The paper presents an application according the reliability and remining life assessment of the reactor (coxing box) from a petrochemical plant, after failure in welding joint of plated shell from W1.5423 (16Mo5) steel with 25 mm thickness, plated with W1.4002 stainless steel with 3 mm thickness. The reactor failure it has associated with initial flaws from welding process, which have accelerated remaining life exhaustion. The assessment made in two steps. It has used VII section of ASME code specifications and iRiS-Thermo expert system for preliminary remaining life assessment. Concomitantly, it was performed the experimental creep and thermal fatigue testing. The program results have defined creep and thermal fatigue exhaustion and its remaining life at common creep-fatigue action, in condition of safety exploitation. It was emphasized the possibility of use an extra 40,000 hours of rehabilitated reactor in the safety condition of normal parameters.