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Weldability Evaluation in Autogenous Welds of Alloys 230, 800H, and 825

Suh, Sanghyun
http://rave.ohiolink.edu/etdc/view?acc_num=osu1471581194

Abstract Details

2016, Master of Science, Ohio State University, Welding Engineering.
Pipes of solid solution strengthened Ni-based alloys, as Alloy 826 and Alloy 800H, have been used for high temperature service in once through steam generators (OSTGs) on off-shore platforms. The oil and gas industry is seeking to increase service temperature, improve service reliability, and extend service life to 40 years of such installations. Alloy 230 has better-high temperature stability and mechanical properties, and higher service temperature than Alloys 825 and 800H, and is therefore considered as a potential replacement of these alloys in newly built OTSGs. However, the weldability and the high temperature service behavior in welds of Alloy 230 have not been thoroughly investigated yet. This study is a comprehensive comparative research focused on susceptibility to solidification cracking and stress relief cracking in Alloys 800H, 825, and 230. To evaluate the solidification behavior and solidification cracking susceptibility in these alloys, the Cast Pin Tear Test (CPTT), thermodynamic simulations with Thermo-Calc, and the technique of Single-Sensor Differential Analysis (SS-DTA) were used. The results revealed that Alloy 230 and Alloy 825 were more resistant to solidification cracking than Alloy 800H, due to narrower solidification temperature range and crack back filling with eutectic constituents. The OSU Stress Relief Cracking (SRC) Test was applied to evaluate the susceptibility to stress relief cracking in autogenous gas tungsten arc welds of the investigated alloys. None of the three alloys failed by stress relief cracking mechanism while loaded at stress equal to 90% of the high temperature yield strength at 650 oC for 8 hours.. Alloys 825 and 800H showed significant amount of stress relief, while Alloy 230 sustained the applied load at 650C with almost no stress relief. Tensile testing at 650 oC after the 8 hours SRC test showed that the autogenous weld in Alloy 230 had significantly higher yield and tensile strength and slightly lower elongation at failure compared to the Alloy 825 and 800H welds. The fracture surface in Alloy 230 autogenous welds exhibited partially brittle interdendritic failure, while welds in the other two alloys failed in completely ductile micro-void coalescence mode.
Boian Alexandrov (Advisor)
Avraham Benatar (Advisor)
194 p.
Materials Science; Metallurgy
solidification cracking; hot cracking; cast pin tear test; ss-dta; thermo-calc; stress relief cracking; gleeble; nickel based alloys; ni based alloys; autogenous weld; tensile test; characterization

Recommended Citations

Citations

  • Suh, S. (2016). Weldability Evaluation in Autogenous Welds of Alloys 230, 800H, and 825 [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1471581194

    APA Style (7th edition)

  • Suh, Sanghyun. Weldability Evaluation in Autogenous Welds of Alloys 230, 800H, and 825. 2016. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1471581194.

    MLA Style (8th edition)

  • Suh, Sanghyun. "Weldability Evaluation in Autogenous Welds of Alloys 230, 800H, and 825." Master's thesis, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1471581194

    Chicago Manual of Style (17th edition)

osu1471581194
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This open access ETD is published by The Ohio State University and OhioLINK.
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