Papers by Keyword: Modified 9Cr-1Mo Steel

Abstract: In order to evaluate the safety and integrity of piping with local wall-thinning at elevated temperature, a numerical method for plastic limit load of modified 9Cr-1Mo steel piping is proposed in the present paper. The limit load of piping at high temperature is defined as the load-carrying capacity after the structure has served for a certain time period. The power law creep behavior with Liu-Murakami damage model is implemented into the commercial software ABAQUS via CREEP for simulation, and the Ramberg-Osgood model is modified to consider the material deterioration effect of modified 9Cr-1Mo steel by introducing the creep damage factor into the elasto-plastic constitutive equation. For covering the wide ranges of defect ratios and service time periods, various 3-D numerical examples for the piping with local wall-thinning defects, and creep time are calculated and analyzed. The limit loads of the defected structures under high temperature are obtained through classic zero curvature criterion with the modified Ramberg-Osgood model, and the typical failure modes of these piping are also discussed. The results show that the plastic limit load of piping containing defect at elevated temperature depends not only on the size of defect, but also on the creep time, which is different from the traditional plastic limit analysis at room temperature without material deterioration.

Abstract: In this paper, the application of the photo-acoustic method to study the thermal properties of modified 9Cr-1Mo Steel is described. The photo-acoustic measurements are carried out for the thermal properties of modified 9Cr-1Mo steel samples of various thicknesses. The theoretical basis for quantitative measurements is discussed, together with the advantages and limitations of these methods as compared with conventional measurements.

Abstract: This study aimed to assess creep crack growth rates on the base and welded metals of modified 9Cr-1Mo steel. For this purpose, welded specimens were prepared by the Shielded Metal Arc Weld method. To obtain mechanical properties concerning the base and welded metals, a series of creep and tensile tests were conducted at 600 °C, and creep crack growth tests were also performed under different applied loads using 1/2" compact tension specimens at 600 °C. Their creep crack growth rates were calculated using the empirical equation of the da/dt vs. C* parameter and compared. It appeared that, for a given value of C*, the rate of creep crack propagation was about 2.0 times faster in the welded metal than the base metal. This reason was that the welded metal was faster in the creep strain rate than the base metal.

Abstract: The nondestructive evaluation technique for the material degradation is necessary because of the limitation of conventional destructive methods. In this study, an ultrasonic velocity measurement method was attempted for the estimation of the creep damage of degraded modified 9Cr-1Mo steel. The specimens with seven different kinds of aging periods were prepared by an isothermal heat treatment at 690
. The ultrasonic velocity was measured by an immersion method. The correlation between the measured ultrasonic velocity and tensile properties were studied. The ultrasonic velocity has an declining tendency with the increase of heat treatment time. A correlation between the ultrasonic velocity and aging parameter were established, which allows one to estimate the material degradation of modified 9Cr-1Mo steel.

Abstract: Evolution of microstructure due to service exposure to high temperature has a strong effect performance of heat resistant steels. In case of modified 9Cr-1Mo steels, precipitation of Fe2Mo-type laves phases and coarsening of M23C6-type carbides are the primary cause of degradation of mechanical properties such as creep resistance, tensile strength and toughness. Therefore creep tests have been carried out on modified 9Cr-1Mo steels to examine the effect of aging and stress on the creep strength. Additionally vibrating sample magnetometer is used to measure hysteresis loop.