| 英文摘要 |
A major concern for boiler users is whether the service time of an aged boiler having exceeded or approaching its design life could be prolonged or not. This paper presents assessment methods for investigating the suitability of aged boilers for prolonged operations. The methods we used to evaluate the current condition and the remaining life of a boiler system included nondestructive testing (NDT) inspections, remaining life assessment in reference to metallography, life assessment based upon API 579 creep damage, remaining life due to high temperature oxidation, and the thinning trend of tube thickness. According to in situ inspections and the remaining life studies, there were several major findings. No anomalies in the boiler system were observed via the NDT inspections. No voids were found at the grain boundaries of the materials by the replica method, and the consumed service time might be below 50% of the expected life time of the boiler. The assessment results obtained by methods of API 579 Level 1 and Ω parameter Level 2 showed that the fraction of creep damage in all tubes was smaller than 0.25, indicating that the boiler system could still be put into service. In view of the high temperature corrosion rate, we found that the effect of high temperature corrosion on the tubes’ thickness was small. Data of historical thickness measurements showed that thinning of the tubes was small. The analysis results demonstrated that the degradation of the tubes was low, due to the low service temperature and internal pressure. Therefore, the condition of the boiler system was good enough to run for a period of time although the service life had exceeded the design life. |
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