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Welding of X65 Internally Clad with Precipitation Strengthened Ni-Based SUperalloy Filler Metal: Application in Pre-Salt Oil Extraction

Penso, Graciela Carolina
http://rave.ohiolink.edu/etdc/view?acc_num=osu1480600980467914

Abstract Details

2016, Master of Science, Ohio State University, Welding Engineering.
Giant oil reservoirs were found off the coast of Brazil in the Santos Basin Bay. They are located under a geological salt layer; thus they are called pre-salt. The fact that these reservoirs are located far from shore, has presented some technological challenges. Currently, X65 pipes internally clad with Alloy 625 are used for traditional subsea oil extraction. Such pipes are joined using Alloy 625 filler material. Since the depth and the amount of risers and pipelines to be installed in the pre-salt oil reserves are very large, pipe reeling is considered the most efficient technology for pipeline installation. For pipe reeling, it is necessary for the welds joining the pipes to overmatch the X65 base metal yield strength by 100 MPa, without any post wed heat treatment, thus Alloy 625 does not meet those requirements. The objective of this project was to explore the applicability of precipitation strengthened nickel-based filler metals for welding of internally clad X65 pipes for application in pipelines and risers for oil extraction from pre-salt subsea oil fields. Ni-base super alloys 718 and 282 were considered as potential welding consumables for this application. The solidification behavior in the weld metal of these alloys diluted with the Alloy 625 pipe cladding was evaluated using thermodynamic simulations with Scheil-Gulliver module of Thermo-Calc™. The Alloy 718 / Alloy 625 system exhibited almost constant solidification temperature range of about 250 oC with formation of Laves phase at the end of solidification throughout the whole dilution range. The Alloy 282 / Alloy 625 system exhibited potential for lower susceptibility to solidification cracking with the solidification temperature range gradually degreasing to 150 oC and no formation of Laves at dilutions lover than 70%. The compatibility of Alloy 718 and Alloy 625 filler metals with alloy the 625 cladding and X65 steel base metal was evaluated by performing bead-on-plate welding and producing multilayer buildups using cold metal transfer (CMT) and gas metal arc welding pulsed (GMAWp) processes. No solidification and liquation cracking or lack of fusion defects were experienced in large range of welding parameters with both filler metals. The precipitation behavior during multipass welding in both alloys was evaluated as a potential strengthening mechanism to meet the weld metal overmatching strength requirement. Hardness mapping on multipass weld buildups has shown that at least two reheats by high heat input subsequent weld passes with GMAWp are needed to cause precipitation hardening in Alloy 718. Significant precipitation hardening in Alloy 282 occurred by three reheat weld passes with CMT. Tensile testing in all-weld metal multipass buildups showed that multipass welding with GMAWp cannot generate sufficient precipitation strengthening in Alloy 718 filler metal to meet the X65 yield strength overmatch requirement of 550 MPa. With yield strength of 620 MPa, Alloy 282 multipass weld buildup produced with CMT met this requirement. Successful test groove welds in low alloy steel were produced with Alloy 718 and Alloy 282 using correspondingly GMAWp and CMT processes. A root pass of Alloy 625 was used to simulate pipe internal cladding. Welding parameter optimization allowed to resolve center line solidification cracking and lack of fusion defects in welds of both alloys. As a final step, narrow groove welding of X65 pipe with Alloy 282 was performed using CMT process. Additional welding parameter optimization was performed to produce welds free of center line cracks and lack of fusion defects. Flat to convex pool surface with elliptic shape was obtained by controlling welding travel speed and wire feeding rate. The weaving amplitude and frequency were adjusted to consistently penetrate the bead toe / groove surface intersection points. Metallurgical characterization was performed on the bead-on-plate samples, weld buildups, and groove welds. The weld metal and heat affected zone microstructure was characterized using light optical microscopy and scanning electron microscopy (SEM). Energy disperse spectroscopy (EDS) within the SEM was used to study the composition gradients across the base metal / filler metal transition zone and across the weld metal layers. The results of this study have shown that Alloy 282 filler metal provides a potential solution for welding X65 pipes internally clad with Alloy 625 in terms of producing defect free welds and meeting the base metal overmatching requirement for reeling applications.
Boian Alexandrow, Dr. (Advisor)
Avraham Benatar, Dr. (Committee Member)
171 p.
Engineering
Welding, precipitation strengthened superalloys, ni-based, GMAW, CMT

Recommended Citations

Citations

  • Penso, G. C. (2016). Welding of X65 Internally Clad with Precipitation Strengthened Ni-Based SUperalloy Filler Metal: Application in Pre-Salt Oil Extraction [Master's thesis, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480600980467914

    APA Style (7th edition)

  • Penso, Graciela. Welding of X65 Internally Clad with Precipitation Strengthened Ni-Based SUperalloy Filler Metal: Application in Pre-Salt Oil Extraction . 2016. Ohio State University, Master's thesis. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1480600980467914.

    MLA Style (8th edition)

  • Penso, Graciela. "Welding of X65 Internally Clad with Precipitation Strengthened Ni-Based SUperalloy Filler Metal: Application in Pre-Salt Oil Extraction ." Master's thesis, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480600980467914

    Chicago Manual of Style (17th edition)

osu1480600980467914
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This open access ETD is published by The Ohio State University and OhioLINK.