Riding Lawn Mowers

I have a LOYTH20F42T, The Kohler engine has been replaced due to a cracked head. This now has over 500 hours on it, serviced on a regular basis, It has gone through 4 exhaust pipes. I put a new one on yesterday and today it blew apart just about an inch from the flange. Do you have any idea on how to remedy this problem? The exhaust pipes are getting a tad expensive and my hearing won't handle running without proper exhaust.