Concurrent design error, poor welding, and code inadequacy cause jet-FIRE on a topping column

The paper reports the analysis of an accident that occurred in a petroleum refinery. During the start-up maneuver of the topping column, the anchoring of the riser pipe to metal guide support on the topping column suddenly failed. This caused a rip in the riser pipe, and gasoline squirted out, followed by the ignition of a jet fire. The investigations showed an unusual differential thermal expansion between the topping column and riser. The riser guide to the column was wrongly installed, preventing adequate relative displacements when thermal expansion occurred. Metallographic and fractographic analyses did not discover any inadequacy in the steel of the failed parts. But the lack of penetration of the welding seam resulted in a weak bond between the support and the riser. The high stress induced by the badly installed guide and the weakness of the welding was the cause of the failure and the jet fire. The paper also analyses the application of existing codes to the riser support installation and shows that the code recommendations do not satisfactorily cover the case of topping column risers. The issue is raised to alert operators in the plant, stimulate the improvement of the codes and standards, and avoid future accidents.