Damage characterization of an ASTM A 213 grade 91 tube after 116.000Â h of service in a reforming plant

Our results suggest that the steel suffered by different damage forms, which appear on definite portions of the tube cross section. The main degradation forms observed, in fact, into the tube bulk are both the martensite recovery and the microstructural evolution. This latter promoted mostly Laves phase precipitation and coarsening. On the other hand, both the outer and the inner wall side, suffered mainly by severe oxidation/carburization. Especially on the outer surface, the massive carbide precipitation has caused an evident loss of ductility so that the mechanical properties of the tube appear appreciably reduced.