During a planned maintenance outage in August 2018, longitudinal cracks were found in the shell section of a customer’s rotary kiln. The 2 cracks were 180 degrees opposed on the shell and ran along the shell axially. The longest crack was approximately 1.8 m in length.
The kiln had to be returned to service as soon as possible and a full repair was not practical at the time, therefore a temporary repair had to be carried out to allow the kiln to operate until a replacement section could be installed. MEL in consultation with the customer and the OEM developed strong backs to locally strengthen the shell at the crack locations to prevent further propagation. The stiffener design and shell stress response were analysed using Finite Element Analysis (FEA) techniques to check for minimised shell stress at the crack tip and avoidance of stress concentrations where the strong backs were to be welded to the kiln shell. To obtain the best solution different geometry’s, sizes, placement and numbers of stiffeners were modelled to meet the space limitations. The final shaped delivered reduced stress concentrations by designing some ‘flexibility’ into the stiffeners.
Strong back plates were profile cut overnight then welded over the cracks as they were received on site. The tips of the cracks were also drilled and dressed to arrest further propagation. MEL construction supervisors managed and supervised the site repair works to enable the kiln to return to service, then continued to develop a program to replace the shell section during the next annual outage in March 2019.