Narrow Gap Welding Research Articles

Study on the Influence of Fusion Ratio on Carbon Migration Phenomenon in the Narrow Gap Welding of Dissimilar Steels

Study on the Influence of Fusion Ratio on Carbon Migration Phenomenon in the Narrow Gap Welding of Dissimilar Steels

Optimization of magnetic arc oscillation system by using double magnetic pole to TIG narrow gap welding

A magnetic arc oscillation system for tungsten inert gas (TIG) narrow gap welding is developed to prevent insufficient sidewall fusion and improve efficiency and quality for thick component welding. The characteristic of the system is that a double magnetic pole is induced by exciting current flowing through the field coil to generate the magnetic field within the welding area. This optimization of double magnetic pole not only enhances magnetic flux density compared with conventional single magnetic pole but also provides reliable melting of the sidewall. In this article, a new experimental method for the determination of the resulting heat input into the workpiece is proposed. Measurements of arc voltage and welding current flowing through the sidewalls are used to validate the redistribution of the arc heat. Furthermore, the difference of linear heat input of the sidewalls caused by current division ratio difference and arc voltage difference was the main reason why the formation characteristics occurred.

Experimental Investigation of Wire Arrangements for Narrow-Gap Triple-Wire Gas Indirect Arc Welding

A new narrow-gap welding process is proposed by applying triple-wire gas indirect arc (TW-GIA). There are double power supplies and triple wires in this system. Power supplies are only connected between electrode wires and base materials are not linked to power supplies. Since there are different wire arrangements with TW-GIA, this article studies these wire arrangements and their effects on sidewall fusion for narrow-gap welding. Results show that different wire arrangements lead to variant arc behaviors and metal transfer, and consequently they lead to different situation of sidewall fusion. The heat to melt sidewalls is mainly from the indirect arc column and metal transfer with narrow-gap TW-GIA. When side wires deviate from the main wire to opposite directions, heat from arc columns and metal transfer can concentrate toward groove sidewalls. When the whole weld torch is lowered, heat from the indirect arc column and metal transfer increases at the weld bead root.

A modified welding image feature extraction algorithm for rotating arc narrow gap MAG welding

Purpose The purpose of this paper is to provide a modified welding image feature extraction algorithm for rotating arc narrow gap metal active-gas welding (MAG) welding, which is significant for improving the accuracy and reliability of the welding process. Design/methodology/approach An infrared charge-coupled device (CCD) camera was utilized to obtain the welding image by passive vision. The left/right arc position was used as a triggering signal to capture the image when the arc is approaching left/right sidewall. Comparing with the conventional method, the authors’ sidewall detection method reduces the interference from arc; the median filter removes the welding spatter; and the size of the arc area was verified to reduce the reflection from welding pool. In addition, the frame loss was also considered in the authors’ method. Findings The modified welding image feature extraction method improves the accuracy and reliability of sidewall edge and arc position detection. Practical implications The algorithm can be applied to welding seam tracking and penetration control in rotating or swing arc narrow gap welding. Originality/value The modified welding image feature extraction method is robust to typical interference and, thus, can improve the accuracy and reliability of the detection of sidewall edge and arc position.

원자력발전 설비의 소재와 용접방법에 대한 최신 기술동향

Recent developing tendency of nuclear power plant are studied by searching of NDSL, KIPRIS, Science Direct and so on. Welding materials such as low alloyed steels, stainless steels, nickel-based alloys, zirconium alloy and welding methods such as narrow gap welding, laser beam welding, friction stir welding, overlay welding are investigated.

A full-field residual stress estimation scheme for fitness-for-service assessment of pipe girth welds: Part I – Identification of key parameters

In this two part series of papers, a recent comprehensive investigation of residual stress distributions in pipe and vessel girth welds is presented, covering component wall thickness from 6.35 mm (1/4″) to 254 mm (10″), radius to wall thickness ratio from 2 to 100, weld preparation from single “V” to double “V” to narrow-gap welds, and welding linear heating input from low (300 J/mm) to high (7,500 J/mm). Through the use of a residual stress decomposition technique, two key parameters that control through-thickness residual stress distributions in terms of their membrane and bending content have been identified by examining a large number of parametric residual stress analysis cases. One is component radius to wall thickness ratio (r/t) and the other is a characteristic heat input (Qˆ) having a unit of J/mm3. With these two parameters, a unified functional form for representing through-thickness residual stress profiles, along with its solution scheme, is proposed and demonstrated in this paper (Part I) for applications in weld region. A shell theory based analytical procedure is then introduced in Part II for estimating through-thickness residual stress profile at any axial distance away from weld regime. The effectiveness of the analytical estimation procedure is then confirmed by finite element residual stress solutions on a large number of component configurations and welding conditions.

Study on Solidification Cracking Under High-speed Narrow Gap Welding with Tandem Torches

In this research, the influence of various factors on solidification cracking under high-speed gap welding was investigated by nonlinear thermal-elastic-plastic analysis using the finite element method (FEM). To investigate the formation of cracks, the plastic strain increment in the brittleness temperature range (BTR) was introduced. In addition, to perform thermal-elastic-plastic analysis of a practical three-dimensional model, Idealized Explicit FEM was employed. In the simulations, the penetration shape was compared between the experimental measurement and the analyses to evaluate the analysis accuracy. As a result, it was found that the penetration shapes agree with each other. The heat input, welding speed, and torch distance were changed and the distribution of the BTR plastic strain increment was also compared to show the influence of the welding conditions. From the investigations, it was found that the BTR plastic strain increment increases with heat input, welding speed and decreases with torch distance.

SAW – Narrow Gap Welding CrMoV Heat-resistant Steels Focusing to the Mechanical Properties Testing

The paper deals with verification of multi-layer SAW welding the raw material W Nr. “1.6946” by different welding consumables (TOPCORE 838 B, Thermanit MTS 616) in the “ultra” narrow gap. An evaluation of the mechanical properties was done for both types welding consumables. The measured values of yield strength and the tensile strength exhibit comparable properties. The welded work piece by the welding consumable “Thermanit MTS 616” was found falling below the specified values of impact energy, ductility.

TIG narrow gap welding — new approaches to evaluate and improve the shielding gas coverage and the energy input

TIG narrow gap welding is one of the most important methods for joining thick components. Using narrow gap welding, steel plates with a gap, being only a few millimeters wide but several centimeters deep can be joined. Today’s developments are aimed at increasing the process reliability as well as the filling speed. Basic requirements are a sophisticated process understanding — especially concerning the arc attachment and the resulting energy input in the workpiece. Furthermore, the quality of the shielding gas coverage is one of the main important aspects for arc stabilization and the final welding result. In this article, new experimental and numerical methods for the determination of the energy input into the workpiece and the shielding gas coverage are presented. Measurements of electrical current and heat flow distribution as well as oxygen concentration at the workpiece surface are used to validate the numerical model. With the help of the validated model, physical effects can be considered separately, which allows a better investigation of narrow gap welding. The numerical model is also capable of visualizing high-speed processes, such as the transient gas flow and shielding gas coverage.

Investigation and development of technology for automatic argon-arc narrow gap welding of Du-850 pipes for reactor cooling plant to water–water reactors

The technology of automatic narrow-gap argon-arc welding of pipes of the main circulation pipeline Du-850 of water–water nuclear reactors is investigated and developed. Welding is carried out using automatic welding systems with Sv-10G1SN1MA welding wire. The welded joints were investigated by metallographic methods, and the mechanical properties were determined.

Applying statistical models optimize the process of multi-pass narrow-gap laser welding with filler wire

Laser welding of thick plates has been used in automobile and shipping industry owing to its focusing heat input, little welding deformation, and high productivity. Using narrow-gap technique can decrease the filling volumes of wire and increase the welding efficiency. However, its process is more complicated since it introduces filler wire to narrow-gap weld configurations. Usually the welding path, planning mainly depends on man’s experiences. Human factors have big influences on the quality of the joint. The aim of this paper is to study the interactions between welding parameters and the geometry of single bead using statistical methods. Then, the founded models were employed to plan the welding path, the number of filling passes, and layers in the multi-pass narrow nap joining. These results will provide supports for automatic multi-pass laser welding. The welding system includes a 10-kW Nd:YAG laser system, a KUKA robot, a Fronius wire feeder, and a 20-mm-thick high-strength ship steel with narrow gap. Laser power, welding speed, and wire feed rate are input variables. The responses include the transversal area of the added metals, bead width, bead height, and the ratio of bead width to height. Verification experiments indicate that all these models can forecast the responses within the factor domain. Transversal section micrographs of the joints show that this method can get welding joint with less defects.

Influences of lumped passes on welding residual stress of a thick-walled nuclear rotor steel pipe by multipass narrow gap welding

The purpose of this study is to investigate the effect of the lumped passes simulation on the distribution of residual stresses before and after heat treatment in a thick-walled nuclear power rotor pipe with a 89-pass narrow gap welding process. The local removal blind hole method was used to measure internal residual stress of the thick-walled pipe after post weld heat treatment (PWHT). Based on the ANSYS software, a two-dimensional axisymmetric finite element model is employed. Two lumped-pass models of M-5th model (five weld beads as one lumped pass) and M-10th model (ten weld beads as one lumped pass) were developed to reduce computational cost. Based on the results in this study, the distributions of residual stresses of a thick-walled welded pipe before and after PWHT are developed. Meanwhile, the distribution of the through-wall axial residual stress along the weld center line is demonstrated to be a self-equilibrating type. In addition, the investigation results show that reasonable and reliable lumped-pass model can not only guarantee the accuracy of the simulated results, but also improve the computational efficiency in the thermo-elastic–plastic FE analysis procedure. Therefore, from the viewpoint of engineering application the developed lumped-pass computational procedure is a promising and useful method to predict residual stress of large and complex welded structures.

Effect of geometric construction on residual stress distribution in designing a nuclear rotor joined by multipass narrow gap welding

The purpose of this study is to investigate the effect of geometric construction on the distribution of residual stresses before and after heat treatment in designing a nuclear welded rotor. The local material removal method was used to measure internal residual stress of the experimental pipe after post weld heat treatment. Three finite element models were employed as follows: a model of experimental pipe, a model with a bottom protrusion existed at the weld region, and a model of two rotor discs butt-welded with a bottom protrusion at the weld region. Investigated results showed that the bottom protrusion existed at the weld region can decrease the residual stress and mitigate the stress evolution significantly on the inner surface. Under the binding effect of the rotor discs, the axial stress of inner surface region is compressive stress; the through-wall axial stress at the weld center line can be deemed to a bending type; both the hoop stress and axial stress at the weld center line on the inner surface are compressive. The impact of geometric construction on the stress evolution at the root bead begins after pass 15 deposited.

Solidification cracking susceptibility of modified 9Cr1Mo steel weld metal during hot-wire laser welding with a narrow gap groove

Hot-wire laser welding with a narrow gap groove was applied to ASTM A213 grade T91 steel in the application of ultra super critical boilers. A filler wire according to AWS A 5.28: ER90S-G was used. The effect of the depth-to-width ratio (D/W) of a weld shape on the susceptibility to solidification cracking was investigated. With a groove width of 3 mm, solidification cracking did not occur with a D/W ratio of less than 0.6 and more than 1.2. The hot-wire laser welding method with a narrow gap groove seemed to be efficient for practical use, when the higher D/W condition was used without solidification cracking. The high temperature strain, which occurred during solidification, was computationally calculated in order to make clear the effect of D/W ratios on the susceptibility of solidification cracking in theory. From in situ observation using a high-speed camera of the hot-wire laser welding phenomena, a three-dimensional Finite Element Method (FEM) was simulated to estimate an equivalent plastic strain in the weld metal during welding. An approach to the moving heat source consistent with such phenomenon was proposed and validated based on experimental measurements. The simulation results presented that a moving heat source by hot-wire laser welding was able to produce a particular weld shape at a higher D/W ratio with a lower strain rate, which corresponded with the relationship between D/W ratios and solidification cracking in experiments. Therefore, such a hybrid process is a very interesting alternative process to reduce the solidification cracking in narrow gap welding, especially in modified 9Cr1Mo steel.

Evaluation of Microstructure and Mechanical Properties in a Thick Plate of G91 Steel and its Weld for High Temperature Nuclear System

The purpose of this study is to investigate the microstructure and mechanical properties in 9Cr-1Mo-V steel and its weld. A 220 mm thick forged plate with a typical composition of G91based on ASME A336 was used. Narrow gap welds were produced by submerged arc welding (SAW) with two different welding speeds. The microstructures in the base metal were typical tempered martensite at all locations, and the sizes of prior austenite grains were increased with the depth from the surface. The yield and tensile strengths tend to decrease with an increase in test temperature, especially at temperatures higher than 500oC. The upper shelf energy of the specimen from center was lower than that from the surface, and it also showed a higher index temperature. The toughness deterioration at the center might be caused by the larger size of the prior austenite grains and the existence of the delta ferrite. In the case of the weld, the larger sizes of the weld beads were observed in the upper region with a lower welding pass speed. There was no significant difference in the strength of the upper and lower welds, but the elongations of the upper weld were slightly larger than those of the lower weld. In the Charpy impact test, the lower weld showed a better impact toughness than the upper weld caused by the relatively smaller size of the weld beads and finer microstructures owing to a lower heat input by the increased welding speed.

揺動レーザを用いた狭開先溶接に関する基礎的検討

Laser welding with oscillation laser beam enables control of the heat input distribution. In this study, we attempted to develop a narrow gap welding process with oscillation laser welding. This process is expected to prevent lack of fusion because the entire bottom of the groove can be melted by the oscillation laser. As the first step of the study, bead-on-plate welding experiments with an oscillation laser beam were performed to investigate the relationship between the welding conditions and welding results. The experiments revealed that the oscillation conditions strongly affect the welding penetration shape. It was clarified that the wire melting phenomena in oscillation laser welding differed from those of straight (non-oscillation) laser welding. Additionally, narrow gap laser welding experiments were performed to investigate the relationship between the oscillation conditions and gap width. The results confirmed the effectiveness of oscillation laser welding for narrow gap welding.

Fatigue Crack Growth Studies on Narrow Gap Pipe Welds of Austenitic Stainless Steel Material

The objective of the present study is to understand the Fatigue Crack Growth (FCG) behavior in austenitic stainless steel pipe welds. The tests have been carried out on Compact Tension (CT) specimens machined from the actual narrow gap pipe welds. The notch was located in Weld Centre Line (WCL), Heat Affected Zone (HAZ), HAZ-Fusion Line (FL) interface and the parent metal. The comparisons have been made for the FCG rate for different locations of the crack. The tests were carried out using standard procedure of ASTM E647. The results of FCG rate of narrow gap welds (HAZ, WCL, HAZ-FL interface and parent material) have been compared with that of conventional V-groove welds of Shielded Metal Arc Welding (SMAW) process. The comparison shows that the fatigue crack growth resistance of narrow gap welds is better than conventional groove welds. The FCG resistance of weld and parent material is better than HAZ location in the Paris regime. However, parent material shows superior threshold crack driving force range.

A Digital Control for Swinging Arc Narrow Gap MAG Welding System

This paper presents a digital control system for swinging arc narrow gap MAG welding based on double single-chip microcomputers. The control system utilizes a single-chip microcomputer to set and display welding process parameters, and then uses another single-chip microcomputer to realize the control functions that are necessary for the swing arc process, in which the two single-chip microcomputers can exchange data through asynchronous serial communication circuit. Experimental results show that the control system works stably and reliably with strong anti-interference capabilities, and can completely satisfy the requirements of swinging arc narrow gap welding process.

Effect of the parameters of pulsed arc welding on the formation of a root layer in a narrow gap

The results of investigation of the effects of the pulse parameters on the formation of a root layer in narrow gap welding are presented.

Improvement in Welding of Austenitic Stainless Steel Thick Pipe: Metallurgical, Mechanical & Full Scale Pipe Weld Tests

The paper aims at demonstration of reduction in residual stress, distortion and sensitisation in austenitic stainless steel pipe welds. The welding processes considered are Gas Tungsten Arc Welding (GTAW) and Shielded Metal Arc welding (SMAW) along with Hot wire GTAW with narrow gap welding technique. It was shown that residual stress is significantly reduced in case of hot wire GTAW. The reduction in residual stress is due to the low heat input and high deposition rate. Lower heat input leads to higher cooling rate giving more margins on sensitization in heat affected zone (HAZ). This has been confirmed by measuring temperature and cooling rate during welding in HAZ of the weld joints. Susceptibility to sensitization of the welds has been compared by carrying out ASTM E262 Practice A and E along with Electo-Potentiokinetic Reactivation (EPR) method. The results of the tests show that values are within acceptable limit for both the cases. However, hot wire GTAW has marginally better sensitization resistance. Fatigue crack growth rate and fracture resistance behavior of the above mentioned weld joints have been compared by carrying out tests on the specimens (Compact Tension) and full scale pipe welds with crack. Fatigue crack growth rate and fracture toughness of the weld joints (hot wire GATW) is superior to conventional GTAW and SMAW. The paper presents the details of the above mentioned studies.