I have been burning corn in a St. Croix Greenfield for many years and have had on going problems with the exhaust pipe cap burning through. I have also replaced the entire pipe one time because the top was corroded. I am using Duravent pipe approved for corn and a stainless steel cap. The pipe runs about 15 feet straight out the roof and appears to accumulate fly ash at the top. I do a mid season exhaust pipe cleaning. Any suggestions?