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Fracture toughness of a 9% Ni steel pipe girth welded with Ni-based superalloy 625 filler metal operating in a sour environment
Journal of Materials Research and Technology ( IF 6.4 ) Pub Date : 2020-04-02 , DOI: 10.1016/j.jmrt.2020.03.044
Vinícius Santiago Fernandes , Francisco Werley Cipriano Farias , João da Cruz Payão Filho

9% Ni steel was adopted, for the first time, to be used in the CO2 injection units in oil wells. It operates at 550 bar in sour environment (CO2 + H2S), in addition to being subject to abrupt temperature variations. Owing to the lack of knowledge on the behavior of 9% Ni steel under these operating conditions, crack tip opening displacement (CTOD) and J-integral tests were performed on base metal (BM), coarse grain heat-affected zone (CGHAZ), and weld metal (WM) of pipe joints girth welded with Ni-based superalloy 625 filler metal, both in air (at 27 °C and −90 °C) and sour environment (CO2 + H2S). The microstructure of the welded joints was characterized by optical and scanning electron microscopy, X-ray diffraction, and microhardness. In air, all welded joints exhibited high toughness and ductile fracture; however, in sour environment, BM experienced a sharp drop in toughness with a quasi-cleavage fracture. Although the CGHAZ was the hardest region of the welded joints, it was less influenced by the sour environment because it was close to WM (Ni-based superalloy 625); however, it exhibited a brittle fracture. Despite the decrease in the fracture toughness in sour environment, the welded joints met DNV-OS-F101 standards.



中文翻译:

在酸性环境下使用Ni基高温合金625填充金属焊接的9%Ni钢管环周的断裂韧性

首次采用9%Ni钢在油井的CO 2注入装置中使用。除了在温度变化剧烈的情况下,它还可以在550 bar的酸性环境(CO 2  + H 2 S)下运行。由于缺乏有关9%Ni钢在这些操作条件下的行为的知识,因此对贱金属(BM),粗晶粒热影响区(CGHAZ)进行了裂纹尖端开度位移(CTOD)和J整体测试,在空气(27°C和-90°C)和酸性环境(CO 2 + H 2)下,用镍基高温合金625填充金属焊接的管接头环围的焊缝金属和焊缝金属(WM)S)。通过光学和扫描电子显微镜,X射线衍射和显微硬度来表征焊接接头的微观结构。在空气中,所有焊接接头均显示出高韧性和韧性断裂。但是,在酸性环境中,BM的韧性急剧下降,并发生准裂解断裂。尽管CGHAZ是焊接接头中最硬的区域,但由于它接近WM(镍基高温合金625),因此不受酸性环境的影响。然而,它表现出脆性断裂。尽管在酸性环境中断裂韧性有所降低,但焊接接头仍符合DNV-OS-F101标准。

更新日期:2020-04-21
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