Stephen Liu

Colorado School of Mines

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D.L. Olson

University of Nebraska–Lincoln

Alexandre Queiróz Bracarense

Universidade Federal de Minas Gerais

Ezequiel Caires Pereira Pessoa

LeTourneau University

Zhenzhen Yu

Fuzhou University

Abdu Yearwood

University of Guyana

Colin Quintyn

University of Guyana

Basheer Khan

University of Guyana

Safrawz Sharief

University of Guyana

Shion Norton

University of Guyana

Namhyun Kang

Pusan National University

Cooperative Institutions

Colorado School of Mines

Oak Ridge National Laboratory

University of Guyana

Los Alamos National Laboratory

Pusan National University

Chinese Academy of Sciences

Universidade Federal de Minas Gerais

The Ohio State University

Materials Science & Engineering

National Aeronautics and Space Administration

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The Effect of Base Metal and Core Rod Carbon Content on Underwater Wet Weld Porosity

Luciano G. D. Andrade Ezequiel Caires Pereira Pessoa Alexandre Queiróz Bracarense Weslley C. Dias Leandro F. Ribeiro

Porosity is a common defect observed in underwater wet welding. Several research programs have been developed to understand how pores form in order to mitigate the problem. No superficial pores and a limited number of internal pores (based on size) are important requirements to classify underwater wet welds according to the American Welding Society – AWS D3.6M standard. The main objective of this work is to study the effect of base metal and core rod carbon content on weld metal porosity. A pressure chamber with 20 atmospheres capacity was used to simulate depth with fresh water. To perform the welds, a gravity feeding system able to open an electric arc and deposit the weld automatically was used. Beads-on-plate were made using Direct Current Electrode Negative (DCEN) configuration on two base metals with different carbon contents (C2 – 0.1 wt. pct. and C7 – 0.7 wt. pct.) at 50 meters water depth. Commercial E6013 grade electrodes were used to deposit the welds. These electrodes were produced with core rods with two different carbon content (E2 – 0.002 wt. pct. and E6 – 0.6 wt. pct.) and painted with varnish for waterproofing. Samples were removed from the beginning, middle and end of the BOP welds and prepared following metallographic techniques including macroetching and image analysis for weld porosity. A data acquisition system was used to record current, voltage and welding time at 1.0 kHz rate. The porosity measurements indicated an increase of about 85% and 70% when E6 electrodes were used instead of E2 electrode on C2 and C7 steel plates, respectively. Simultaneously, the increase in porosity was followed by an increase in short circuiting events, an increase in weld bead penetration and a decrease in welding voltage. These observations seem to confirm, a direct effect of carbon content of the core rod on weld metal porosity and that porosity is associated with the CO reaction that can occur during metal transfer in that molten droplets carry gas bubbles to the welding pool. On the other hand, the increase of carbon content in the base metal was seen to decrease the porosity in the weld metal. This result can be related with the decrease in penetration observed when changing C2 to C7 plates. The smaller participation of carbon from the base metal in the weld pool reactions should then reduce the CO formation and, consequently, the amount of pores in the weld.

Base metal

Carbon fibers

Rod

10.1115/omae2010-20877

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Citations (1)

インジウム富裕SACはんだ合金と銅基板の間に形成した金属間化合物(IMC)の調査

Welding in the World (2017)

Rodrigues Felipe Watson Jonathan Stephen Liu C Madeni Juan

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Corrosion Protection of Ships

Elsevier eBooks (2018)

Chao Wei George Wang Marcus Cridland D.L. Olson Stephen Liu

Shipyard

Service life

10.1016/b978-0-323-52472-8.00026-5

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Citations (18)

Author Correction: Development of a numerical model for simulating stress corrosion cracking in spent nuclear fuel canisters

npj Materials Degradation (2021)

Xin Wu Fengwen Mu Scott D. Gordon D.L. Olson Stephen Liu

10.1038/s41529-021-00200-6

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A study on creep and mechanical properties at high temperature of SMAW welds for a Cr–Mo-X steel

Welding in the World (2023)

Sanghyun Bae Yong‐Cheol Kim Stephen Liu

Brittleness

10.1007/s40194-023-01560-0

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Effect of tin on microstructure and mechanical properties of compacted graphite iron

International Journal of Cast Metals Research (2015)

Yezhe Lyu Yang Sun Stephen Liu Jianhui Zhao

This experiment investigated the effect of tin in an amount up to 0·121 wt-% on the microstructure and mechanical properties of compacted graphite iron. Graphite and matrix evolution was emphasised with the help of scanning electron microscopy. The results indicate that Sn in experimental range reduces graphite size. Pearlite quantity would increase with the increasing Sn and reaches over 95% when Sn is >0·057 wt-%. Sn helps to narrow the lamellar spacing of pearlite from sorbitic pearlite (320 nm) to troostitic pearlite (83 nm) when Sn increases from 0·003 to 0·057 wt-%. Appropriate Sn addition promotes the tensile strength and impact toughness, and the samples containing 0·057 wt-%Sn perform the highest values of 410·7 MPa and 9·11 J cm− 2 respectively. Elongation declines with increasing Sn content because of the emergence of more pearlite. Samples containing excessive Sn experience sharp deterioration in mechanical properties due to brittle cementite.

Elongation

10.1179/1743133615y.0000000009

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Citations (18)

Effect of prestrain on hydrogen diffusion and trapping in structural steel

Materials Letters (2018)

Chulho Park Namhyun Kang Myunghyun Kim Stephen Liu

10.1016/j.matlet.2018.10.049

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Stress Corrosion Cracking Assessment of a Quenched and Tempered HSLA Steel in Two Alkaline Environments

Ali H. AlShawa Alyaa G. Elramady Stephen Liu

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Spreading and solidification behavior of nickel wide-gap brazes

Welding in the World (2014)

Scott D. Nelson Stephen Liu Srikanth Kottilingam Juan C. Madeni

Brazing

Fusion welding

Isothermal process

10.1007/s40194-014-0144-9

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Effect of Nickel on Toughness of Underwater Wet Welds

Faustino Pérez Stephen Liu Charles T. Smith Efrain E. Rodriguez

Underwater wet welding has been used as an option for the repair of offshore platforms. Rutile-grade electrodes are typically used to carry out the underwater repairs because of their good arc stability, bead appearance, and bead morphology. However, the main problems to overcome are porosity and reduction of toughness and strength as the water depth increases. During wet welding, the welding arc decomposes water into hydrogen and oxygen, which results in the formation of oxides and pores in the weld metal. The loss of alloying elements in the oxidation process and the fast cooling rate due to the quenching effect of water surrounding the weld are responsible for the deterioration in mechanical properties. This paper presents evidence of toughness improvements on wet welds made with experimental rutile-grade electrodes. Experimental electrodes with nickel added to the flux covering (0, 1.2, 2.3, and 3.0 wt. pct.) were extruded. A commercial rutile electrode was used for comparison. Bead-on-plate and multipass V-groove wet welds were made at 1 ft. water depth in fresh water. Charpy impact test specimens were machined from the V-groove welds and tested at four temperatures. The toughness measured at −50°C of wet welds with 3.0 wt pct. nickel was improved by a factor of four over the wet welds without nickel content. Smaller improvements were obtained with 2.3 wt. pct. nickel at −50°C. At higher temperatures, the toughness did not increase with nickel additions. All-weld-metal reduced-size tensile specimens made from the wet welds deposited with the commercial and experimental electrodes presented similar yield and tensile strength. The tensile specimen with 3.0 wt. pct. nickel presented lower ductility.

Charpy impact test

10.1115/omae2003-37261

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Citations (6)