"We had a failure of convection tubes in our furnace. Can we restart and continue to operate until our next planned shutdown?" A brittle fracture failure of several HK-40 tubes in a convection section occurred in 2012. The failed convection section tubes were removed and submitted for metallurgical failure analysis. Hydrotesting was performed on the remaining tubes in the convection section to confirm that additional tubes were not substantially damaged and return the furnace to operation without further repairs. A failure analysis and API 579 Fitness-for-Service assessment were performed to determine the mode of failure and to determine the remaining life of the HK-40 tubes. The remaining life assessment determined the permissible existing flaw sizes in the tubes, which would not grow to a critical flaw prior to a future shutdown date. Several shutdown dates were evaluated to determine the timing of the next shutdown. This information provided the operator with a sound basis to evaluate the business and safety risks of continued operation until long-term repairs and system improvements could be implemented.
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