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Waveform controlled gas metal arc welding of corrosion resistant alloys without back purging

McNicol, Jeremy M
http://rave.ohiolink.edu/etdc/view?acc_num=osu1650579445616494

Abstract Details

2022, Master of Science, Ohio State University, Welding Engineering.
Austenitic SS is commonly implemented in a variety of industries, such as oil and gas, chemical, and power for piping. Inert backing gas is typically employed in welding stainless steels to prevent deleterious oxidation that forms because of exposure to high heat and ambient conditions. However, studies in recent years and advancements in waveform technology have begun to show that no backing gas (NBG) austenitic SS pipe welding is possible and can achieve code acceptable and corrosion resistant weldments. Removing the necessity for backing gas, where spatial constraints may necessitate it, will lower complexity, cost, and risk to the operator. The primary objective of this study was to determine corrosion properties of NBG welds on Type 304L austenitic stainless steel, created with a modified short circuit-gas metal arc welding (SC-GMAW) waveform, compared to welds made with inert backing gas and develop an understanding of the factors that result in comparable corrosion properties of the welds. Previous work has shown that mechanical tests of NBG welds are comparable to backing gas welds but show evidence of pitting corrosion in the weld metal and base metal. The heat affected zone (HAZ) where the heat tint oxidation forms showed resistance to pitting corrosion. This work analyzes the corrosion resistance in the weld metal, HAZ, and base metal separately using electrochemical droplet corrosion testing techniques. Additional analysis of weld microstructures, sensitization, sugaring, and oxidation composition were included to further develop an insight into the key differences between NBG and backing gas welding. Results show that NBG welding produced with a modified SC-GMAW waveform have comparable pit initiation in the weld metal and HAZ to welds made with 100% Ar and 95% Ar/5%O2 backing gas. The NBG welds were however more susceptible to stable pitting at high potentials determined through electrochemical corrosion testing. Filler metals used in this study contained varying amounts of silicon (Si), addition of which to the filler metal composition resulted in a slight increase in corrosion resistance. The chemical make-up and sugaring analysis of the heat tint oxidation showed that the NBG welds and 100% Ar backing gas welds are very similar, except for the NBG welds showing a greater content of oxygen (O) at the fusion boundary and over various distances into the HAZ. In this study, an electrochemical syringe cell was also adapted to test for degree of sensitization. This testing showed no sensitization in the HAZ in the NBG welds, owing to a low carbon (C) content, but the method provides a novel approach to localized analysis of sensitization in welds. Preliminary testing using this approach was conducted on a Type 316LSi austenitic stainless steel wire arc additive manufacturing (WAAM) build. This work intends to add to the growing field of additive manufacturing by performing syringe cell electrochemical corrosion testing at different build height. The results have shown the pitting corrosion resistance in the initial layers and the layers at the top of the build have similar resistance to pit initiation and stable pitting as well as a similar metallography and ferrite content.
Narasi Sridhar, Dr. (Advisor)
Carolin Fink, Dr. (Advisor)
Engineering; Materials Science
Stainless steel; welding; no backing gas; corrosion; wire arc additive manufacturing

Recommended Citations

Citations

  • McNicol, J. M. (2022). Waveform controlled gas metal arc welding of corrosion resistant alloys without back purging [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1650579445616494

    APA Style (7th edition)

  • McNicol, Jeremy. Waveform controlled gas metal arc welding of corrosion resistant alloys without back purging. 2022. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1650579445616494.

    MLA Style (8th edition)

  • McNicol, Jeremy. "Waveform controlled gas metal arc welding of corrosion resistant alloys without back purging." Master's thesis, Ohio State University, 2022. http://rave.ohiolink.edu/etdc/view?acc_num=osu1650579445616494

    Chicago Manual of Style (17th edition)

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