Papers by Keyword: T91

Abstract: Failure of steam-side oxide scales in high temperature components of boilers such as superheater and reheater tubes has significant effect on the safety of thermal power plants. Finite element analysis is carried out to investigate the failure issues of steam-side oxide scales in boiler tubes during thermal shock processes. The effects of different steam temperature variation durations on oxide scale failure issues have been analyzed. According to the results, appropriately lengthening variation duration can contribute to relieving oxide scale failure issues, and are subsequently proposed.

Abstract: The T91 steel is considered a perspective structural material for Generation IV (GEN IV) nuclear reactors components. The operating conditions of GEN IV nuclear reactor, which include higher operating temperatures, higher neutron fluencies and using liquid metals as coolants, constitute new challenges for structural materials validation. To properly assess the impact of radiation, thermal, load and environmental damage the screening test procedures for initial overview of the induced changes of mechanical properties need to be developed and validated. One of the test procedures with potential to be used for the mechanical properties screening is Small Punch test. Small Punch test receive considerable attention since their development in the 1980's. The use of miniaturized test specimen constitutes minimal requirements for the test material and the option of obtaining the test material directly from the component. They have been successfully used on industrial scale for design life extension of components for energy industry in the past. In this paper we address the issue of the Fracture Appearance Transition Temperature (FATT) determination by the means of Small Punch test for the T91 steel, manufactured according to ASTM standard A387-Ed99. The test specimen were manufactured and used for the experiments in a wide range of test temperatures. Multiple levels of deformation energy were used to provide more representative interpretation of the test data. A data fit is applied on the deformation energy – test temperature dependence to obtain the value of FATT from Small Punch test, which is subsequently correlated to the values obtained from testing sub-size Charpy specimens.

Abstract: A novel two-step heating process, consisting of a short-time high temperature heating followed by isothermal solidification at a lower temperature, was used to transient liquid phase (TLP) bond T91 steel. The interface morphology of the joint was investigated and compared with that of conventional TLP bond made at a constant bonding temperature. The results show that the two-step heating process produces a non-planar interface at the initial stage, which is different from the planar interfaces associated with conventional heating process. No interface can be found in the final joint by two-step heating process, however, a planar interface still exists in the final conventional TLP bond. Therefore, the bending ductility of the joint is dramatically improves by the two-step heating process, and the joint properties are similar to that of base metal.

Abstract: 12Cr2MoV steel pipe and T91 steel pipe were joined by transient liquid phase diffusion bonding process (TLP) in argon atmosphere using FeNiCrSiB amorphous filler. TP304H steel pipe and 12Cr2MoV steel pipe were joined by the same method using Fe₇₈Si₉B₁₃ and BNi₂ amorphous filler. The qualified welding joint can be achieved by suitable adjustment of process parameters. The diffusion asymmetry in TLP of different metals has been analyzed. The research shows that there exists a diffusion asymmetry in TLP of different metals. The main reason is the difference of isothermal solidification rate in different materials, which results in a deviation of the bonding interface from the original centerline to T91 and TP304H side.

Abstract: The knowledge of the quinary Pb–Bi–O–Fe–Hg is necessary for understanding the degradation mechanisms of the T91 steel used as structural material in future ADS nuclear reactors. In this device, the steel will be in direct contact with the liquid spallation target (which is constituted by lead or lead-bismuth eutectic) surrounded by a reduced oxygen pressure atmosphere. In the present work, the characterization of the pseudo-binary PbO–Fe2O3 cut has been performed. In order to complete the available data in the literature, some experimental investigations by DTA, isothermal annealing, SEM and EPMA have been done. These results have allowed proposing a thermodynamic assessment using the Calphad method by the ThermoCalc software.

Abstract: The hot workability of modified 9Cr-1Mo, as a grade of heat resistant steels, is inferior to that of low-alloy steel, so the inner surface crack (ISC) easily occurs in seamless boiler tubes produced by the Mandrel Mill under improper rolling conditions. With the aid of FEM, the metal flow status during the rolling process was analyzed in 140mm 8-stand mandrel mill of Bao Steel. Both the metallographic shape and size of the ISC together with the result from the simulation show that the ISC of seamless tube forms at the elongation stage of shell. The mechanism of the ISC was discussed. With its initiation in stand No.1 and No.2 due to poor hot workability of modified 9Cr-1Mo steel, the ISC develops in subsequent passes. Based upon the mechanism devised was a special roll pass system which substantially upgraded the yield of qualified products.

Abstract: The behavior of three different materials with respect to their Fe, Cr, Ni contents have been studied between 450°C and 700°C, in waste incinerators combustion conditions, where it occurs a main influence of chlorine, sulfur and water vapor. This works analyzes the behavior of these materials which depends on their capability to form melted compounds and on the nature of these melted phases. Also as the corrosion mechanism is influenced by the presence or missing of any corrosive species, the study focalizes on the specific influence of SO2 and alkaline chorine. Effect of additive ashes on the corrosion behavior of tested materials is also studied. The mechanism of corrosion in waste incinerators is supported by thermodynamic calculations performed with the “Thermocalc” software.

Abstract: This paper describes the evaluation of the creep behavior with two types of matching filler metals for 2.25Cr-1.6W(T23)/Mod. 9Cr-1Mo(T91) dissimilar weld joint. Through the welding procedure qualification tests prior to the creep tests, optimum PWHT holding times at 745±5oC were determined as 30minutes for T23 matching filler metal and 60minutes for T91 matching filler metal. It was also confirmed that carbon migration across the weld interfaces and the softened area at HAZ occurred during PWHT. Creep rupture tests were carried out at 575-650oC and 70-220MPa for two dissimilar metal welds manufactured by an optimum PWHT condition. From the comparison of creep rupture strength, it was shown that the creep strength of the welded joint including T23 matching filler metal was similar to that of T23 base material and somewhat higher than that of the welded joint including T91 matching filler metal. From metallurgical study on the crept specimen, the creep damage of T23/T91 dissimilar weld joints could occur at T23 side IC HAZ and near the T23/T91 weld interface simultaneously. However, the final failure locations seemed to depend on the filler metal and the cause of this phenomenon might be regarded as the additional effect of carbon migration across the weld interfaces. It is thought that the dissimilar weld including T91 filler metal which failures at T23 side CG HAZ subject to both metallurgical notch and carbon migration become more susceptible to creep damage than that including T23 filler metal in which the carbon depletion occurs at the T23 filler metal with higher creep strength than T23 HAZ. T23 filler metal can therefore be proposed for matching filler metal of T23/T91 dissimilar weld joints