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Timothy Babyak Master's Thesis.pdf (20.48 MB)

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Corrosion Resistant Weld Overlays for Pipelines, Oil and Gas, and Petrochemical Installations

Babyak, Timothy Olegovich
http://rave.ohiolink.edu/etdc/view?acc_num=osu1620613360761292

Abstract Details

2021, Master of Science, Ohio State University, Welding Engineering.
Nickel-base alloy corrosion resistant weld overlays (WOLs) are used in the oil and gas and petrochemical industry to protect against pipeline failure due to corrosion while also reducing costs. Currently, for some industry specific applications, these WOLs are produced using hot wire gas tungsten arc welding (HW-GTAW), a high heat input process. Per specifications such as API 5LD and DNV-OS-F101, additional iron content in the weld metal of nickel-base WOLs must be sufficiently reduced to ensure adequate corrosion resistance of the WOL. The amount of additional iron in the weld metal is a result of dilution of the clad layer by the substrate. High heat input processes such as HW-GTAW tend to produce welds with higher dilution, and as a result, up to three layers of weld metal are needed to sufficiently reduce iron content in the weld metal. Previous projects at OSU, addressing corrosion resistant WOLs in the nuclear industry, have demonstrated that low heat input gas metal arc welding (GMAW) processes, such as cold metal transfer (CMT), can produce WOLs with lower dilution, higher deposition rates, and greater corrosion resistance than similar overlays produced with HW-GTAW. However, concerns of lack of fusion and lack of penetration defects along with insufficient process optimization have hindered the widespread application of low heat input GMAW for WOLs. This study aimed to investigate the viability of CMT for production of WOLs for the oil and gas and petrochemical industry. Bead-on-plate welds of three nickel-base alloys (alloy 625, alloy 686, and alloy 825) were produced with CMT on low alloy steel X65 using a design of experiments approach. Bead geometry, heat input, deposition rate, and the presence of lack of penetration defects from each sample were measured and categorized to identify parameter sets that produced welds adhering to certain criteria such as low dilution, moderate toe angles, and lack of defects. Deposition rates for CMT were around 3.5 times higher than HW-GTAW. Analysis of CMT sample microstructure revealed smaller planar growth regions, less swirls as well as smaller swirls, and smaller secondary dendrite arm spacing (SDAS) as compared with HW-GTAW. These characteristics respectively contribute to a lower potential for solidification cracking, a lower potential for hydrogen assisted cracking (HAC), and increased corrosion resistance. Microhardness maps revealed CMT produced samples with lower heat affected zone (HAZ) hardness values along with higher weld metal (WM) hardness values. Higher WM hardness increases erosion resistance and lower HAZ hardness decreases the need for PWHT. Thermodynamic simulations between each of the filler metals and the base metal revealed CMT samples were less susceptible to solidification and liquation cracking due to the widest solidification ranges occurring in planar growth regions. Overlays of all three filler metals were constructed using both processes. Specimens extracted from the CMT overlays passed ASME Section IX bend tests. The bend tests were validated using digital image correlation (DIC) as lack of strain concentration along fusion boundaries indicated proper fusion had occurred. EDS traverses across fusion boundaries showed a transition from base metal to minimally diluted filler metal within tens of micrometers for CMT as compared with millimeters for HW-GTAW. Compositional comparisons from EDS traverses parallel to fusion boundaries and top surfaces showed nearly identical compositions for CMT at both locations but not for HW-GTAW. Corrosion testing following ASTM G48 found critical pitting temperatures (CPT) of 60°C, 85°C, and 20°C, respectively, for alloy 625, 686, and 825 single-layer overlay samples created using CMT. Double-layer HW-GTAW samples tested at the same temperatures, as their CMT counterpart, had deeper maximum pitting as well as greater overall weight loss. Through comparative analyses, CMT was determined a superior WOL production process to HW-GTAW as CMT increases structural integrity and decreases cost with its ability to produce defect-free, corrosion-, erosion-, and cracking-resistant WOLs at higher deposition rates and with less filler material.
Boian Alexandrov, Dr. (Advisor)
Gerald Frankel, Dr. (Committee Member)
165 p.
Engineering; Materials Science
nickel base alloys; alloy 625; alloy 686; alloy 825; low alloy steel; x65; cold metal transfer; cmt; corrosion resistance; overlays; hot wire gtaw; hw-gtaw; low heat input versus high heat input; process optimization; design of experiment

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Citations

  • Babyak, T. O. (2021). Corrosion Resistant Weld Overlays for Pipelines, Oil and Gas, and Petrochemical Installations [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1620613360761292

    APA Style (7th edition)

  • Babyak, Timothy. Corrosion Resistant Weld Overlays for Pipelines, Oil and Gas, and Petrochemical Installations. 2021. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1620613360761292.

    MLA Style (8th edition)

  • Babyak, Timothy. "Corrosion Resistant Weld Overlays for Pipelines, Oil and Gas, and Petrochemical Installations." Master's thesis, Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1620613360761292

    Chicago Manual of Style (17th edition)

osu1620613360761292
412
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