Reformer furnaces are widely used in petrochemical industry to obtain hydrogen from hydrocarbon through an endothermic catalytic reaction. This production takes place in radiant tubes, that are very critical components being designed for a nominal life of 100,000 h at temperatures up to 980°C and internal pressures of 10-40 bar. During the last two decades, the HP-40 grade (25Cr-35Ni-0.4C-Fe) has become common because of its good mechanical properties at high operating temperature. As known the high temperature strength of this alloy depends on Cr carbides, which undergo thermal damage effects during long service time and can be stabilized by the addition of micro-alloying elements. In this work results of mechanical tests and metallurgical investigation on samples cut from reformer tubes, decommissioned after long service time, are reported and discussed. Tubes, made of HP-40 grade modified with the additions of stabilizing elements (Nb and Ti), were inspected in situ by a laser optic system and put out of service because of their excessive creep deformation. Mechanical properties were evaluated by Vickers hardness and creep tests. Metallographic samples were observed by optical and scanning electron microscopy; moreover energy dispersive X-ray microanalysis was performed in order to measure locally their chemical composition.
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