This paper describes the analysis of recurrent failures experienced on 1%Cr – ½%Mo steam superheater tubes of two boilers at an oil refinery. In all cases, metallurgical analysis of failed tubes has shown overheating of material, high temperature oxidation, bulging, cracks and creep degradation as a result of internal deposits on tube wall. Chemical analysis of deposits samples has determined the presence of sodium sulfate attributable to boiler water carryover to the superheater. To determine the root cause, a comprehensive assessment of actual boiler conditions was carried out, considering operation variables and procedures, maintenance and inspection programs, combustion and control system modifications. On the basis of this assessment, an integral program was implemented to improve boiler reliability.