are great, maybe you have to use heal every time and change the other 3 depending on the situation. :) hope i helped

i don't think it's permanent.