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This paper describes the fatigue failure of a rotary dryer in a chemical plant. The process conditions required the dryer to be rotated continuously at a speed of about two and half revolutions per minute. The shell structure of this large drum is formed by combining segmented shell parts using bolted ring flange joints. Because of the gross weight of the dryer in operation time, each joint was subjected to bending moment. In the first two years in service, micro cracks were occurred by fatigue. The failure was analyzed using the fatigue curves given in ASME Boiler and Pressure Vessel Code Section VIII Division 2 and EN 13445 Unfired Pressure Vessels Part 3 Codes. Finally, flange joints were removed from the drum and new cylindrical parts adapted to the drum using butt welding after reaching better results in FEM and fatigue calculation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Revealed that bending moment is the cause of thread gluing at the HDD exit side. [•] A 3D drill pipe thread FEM model was established which could load combining loads. [•] Put forward some improvement measures and successfully used in HDD. [•] Proposed the beveled shoulder thread which could strongly withstand bending load. [ABSTRACT FROM AUTHOR]