Browsing by Author "Ghomashchi, R"

Now showing 1 - 8 of 8
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    Experimental investigation of welding stresses in MWIC weldability test
    (Materials Research Forum LLC, 2016-07-03) Alipooramirabad, H; Paradowska, AM; Ghomashchi, R; Hoye, N; Reid, M
    The use of high-strength steels in the manufacture of energy pipelines, coupled with the transition to larger pipe diameters and greater wall thicknesses, has led to an increased potential for cracking including hydrogen assisted cracking of energy pipelines due to higher constraint induced stresses. In the present study, a modified version of the Welding Institute of Canada (MWIC) restraint test was used to simulate the constraint conditions of full-scale girth welds on energy pipelines, allowing the influence of welding process parameters on crack formation to be assessed. MWIC test samples of X70 grade high-strength low alloy pipeline steel were manually welded using two different welding processes, namely shielded metal arc welding (SMAW) and modified short-arc welding (MSAW). Residual strains, and hence stresses, in these samples were analysed quantitatively using neutron diffraction technique. Overall, results indicate that the modified WIC restraint test produces significant residual stresses and so is effective in constraining the root run and in consequence studying the hydrogen assisted cracking of high-strength pipeline steels. © The Authors
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    In situ neutron diffraction measurement of strain relaxation in welds during heat treatment
    (Taylor & Francis Online, 2016-12-11) Alipooramirabad, H; Paradowska, AM; Lavigne, O; Ghomashchi, R; Reid, M
    Neutron diffraction (ND) is commonly used to investigate the stress redistribution before and after post-weld heat treatment (PWHT) in welded structures. However, there is a lack of information on the evaluations of strains during PWHT. The present work employed in situ ND to measure the relaxation of residual strains during conventional PWHT in multi-pass high-strength low-alloy steel welds. It was found that strain relaxation occurs principally during the heating stage of the heat treatment. The findings have important economic bearings and can be used to characterise comparable material combinations and optimise the PWHT process for high-strength low-alloy weld joints. This unique information also provides a valuable benchmark for the finite element modelling of this complex process. © 2021 Informa UK Limited
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    Investigating the effects of mitigation techniques on residual stress and microstructure of HSLA welds
    (Materials Research Forum LLC, 2016-07-03) Alipooramirabad, H; Ghomashchi, R; Paradowska, AM; Reid, M
    Post-weld heat treatment is often required for pressure vessel and piping components for relaxing residual stresses and increasing the resistance to brittle fracture. The present study employed neutron diffraction to examine the effects of conventional post-weld heat treatment (PWHT) on the residual stresses in multi-pass, high-strength, low-alloy-steel, weld joints made by combined Modified Short Arc Welding (MSAW) and Flux Cored Arc welding (FCAW) processes. Residual stresses in excess of yield strength were developed in the Heat Affected Zone (HAZ) and the weld metal of the as-welded specimen (particularly the upper layers of the weld) which were reduced significantly as a result of applying PWHT. Also PWHT lead to substantial changes in the microstructural characteristics of high-strength, low-alloy-steel welds. © The Authors
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    Investigating the effects of welding process on residual stresses, microstructure and mechanical properties in HSLA steel welds
    (Elsevier, 2017-08-01) Alipooramirabad, H; Paradowska, AM; Ghomashchi, R; Reid, M
    One of the important steps in the design and fabrication of welded structures is the selection of the welding process and the filler consumables. This is because these two factors control the mechanics of thermal distribution and the chemistry of the welded join, which in turn affect weld integrity through the resulting microstructure and residual stresses. The present study employed neutron diffraction to investigate the effects of welding process on the residual stresses in high-strength low-alloy steel weld joints made by SMAW (shielded metal arc welding) and combined MSAW (modified short arc welding) and FCAW (flux cored arc welding) processes. A significantly higher level of residual stress was found in the MASW + FCAW combination which was shown to be in line with the microstructural and mechanical properties. Higher levels of residual stresses may be related to the formation of bainite and Widmanstätten ferrite in the weld metal and HAZ of the combined MSAW and FCAW processes. © 2017 The Society of Manufacturing Engineers. Published by Elsevier Ltd.
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    Post-weld heat treatment of API 5L X70 high strength low alloy steel welds
    (MDPI, 2020-12-18) Alipooramirabad, H; Paradowska, AM; Nafisi, S; Reid, M; Ghomashchi, R
    High Strength Low Alloy (HSLA) steels are the materials of choice in pipeline construction with the API X70 grade as the steel for the majority of pipeline networks constructed during the late 20th and early this century. This paper reports on the influence of Post-Weld Heat Treatment (PWHT) on the reduction of residual stresses, resulting changes in the microstructure, and mechanical properties of a multi-pass, X70 HSLA steel, weld joints made by a combined Modified Short Arc Welding (MSAW) and Flux Cored Arc Welding (FCAW) processes. Neutron diffraction results highlighted high magnitude of tensile residual stresses, in excess of yield strength of both parent and weld metal, in the as-welded specimen (~650 MPa), which were decreased substantially as a result of applying PWHT (~144 MPa). Detailed microstructural studies are reported to confirm the phase transformation during PWHT and its interrelationship with mechanical properties. Transmission Electron Microscopy (TEM) analysis showed polygonization and formation of sub-grains in the PWHT specimen which justifies the reduction of residual stress in the heat-treated weld joints. Furthermore, microstructural changes due to PWHT justify the improvement in ductility (increase in the elongations) with a slight reduction in yield and tensile strength for the PWHT weld joint. © 1996-2021 MDPI
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    Prediction of welding stresses in WIC test and its application in pipelines
    (Taylor & Francis, 2016-07-20) Alipooramirabad, H; Paradowska, AM; Ghomashchi, R; Kotousov, A; Hoye, N
    In the present study, the Welding Institute of Canada (WIC) restraint test was used to simulate the restraint conditions of full-scale girth welds on energy pipelines to ascertain the influence of welding process parameters on welding stresses. Finite element models are developed, and validated with neutron diffraction measurements, to evaluate the welding stresses for under-matched, matched and over-matched welds. The effects of heat input, wall thickness and variable restraint lengths of WIC sample are systematically investigated. As a practical outcome, this work can help in selection of the appropriate restraint length for WIC tests to simulate the specified stress conditions in the pipeline, and, ultimately, reduce the risk of Hydrogen Assisted Cold Cracking (HACC) in high strength low alloy. © 2021 Informa UK Limited
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    Quantification of residual stresses in multi-pass welds using neutron diffraction
    (Elsevier, 2015-12-01) Alipooramirabad, H; Paradowska, AM; Ghomashchi, R; Kotousov, A; Reid, M
    Neutron diffraction results highlighted the effect of heat input through changes of travel speed and welding sequence (direction) on the residual stresses in multi-pass weldments of high strength low alloy steel. Residual stresses in excess of yield strength were developed in the weld metal and HAZ particularly for the upper-layers of welds which were not affected by the tempering of the subsequent weld layers. The magnitude of the residual stresses was significantly reduced by increasing the heat input. There was no substantial difference in the magnitude of the residual stresses when the direction of weld deposition was varied but the distribution was more uniform. © 2017 Elsevier B.V.
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    Residual stress- microstructure- mechanical property interrelationships in multipass HSLA steel welds
    (Elsevier, 2016-05-01) Alipooramirabad, H; Ghomashchi, R; Paradowska, AM; Reid, M
    Higher levels of residual stresses in excess of yield strength of the both weld and parent metals were developed within the upper-layers of the modified short arc and flux cored arc welding combination of HSLA steel. The magnitude of the residual stresses was significantly reduced by increasing the heat input. High level of residual stresses was found to be correlated with the existing of microstructural constituents of bainite and Widmanstätten ferrite in the weld metal and HAZ of low heat input specimens. There was no substantial difference in the magnitude of the residual stresses, microstructural characteristics and mechanical properties when the direction of weld deposition was changed. © 2016 Elsevier B.V.