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<p>This study investigates the tensile behavior of service-exposed Super304H boiler tubes that operated for approximately 42,000&#xa0;h under ultra-supercritical (USC) steam conditions. The primary objective was to establish a quantitative correlation between ASTM E8 sub-size and miniature tensile specimens. Tensile tests were conducted at 25-600&#xa0;°C using specimens taken from the same boiler tube to evaluate the influence of specimen geometry and to assess the applicability of the miniature tensile test (MTT) for degraded components. True stress–strain analysis showed that both specimen types exhibited similar elastic responses and strain-hardening exponents (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(n\)</EquationSource> <EquationSource Format="MATHML"><math> <mi>n</mi> </math></EquationSource> </InlineEquation>) across all temperatures. This indicates that strain-hardening behavior is largely independent of specimen geometry. However, the miniature specimens showed consistently higher yield strength (YS) and ultimate tensile strength (UTS), with differences of 15-16% at room temperature and 20-25% above 200&#xa0;°C. At lower temperatures, the elongation showed size-dependent differences, whereas at higher temperatures the difference became smaller and then reversed at 600&#xa0;°C. Linear regression analysis identified consistent correlations between ASTM sub-size and miniature specimens for both YS and UTS (<i>R</i><sup>2</sup> = 0.996-0.998). Based on this relationship, conversion coefficients were derived to estimate ASTM-equivalent strength from miniature tensile data. These results suggest that miniature tensile testing can serve as a practical method for evaluating high-temperature strength and degradation in components where ASTM sub-size specimen extraction is limited, such as service-exposed boiler tubes.</p>

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Comparative Evaluation of Tensile Properties of Service-Exposed Super304H Using ASTM Sub-Size and Miniature Tensile Specimens

  • 期刊论文

  • 发表日期：

    2026年4月17日

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  • Youngdae Kim,
  • Jinesung Jung,
  • Inhwan Song,
  • Seonho Choi

摘要

This study investigates the tensile behavior of service-exposed Super304H boiler tubes that operated for approximately 42,000 h under ultra-supercritical (USC) steam conditions. The primary objective was to establish a quantitative correlation between ASTM E8 sub-size and miniature tensile specimens. Tensile tests were conducted at 25-600 °C using specimens taken from the same boiler tube to evaluate the influence of specimen geometry and to assess the applicability of the miniature tensile test (MTT) for degraded components. True stress–strain analysis showed that both specimen types exhibited similar elastic responses and strain-hardening exponents ( \(n\) n ) across all temperatures. This indicates that strain-hardening behavior is largely independent of specimen geometry. However, the miniature specimens showed consistently higher yield strength (YS) and ultimate tensile strength (UTS), with differences of 15-16% at room temperature and 20-25% above 200 °C. At lower temperatures, the elongation showed size-dependent differences, whereas at higher temperatures the difference became smaller and then reversed at 600 °C. Linear regression analysis identified consistent correlations between ASTM sub-size and miniature specimens for both YS and UTS (R2 = 0.996-0.998). Based on this relationship, conversion coefficients were derived to estimate ASTM-equivalent strength from miniature tensile data. These results suggest that miniature tensile testing can serve as a practical method for evaluating high-temperature strength and degradation in components where ASTM sub-size specimen extraction is limited, such as service-exposed boiler tubes.