Doctor of Philosophy, The Ohio State University, 2023, Welding Engineering

Coke drums are large pressure vessels used in the oil refining process, which generate lightweight oil products and solid cokes as a byproduct from the heavy residual oil. Coke drums are critical units in the delayed coking process and often undergo severe thermo-mechanical loadings that cause plastic deformation in the vessels. The accumulative damage in coke drums over operation cycles leads to low-cycle fatigue failure that significantly reduces the lifetime of coke drums. Many factors can contribute to the low-cycle fatigue damage in coke drums, including design, fabrication, operation, and repair. One of the inherent reasons is the thermal and mechanical incompatibility between the base metal and weld metal, as low-cycle fatigue damages are frequently observed adjacent to the weld seams. The structural integrity is significantly compromised at a bulging or cracking region, so coke drum repair is required before continuing the operation. Welding repair has been widely adopted in industry to restore the structural integrity of damaged regions. However, the repaired regions are also susceptible to subsequent failures due to welding defects and mechanical incompatibility. A careful selection of filler metal and the welding process is critical to improve the efficacy of welding repair. To address the issue of selecting the optimal filler metal and welding process for coke drum repair, a study regarding coke drum welding repair was initiated in the Manufacturing & Materials Joining Innovation Center (MA2JIC) at OSU in the year of 2016. In Phase-I, a novel isothermal low-cycle fatigue (ILCF) testing approach was developed using the Gleeble® thermo-mechanical simulator, and a wide range of filler metals and welding processes were evaluated using this technique. The project entered Phase II in the year 2019. The Phase-II study continues Phase-I efforts on filler metal selection based on low-cycle fatigue evaluation and expands the materials selection scope to coke drum (open full item for complete abstract)

Committee: Antonio Ramirez (Committee Chair); Yannis Korkolis (Committee Member); Avi Benatar (Committee Member); Chyongchiou J. Lin (Committee Member) Subjects: Chemical Engineering; Civil Engineering; Energy; Engineering; Materials Science; Mechanical Engineering; Metallurgy; Petroleum Engineering

Master of Science, The Ohio State University, 2021, 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 (open full item for complete abstract)

Committee: Boian Alexandrov Dr. (Advisor); Gerald Frankel Dr. (Committee Member) Subjects: Engineering; Materials Science

Doctor of Philosophy, The Ohio State University, 2021, Welding Engineering

This study focuses on the development of low alloy steel (LAS) girth welds on internally clad API 5L Grade X65 steel by investigating the metallurgical phenomena of welds made using a high melting temperature consumable over a low melting temperature substrate. The metallurgical phenomena of welds made using a low melting temperature consumable over a high melting temperature substrate have been widely reported in literature. The solidification behavior of alloy 625 overlays on high-strength steel (HSS) has been reported in works pertaining to the oil and gas, petrochemical, and power generation industries. Extensive investigations have been conducted analyzing microstructural and compositional gradients along the fusion boundary and transition zone that degrade the mechanical properties of such welds. Alloy 625 girth welds on internally clad HSS have also become a topic of continued discussion as premature failures have been associated to the fusion boundary between the Ni-based alloy weld metal and HSS pipe. The oil and gas industry is investigating the potential replacement of alloy 625 girth welds with LAS girth welds. LAS girth welds could possibly reduce susceptibility to premature failures while also reducing pipeline manufacturing and installation expenses. Reel pipelay is a method of installing pipelines to the ocean floor from giant reels mounted on an offshore vessel. Reel pipelay is known to increase installation rates and reduce manufacturing expenses since welding and inspection is performed onshore. DNV-OS-F101, however, states that girth welds intended for reel pipelay applications shall overmatch the base metal yield strength by 100 MPa. Careful consideration is also required during girth welding to ensure that the corrosion resistant properties of the internally clad layers remain intact. Such girth welds have been challenging to develop due to poor weldability. Dilution from the low melting temperature substrate into the high melting temper (open full item for complete abstract)

Committee: Boian Alexandrov Dr. (Advisor); Carolin Fink Dr. (Committee Member); Dennis Harwig Dr. (Committee Member) Subjects: Composition; Design; Engineering; Materials Science; Metallurgy; Ocean Engineering; Petroleum Engineering

Master of Science, The Ohio State University, 2016, Welding Engineering

In the oil & gas industry, extraction of oil reserves from pre-salt subsea oil fields requires pipelines and risers to be joined with welds that overmatch the X65 pipe yield strength by 100 MPa, have high toughness, and do not utilize a PWHT. In typical oil extraction, these internally clad pipes are welded with fill passes of Alloy 625 that match the internal clad, however, the strength requirement for reeling is not met with this alloy. To meet the strength requirement, low alloy steel consumables were studied as fill passes to join X65 pipes that are internally clad with Alloy 625 with root passes welded using 625 filler metal. The problem with this metallurgical combination is that solidification cracking can occur in the low alloy steel weld passes that have been diluted by Alloy 625. Computational modeling was performed to screen potential consumables and welding trails were completed for consumables that demonstrated compatibility. Upon establishing welding parameters, bead-on-plate design of experiments were performed with low alloy steel (ER100S-G) welded over two different nickel-based alloys (Alloy 625 and Alloy 686). Buffer layer solutions were also tested using two other Ni-based alloys, UTP A 80 Ni and Alloy 625 LNb, to isolate the root pass material from the fill pass material. Solidification cracking was eliminated in bead-on-plate welds of ER100S-G over Alloy 625 using small weave amplitudes, however, Alloy 686 was determined to have better compatibility with the low alloy steel filler metal to avoid solidification cracking. Welding experiments in a narrow groove were performed for the compatible combination, ER100S-G fill passes over a root pass of Alloy 686, and solidification cracking was eliminated from the fill pass welds. During this study, a defect previously thought to occur only in castings has been identified in welds of low alloy steel filler metals over Ni-based alloy substrates. Referred to in this study as “shrinkage porosity”, (open full item for complete abstract)

Committee: Boian Alexandrov Dr. (Advisor); Avraham Benatar Dr. (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

Master of Science (M.S.), University of Dayton, 2014, Chemical Engineering

The pipelines used for hydraulic fracturing (aka. "fracking") are often operating at a pressure above 10000psi and thus are highly susceptible to Stress Corrosion Cracking (SCC). This is primarily due to the process of carrying out fracturing at a shale gas site, where the hydraulic fracturing fluid is pumped through these pipes at very high pressure in order to initiate fracture in the shale formation. While the fracturing fluid is typically more than 99% water, other components are used to perform various functions during the fracturing process. Research into the occurrence of SCC reveals that SCC is engendered by a number of factors, of which two main contributors are stress in the pipe steel and a particular type of corrosive environment in contact with the pipeline in the service setting. The variety of fracturing fluid formulas which could be used and the insufficient reported information about the fracturing fluid chemistry makes it very important to carry out analysis to ensure the integrity of the pipelines used for this process. The current research described here is focused on the evaluation of the susceptibility of low alloy steel (AISI 4340) to stress corrosion cracking in different environments as it relates to hydraulic fracturing fluid chemistry and operating conditions. These different environments are achieved by varying the solution pH, the pH adjusting agent and the applied stress. Electrochemistry and stress measurements showed that at near neutral pH solution, AISI 4340 showed a higher SCC susceptibility in solutions where Na2CO3 was used as the pH adjusting than in solutions where NaOH was used as the pH adjusting agent. Scanning electron microscopy and Auger electron spectroscopy was used to analyze the oxide film in solution with the two pH adjusting agents at a pH of 7. Depth profiles of the passive film formed in a solution with pH adjusted to 7 using NaOH pH adjusting agent suggests the presence of a complex, FeOCl, which dissolves activ (open full item for complete abstract)

Committee: Douglas Hansen (Committee Chair); Sean Brossia (Advisor); Robert Wilkens (Committee Member) Subjects: Chemical Engineering; Chemistry; Materials Science