I got into a heated back-&-forth about that escape scene with someone here years ago, and it got to the point we were actually looking up the actual piping manufacturing details of the prison the movie was filmed at.
Long story short - Yes, the piping actually was prone to corrosion, but at the bottom of the piping, not at the top. And corrosion is a weakening of metal, but not to the point it'd shatter with the force of a human hand.
Corrosion, namely rust, effects a the top tenth of an inch deep of metal, and the thickness of the pipe in the movie was over 2"... as evidence of the movie scene itself.
And... in the movie the pipe was pressurized, as shown when Andy punctured the pipe @2:17, meaning the pipe was of sound structural integrity.
So, I was trying to keep my initial summary of the ridiculous escape short, but the further you dive into the details the more and more ridiculous it becomes.