In most cases, welding is a critical issue and one that motivates a constant search for alternative solutions that can both reduce costs and increase efficiency. Supported by numerical simulation ...data, the present work evaluated the microstructure across the weld cross-section and the respective Charpy impact toughness at 0 °C for the different regions formed for the pipeline girth friction welding of the UNS S32205 alloy. The results indicated that the most important microstructural modifications occurred at the weld interface as a consequence of the combination of very high temperature and a great deal of plastic deformation. The considerable drop in impact toughness for this region is related to substantial changes in austenite morphology and an excessive ferrite grain growth. Moreover, pronounced austenite reorientation and increased ferrite fraction surrounded the weld interface, which in turn took its proportional toll on toughness. Finally, the analyses of the crack profiles revealed that as the crack advances to regions of either reformed or reoriented austenite crystals, cleavage facets appear on fracture surfaces in varying intensity, producing the corresponding reduction in impact toughness.
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High-performance alloys such as super duplex stainless steels (SDSS) are of interest to the oil and gas industry, especially in deep and ultra-deep reservoirs where high pressures and highly ...corrosive environments are prevalent. SDSS have high nitrogen contents and pitting resistant equivalent number (PREN) values greater than 40, however, fusion welds of these alloys can exhibit unsuitable microstructures and defects that may result in failure during usage. Solid-state linear friction welding (LFW) offers an alternative for the effective joining of SDSS with a less detrimental effect on microstructure and properties. In this work, four LFW joints in UNS S32760 SDSS were produced and investigated by evaluating the process parameters required to achieve a high-quality joint with the desirable metallurgical, mechanical, and localized corrosion properties. These properties were assessed through metallography (optical microscopy and scanning electron microscopy), tensile and microhardness tests, and corrosion analysis according to the ASTM G48A standard. Results indicated that one specific combination of LFW parameters led to a defect-free joint, and that the mechanical properties of the weld in this case were comparable to those of the base material. Additionally, an adequate balance between ferrite and austenite phases was achieved throughout the microstructural gradients seen in the weld region. Microhardness values were below 350 HV, thus complying with the DNV–OS–F101 standard. Furthermore, no pitting corrosion was observed in this joint under the testing conditions suggested by ASTM G48A.
9Ni steels have been recently adopted in supercritical CO2 injection systems in deepwater oil fields. The manufacture of these reinjection systems involves multi-pass welding procedures, which ...produce an Heat-Affected Zone (HAZ) with a high heterogeneity level regarding the microstructural features and the local mechanical properties. An extensive microstructural and micromechanical characterisation was performed over the HAZ of three welded joints with different heat-input conditions to evaluate the effects of the reheating cycles and the welding parameters on the microconstituents. Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD) analyses were performed to identify microstructural features that correlate to the local mechanical responses evaluated through an extensive microhardness mapping. Regarding the Coarse Grained HAZ (CGHAZ), the highest microhardness values for all welding conditions are found at the Supercritically Reheated CGHAZ (SCR-CGHAZ), characterised by its refined microstructure and a quite low area fraction of coarse martensite laths. The Subcritically Reheated CGHAZ (SC-CGHAZ) and the Intercritically Reheated CGHAZ (IC-CGHAZ) – regions where wider martensite blocks and higher coarse martensite lath area fractions were observed – composed the softer zones of the microhardness map. It was also found that reheating at intercritical temperatures induces the formation of supersaturated fresh martensite and may contribute to retained/reversed austenite particles’ C-enrichment, which may degrade the mechanical properties at the IC-CGHAZ.
Full-scale friction welding system for pipeline steels Chludzinski, Mariane; dos Santos, Rafael Eugenio; Pissanti, Daniela Ramminger ...
Journal of materials research and technology,
April 2019, Letnik:
8, Številka:
2
Journal Article
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A fully automatic friction welding system was specially developed for the girth friction welding of pipelines with a diameter of up to 400mm. The friction welding methods were solid-state joining ...processes based on the generation of heat through the contact and rotation of an intermediate ring placed between two pipes ends. The thermomechanical process used in this non-fusion method generated different welding zones and microstructures. This resulted in the production of defect-free API 5L X46 welded pipes in less than 5min. The microhardness profile of the welded joints showed an increase in the intermediate ring hardness. A fracture toughness test and fractographic analyses showed reduced values in the centre of the ring, which were associated with dimples nucleated at small inclusions.
High-strength low-alloy steels (HSLA) have been considered key materials for the petroleum industry for the construction of pipelines to move oil and gas for long distances. Conventional welding ...processes may produce important microstructural changes, which negatively impact the mechanical behavior of the pipeline material. Alternatively, pipeline girth friction welding is an excellent choice to lessen the detrimental effect on microstructure since it is a one-shot low heat input process. This work aims to optimize impact toughness – the most affected mechanical property - to qualify pipeline girth friction welded API 5L X65 steel joints according to the requirements of the DNV OS F101: 2013 international standard. The impact toughness optimization process relied on the evaluation of the welding parameters' effect on heat input and on post-weld heat treatment (PWHT). The results indicated that even though the single thermal cycle imposed lowered the size and fraction of martensite-austenite (M/A) constituent in the as-welded condition, impact toughness was notably reduced due to previously austenite grain growth and unfavorable crystallographic texture. However, at least part of the original base material's impact toughness can be restored by decreasing the heat input, although not sufficient to qualify the weld. Otherwise, PWHT led to grain size refinement and reduced crystallographic texture, which in turn improved impact toughness beyond the minimum level specified by the technical standard.
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•M/A constituent plays a minor role in the toughness of one-shot friction welded X65 steel.•Effective grain size and texture dictated the toughness of X65 steel welding joints.•Lower heat input showed to mitigate the texture in the thermo-mechanical affected zones.•PWHT lowered the grain size and the texture, producing qualified joints.•Weld interface oxidation hindered an even higher toughness, revealing a research path.
In this study, a new method for welding an API 5L X65 steel pipe that is internally clad with Alloy 625 cladding using Alloy 22 and AWS ER100S-G steel was developed. The first and second weld passes ...were made using Alloy 22 to provide excellent corrosion resistance for the Alloy 625 cladding region. The remaining weld passes were made using 100S-G steel to provide high mechanical strength. The welded joints were evaluated for their microstructure and mechanical properties. No significant solidification defects were found in the welded joints, as confirmed by bending and transverse tensile tests. The yield strength of the welded joint showed that welding was capable of delivering the necessary strength compatible with API 5L X65, X70, and X80 steels for subsequent installation using the reel lay process. The microstructure of the welded joint was complex, with the first two weld passes having a soft Ni-fcc matrix composed mainly of Alloy 22, while the first three 100S-G steel weld passes had a hard martensite matrix. The main region of the welded joint had a soft acicular ferritic matrix. Impact toughness testing showed that the energy absorbed by the notch positioned at the first steel weld pass was better than that for the notch positioned at the steel weld pass without a dilution effect for Alloy 22 (approximately 46 J and 14 J, respectively). The toughness of the weld pass increased due to the high Ni incorporation by dilution with Alloy 22, even at − 15 °C, while the steel weld passes that were not affected by dilution with Alloy 22 exhibited very low energy absorption, which is characteristic of steel materials assessed under conditions below the ductile-to-brittle transition temperature (DBTT). The fracture toughness tests confirmed this result, as the major steel weld passes exhibited brittle features that caused abrupt failure during the test at − 15 °C.
Experimental tests were carried out to evaluate and compare welding bead characteristics depending on wire’s oscillation frequency in the GTAW with dynamic wire feeding. Two constant currents (200 A ...and 250 A) and three frequencies (0 Hz, 5 Hz and 18 Hz) were used to lay an Inconel 625 filler metal over ASTM A36 steel substrates. The weld metal microstructure analysis was based on Scanning Electronic Microscopy (SEM) and the corrosion performance was assessed by means of the Cyclic Potentiodynamic Polarization method. As main results, the increase in wire’s frequency tends to promote more convex welding beads and a 22 % reduction of dilution, in addition to a higher spreading (and higher isotropy) of the precipitates in the material’s structure. For the high energy condition (250 A) the highest frequency also increased significantly the welding bead corrosion resistance. However, for 200 A cases the effect of the wire’s oscillation in the dilution and bead’s reinforcement was not so pronounced, although with higher frequency a greater spreading in phases precipitated was verified.
Effect of dynamic wire in the GTAW process Gonçalves e Silva, Régis Henrique; Correa Riffel, Kauê; Pompermaier Okuyama, Marcelo ...
Journal of materials processing technology,
July 2019, 2019-07-00, 20190701, Letnik:
269
Journal Article
Recenzirano
Odprti dostop
Experimental tests were carried out to evaluate and compare metallic transfer aspects and welding process behavior, in GTAW with dynamic wire feeding in relation to conventional mode (wire insertion ...in a continuous way with constant speed / steady state). Inconel 625 cladded steel plates were laid out at four main welding positions (overhead, vertical up, vertical down and flat). The metallic transfer analysis was based on wire’s tip monitoring, by means of high speed videography and monitoring of the difference of electric potential between tungsten electrode, wire and plate. Continuous wire feeding resulted in rupture of the contact between wire and puddle, which generated large droplets on the wire’s tip, which transferred in irregular intervals. This fact is a common occurrence mainly out of flat position and incurs in irregularity of metal transfer and of oscillographic behavior. For dynamic wire feeding the amount of molten metal in the wire’ tip (droplet) was minimized and the transfer frequency became regular, rendering a more stable and robust process. Also, the risk of electrode contamination was reduced. The benefits of dynamic feeding were observed for both constant and pulsed current.
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