Introduction  The imported boiler tertiary superheater of Zhuhai power station which was designed and manufactured by Mitsubishi Heavy Industries has occurred tube failures frequently in recent years, the types were typical long-term overheating failures, the metallographic spheroidization were occurred and mechanical properties were declined, indicating that the furnace tube was in a long-term high temperature operation state.

  Method  To find out the reasons of long-term overheating and to propose solutions, the thickness of oxide of tertiary superheater tubes was tested, the flow deviation and heat absorption deviation of tertiary superheater were studied.

  Result  The residual creep life of 59% T91 tubes were less than fifty thousand hours, 39% T91 tubes were less than ten thousand hours, the residual creep life of 25% T23 tubes were less than fifty thousand hours, 9% T23 tubes were less than ten thousands hours. The flow deviation of the superheater header was 10.6%, the heat deviation of the tubes temperature in the width direction was 60 ℃. The problem couldn't be solved by replacing the new pipe section, the overall design Modification was required.

  Conclusion  According to the above researches, the modification design by China-manufacturer was proposed. After the modification the flow deviation of the superheater header was reduced to 2.24% and the heat deviation of the tubes temperature in the width direction was reduced to 40 ℃. In addition, considering the working environment of the tertiary superheater, properties of the tube materials had been upgraded, the types of the material were reduced from 5 to 4, and the specification were reduced from 23 to 12, the procurement and maintenance costs were reduced.