Jerry Wilks - CITGO Lemont
A 9Cr-1Mo tube in the convection section of a coker furnace at Lemont Refinery failed on the morning of February 8, 2017 while this furnace was being started after being decoked with mechanical pigging. The leak resulted in a small, short duration fire inside the furnace, and the furnace was taken off-line. The failed tube was replaced, and the furnace was given a hydrotest to evaluate if it was fit-for-service. During the hydrotest two more tubes failed, but these failures weren’t the same as the original failure. Tube samples were obtained and analysis revealed that the cause of the original failure was carburization of the ID surface of the tubes. For carburization to occur inside furnace tubes there would have had to be some source of oxygen inside the tubes because CO is needed for transport of the carbon into the steel surface. It is believed that crude composition has changed resulting in oxygen containing molecules being present inside the tubes. Those molecules break down to produce CO inside the tubes. The carburization also was the root cause of the brittle tube failures that occurred during the hydrotest.