I'm not a pro and it's possible some of them will chime in here with more scientific data, but I use 24" pipe wrenches and pipe dope alone. I turn the until I can't turn anyone. Is there a risk of breaking the pipe? Can't say for sure, but I've never broken a pipe by tightening too tight. I'd say that with a 14" wrench, you need to put the muscle to it. If it moves, give it some more.