Abstract
The small punch (SP) testing technique was applied to five heats of Gr.91 steel, which had been actually used for boiler pipings in different USC power plants for long periods of time to investigate the applicability of this technique to the assessment of heat-to-heat variation of creep property. The experimental results revealed that the SP creep rupture strength and deformation behavior were quite different depending on the heat. Those differences in SP creep property, which could not be evaluated by hardness measurement, were qualitatively similar to those in standard uniaxial creep one. It was expected that the SP creep testing technique was applicable to the assessment of heat-to-heat variation for in-service boiler pipings.
Highlights
9-12%Cr heat resistant ferritic steels, such as Gr.91, Gr.92 and Gr.122 steels, have been widely used in ultrasuper critical (USC) power plants, because of their superior high temperature strength and resistance to corrosion/oxidation
The small punch (SP) creep test was carried out at the temperature of 650°C and under the loads of 190, 230, 300 N using the Gr.91 steel base metals removed from five different boiler pipings, which had been used in the USC power plants for a long period of time
As reported in the previous studies [3,4,5], the overall shape of curve is qualitatively similar to that obtained from standard uniaxial creep test, the instantaneous deflection is significant at the time of initial load application in the SP creep test (Figure 4 (a))
Summary
9-12%Cr heat resistant ferritic steels, such as Gr., Gr.92 and Gr.122 steels, have been widely used in ultrasuper critical (USC) power plants, because of their superior high temperature strength and resistance to corrosion/oxidation. Premature failures at their welded joint have been a worldwide issue in recent years This failure occurs at the outer edge of the heat affected zone (HAZ), and it is well known as “Type IV creep damage”. The SP creep test was carried out at the temperature of 650°C and under the loads of 190, 230, 300 N using the Gr. steel base metals removed from five different boiler pipings, which had been used in the USC power plants for a long period of time
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