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Alejandro Alvarez PhD Dissertation.pdf (86.55 MB)

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Abstract Header

Girth Welding of Internally Clad API 5L Grade X65 Pipes using Low Alloy Steel Filler Metal

Alvarez, Alejandro
http://orcid.org/0000-0001-9762-1230
http://rave.ohiolink.edu/etdc/view?acc_num=osu1620480246867208

Abstract Details

2021, Doctor of Philosophy, Ohio State University, 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 temperature girth weld metal increases susceptibility to solidification cracking, liquation cracking and shrinkage porosity. Industry has not yet developed single U-groove LAS girth welds on internally clad HSS pipes due to a lack of understanding of the metallurgical phenomena in such welds. This study presents a methodology used for determining material compatibility to alleviate weldability concerns. Thermodynamic computational modeling is used to analyze the solidification behavior, partitioning characteristics, and phase transformations. Button melting, SS-DTA, and dilatometry is used to analyze the microstructural evolution in ER80S-G as a function of dilution from FM-686. Such testing methods help identify critical transformation temperatures such as AC1, AC3, Ms and Mf and, mechanisms that could be used to alleviate cracking susceptibility. Upon identifying the material compatibility between ER80S-G and FM-686, this study presents a procedure optimization approach to develop defect-free LAS girth welds. LAS girth welds are developed utilizing a combination of arc welding processes (i.e., CMT and GMAW-P) to minimize dilution from the Ni-based alloy substrate. A controlled sequence for depositing weld passes is also applied to further decrease dilution and create a temper bead welding effect to help reduce hardness. Lastly, this study subjects the newly developed LAS girth welds to metallurgical characterization and mechanical testing to develop a correlation between microstructure and mechanical properties. Testing is first conducted in accordance with DNV-OS-F101 to determine strength properties. Afterwards, hardness mapping and customized tensile testing utilizing Digital Image Correlation (DIC) is performed to determine the local mechanical properties of regions that contain both compositional and microstructural gradients. This study presents the successful development of LAS girth welds on internally clad API 5L Grade X65 steel. Girth welds exhibit a 200 MPa overmatching strength but failed to meet bend and hardness requirements stated by DNV. 1 of 3 bend specimens contained a crack longer than 3-mm that propagated from a pore. Per DNV, re-testing is required. Hardness is also above the 250 HV10 maximum requirement. Further testing is required to determine if PWHT could reduce hardness below the desired requirement.
Boian Alexandrov, Dr. (Advisor)
Carolin Fink, Dr. (Committee Member)
Dennis Harwig, Dr. (Committee Member)
343 p.
Composition; Design; Engineering; Materials Science; Metallurgy; Ocean Engineering; Petroleum Engineering
dissimilar materials; dissimilar metal welds; DMW; girth welds; girth welding; pipelines; Ni-based alloys; Low alloy steel; welding of internally clad pipes; welding of high strength steel; arc welding; alloy 686; ER80S-G; CMT; GMAW-P

Recommended Citations

Citations

  • Alvarez, A. (2021). Girth Welding of Internally Clad API 5L Grade X65 Pipes using Low Alloy Steel Filler Metal [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1620480246867208

    APA Style (7th edition)

  • Alvarez, Alejandro. Girth Welding of Internally Clad API 5L Grade X65 Pipes using Low Alloy Steel Filler Metal. 2021. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1620480246867208.

    MLA Style (8th edition)

  • Alvarez, Alejandro. "Girth Welding of Internally Clad API 5L Grade X65 Pipes using Low Alloy Steel Filler Metal." Doctoral dissertation, Ohio State University, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=osu1620480246867208

    Chicago Manual of Style (17th edition)

osu1620480246867208
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This open access ETD is published by The Ohio State University and OhioLINK.
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