Problem:Thermal Bowing of catalyst tube observed could be due to some form of degradation of the uniform density of catalyst packed in the catalyst tube that may have resulted in a preferential heat absorption. Also short-term overheating of the catalyst tubesover the current operating temperature range (1575^oF to 1773.2^oF) of the catalyst tubes was recorder by thermal imaging.

Analysis: Thermal-Mechanical modelling of the catalyst tubes was done to simulate creep stress rupture utilizig FEA techniques.

Benefits: Also, in the anticipation that the steam reformer will be available for shut-down in one year time (8670 hrs) from this event, the plant could continue to operate it for the next 8760 hrs (1 year) from now with the current operating temperature range (1575^oF to 1773.2^oF) of the catalyst tubes, and still be within the 3-year (20,000 hrs) limit without expecting to see creep-stress rupture damage BEGIN TO APPEAR. As with regards to thermal bowing, possibly a non-uniform heat distribution in the radiant section, that may be resulting in a thermal gradient across the catalyst tube (C-row, number-48) cross-section area. This could be a strong possibility as it was observed that catalyst tubes along the east-end wall (number-1) & west-end wall (number-48) on each of the seven (A to G) rows were bent, but to a relatively lesser degree (about 1 €� to 2€� max).

Results Conclusion:Based on the material properties received from the manufacturer, the following are the conclusions from mechanical strength aspect @ 982^oC (1800^oF). Thus the higher temperature of 982^oC (1800^oF) will result in 80% reduction in creep-stress rupture life. As confirmed by the ECT report / inspection, there has been negligible creep related damage when inspected in 2015, since the catalyst tubes were replace in 2009. As a part of the investigation for the bent catalyst tube, the following were the conclusions. A thermal gradient of 104^oF (conservative) was found to exist across the catalyst tube cross-section area. This was based on a  1545^oF on the north-side (convex) and 1441^oF on the south-side (concave). The observed thermal (lateral) deflection of the catalyst tube was around 6€� to  8in as previously noted. The calculated the resulting thermal deflection = 8inches. This correlates extremely well with the observed deflection. The primary cause of this lateral displacement of catalyst tube isThermal Bowing.