Effect of Welding Process Parameters on the Mechanical Properties of TIG and MIG Welds in HSS X65 Pipe-A Review

The study focused on the importance of the different welding parameters on the mechanical behavior of High Strength Steel (HSS) X65 steel pipes by reviewing the advantages of parameter optimization for the Tungsten Inert Gas (TIG) - Metal Inert Gas (MIG) welding processes. The parameters considered in the study include welding speed, welding current, welding voltage and gas flowrate of the welding. The effects of improper selection and parameter optimizations were highlighted and illustrated using different metallurgical and mechanical instances. The outcome of the study indicates that adequate parameter optimization aids in obtaining good weld quality with adequate mechanical and microstructural properties. Furthermore, it helps in the determination of variation in hardness in the heat affected zone as well as the base metal. Thus, this study provides insight to welding engineers on the importance of parameter optimization in the welding of steel pipe.


Introduction
The increasing development in marine industries has led to more problems in marine structures which requires urgent attention during fabrication and maintenance [1].The use of underwater welding technology is very vital in the fabrication of SUS304 structures.This welding technology is divided into wet, dry and local dry underwater welding.In the case of the local dry underwater welding method, it involves the use of micro drainage device which is used to drain the water in the region of weld and local dry cavity is then created and then overcomes the obstruction caused by the underwater [2].All these would not have been possible without adequate process welding parameter selections.Based on this, [3] investigated the impact of welding speed on the stability of the process, mechanical behavior and microstructures of SUS304 structure fabricated using the local dry underwater pulsed metal inert gas welding.The result showed that increase in welding speed from 9 to 16.2 mm/second led to a significant improvement in the stability of the process and later deteriorated [4].
However, the rapid cooling using water as coolant caused the formation of δ-ferrite morphology and this caused a change from brittleness to ductility in the weldment.According to [5], the electric water heater is associated with leakages during service, especially at the weldment of the inner tank.This is 1322 (2024) 012009 IOP Publishing doi:10.1088/1755-1315/1322/1/012009 2 usually caused by stress concentration.Reducing the stress and the deformation will help in improving the service life of the equipment [6].Hence, the study investigated the process parameter optimization of the inner tank using numerical and experimental approach.The result indicates that sequential welding has minor impact on the reduction of the welding residual stress and deformation [7].The study confirmed that the welding stress and deformation gave a minimum value of 170 Mpa and 0.897 mm respectively.It was reported in the study of [8] that several industrial sectors usually deploy the nondestructive evaluation method in the manufacturing of components throughout their service life.However, the welded structures consist of have thick sections which require high integrity selection of welding parameters.Especially the use of multi-pass weld deposition selections.
Furthermore, it is a general rule that non-destructive evaluation of multi-pass weld must be done at the last step during the manufacturing timeline on the cold components and a sufficient period need to be achieved to be able to achieve defects like hydrogen cracking [9].Hence, real-time monitoring of welding can significantly help in reducing the defects and cost of weldments.In the study of Zhuang et al. [4], it was reported that high-temperature industrial processes like welding is associated with emission of particles which when mixed with hot air, is harmful and toxic to the environment and human being.Adequate parameter variation is known to curtail all these emissions which will help in achieving excellent weld joint especially in pipes.According to the study of Cai et al. [5], the mechanical properties and service life of welded pipes are influenced by parameter variations.This was validated by investigating the influence of using a higher heat input in activated TIG welding than the ordinary TIG welding.It was reported that higher temperature and dislocations were observed and this caused an increase in the strength of the A-TIG welding by about 10 % [10].
Furthermore, the TIG welding was observed to have higher proportion of ferrite and better in toughness and impact energy of about 10 % more than the A-TIG welding.Welds of high quality, adequate strength as well as mechanical properties are possible via the selection of parameters for welding [11].This is common in the combined TIG-MIG welding process.It was reported that localized melting and recrystallization results in microstructural variation and this melting depends on the selected welding parameters like current, welding speed, voltage etc. stabilizing the parameters for welding is very important as it helps in reducing the resistance of the arc, rooting effect and increase in the thermionic emission, increase in the efficiency of the melting process as well as depth of penetration especially in the welding of thick sections like HSS X65 pipes [12].In the study of Wu et al. [8], it was reported that TIG-MIG welding produces excellent weld formation compared to the conventional MIG welding process when high welding speed is considered.Based on this, the study considered the use of 3D transient model of heat and mass transfer using a weld pool to investigate the effect of varying welding parameters on high speed TIG-MIG welding process.Process parameters, behavior of the welding pool and the formation of beam in the weld to obtain the quantitative relationship between them was simulated by using parameters like current of the TIG, distance between the electrodes and welding speed [13].Furthermore, simulation of the heat flux, temperature field as well as the flow of fluid both on the longitudinal part and the upper part was carried out using the appropriate welding conditions [14[.
According to [9], the increasing demand in the use of low cost and weight reduction of structures, but with adequate strength has resulted in the application of titanium and aluminium structures in the automotive and the aerospace industries.This is because these elements provide adequate strength and low weight when combined compared to the use of a single material.However, it is important to know that to have these properties, there is a need to consider several properties because of the variation in the physical and chemical properties of the two elements.It was reported in the study that such dissimilar metals exhibit inadequate mechanical properties due to the complex and irregular weld pools which usually show up during welding.According to the study by [15], it was established that TIG and MIG welding process involves the use of gas shield especially in the fabrication of pipes and other structures.However, there is variation in their efficiencies.While the MIG welding has a higher efficiency when compared with the TIG welding process, incidentally, the MIG welding is associated with inadequate strength compared to the TIG welding.Hence, there is a need to improve the efficiencies via the use of technology especially when higher welding speed is required.These can happen by adequate parameter selection and parameter variation [16].
According to Chen et al. [11], it is possible to predict the synergetic behavior of the welding process by modelling the influence of the welding parameters.This is possible by adopting both the adaptive plane and the volumetric heat source model for each welding technique [17].The study developed an algorithm for the source of heat which could predict the quantity of heat deployed during the TIG-MIG welding process.Several control systems are important in the selection of the welding parameters during TIG-MIG arc welding process [18].This will not only help in obtaining the weld quality, but adequate parameter variation also that will cause reduction in the weld expenses as well as increasing the reliability of the welded component [19].

Welding Parameters in TIG-MIG Welding Process
Welding is a very vital process deployed in the joining of different metals together.While several methods existed for welding materials, it is important to note that the specification of weldment depends on the welding process involved.Thus, the parameter selection also varies irrespective of the material and its properties [20].Hassan et al. [12] investigated the effect of electrical current on the mechanical properties of weldment which involve medium carbon and stainless steels using both single lap joint and single V-groove Butt joint.The result indicates that there was increase in temperature when electrical current increases.It was equally reported that the increase in electric current resulted in the ultimate tensile strength and this depend on the type of joint.Furthermore, heat generated increases with increasing electric current for both the lap and butt joints in the TIG-MIG welding process [21].

Figure 1.
Output Heat for both MIG-TIG welding process for (lap and butt joint).[12] From the plots, there was a significant improvement in the welding temperature for an increasing current during TIG lap welding process.However, in the case of the MIG lap welding process, there was no significant improvement with the current.Overall, the value of temperature is higher for TIG welding process for both lap and butt joints.Furthermore, it was concluded that the ultimate tensile strength for the welded joints in the case of the butt joint was higher than the lap joints for the TIG welding.This information gave an insight in the right parameter optimization during TIG-MIG welding process [22].
Mahesh and Appalaraju [13] established that control of the process parameters is a major problem in welding process.This is because the process is time consuming and associated with numerous errors.Thus, there is a need to choose the appropriate welding parameter that can meet the weld quality.Similarly, another major problem associated with parameter selection is parameter optimization.This is because, different weld parameters are involved, hence the need for its optimization in other to obtain quality weldment.According to [23], there exist a residual stress with lesser degree when pulsed welding current was used in the welding of 304L austenitic stainless steel compared to the constant welding current.It was reported that there was formation of fine grains in the microstructure as well as higher ultimate tensile strength, also yield strength tends to be high for the non-pulsed current compared to the pulsed welding current for the welding of the stainless steel [24].For the TIG welding, the impact of the welding current was observed to produce excellent ultimate tensile strength compared with the weld done at higher current supply.According to [25], optimization of welding parameters will help in obtaining better microstructural and mechanical properties of combine TIG-MIG welding when compared to the standalone TIG and MIG welding process.This was validated by using TIG and MIG welding machine having a combine heat source of 400 A. Characterization of the welds was done using tensile tester, hardness tester and X-ray diffraction as well as the microstructural study for the TIG-MIG samples and the standalone TIG and MIG samples [26].While the input parameters selected are the welding speed, voltage and the gas flow rate in different variations.The result indicates that the combine TIG-MIG weld produced excellent tensile strength, percentage elongation and yield strength when compared to the standalone TIG and MIG weld respectively [27].Furthermore, it was observed that the fractography of the TIG-MIG was characterized by fine dimples which was uniform showing the characteristics of ductile failure [28].Similarly, the macrostructural assessment revealed that the heat affected area of the combined welding process was larger when compared with the standalone TIG and MIG welding techniques.There was heavy presence of acicular ferrite with evidence of cementite at the ferrite grain boundaries [29].
According to singh et al. [16], parameters of welding and processes aid in the penetration of the beads which eventually contribute to the development of weld with adequate qualities.To achieve this, the material composition must be the first step of the welding.In addition, physical properties such as density, specific heat, thermal conductivity, latent heat coefficient of thermal expansion must be well known.Furthermore, removal of dirt, oil, paint and other contaminants must be removed from the surface of the weld before the commencement of the TIG welding.Hence a way of inspecting the parameter is to check the weld beads of which the appearance will help in the adjustment of the welding parameters.Figures 2-6 showed the different beads formed due to some variations in the choice of parameters.From Figure 2, it was observed that there was adequate penetration into the base material [30].It was characterized by adequate bead width, flat bead profile and the toes of the weld experienced good tie-in, which is the edges where both the weld metal meet the base metal.Also, for Figure 3, it was observed that there was excessive voltage which led to inadequate control of the arc, thus causing inconsistent penetration and formation of turbulent weld pool which could not penetrate through the metal [31].

Figure 2. Good weld. [17]
On the other hand, Figure 4 demonstrates that there was low voltage during the weld which resulted from poor arc start, control as well as penetration.This led to the formation of excess spatter, inadequate tie-in of the weld and a formation of convex bead patterns.In the same vein, Figure 5 showed evidence of fast travel speed which led to the formation of narrow and convex bead on the weld surface with inconsistent tie-in at the weld toes causing inadequate penetration and formation of weld beads with inconsistency as a result fast travelling speed.Similarly, Figure 6 showed the result of using very low traveling speed which caused the formation of excessive heat in the weld and causing excessive width in the weld bead as well as poor penetration.For thinner materials, burn-through could occur [32].

TIG-Welding of Steel Pipes
The joining of steel pipes by incorporating fiber-based composites requires adequate parameter selection and optimization.In a study by Reddy et al. [18] carried a new technique for the welding of steel pipe by developing a systematic experimental programme using some selected weld parameters like current of about 600 A, voltage 80 V and temperature of 1200 degree Celsius.The first phase involves the use of black steel pipes with ASTM 795-grade B. It has 3-inch diameter and length of 200 mm and butt joint was created using TIG welding technique.The second phase involved carbon fiber and epoxy which were taken as matrix.20 % of carbon reinforcement and 18 % HY955 was deployed as a hardener while 62 % was used as the epoxy material, the composite was later applied on the different layers on the pipe and dried adequately.The third phase requires the preparation of the specimen from the joints of the steel pipes for the characterization process.Thus, tensile and flexural strength test as well as the hardness test were carried out from these specimens.It was observed that there was consistency in the weld and analysis easily examined during the TIG welding process.The overall result demonstrates that there was improvement in the tensile strength by about 26 % while hardness improves by 2 % and flexural strength by 4.16 %.It concluded that the improvement in the properties of the welded joints was because of the parameters selected.
According to [33], TIG welding process is applicable in robotics and automation processes.It has a superb weld bead in appearance with reduced slag and splatter which make it possible for clean weld.However, the use of high input heat during TIG welding limits its application in heavier foundation materials.Process parameters like travel speed, filler rod and current will help in the increase in the depth of weld as well as width ratio.Also, there will be reduction in the heat affected zone and reduction in angular distortion in the weldment.
According to [34], the performance of load bearing structures and pressure vessels are affected by defects and corrosion.TIG welding using adequate parameters will help in replacing the damaged parts.However, disruption in production always ensue whenever this problem occurs.It as well imposes huge cost on the operation.Thus, in-service welding using TIG welding is appropriate in restoring the strength of the failed piping systems developed from HSS X65 pipe.[35] developed a numerical method to analyze the temperature and the residual stress field during a multi-pass TIG welding using different pipes and electrode material.The study focused on the use of Abaqus software and Fortran programming to raise the temperature field and the residual stresses over the TIG process while the weld deposit was obtained by using the silent element technique.Furthermore, TIG welding was then conducted in two passes on SUS304 stainless steel pipe while the process was further modelled for three and four passes in axial and hoop stresses on the outer surface and the inner surface of the welded pipes.The result demonstrates that the base material has stronger impact on the tensile axial residual stresses of the outer surface compared to that on the inner surface.Similarly, welding pass number was observed to show no effect on the tensile residual stress on the inner surface of the pipe.In the study of [36], the residual stress in pipes can be reduced by controlling the external constraint.This is because the thin-walled pipe is widely deployed in the chemical and propulsion industries, hence there is a possibility of failure problems usually caused by the welding process.Thus, external constraints will help to control the residual stress as well as the deformations.

MIG-Welding of Steel Pipes
To increase machine/equipment reliability, it is important to focus on the various aspect of the product.Joints and strength of the material are very vital in the machine element design according to the engineers.The various parts of machines and its elements are joined via welding and an important concept of evaluating the reliability of the MIG welded joints is finite element analysis.This was established to be the best method of assessing the reliability and strength of welded joints.To this end, parameters for welding can have an optimized welding process with adequate qualities [38].According to [37], the significance of welding parameter optimization can never be overemphasized as it helps in the intelligent prediction and make it possible for data availability as well as reduction of experimental cost.To this end, the study deployed two-stage methods which incorporated Taguchi technique and the adaptive neurofuzzy system model for the optimization of the tensile strength of AISI1008 steel plates by focusing on the butt welds via MIG welding process.The welding parameters engaged include welding current, welding voltage and gas flow rate, which represent the input parameters of the model while the output parameter considered is the tensile strength.The result showed that the highest ultimate tensile strength was 99 Mpa while the result of the analysis of variance showed that the voltage contributes 57.3% compared to the welding current which contributed only 20 % while 10% was contributed to the strength of the weld by the gas flow rate.
The study of Chennaiah et al. [24] established that variation in the input heat of MIG welding of IS2062-EN31 dissimilar weldments have impact on the behavior of the welded components.The study established that application of low heat to fabricated joints demonstrates excellent metallurgical and mechanical behavior.Similarly, [39] established that welding parameters like speed, voltage, current and welding gas flow rate has significant impact on weld beads and its features such as bead height and width as well as bead penetration especially for stainless steel pipes like HSS X65 [40].

Conclusion
Residual stress is associated with welding processes and in most cases welding repair.This could threaten the safety of the welded pipes used in the power plants reactors, stainless steel pipes and in the pressure vessels.Thus, this study focused on the prediction of residual stress during the TIG and MIG welding processes and to determine its impact on the welded joint as well as the overall reliability of the pipes.From the review, it was established that residual stresses could result into fatigue damage and stress corrosion especially the tensile residual fatigue test.Thus, minimizing or its elimination will help the reliability and safety of weldments.
Considering the comprehensive review on the impact of welding process parameters on the mechanical properties of TIG and MIG welds in HSS X65 pipes, several key recommendations emerge to guide future research and industrial applications: Further exploration to identify specific parameter combinations that consistently yield optimal mechanical properties, balancing strength, ductility, and IOP Publishing doi:10.1088/1755-1315/1322/1/0120097 toughness in HSS X65 welds.Future research efforts should delve deeper into microstructural analyses of TIG and MIG welds, considering variations in welding conditions.Understanding the correlation between microstructural features and mechanical properties will contribute to refining welding strategies for enhanced performance.
Investigating the specific scenarios where TIG or MIG welding excels in terms of mechanical properties can inform practitioners in selecting the most suitable technique for HSS X65 pipe applications.Incorporating advanced characterization techniques, such as non-destructive testing and in-situ monitoring, can provide a more comprehensive understanding of the welding process.This recommendation aims to enhance the precision of assessing mechanical properties and identifying potential defects or irregularities.
Another recommendation is to explore the environmental impact of welding processes on HSS X65 pipes and aassess factors such as energy consumption, emissions, and material waste to align welding practices with sustainable engineering principles.By addressing these recommendations, researchers and practitioners can advance the field of welding technology for HSS X65 pipes, ultimately optimizing weld quality and contributing to the reliability and longevity of structures in diverse applications.