The shadowed side is therefore considerably cooler than the heated side, resulting in a thermal gradient across the tube and causing a bow to develop in the tubes. The combination of elevated temperature, tube bow, dead weight and internal pressure results in creep strains which produce permanent deformation of the tubes. Failure Study of a Petrochemical Rotary Dryer - A large rotating dryer is used to produce purified terephthalic acid. The dryer is of cylindrical shape and rotates over 1.5 million revolutions per year. The dryer is heated by steam, which passes through tubes situated around the periphery of the cylinder on the inside diameter.
Perforated plates welded to the inside surface of the shell support the steam tubes.
Cracking was observed in the perforated plates, known as baffle supports. The cracks propagated through the baffle supports and into the shell resulting in unscheduled shutdown and repair. The purpose of the investigation by ESG was to determine the cause of the crack initiation and suggest methods of repair to existing units and design changes to new units that would extend the life of the dryer.