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<p>This study investigates the long-term performance of ASTM P91 steel used in a 700 MW sub-critical power plant after 130000 hours of operation at 550 °C and 19.4 MPa. Three sample conditions were analyzed: (1) virgin P91 steel, (2) service-exposed material after 130000 hours, and (3) a service-exposed sample subjected to creep testing that failed after an additional 9000 hours. Microstructural analysis revealed progressive precipitate coarsening and grain boundary degradation with exposure. Hardness decreased from 224 HV (virgin) to 214 HV (service-exposed), and to 176 HV after creep testing, falling below ASME limits. Tensile strength decreased from 705.9 MPa to 671.6 MPa, accompanied by a marginal increase in elongation at break (21.3 mm versus 20.5 mm), reflecting reduced plasticity. Creep testing at 610 °C and 100 MPa confirmed advanced damage, including intergranular cracking. Remaining life was estimated using the larson-miller parameter (LMP) method. A direct calculation based on test data (LMP = 21150) predicted a remaining life of ∼507263 hours, while a literature-based interpolation (LMP = 20700) estimated ∼141868 hours. Despite numerical differences, both methods confirm the extended service capability of P91 steel under moderate conditions. These results validate the material’s suitability for high-temperature applications and highlight the effects of thermal aging and creep degradation. The study emphasizes the importance of routine inspections, microstructural evaluation, and predictive maintenance to ensure long term reliability of pressure components in critical power plant operations.</p>

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Microstructural and mechanical property assessment of P91 main steam pipes in a 700 MW sub-critical power plant

  • 期刊论文

  • 发表日期：

    2026年7月11日

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  • Robiah Ghazali,
  • Mohd Zaidi Omar,
  • Wan Fathul Hakim W. Zamri,
  • Nur Syahirah Zainuddin,
  • Mazmi Yahya

摘要

This study investigates the long-term performance of ASTM P91 steel used in a 700 MW sub-critical power plant after 130000 hours of operation at 550 °C and 19.4 MPa. Three sample conditions were analyzed: (1) virgin P91 steel, (2) service-exposed material after 130000 hours, and (3) a service-exposed sample subjected to creep testing that failed after an additional 9000 hours. Microstructural analysis revealed progressive precipitate coarsening and grain boundary degradation with exposure. Hardness decreased from 224 HV (virgin) to 214 HV (service-exposed), and to 176 HV after creep testing, falling below ASME limits. Tensile strength decreased from 705.9 MPa to 671.6 MPa, accompanied by a marginal increase in elongation at break (21.3 mm versus 20.5 mm), reflecting reduced plasticity. Creep testing at 610 °C and 100 MPa confirmed advanced damage, including intergranular cracking. Remaining life was estimated using the larson-miller parameter (LMP) method. A direct calculation based on test data (LMP = 21150) predicted a remaining life of ∼507263 hours, while a literature-based interpolation (LMP = 20700) estimated ∼141868 hours. Despite numerical differences, both methods confirm the extended service capability of P91 steel under moderate conditions. These results validate the material’s suitability for high-temperature applications and highlight the effects of thermal aging and creep degradation. The study emphasizes the importance of routine inspections, microstructural evaluation, and predictive maintenance to ensure long term reliability of pressure components in critical power plant operations.