I know my duck egg shells are super tough, and I've had some where the ducklings have pipped (can you call it pipping when it leaves a huge gaping hole? lol) and then rested, and been unable to get the rest of the way out because the membrane has dried. I cracked the shell around with light pressure so it made a circle from the hole they made, and depending on how bad the membrane was, sometimes I've ripped the membrane partway, then I put the baby back in the bator and see if they can get out on their own. Most have. I had to help one out completely because there was some blood in the sack (it was weird), and it dried hard as a rock. That ducky is doing well though he's smaller than the rest of the group. I used a cup of warm (100-110 degree--warm to the touch, but not too hot ) water and slowly worked the membrane off of the duck, then popped him back in the bator to dry and rest up until he was running around, then added him to the brooder.
Helping them out is not advised if there is any other choice, but 9 times out of 10, they seem to do okay if I help them when they are seriously in distress. Remember, last resort only.