WHI Formula as a New Criterion in Automatic Pipeline GMAW Process

High-Strength Low-Alloy (HSLA) steel is a preferred material for pipeline construction due to its high strength, toughness, and resistance to environmental degradation. However, welding HSLA steel introduces significant challenges, particularly concerning the structural integrity, mechanical performance, and long-term durability of butt-fusion welds. The welding process produces fusion and heat-affected zones with microstructures that differ significantly from the parent material, often leading to graded structures, residual stresses, hardness variations, and susceptibility to brittle fracture or corrosion. This study investigates the influence of key welding parameters—including heat input, welding sequence, weld bead geometry, and post-weld heat treatment (PWHT)—on the microstructure, mechanical properties, and corrosion behaviour of HSLA pipeline steel butt-fusion welds. A series of controlled experiments were conducted in which standard butt-weld joints were fabricated under varying welding conditions. Tensile testing revealed that the base HSLA steel had an ultimate tensile strength of 426.62 MPa, yield strength of 404.27 MPa, and elongation at break of 32.5%. Optimized welded joints exhibited improved ultimate tensile strength of approximately 460 MPa. Impact toughness more than doubled, increasing from 30.4 J in the untreated material to 75.78 J in PWHT-treated welds. Hardness measurements indicated peak values of 653.3 HV in high-hardness HAZ regions, which decreased to 310.3 HV after PWHT, balancing strength with ductility. Electrochemical corrosion testing demonstrated that PWHT improved performance, with open circuit potential shifting from −0.58 V to −0.21 V and current density reducing from 2.2 × 10⁻⁴ A/cm² to 1.0 × 10⁻⁴ A/cm². Microstructural analysis confirmed the transition from ferrite–pearlite in the base material to acicular ferrite in the as-welded HAZ and tempered martensite after PWHT. Multi-response optimization using Taguchi signal-to-noise ratios and Grey Relational Analysis identified the optimal welding condition as Experiment 25 of the L25 Taguchi array, combining a 180 A welding current, 26 V arc voltage, 140 mm/min travel speed, and a heat input of approximately 1.8 kJ/mm, achieving a Grey Relational Grade of ~0.88. The results demonstrate that controlled heat input, appropriate multi-pass welding sequences, and effective post-weld heat treatment are essential for achieving HSLA welds with balanced mechanical properties, reduced susceptibility to cracking, and improved corrosion resistance. This study provides quantitative guidance for pipeline welding, enabling safer, more reliable, and cost-efficient fabrication while advancing the understanding of how welding parameters influence the microstructure and performance of HSLA steel butt-fusion welds. The findings are directly applicable to industrial pipeline fabrication and have implications for optimizing welding practices to prevent joint failure in service.

Arc welding is one of the most commonly applied methods in the welded manufacturing industry. The pulse MIG/MAG welding method (GMAW-P) was developed to prevent problems that may occur in the weld bead due to high heat input to the base metal during the feeding of the weld metal in MIG/MAG welding applications. The synergistic controlled welding machines have been developed that facilitate the selection of welding parameters and provide simultaneous feeding of pulsed welding wire by adjusting the variables to the most appropriate values relative to each other. Weld bead geometry is greatly influenced by welding process parameter, i.e., welding speed, welding current, shielding gas flow rate, voltage, arc travel speed, type of shielding gas, etc. In this study, steel welding samples in T-joint shape were produced with synergistic controlled GMAW-P. The effect of welding parameters on weld bead geometry was investigated. As a result of this study, it was determined that increases in weld wire feed speed, arc voltage, and welding current increased weld depths of penetration and weld bead thickness.

Statistical models were developed to study the effect of gas metal arc welding process parameters (i.e., wire feed speed, voltage, travel speed, and shielding gas chemistry) on the resultant weld bead width, penetration, and reinforcement height, using a factorial design of experiment. Analysis of variance (ANOVA) indicated that the weld width depended on voltage, travel speed, gas type, and the interactions between these factors. The weld penetration depended only on wire feed speed and gas type, as well as the two-way interactions of wire feed speed with travel speed and gas type. Reinforcement height depended on travel speed, wire feed speed, and their two-way interactions with gas type. Residual analysis revealed that all assumptions inherent in the regression analysis were satisfied over the range of welding parameters considered in this study. The predictive power of the statistical models was validated using intermediate process parameter values in the experimental design, and it was found that predicted values were mainly in agreement with the measured values for a 95% prediction interval.

Shielded metal arc welding (SMAW) and metal inert gas (GMAW) welding process are the two most widely used welding processes. These processes are widely used for the construction and fabrication purpose in almost all type of industries. Some of the important factors which govern the weld quality in these welding processes are welding power sources, role of shielding gas (for GMAW process), welding consumables and skill of the welders. Currently, effects of these factors are evaluated by examining the quality of the weld produced and not by monitoring how welding process is affected by change in these factors. This is an indirect method because actual contribution made by individual parameter in physical process is effectively ignored. Further, this is expensive and time-consuming as the assessment can be carried out only after the weld is completed. Hence, a procedure to assess the quality of welding process using the data acquired while welding is in progress is preferred to testing of the weld for this purpose. In both SMAW and GMAW processes, welding speed, voltage and current are important parameters that affect the quality of the welds. Among these, monitoring of welding speed is relatively easy; but monitoring voltage and current is not. This is because, welding is a stochastic process in which wide variation in voltage and current occurs and duration of these variations is so short that they are not observed in the voltage and current displayed in the power source. However, with the help of a high-speed data acquisition system, voltage and current variations during actual welding process can be recorded and subsequently analysed to reveal very useful information on the welding process, and subsequently quality analysis of individual welding parameters can also be done. In the present study, the voltage and current signals acquired using a digital storage oscilloscope have been used to study SMAW and GMAW processes. Data was acquired for duration of 20 s at a sampling rate of 100,000 samples/s while welding is in progress. In the case of SMAW process, welding data was acquired for welds made using different welding power sources, but with same welder and same type of electrode. In the case of GMAW process, welds were made using same wire and same welder but with different gases for shielding and at different set currents. Dynamic variation in the voltage and current signals were carefully studied using time domain and statistical analyses. Results showed that differences in the characteristics of the different power sources used for SMAW process and effect of shielding gases and arc current on GMAW process could be easily revealed by such analysis. For SMAW process, results obtained could also be correlated with the appearance of the weld beads. Hence, a procedure involving high-speed data acquisition of voltage and current signal while welding is in progress and the statistical analysis of the acquired data have been proposed for monitoring of these two arc welding processes.

ABSTRACTGas tungsten arc welding-tungsten inert gas (GTAW-TIG) is focused in literature as an alternative choice for joining high strength low alloy steels; this study is performed to compare the differences between gas metal arc welding-metal inert gas (GMAW-MIG) and GTAW welding processes. The aim of this study is to characterize microstructure of dissimilar transformation induced plasticity steels (TRIP) and martensitic welded joints by GMAW and GTAW welding processes. It was found that GMAW process lead to relatively high hardness in the HAZ of TRIP steel, indicating that the resultant microstructure was martensite. In the fusion zone (FZ), a mixture of phases consisting of bainite, ferrite and small areas of martensite were present. Similar phase’s mixtures were found in FZ of GTAW process. The presence of these mixtures of phases did not result in mechanical degradation when the GTAW samples were tested in lap shear tensile testing as the fracture occurred in the heat affected zone. In order to achieve light weight these result are benefits which is applied an autogenous process, where it was shown that without additional weight the out coming welding resulted in a high quality bead with homogeneous mechanical properties and a ductile morphology on the fracture surface. Scanning electron microscopy (SEM) was employed to obtain information about the specimens that provided evidence of ductile morphology.

Laser welding of NiTi shape memory alloy (SMA) and 2A12 aluminum alloy was realized by using a TC4 wire. Due to the poor metallurgical compatibility of Ti and Al elements, the surface appearance of welded joints was uneven and fluctuated. No obvious cracks were found on the surface. When the wire feeding speed increased to 280 cm/min, the pores at the interface disappeared. There were mainly a fusion zone (FZ), the NiTi SMA/FZ interface, and the 2A12 aluminum alloy/FZ interface in the welded joints. Some dendritic microstructures grew vertically toward the FZ at the NiTi SMA/FZ interface. The distance grown of the microstructure at the interface reduced while the wire feeding speed increased. Due to the increase of wire feeding speed and the decrease of the heat input per unit volume, the ability of the atoms to diffuse and migrate reduced and the trend grown of the microstructure was inhibited. For the FZ, there were α-Ti + β-Ti + Ti2Ni phases. The difficulty of decomposition for the β-Ti phase increased because the molten pool contained a large amount of the Ni elements and a small amount of Fe and V elements. After the molten pool cooled, there would be the β-Ti phase in the FZ. With the increase of wire feeding speed, the intermetallic compounds changed from Ni–Ti to Al–Ti. Besides, the fracture load of welded joints first increased and then decreased. When the wire feeding speed was 280 cm/min, the maximum fracture load of the welded joint was 176 N/mm and the fracture mode of the joint was an intergranular brittle fracture.

This study investigates the influence of Gas Metal Arc Welding (GMAW) parameters, current, voltage, and travel speed, on the penetration and quality of welds in AISI 304 stainless steel. A full factorial Design of Experiments (DoE) was employed to assess both the individual and interactive effects of these parameters. The results demonstrated that welding current is directly proportional to penetration, whereas travel speed exhibits an inverse relationship, reflecting their combined control over heat input. Voltage, in turn, presented a non-linear effect, with a marked increase in penetration observed specifically at 25 V. The interaction plots further revealed that the combination of high current and low travel speed maximizes penetration, corroborating fundamental arc welding principles. Moreover, a synergistic effect was identified between intermediate current levels (116–120 A) and a voltage of 25 V, which substantially enhanced penetration. These findings highlight that weld bead geometry and metallurgical properties are direct consequences of the thermal cycle imposed by the selected process parameters. Consequently, effective optimization requires an integrated approach that considers not only the isolated effects but also the interactions among current, voltage, and travel speed, thereby ensuring the geometrical control, metallurgical integrity, and overall performance of the welded joint.

The weld bead geometry is very important in predicting the quality of weld as cooling rate of the weld depends on it. For this purpose, the Taguchi technique was applied to determine optimum process parameters of weld bead geometry in submerged arc welding. The study involves using Taguchi’s L9 orthogonal arrays to conduct nine experiments on a 6 mm plate of IS2062 grade mild steel by using SKU MIL-SubArc AC/DC submerged arc welding machine with constant voltage. Three-levels of the four process parameters- arc voltage, welding current, welding speed and electrode stick out were considered and their effect on weld bead geometry−bead width, depth of penetration and weld reinforcement was observed. The signal to noise ratios was computed to determine the optimum parameters. From the results obtained, optimum process parameters of , and was suggested for weld bead width, weld penetration and weld reinforcement respectively. Regression analysis is done to establish the relationship between the input parameters and geometrical parameters of weld bead. The proposed mathematical model can be used to predict bead width, weld penetration and weld reinforcement values for any given SAW welding conditions.

The aim of the present work was to study the effect of flux, welding current, arc voltage, and travel speed on changes in microhardness and microstructure of the heat-affected zone (HAZ) and to optimize the process so that minimal changes occur in the material properties after completion of a submerged arc welding (SAW) process following suitable Taguchi experimental design. Micrographs of the welded samples were studied to analyse the changes in the microstructure of the material and the resultant changes in ferrite percentage, pearlite, bainite, and martensite formations. Welding current and type of flux were found to be the most significant factors leading to changes in microhardness and metallurgical properties. The microhardness tended to increase significantly with the increase of welding current from 350 to 450 Amp whereas higher hardness was observed when flux type I (basicity index 0.8) was used. Travel speed and arc voltage were found to be insignificant in relative comparison. Flux with basicity index of 0.8 showed a significantly higher microhardness compared to flux with basicity index of 1.6 (flux II). A higher amount of CaO and MgO present in flux II has a tendency to pick up carbon from steel workpiece, thus lowering the microhardness.

Experimental investigations and statistical modelling of dilution rate and area of penetration in submerged arc welding of SS316-L

Due to their simplified spatial shape, shell cylindrical designs have acceptable manufacturability. The latter makes it possible to use a variety of fusion welding methods in their manufacture, including the option of mechanized welding in protective gas environments. Such a technological process is considered to be sufficiently developed in terms of theory and application, as evidenced by specialized equipment for it and numerous recommendations for the selection of installation and running welding parameters. Analysis of such material demonstrates that the basic technology is welding in the lower position with a seam root lining or with the use of a suitable technological arrangement for rotating large structures to provide such conditions. Much more difficult to meet the quality requirements for a welded joint are repair and welding works of non-rotating structures with a one-sided approach to the welding zone and the absence of a seam root lining. In this case, welding equipment with electric or electric-mechanical control of the process of dropwise transfer of metal into the bath is used, regardless of the spatial position of the seam. However, in cases of single production or repair welding, classical welding sources are still widely used, in which the regulatory requirements for the weld are provided by its appropriate external characteristics, the effect of self-regulation of the arc and dynamic characteristics. Here, the variant of droplet transfer with a short circuit of the droplet to the bath is typical, with the characteristic instability of energy accumulation / return of the source choke at the stages of the arc and droplet and the corresponding behavior of the arc in different spatial positions. Since the parameters of the mode are interdependent and, thus, welding itself represents a poorly organized system that has a variety of physical parameters that cause different in nature, but tightly interconnected processes in the zone of weld formation. The best tool for assessing the condition and regulation of such a system today is planning an experiment with independent controlled (setting) parameters of the welding mode and quality feedback – the optimized amount of weld penetration. On the basis of the processing of the array of recommended data regarding the selection of the value of the setting parameters of the welding process by the procedure of constructing symmetric histograms and the distribution polygon and calculating the analytical model of the description of the distribution density for each setting parameter of the process, their average values are set with a probability of 0.9. The latter were used to calculate the actual values of the following parameters for welding a given material thickness – electrode wire diameter 1.6 mm, welding current 190 A, voltage 25±1 V, welding speed – 26–42 m/h, wire feed speed 21–29 m/h, electrode discharge wire 16 mm. On the basis of the specified reference base of parameter values, a planned experiment was set up and implemented to find the optimum on a matrix of a composite symmetrical three-level plan, as variable factors are set – process voltage, welding wire feed speed and welding speed; the height of penetration of the assembled parts is set by the response. The region of the optimum and the influence of the setting parameters of the mode on it, as well as the analysis of its response surfaces and cross sections of such surfaces demonstrate that the setting parameter – the source voltage should practically be constant at the level of 24 V and does not have a significant adjustment ability for the correction of the welding mode. The setting kinematic parameters of the mode are the wire feed speed and the welding speed, respectively 23 and 27 m/h, at the given arc voltage, they provide welding in one pass. In terms of the depth of the ability to adjust the quality of the seam formation, the welding speed prevails, since, all other things being equal, the wire feed speed is strictly correlated with the speed of its melting at a given diameter and electrode distance. The latter determine the actual value of the current, the value of which is limited by the source voltage, which is strictly specified and constant for the given process under study.

Within this manuscript, the comprehensive heat flow, as well as the energy balance for gas-shielded arc welding processes based on experimental investigations is discussed. The main focus lies on the gas metal arc welding (GMAW) process which is further analysed. Different calorimetric measurement methods and results for the separate determination of the energy content of droplet and welding arc as well as energy input into the component are presented. Additionally, heat losses to the surrounding atmosphere and the cooling energy of the external cooling power source system are analysed. The mean droplet temperatures are within a range of T dr = 2,350 … 2,700 °C. The studies also show that a specific manipulation of the droplet temperature during the welding process is not possible and droplet temperature depends on several parameters. Increasing the wire feed speed, reducing the diameter of the filler material or increasing the stick out length result in an increase of the droplet temperature. The analyses allow to conclude that the welding arc is mainly responsible for the weld seam penetration and the droplet temperature only contributes in a minor manner. Preliminary experiments also show that the heat input into the component is highly influenced by the selection of welding parameters. Measurements confirm that it is possible to increase the efficiency of welding processes for example by reducing the wire feed speed, using carbon dioxide shielding gas or increasing the stick out length. On the contrary, increasing the current or voltage or reducing the shielding gas flow reduces the process efficiency. The difference between the lowest and highest achievable value of efficiency can be more than 15 % for one specific welding process.

O processo A-TIG (soldagem TIG com fluxo ativo) consiste em depositar uma fina camada de fluxo sobre a superfície da peça antes da soldagem. A deposição da camada pode ser feita através de pincel ou spray, e a soldagem é realizada após a secagem. Verifica-se que com este processo é possível aumentar a produtividade (velocidade de soldagem) em até três vezes em comparação ao processo TIG convencional. Entretanto, os fenômenos físicos associados a este ganho prático de produtividade ainda permanecem sob discussão. Desta forma, o objetivo deste trabalho é analisar a eficiência térmica (rendimento térmico) e aporte térmico na soldagem com o processo A-TIG em comparação com o processo TIG convencional, utilizando-se de um calorímetro por nitrogênio líquido, como forma de contribuir para o melhor entendimento dos fenômenos físicos associados. Pelos resultados encontrados, se verifica que os efeitos da soldagem A-TIG sobre a geometria do cordão de solda se apresentaram de acordo com trabalhos anteriores. Em adição, de forma inédita, se destaca a menor eficiência térmica da soldagem A-TIG em comparação com a soldagem TIG convencional. A partir dos resultados encontrados, se nota que a constrição do arco é mais importante que a redução da eficiência térmica.

Numerical simulation of gas tungsten arc welding for ZW61 magnesium alloy thin plates

This paper presents a method for automatic control of arc length in tungsten inert gas (TIG) welding process using the arc voltage. By using this method, the role of operator in arc length control is played by an automatic control system based on a predefined arc voltage value for any special welding operation. A dynamic model for feed-rate mechanism and the relation between variations of arc length and voltage are described in details. Using a proportional-integral controller, variations of arc length in welding path is compensated with an automatic feed-rate mechanism in a normal direction to the welding path. By keeping the voltage constant during the process, a stable weld with higher quality and better appearance is obtained specially in welding of uneven surfaces. Theoretical and practical investigations show that the suggested method is able to control the TIG welding process successfully. Test results show that an accurate weld is obtained without the interference of the operator, and by comparing the predefined values of arc voltage with what is practically obtained, the welding gap is automatically adjusted.