Numerical Simulation of Transient Temperature in SMAW

Study of arc characteristics using varying shielding gas and optimization of activated-tig welding technique for thick AISI 316L(N) plates

This study investigates the influence of a nickel interlayer on the microstructure, mechanical properties, and creep performance of Tungsten Inert Gas (TIG)-welded AA2219 aluminum alloy, widely used in aerospace structures. A novel welding approach was employed by inserting 99.9% pure nickel foil between solution-treated AA2219 plates to enhance joint integrity. Optimized TIG welding trials were conducted under both single-pass and double-pass weld conditions, followed by comprehensive microstructural characterization, Vicker’s microhardness measurements, and thermo-static creep testing at 300°C under varying stress levels. The nickel interlayer promoted the formation of intermetallic compounds, including Al 2 Cu and Al 2 Ni, which refined the weld-zone grains and improved mechanical performance. The weld nugget exhibited a 25.18% increase in microhardness (94 HV) compared to the base material (70 HV). In creep testing, double-pass welds sustained 70 MPa with 2.71 mm elongation, representing a ∼20-fold improvement over single-pass welds. The findings demonstrate that nickel interlayers enhance weld texture, reduce defects, and improve directional strength, offering promising benefits for high-stress aerospace applications.

Influence of weld and plate geometry on the fatigue strength of cruciform joints

Force Reduction in Bending of Thick Steel Plates by Localized Preheating

In the current study, Tungsten inert gas welding is utilised in order to successfully combine the AISI 409 M samples, each of which has a thickness of three millimetres. The stainless steel used in the making of the filler rod has an ER308L designation and is 1.2 millimetres in diameter. The purpose of this research was to examine and explain the effects of increasing degrees of heat input on the microstructure and mechanical properties of welds produced by GTAW (gas tungsten arc welding) of AISI 409 M ferritic stainless steel with austenitic filler wires ER308L. Three unique heat input levels were utilised in order to complete square butt welding with a root spacing of 1.2 mm. These heat input levels were as follows: 0.57, 0.63, and 0.69 kJ/mm correspondingly. Metallographic analysis and mechanical testing were utilised in order to investigate the influence that the amount of heat input had on the characteristics of the welded joint. According to the findings of the research, joints created with a low heat input had superior mechanical properties compared to joints that were made with either a medium or high heat input.

The growing interest of using thick section of high strength aluminum alloy like Al- Zn-Mg in the fabrication of lightweight large transport container and pressure vessels necessitates the gas metal arc welding (GMAW) of this alloy. Due to its high strength, the weld joint of AI-Zn-hAg alloy is highly sensitive to fatigue failure, thus in any engineering application, an assurance about its desired tensile, fatigue and fracture toughness properties are of utmost importance. In the light of the recent observations on the superiority of using pulsed current GMAW over the conventional continuous current one to improve the mechanical properties of single pass weld of A/-Zn-Mg alloy, the present investigation has been planned to study the characteristics of multipass weld of thick section of this alloy prepared by employing pulsed current GI^AW process. The multipass welding of 25mm thick extruded section of an Al-Zn-Mg alloy has been carried out using pulsed current and continuous current gas metal arc welding (GMAW) processes. The welding has been carried out by employing 1.6mm diameter AI-!\/lg ('/41VS ASME: SFA-5.10 ER 5183) filler wire and commercial argon as shielding gas. The pulsed current welding has been performed by varying the pulse parameters such as the pulse frequency and duration and their effects on dilution, zinc pick-up, precipitation behavior, porosity content and tensile properties of the weld are studied. It is observed that the variation in pulse parameters affects the microstructure and dilution of weld deposit. The change in weld dilution has been found to control its chemistry (especially zinc level) and precipitate content dictating tensile properties of the weld. The characteristics of the pulsed current weld has been compared to those of the weld prepared by continuous current GMAW. The properties of the pulsed current weld are found superior to those of the conventional continuous current weld.

Efforts are made in this article to investigate the thermal and mechanical phenomena by presenting a coupled thermal and structural analysis of SA516 Grade-70 steel. This material has wide applicability in the fabrication of pressure vessels, boilers, etc., due to its excellent weldability and formability. An actual ongoing problem from a reputed industry, related to distortion during the shielded metal arc welding process, is considered and experiments are carried out on the chosen steel. Results are evaluated employing a two- step methodology, involving simulation. The first step encompasses thermal analysis, providing insights into transient temperature distribution, while the subsequent mechanical analysis offers data on residual stresses and distortion. In the case of heat input, a volumetric heat source with double ellipsoidal heat distribution is used whereas a plasticity material model with rate-independent bilinear kinematic hardening is adopted for the structural analysis. Additionally, temperature-dependent material properties are factored into both scenarios. The data derived from numerical analysis align closely with experimental findings, presenting valuable insights for fabricating industries.

Heavy section steel pressure vessels for light water reactor and aluminum tank for liquefied natural gas carrier are chosen to review the fabrication of pressure vessels. With regard to RPV, materials, effects of fabrication thermal history, fabrication procedure and advanced welding technique are dealt with. For the fabrication of aluminum cryogenic tanks for LNG carrier, a special factory equipped with plasma arc cutting, various automatic gas metal arc welding machines and so on, is advisable.

For many years, process licensors and/or end-users have frequently specified that the tempering temperature of C-Mn alloys and low alloy steels (i.e. Cr-Mo, Mn-Mo-Ni alloys) should be greater than the post-weld heat treatments (PWHT). Most of the time, tempering temperature is then required as much as 30°C (54°F) above the PWHT temperature, making it very difficult for steelmakers to be able to supply compliant materials, especially for heavy wall components. Application of rules in the applicable codes often leads steelmakers to request for deviations in cases where they become not compatible with material capabilities. This report is intended to illustrate the combined effect of tempering and PWHT on materials properties and to provide recommendations on how to tune smart the tempering treatment with the aim of proposing the most efficient complete heat treatment sequence. Data provided within this paper for C-Mn steels and low alloy grades (Cr-Mo and Mn-Mo-Ni alloys) prove that tempering can be performed at temperatures below, at or above one of PWHT without any adverse effect. Data from actual mill production records show that stringent material specifications can be met by steelmakers when they are allowed to tune smartly the heat treatment parameters (tempering temperature) in accordance with applicable construction codes. The data also demonstrate that limiting the tempering temperature in the lower range of allowed temperatures may be beneficial to customers as it gives more safety margins for fabrication and maintenance (i.e. potential repairs/modifications) of pressure vessels. It permits either to consider more cycles for PWHT or to perform PWHT at higher temperatures or for longer durations, while on the opposite, current trend imposing high tempering temperatures limits flexibility.

The efficiency, quality, and reliability of shell and tube heat exchangers are significantly influenced by the design and execution of tube-to-tubesheet (TTS) welding. The key factor includes the selection of materials, welding process, and accuracy of dimensional specifications. There are three commonly used TTS joint designs such as the expanded joint (no welding), seal-welded joint (single pass welding with or without expansion), and strength-welded joint (two pass welding followed by expansion) as per the American Society of Mechanical Engineers (ASME) Section VIII Div. 1 UW-20. An extensive literature review revealed a strong reliance on various welding processes but the designs were limited to traditional joint configurations. In the proposed study, an attempt was made to investigate TTS welding using the gas tungsten arc welding (GTAW) process with a three pass or three layer technique following the inspection standard (ASME Section IX QW 193). Experimental investigations were conducted on a 50 mm thickness carbon steel tubesheet (SA 516 Gr. 70 N) and 19.05 mm outside diameter (OD) with 2.11 mm thickness of carbon steel tubes (SA 179) using a GTAW welding machine for ten samples. The quality of the TTS joint was assessed through various inspection techniques in accordance with ASME Section IX QW 193.1-191.3, encompassing visual inspection, liquid penetrant testing, and macroscopic examination to identify the minimum leak path (MLP). The experimental findings demonstrated that the three pass GTAW technique significantly enhances the quality and reliability and also extends the life of TTS welds in heat exchangers due to better MLP.

High Strength low alloy steels containing various levels of C, Nb and Mn were used and for each of which, a simulated double thermal cycle was applied with the same first peak temperature and different second peak temperatures to produce HAZ microstructure corresponding to multi-pass weld. Effect of double cycle second temperature on the microstructure was observed and compared with single cycle results obtained from previous works, it was found that the percentage of martensite austenite constituent (MA) increases by Nb addition for all steels with the same Mn content and the increase in Mn content at the same Nb content shows an increase in MA area fraction as well. MA area fraction obtained for the double cycle is larger than that obtained for the single cycle for all steels used which imply that MA will have great role in the brittle fracture initiation for double cycle and the inter-pass temperature should be controlled for medium and high-carbon Mn steel to avoid large area fraction of MA. The beneficial effects of Niobium obtained in single pass weld were not observed for the double cycle or multi pass welds.

The amount of heat input during welding impacts the weld's thermal and mechanical behavior and the joint's properties. The current study involved conducting AA 6061 and AZ31B Mg dissimilar welding, using friction stir lap welding (FSLW) and ultrasonic vibration-enhanced FSLW (UVeFSLW). The comparison and analysis of the welding load, the weld's macro-microstructure, intermetallic compounds (IMCs), and joint properties were conducted by adjusting the process parameters. The study also examined the effect of ultrasonic vibration (UV) variations on welding heat input. The study demonstrated that it is possible to reduce the welding load by employing UV. Moreover, this impact becomes more pronounced as the welding heat input decreases. Additionally, the material flow in the weld, the width of the weld nugget zone, and the continuous IMC layer are significantly influenced by ultrasonic vibration, irrespective of the heat input during welding. However, the impact on large areas of irregular IMCs or eutectic structures is relatively small. Furthermore, achieving better joint properties becomes more feasible when a higher welding speed is employed for the Al alloy placed on top. Specifically, the impact of UV becomes more evident at higher welding speeds (≥220 mm/min).

The formation of dissipative mechanical fluctuations is due to the utilization of the frictional heat, generated by dissipative motion of the fluid, for the performance of mechanical work. Such dissipative energy conversions take place by means of cyclic thermodynamic work processes. [A. C. Peter, J. Acoust. Soc. Am. 58, S36(A), S108(A) (1975)]. These fluctuations consist of two distinct kinds: namely, those whose physical nature is purely “hydrodynamic” and those transmitted by the fluid in the form of acoustic disturbances. The current investigation highlights the energy balances of hydrodynamic fluctuations for the case of perfect gases. It is shown that for a given amount of heat input into the fluid due to the dissipation of its kinetic energy, the following energy balances apply when the specific heat ratio γ = 1.4: 89.3% of the dissipative heat input is used to build up the internal energy of the fluid, the remaining 10.7% being utilized in the performance of expansion work upon the surroundings. The succeeding collapse of the disturbance uses 17.9% of the frictional heat input for the performance of isentropic expansion work. The isentropic collapse is followed by a succession of fluctuations around the ambient pressure of the surroundings whose average work contribution may be considered isobaric. These fluctuations, which return the fluid to its initial equilibrium state, consist of a total work output utilizing 28.6% of the frictional heat (this work is implented on the fluid by the surroundings). In the same process the internal energy of the fluid loses 71.4% of the original frictional heat to the surroundings, thus completing the dissipative work cycle.

The microstructure and properties of welds of duplex stainless steels are affected by cooling rate, so it is important to control welding heat input, and welding is performed in accordance with the recommended welding heat input range. In recent years, the demand for thick plates has been increasing, and there is a need to improve the efficiency of thick plate welding (high heat input). However, the range of welding heat input for welding thick plates has not been studied. The purpose of this study was to examine whether high heat input welding is possible for duplex stainless steels, and to propose a new welding heat input range that contributes to higher efficiency in welding thick plates. No sigma phase precipitation or hot cracking was confirmed in the weld metal and HAZ of 20 mm-thick duplex stainless steel (SUS329J3L) welded with heat inputs of 5 kJ/mm and 7 kJ/mm, which exceed the recommended heat input range, and good mechanical properties and pitting corrosion resistance were confirmed. Based on the TTT diagram, we examined the conditions under which sigma phase does not precipitate in SUS329J3L. As a result, the effective heat input is 3 kJ/mm, which is the upper limit of the recommended heat input range, when the plate thickness is about 10 mm. However, as the plate thickness exceeds 10 mm, the effective heat input at which sigma phase does not precipitate increases with increasing plate thickness, and the upper limit of the weldable heat input range becomes considerably larger, and good properties of welds were obtained even at a heat input of 7 kJ/mm in this study. Therefore, the upper limit of heat input to obtain sound welds in duplex stainless steel should be determined by the plate thickness, which will allow high heat input welding for welding thick plates and improve the efficiency of welding.

Fatigue crack growth experiments were conducted on low alloy steel submerged arc weld metals representative of those used in the fabrication of pressure vessels. Variations of wire composition, flux type, and postweld heat treatments were used to produce weld deposits of different microstructures and tensile and toughness properties. Fatigue crack growth experiments were conducted on 25.4-mm (1-in.) thick modified wedge opening loaded (WOL) specimens at room temperature and 288 °C (550°F). A compliance calibration curve was developed at room temperature and adjusted for use with elevated temperature compliance measurements. Results of these experiments indicate: (a) a slight effect of flux type on crack growth rates, (b) incomplete tempering or relief of residual welding stress, or both, has an appreciable effect on crack growth behavior, (c) comparable or lower crack growth rates at 288°C (550°F) compared to room temperature, (d) comparable or lower crack growth rates than those predicted in Section XI of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, and (e) variations in crack growth rates due to wire, flux, and postweld heat treatment were less pronounced than the variations in toughness and tensile properties.