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<p>Failure analysis of failed boiler bed coil tubes of boiler of the thermal power plant was investigated in the present investigation. Failed boiler bed coil tubes N-5 and N-6 tubes as well as virgin tube were used for these investigations. Metallurgical failure analysis of boiler bed coil tubes was carried out through visual inspection, chemical analysis, microstructure evolution by optical microscopy and scanning electron microscopy analysis, and mechanical properties evaluation. Fish mouth opening and pin-hole leakage of tubes N-6 and N-5 are observed by visual observation, respectively. Significant wall thinning of tubes occurred by outer surface followed by scale formation, corrosion and corrosion erosion processes. However, thin corrosion oxide layer and very fine pitting were observed at inner surface of these tubes. Significant corrosion or any other degradation was not found on inner surface of bed coil tubes. The chemical composition of bed coil tube meets the requirement as per standard. The microstructures of both the tubes consist of typically ferrite and pearlite. Pearlite agglomerations along a line have occurred partially at near rupture of tube N-6. There were no significant anomalies in the microstructures and mechanical properties of the tubes. Severe corrosion and short-term overheating had been occurred in the tube due to excessive coal ash/fly ash corrosion and erosion by fly ash deposition on the outer surface. It causes significant wall thinning from outer surface and exceeded the hoop stress. Subsequently, the tubes had experienced operational stress at elevated temperature, which is approximately twice of maximum allowable stress values, which causes fish mouth opening in Tube N-6. The pin-hole rupture in tube N-5 was caused by fly ash corrosion, leading to the excessive pitting in the localized tube with surface thinning on outer surface, and eventually results in the pin-hole tube puncture. Detailed structure–properties correlations have been made of obtained results. Use of good quality coal with low sulfur, phosphorus and ash contents is recommended to reduce such kind of failures.</p>

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Metallurgical Failure Investigation of Boiler Bed Coil Tubes made of Carbon Steel of a Thermal Power Plant

  • 期刊论文

  • 发表日期：

    2025年1月31日

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  • Md Murtuja Husain,
  • Parikshit Munda,
  • V. Rajinikanth,
  • Rajat Kumar Roy

摘要

Failure analysis of failed boiler bed coil tubes of boiler of the thermal power plant was investigated in the present investigation. Failed boiler bed coil tubes N-5 and N-6 tubes as well as virgin tube were used for these investigations. Metallurgical failure analysis of boiler bed coil tubes was carried out through visual inspection, chemical analysis, microstructure evolution by optical microscopy and scanning electron microscopy analysis, and mechanical properties evaluation. Fish mouth opening and pin-hole leakage of tubes N-6 and N-5 are observed by visual observation, respectively. Significant wall thinning of tubes occurred by outer surface followed by scale formation, corrosion and corrosion erosion processes. However, thin corrosion oxide layer and very fine pitting were observed at inner surface of these tubes. Significant corrosion or any other degradation was not found on inner surface of bed coil tubes. The chemical composition of bed coil tube meets the requirement as per standard. The microstructures of both the tubes consist of typically ferrite and pearlite. Pearlite agglomerations along a line have occurred partially at near rupture of tube N-6. There were no significant anomalies in the microstructures and mechanical properties of the tubes. Severe corrosion and short-term overheating had been occurred in the tube due to excessive coal ash/fly ash corrosion and erosion by fly ash deposition on the outer surface. It causes significant wall thinning from outer surface and exceeded the hoop stress. Subsequently, the tubes had experienced operational stress at elevated temperature, which is approximately twice of maximum allowable stress values, which causes fish mouth opening in Tube N-6. The pin-hole rupture in tube N-5 was caused by fly ash corrosion, leading to the excessive pitting in the localized tube with surface thinning on outer surface, and eventually results in the pin-hole tube puncture. Detailed structure–properties correlations have been made of obtained results. Use of good quality coal with low sulfur, phosphorus and ash contents is recommended to reduce such kind of failures.