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Transverse weld macrograph highlighting the various weld region: fusion zone (FZ), fine grain heat affected zone (FG-HAZ), coarse grain heat affected zone (CG-HAZ), base metal (BM), and location of Vickers hardness indentations.
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The role of micro-alloying in the submerged arc welding (SAW) of high strength low alloy steel linepipe is paramount in facilitating the high strength properties of the linepipe. In this study, transmission electron microscopy analysis revealed the presence of large (0.85 µm) Ti (C,N) precipitates within the predominantly acicular ferrite SAW joint...
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... software package. A FIB microscope (FEI FIB200) and a dual-column FIB (Carl Zeiss Nvision N40) were used to prepare TEM specimens. The TEM specimen preparation methodology for steel samples has been documented in [20,21]. Cross weld Vickers hardness tests were made at 1 mm intervals across the OD weld, transverse to the SAW joint, as depicted in Fig. 1 using a 10 kg load with a 10 s loading time. Cross-weld Charpy V-notch (CVN) samples (50 mm  10 mm  10 mm, with 2 mm notch depth and 0.25 mm root radius) were produced and tested at 0 1C in accordance with API standard [18], the details of which including the location and orientation of the CVN samples with respect to the weld joint ...
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... . 1 shows the macrograph of the SAW seam weld of the UOE linepipe section used for the current investigation. When welding materials of a similar composition, epitaxial growth rather than nucleation occurs [22]. The solidifying grains grow anisotropically towards the heat flow resulting in the coarse and columnar FZ grain structure as ...
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... . 1 shows the macrograph of the SAW seam weld of the UOE linepipe section used for the current investigation. When welding materials of a similar composition, epitaxial growth rather than nucleation occurs [22]. The solidifying grains grow anisotropically towards the heat flow resulting in the coarse and columnar FZ grain structure as depicted in Fig. 1(a). Fig. 1(b) also highlights the various weld regions under examination across the SAW joint. It is clear from the image that the combined heat input of the two pass SAW has produced a defect free, fully penetrated weld, with a good weld bead shape. The high heat input from the SAW also created a visible HAZ of between 2 and 4 mm in ...
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... macrograph of the SAW seam weld of the UOE linepipe section used for the current investigation. When welding materials of a similar composition, epitaxial growth rather than nucleation occurs [22]. The solidifying grains grow anisotropically towards the heat flow resulting in the coarse and columnar FZ grain structure as depicted in Fig. 1(a). Fig. 1(b) also highlights the various weld regions under examination across the SAW joint. It is clear from the image that the combined heat input of the two pass SAW has produced a defect free, fully penetrated weld, with a good weld bead shape. The high heat input from the SAW also created a visible HAZ of between 2 and 4 mm in width at either ...
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... Δσ p is increment of yield strength in MPa, G is shear modulus (81,600 MPa), b is Burger's vector in mm (0.248 nm), D p is the average diameter of precipitates (0.85 mm) in mm, and f p is the volume fraction (0.103) of precipitates. Fig. 10 shows the increment of yield strength contribution for a range of precipitate sizes and volume fractions. For the SAW joint with a 0.103 volume fraction and 0.85 mm average diameter Ti (C,N) precipitates, a strengthening contribution of around 32.1 MPa is achieved. Fig. 10 also indicates that significant increase in weld metal strength ...
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... (0.85 mm) in mm, and f p is the volume fraction (0.103) of precipitates. Fig. 10 shows the increment of yield strength contribution for a range of precipitate sizes and volume fractions. For the SAW joint with a 0.103 volume fraction and 0.85 mm average diameter Ti (C,N) precipitates, a strengthening contribution of around 32.1 MPa is achieved. Fig. 10 also indicates that significant increase in weld metal strength could be achieved if the average precipitate size is below 0.5 mm due to the exponential nature of the curve. By plotting at 720% of the measured 0.103 volume fraction, it is also clear that an increase in the volume fraction of precipitates could also increase yield ...
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... the mean D p (0.85 mm) and d p (5.67 mm) values calculated from microstructural observations in our study, it is possible to assess the effect of mean size and spacing of precipitates on plane- strain fracture toughness. The results in Fig. 12 show a fracture toughness value of 36.6 MPa m 1/2 using the input data presented. This offers a conservative estimate around 11% below the fracture toughness values determined experimentally in Table 2. The low deviation and conservative nature of the prediction validates the integrity of the model presented. The stress triaxiality ...
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... fracture toughness values determined experimentally in Table 2. The low deviation and conservative nature of the prediction validates the integrity of the model presented. The stress triaxiality values predicted using Eqs. 3 and 4 give slightly low values ( $1.5) but offer good fracture toughness estimates in the case of this study. As shown in Fig. 12, fracture initiation toughness increases as the size of precipitates become smaller. The drop in fracture toughness as a result of coarsening is attributed to the reduced local ductility around the precipitate as a direct result of growth. Once nucleated, the cracks develop into spherical and ellipsoidal holes by plastic deformation, ...
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... perspective, an optimum combination of toughness and strength can be achieved by controlling the size of Ti (C,N) precipitates to less than 0.5 mm in the SAW weld X65 linepipes. However, if the volume fraction of particles is kept the same, reducing the precipitate size will cause the spacing of the precipitates to also reduce, as demonstrated in Fig. 13. This will lead to a reduction in fracture toughness according to Eq.(8). So, in order to be certain that K ic could be increased, while reducing mean precipitate size, the volume fraction of particles also needs to be reduced in order to increase the particle spacing or to at least to maintain its same level. But a reduction in the ...
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... Eq.(8). So, in order to be certain that K ic could be increased, while reducing mean precipitate size, the volume fraction of particles also needs to be reduced in order to increase the particle spacing or to at least to maintain its same level. But a reduction in the volume fraction of particles will cause yield strength to drop, as presented in Fig. 10. This is the classical scenario that an increase in yield strength of the steel will have to be compromised by a reduction in toughness, which is adequately demonstrated through the mathematical equations presented in the paper. Therefore these equations could be used the guide the design or selection of the steel chemistries for the ...
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Citations
... Moreover, diversity in the microstructure of the weld metal was inevitable because the proportion and size of the microstructure are easily influenced by welding process parameters and differences in the chemical composition of the filler metal. In the multi-pass weld metal, different heat inputs and cooling rates [23] generally influence the proportions of the columnar grain zone and reheated regions [24] and the characteristics of the transformation products, such as grain size, impurity or precipitate coarsening of alloying elements [25], then further affect the tensile strength and impact toughness. Furthermore, the welding speed, inter-pass temperature, and post-weld heat treatment (PWHT) can affect the properties of weld metals, particularly the impact toughness. ...
The demand for heat-resistant steel has increased owing to its utility in numerous devices that must withstand high steam pressures and high temperatures, such as turbine rotors and blades in ultra-supercritical power plants. It is inevitable to join heat-resistance steel part by welding method, so it is important to maintain the toughness of the weld metals. In this study, the microstructure, low-temperature impact toughness, and fracture surface of as-welded and post-weld heat treatment (PWHT) of 2.25Cr-1Mo-0.25V weld metal were investigated. The microstructures of the as-welded and PWHT specimens are granular bainite and ferrite, respectively. This work revealed the relationship between effective microstructure nearby crack initiation origin and low temperature impact toughness for both the as-welded and PWHT specimens. The evolution of the microstructure and prior austenite was then investigated using confocal laser scanning microscopy (CLSM) to observe the formation of coarse ferrite grain structures. A suggestion for enhancing the low-temperature toughness was provided based on the effect of adjusting Mn content and forming acicular ferrite.
... However, the mechanisms causing poor welding forming and low performance are not clear, which are mainly ascribed to the lack of understanding of the melt pool dynamic. Flow dynamics and geometrical evolution of the liquid melt pool have been suggested to have strong relationships with the subsequent mechanical properties of welded materials [10][11][12][13][14]. However, it is difficult to observe and character the motion of a liquid metal in the melt pool due to the high temperatures, strong electromagnetic radiation and an opaque liquid metal [15]. ...
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... In the case of additive manufacturing, the whole component can be considered as a collection of successive fusion zones or deposits. Flow dynamics and geometrical evolution of the liquid melt pool have been suggested to have strong relationships with the subsequent mechanical properties of additively manufactured 1-3 and welded materials [4][5][6] . Consequently, the lifetime and performance of the additively manufactured components or welded joints, and hence the entire structural or functional components, can be significantly dictated by the geometric evolution and flow dynamics of the melt pool 1,2,[7][8][9][10] . ...
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... ITAB, katılaşmanın başladığı çizgiden ana metale kadar uzanan ve yapısal farklılıkların, geçiş bölgesi olarak net bir şekilde makro olarak görülebildiği bir yapıdır. Ana metal ve kaynak metali arasında ergimekatılaşma olmadan yüksek ısı etkisi ile yapısal olarak değişime uğrayan bu bölgeler makroyapı fotoğraflarında açıkça görülmektedir [30,31]. Kaynak metali sınırında iri tanelerden oluşan ITAB makroyapısının, ana metale yaklaştıkça daha ince tanelerden oluştuğu görülmektedir. ...
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... Diffusible hydrogen content in submerged arc welds of a S960 type steel i. e., niobium, vanadium, titanium and boron (0.001-0.1 wt.-%), combined with controlled rolling [18][19][20][21]. Microalloy carbides, nitrides and carbonitrides are critical in the control of austenite recrystallization and grain growth during steel processing and welding, leading to a desirable grain refinement. ...
Hydrogen induced damage is a dangerous phenomenon affecting the weld quality with regard to construction service life even without visible indication. The determination of diffusible hydrogen in weld metal has been standardized at an international level in ISO 3690:2012. This international standard specifies the sampling and analytical procedure for the determination of diffusible hydrogen in martensitic, bainitic and ferritic steel weld metal which arises from the welding of such steels using arc welding processes with filler metal. In this study, S960QL steel is extensively used in the heavy transport, lifting and mining industry, where mobile or fixed structures have to carry high loads - often in safety critical situations. In order to sustain extreme characteristics of these high strength low alloy steels, it is a must to reduce the manufacturing defects. In the investigations presented in this paper, the influence of arc length on the weld metal hydrogen concentration was studied according to the ISO DIS 3690 in S960QL type steel with submerged arc welding. Measurement of the diffusible hydrogen was carried out by means of carrier gas hot extraction method. The weld seams with different arc length have similar chemical compositions. Maximum hardness values in the range of 410-425 HV1 were measured in the HAZ on both vertical and horizontal rows in welded structure with two mm wire diameter due to recrystallization condition. For four mm wire diameter, the hardness decreasing which is depending on the grain coarsening in the welded samples with two mm was not occurred in the weld seamHAZ interface. The larger weld pool and the long arc length increased possibility of hydrogen pick-up and absorbing. Because of this reason, the diffusible hydrogen contents in the welded structure increased in accordance with the arc length.
... Some recent studies were performed to analyze the molten pool behavior 27 and to determine the influence of activated flux on mechanical properties. 28,29 Effect of heat input on weld bead geometry 30 and influence of process variables on the quality of weld was studied by Kiran et al. 31 Several researchers 32,33 have done extensive study on the analysis of microstructure of submerged arc welded (SAW) steel joints. The effect of root opening on the mechanical properties, deformations, and residual stress is investigated by Jang et al. 34 FEA of residual stresses in case of butt weld is reported by Hong et al. 35 Cho et al. 36 have reported detailed analysis on the determination of residual stress distribution after welding and after a post-weld heat treatment using a FE transient heat flow analysis in conjunction with a coupled thermo-mechanical analysis. ...
... Also, the Young's modulus, E, is same for weld bead and adjacent plate as both are of same material that is MS. Thus, equation (24) can be modified to calculate the restraint coefficient (b) using equations (28) and (29) ...
Angular distortion in fusion welded joints is an alarming issue which affects the stability and life of the welded structures,
occurs due to the changes in the temperature gradient during the welding process. This degrades the dimensional quality
of a large structure during assembly which leads to rework the products and hence decreases the productivity.
Predicting the weld-induced residual deformation before the production saves the valuable time and resources for
rework. The conventional coupled transient, nonlinear, elasto-plastic thermo-mechanical analysis involves huge computational
time. Computing a weld sample of small size with single pass itself takes several hours, which will be a huge
amount of time in case of large structures consisting of several welding passes; thus, there is a real need of an efficient
alternative technique to predict the post-weld distortions. In this work, an attempt has been made to determine the
deformation in a submerged arc welded structure using equivalent load technique which reduces the total analysis time
by one-third of the conventional techniques in case of a small weld structure. In this proposed method, the transient
nonlinear elasto-plastic structural analysis part which is the major time-consuming part of analysis has been almost eliminated.
So, this method can effectively use to predict the weld-induced distortion of very large structure with a computation
time almost equal to the time required for transient thermal analysis of a small weld structure only. It is not feasible
to analyze such a large welded structure with conventional coupled transient, elasto-plastic, nonlinear thermomechanical
analysis. The predicted results of distortions have been validated with the experimental as well as published
results and good agreements have been found.
... Solidification affects the microstructure [83,84], mechanical properties [85,86], and defects [24,87] in the resultant weld joint. However, solidification and the geometry of weld joint are highly dependent upon the prior fluid flow. ...
Weld solidification cracking is an important issue in fusion welding. If undetected, the cracking defects can act as stress concentration sites which lead to premature failure via fatigue, as well as offer favourable sites for hydrogen assisted cracking and stress corrosion cracking. For welded steel products such as deep sea oil and gas transportation pipes, such defects heighten the risk of catastrophic in-service failures. Such failures can lead to devastating environmental, economic, and social damage.
In this thesis, a comprehensive review of literature associated with steel linepipe and solidification cracking defects is first presented. Fluid flow prior to solidification is then observed and quantified in situ using a novel synchrotron X-ray radiography approach. The flow is dynamic at velocities up to 0.52 m/s and primarily driven via Marangoni flow.
The relationship between the microstructure and mechanical properties of the welded linepipe are extensively characterised, with a new equation derived to assess fracture toughness based on the size and distribution of carbonitride precipitates. Weld residual stresses are measured both before and after linepipe expansion in the U-forming, O-forming and expansion process for the first time using a neutron diffraction technique.
To further understand the fundamental mechanisms of solidification cracking during welding of high strength steels for subsea linepipe, a novel small-scale Varestraint test rig was developed for use in synchrotron X-ray imaging experiments and a Transvarestriant test rig utilised for industrial scale weldability tests. Solidification cracking during the welding of steel is observed in situ for the first time using a micro-radiography approach and the 3D crack network is rebuilt using a micro-tomography technique. It is proposed that solidification cracks nucleate from sub-surface cavities associated with: i) residual liquid high in solute and impurity concentration (hot cracks), ii) Ti (C,N) precipitated during solidification (that induce ductile microvoids). Solidification cracks then propagate via inter-dendritic hot tearing.
Underwater welding is the process of connecting materials underwater in the presence of water. It is used to maintain and improve the structure in marine and offshore applications. It's utilized for underwater pipeline maintenance, submerged offshore oil drilling, and ship repairs. It can also be found in nuclear power plants and deep-sea mining. Underwater welding is divided into two categories dry welding and wet welding. Dry welding entails enclosing the weld zone in a hyperbaric tank filled with a gas mixture and welding at the prevailing pressure. Wet welding is a type of welding that uses waterproof electrodes and is done directly on the component to be welded. The major benefit of this welding is its simplicity and cost effectiveness, but we can't obtain high weld quality as easily as we can with dry welding. Dry welding, on the other hand, may provide high weld quality, but it is a time-consuming procedure that needs the welder to secure the region with the hyperbaric vessel, and it is also a costly method. Underwater welding has a number of issues, including bubble arc generation, cold cracking, microstructural deformation, and more. We attempted to bring together the most recent developments in the field of underwater welding. We've outlined several techniques that were used to improve welding characteristics as well as important issues that must be addressed. This review article may be used to figure out what measures need to be taken to enhance the underwater weld joint quality.
