Abstract
The 2.25Cr1Mo0.25V steel is a vanadium-modified 2.25Cr1Mo steel and is being widely used in the manufacture of heavy-wall hydrogenation reactors in petrochemical plants. However, the harsh service environment requires a thorough understanding of high-temperature tensile and creep behaviors of 2.25Cr1Mo0.25V steel and its weld for ensuring the safety and reliability of hydrogenation reactors. In this work, the high-temperature tensile and creep behaviors of base metal (BM) and weld metal (WM) in a 2.25Cr1Mo0.25V steel weldment used for a hydrogenation reactor were studied experimentally, paying special attention to its service temperature range of 350–500 °C. The uniaxial tensile tests under different temperatures show that the WM has higher strength and lower ductility than those of BM, due to the finer grain size in the WM. At the same time, the short-term creep tests at 550 °C reveal that the WM has a higher creep resistance than that of BM. Moreover, the creep damage mechanisms were clarified by observing the fracture surface and microstructures of crept specimens with the aid of scanning electron microscopy (SEM). The results showed that the creep damage mechanisms of both BM and WM are the initiation and growth of creep cavities at the second phase particles. Results from this work indicate that the mismatch in the high-temperature tensile strength, ductility, and creep deformation rate in 2.25Cr1Mo0.25V steel weldment needs to be considered for the design and integrity assessment of hydrogenation reactors.
Highlights
base metal (BM), which is due ittoshould the grain refinement size of the is smaller than that of the BM, which is due to the grain refinement caused by the post-weld heat treatment (PWHT) process
The fracture surface of the BM consists of several primary dimples with large size and depth and a number of dimples with small size, as shown in Figures 5b and 6b, whereas the fracture surface of the weld metal (WM) mainly consists of numerous small and shallow dimples, as presented in Figures 5d and 6d. These results indicate that the BM is more ductile as compared with the WM, because more plastic strain and energy would be consumed during the formation of dimples with larger size
Several dimples with much larger size and depth can be seen in the macroscopic fracture surface of the BM size and depth can be seen in the macroscopic fracture surface of the BM compared with the WM specimen. These results indicate that the BM is compared with the WM specimen. These results indicate that the BM is more ductile than the WM, which is in good agreement with the higher ductility of the more ductile than the WM, which is in good agreement with the higher ductility of the WM obtained from high-temperature tensile tests
Summary
Results from this work indicate that the mismatch in the high-temperature tensile strength, ductility, and creep deformation rate in 2.25Cr1Mo0.25V steel weldment needs to be considered for the design and integrity assessment of hydrogenation reactors. An upgraded version of 2.25Cr1Mo steel, i.e., 2.25Cr1Mo0.25V steel, has been developed and is being employed in the fabrication of new heavy-wall hydrogenation reactors [1] This is because the addition of vanadium leads to higher strength and enhanced resistance to hydrogen attack and high temperature damage as compared to traditional 2.25Cr1Mo steel [1,2]. The weld is generally regarded as the weak link of the components operated at high temperatures because of the mismatch of microstructures and, the mechanical properties. Reactors, the high-temperature strength and creep performance of the 2.25Cr1Mo0.25V steel and weld metal must be understood
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