Weld Location Research Articles

Residual stresses prediction on clad pipeline girth welds through numerical simulation

It is generally known that different welding processes induce residual stresses into the weld joints, which may have a negative impact on fatigue and durability or other aspects of the in-service performance. This effect is of high interest in offshore pipeline girth welds, since they are typically not subjected to PWHT (Post Weld Heat Treatment). Although different methods of experimental measurements of the residual stresses are available their application in real context is extremely challenging or not convenient for several reasons, as a matter of example often the weld location and surface can make it problematic to access with the equipment, the execution of the measurements in a true non-destructive way is not feasible or more simply the execution of weld samples with very expensive equipment as the one used in offshore pipelines is not economical. In addition to this the stress field within or in the proximity of welds is of very complex and variable character and there appears a high level of plasticity, which makes the interpretation of local experimental measurements very difficult. For these reasons the prediction of residual stresses using numerical simulation of the welding process is today a very interesting and cost-efficient alternative. In this paper authors present the work where thermo-metallurgical and mechanical analysis of the thermal effects of the welding process using FEM based solver SYSWELD was done in order to determine residual stress field after girth welding of pipes made of carbon steel grade API 5LD X65 with internal alloy 625 cladding. The simulated process involves the execution of several external weld passes in gas metal arc welding technology and root re-melting with plasma arc welding process. Further variant simulations of the process were executed in order to evaluate the impact on residual stress field changing selected process parameters, namely the welding sequence. The use of numerical simulation finally allowed a deeper understanding of residual stresses field generation phenomena for the specific and quite complex welding process conditions.

Experimental study of rigid connection of drilled beam to CFT column with external stiffeners

This research is intended to investigate the behaviour of rigid connection of steel beam to CFT column with external T stiffeners. However, the investigations have shown that the stress concentration in the location of stiffener groove welds to the beam flange and column web causes abrupt fragile failure leading to ductility reduction of the connection. In the current study, beam section is reduced using the method of drilling beam flange so as to diminish the stress concentration and increase the ductility. This method is much easier to fabricate compared to RBS (cutting with CNC machine) and more applicable for existing buildings as well. In this research project two series of analytical models with constant and variable holes are investigated to evaluate the effects of different parameters of drilling on the local behavior of connections. Finite element method using ABAQUS software has been employed for analyses. In another part of this survey, two full scale samples are selected out of the analytical models, and experimentally investigated. According to the obtained results, drilling the beam flange results in decrease in stress concentration in the connection location of stiffener to the beam and column. In addition, it decreases the probability of failure in the expected modes 1 (shear failure of T-shaped horizontal stiffener) and 2 (tension failure of T-shaped vertical stiffener in connection to the column web) and increase the ductility of connection. Moreover, such connections can be used in the intermediate as well as special moment resisting frames.

Analysis of welding residual stress formation behavior during circumferential TIG welding of a pipe

The objective of this study is to analyze the formation behavior of welding residual stresses during the circumferential TIG butt welding of pipes. A three-dimensional thermo-elastic-plastic numerical model has been developed by using MSC-Marc software to predict welding residual stress distributions during single-pass welding of pipes. Using a numerical computational approach, the mechanisms of the changes in stress and strain throughout the pipe welding process is described. Compared with the features of butt welded plate joints, the distribution of welding residual stress in butt welded pipe structures is obviously different. Considering the deformation effect on the plastic strain distribution, the calculation results indicate that the axial and hoop compressive plastic strain at the inner surface of welded pipes is much larger than that at the outer surface. As a result, the tensile axial and hoop residual stress is generated at the inner surface due to the thermal contracting deformation. Consequently, compressive axial residual stress occurs at the outer surface because of the inward contracting deformation and internal stress self-balance. Moreover, it is investigated and explained the phenomenon in which both axial and hoop residual stresses have sharp gradients near the weld stop location at the overlapped weld line of pipe. Because of redistribution of axial residual stresses and hoop plastic flow behaviors, residual stresses near the weld stop location could be changed.

An approach to the path planning of intersecting pipes weld seam with the welding robot based on non-ideal models

Abstract In welding, the actual weld seam is the target path of welding robot. When the deviation between the actual pipelines and the ideal models cannot be ignored, special research should be carried out. This paper introduces a novel method to quantify and compensate the path deviation of actual intersecting curve, which is used to determine the welding path of robot. Weld location is a technical means, which can be used to find the position of some key points on intersecting curve. Combining the information of weld location with the inherent characteristics of intersecting curve, this paper has analyzed the results of actual welding experiments, all these works laid the foundation for the proposed algorithm. First of all, on the basis of previous studies, this paper introduces a kind of geometric model for ideal intersecting pipelines, this model can cover most of the ways of intersection. Secondly, based on this model, the factors leading to the deviation between the theoretical intersecting curve and the actual are analyzed. Generally speaking, there may be some connections or coupling between the deviation sources. In view of the above problem, this paper constructs model for each source of deviation and discusses the relationship between them, then quantifies the main sources of deviation by using the weld location information, especially the quantification of the main pipe's ovality. Subsequently, the deviation after the quantification is compensated to the parametric equations of the theoretical intersecting curve. As the goal of this paper, the actual intersecting curve's equations based on non-ideal model are obtained, which is regarded as the path of welding robot. The correctness and flexibility of the path planning approach are verified by the welding robot at last.

Recognition and identification the position and location of tooth saw butt joint shape

This research presents a new approach vision-based to recognize and locate the tooth saw joint position in butt welding joint. The research came out because some joints are quite difficult to recognize the butt welding position and location especially in a corner side or which one belongs to the tooth saw shapes. Thus, the main objective of this paper is to synthesize a novel approach that is related to weld joint identification and detection, and then develop a new approach based on contour regions for recognition and identification of butt welding joint in robot welding. The methodology involved in identification and detection approach was implemented in two stages: (1) pre-processing and (2) segmentation. The butt welding joint for recognizing position from the starting, auxiliary 1, auxiliary 2, and ending of the joint shape was obtained from contour and region points. The recognized process was done in two stages: (1) a new approach based on the shape of weld joints and (2) weld joint representation in three approaches which are (1) middle point of each end of two lines, (2) maximum or minimum row of the lines depending on auxiliary points, and (3) intersection point between the two lines. The findings of the approach show that the largest image-matching error happened in approach (3); however, this approach has a smaller matching error compared to the actual position. The expected output is that a weld joint can allocate the position from the start, auxiliary 1 and auxiliary 2, and end points in x-y coordinates to instruct the welding robot to weld. This research will significantly increase the welding process of mass production from low to medium volume manufacturing either repair or maintenance work should be faster than welding parts manually.

Critical Crack Size Investigation Method for a Land Launcher

Structural integrity evaluation of military systems is vital in such applications as rocket launchers. In safe life design, for a certain operational life the system is ensured to function well and no failure would occur even in the presence of some imperfections or flaws. This paper considers the fracture analysis as part of the safe life design approach that is used in the design of a rocket launcher. A methodology based on sub modelling technique is introduced. It was made sure that unstable crack growth would not occur upto certain crack sizes. Subsequently, after actual manufacturing of the launcher, critical locations of welds in the system were checked for presence of any cracks after repeated firing loads. After these controls no cracks were detected due to operational conditions until the time when this document was prepared.

Deviation quantification of the intersecting curve weld seam based on non-ideal models

When the deviation between the actual pipelines and the ideal models cannot be neglected, the intersecting curve weld seam based on non-ideal models should be specially studied. This paper will introduce a novel method to quantify the deviation of the intersecting curve weld seam based on the non-ideal models. Weld location is a technical means for obtaining the actual position of weld seam, which may be used to obtain the location information of some key points on the intersecting curve. Combined with the information of weld location and the inherent characteristics of the intersecting curves, this paper analyzes the experimental results of actual intersecting curve welding, and all these works laid the foundation for the proposed algorithm. First of all, on the basis of previous studies, this paper introduces a kind of model for intersecting pipelines, which can cover most of the ways of coherence. Secondly, based on this model, the factors which may lead to the deviation of the theoretical intersecting curve from the actual intersecting curve are analyzed. Generally, there may be some connections or coupling between the sources of deviation. Against the above problem, the paper gives a solution to model each source of deviation and discuss the relationship among them, and then makes use of the information of weld location to quantify the main sources of deviation one by one, especially the quantification of the main pipes ovality. Finally, the correctness and flexibility of the algorithm are verified by the MATLAB simulation.

Blade fracture analysis of a motor cooling fan in a high-speed reciprocating compressor package

Abstract This paper presents the root cause analysis of the blade fracture of the motor cooling fan in a reciprocating compressor package. The dynamic analyses results showed that the first-order torsional natural frequency of the fan was within ±5% of the fifth-order excitation frequency. In addition, the maximum dynamic stress of the fan operating in conditions of torsional resonance was 40.88 MPa, and exceeded the allowable stress of 36.12 MPa. Furthermore, the maximum dynamic stress occurred at the same locations where the cracks initially emerged. It was concluded that the excessive dynamic stress caused by the torsional resonance was the root cause of the fatigue fracture of the fan blade. Design improvements were implemented to adjust the natural frequencies of the fan, and included reducing the height of the blades, increasing the number of blades, and changing the weld locations. After the implementation of these modifications, the first-order torsional natural frequency of the new fan avoided the resonance regions, and the maximum dynamic stress of the new fan was 0.69 MPa, which was considerably lower than the allowable stress. No fracture problems occurred on the new fan.

Butt welding joints recognition and location identification by using local thresholding

Abstract Manual detection and identification of butt weld joints through welding image in real-time by human observation is subjective in nature, requires experience and can be biased at times. Furthermore, since that most of the welding robots application are programmed by teach and play means that they need to be reprogrammed each time they deal with new task. This is time consuming, plus welding parameters also need to be refined for every new program. Hence, this research aims to tackle the aforementioned issues by suggesting an alternative method that can automatically recognize and locate the butt welding position at starting, middle, auxiliary and end point under three scenarios which are; (1) straight, (2) saw tooth and (3) curve joint. This is done without any prior knowledge of shapes involved. A new approach known as local thresholding is proposed in the segmentation process which consists of image pre-processing, noise reduction and edge region points generation for butt welding joint identification. Region points for butt welding seam path are selected by shape selection generated from contour points according to the three scenarios. Each point is located by 2D coordinates that is usually used by robot controller for path planning. Experimental results showed that the local thresholding approach has managed to fulfill the research objective in detecting, identifying and locating the butt welding joint position in the three different scenarios. When compared with other methods such as background subtraction, local thresholding narrowly loses out in terms of less mismatch error produced. However, it gives the best results in the detection of the butt welding joint edges. Besides having the advantage of the ability to perform identification without prior knowledge from an image, local thresholding also showed that it can work just fine even in the presence of imperfections such as scratches on the surface of mild steel.

Experimental and numerical investigation of strengtheneddeficient steel SHS columns under axial compressive loads

In past years, numerous problems have vexed engineers with regard to buckling, corrosion, bending, and over-loading in damaged steel structures. This article sets out to investigate the possible effects of carbon fiber reinforced polymer (CFRP) and steel plates for retrofitting deficient steel square hollow section (SHS) columns. The effects of axial loading, stiffness, axial displacement, the position and shape of deficient region on the length of steel SHS columns, and slenderness ratio are examined through a detailed parametric study. A total of 14 specimens was tested for failure under axial compression in a laboratory and simulated using finite element (FE) analysis based on a numerical approach. The results indicate that the application of CFRP sheets and steel plates also caused a reduction in stress in the damaged region and prevented or retarded local deformation around the deficiency. The findings showed that a deficiency leads to reduced load-carrying capacity of steel SHS columns and the retrofitting method is responsible for the increase in the load-bearing capacity of the steel columns. Finally, this research showed that the CFRP performed better than steel plates in compensating the axial force caused by the cross-section reduction due to the problems associated with the use of steel plates, such as in welding, increased weight, thermal stress around the welding location, and the possibility of creating another deficiency by welding.

Integration process of stamping and welding for DP600 advanced high strength steel sheets

The springback behavior of AHSS (Advanced High Strength Steels) is more serious than ordinary mild steels. Currently, deformations due to springback can be compensated by modifying the tool geometry in the industry, which often consumes for a long time. In addition, the stamping parts usually need welding and assembly, and the welded part also has deformation. Therefore, an integrated process combines stamping and welding is presented in this paper, including stamping, placing welding parts and spot welding a total of 3 processes. This paper takes Ω-shaped parts as the object of study. The dynamic explicit method is adopted in the stamping process, and the static implicit method is used for the analysis of the stress release process. The effect of welding location, thickness of welding plate and width of welding plate on geometrical dimension are considered. Finally, the results of finite element analysis is evaluated by the validation experiment. The result shows that the combination of stamping and welding process can effectively reduce the springback value, and the deformation of the stamping part is less than 1mm. After the stress of the welded part is released, the stress on the inner and outer surface of the Ω-shaped part can be greatly reduced along the thickness direction.

Weld Seam Tracking System Based on Vision Sensing

The seam tracking system is designed for welds with very small gaps. This system is based on vision sensing technology. This system uses LED lamp as auxiliary light source, CCD camera as image acquisition unit and industrial computer as system control core. This system can extract the weld location information through a variety of image processing algorithms. After calculating the position deviation between the weld seam and torch, the system can control the actuator to look for the center of the weld. So the goal of weld seam tracking can be achieved.

Experimental Investigation of Tensile Test on Connection of Cold-formed Cut-curved Steel Section

Cold-formed steel (CFS) is widely used as structural and non-structural components such as roof trusses and purlin. A CFS channel section with double intermediate web stiffener and lipped is chosen based on the broader usage in roof truss construction. CFS section is cut to form cold-formed pre-cut-curved steel section and lastly strengthened by several types of method or likely known as connection to establish the cold-formed cut-curved steel (CFCCS) section. CFCCS is proposed to be used as a top chord section in the roof truss system. The CFCCS is to resist the buckling phenomena of the roof truss structure and reduced the compression effect on the top chord. The tensile test connection of CFCCS section, especially at the flange element with eight types of connection by welding, plate with self-drilling screw and combination is investigated. The flange element is the weakest part that must be solved first other than the web element because they are being cut totally, 100% of their length for curving process. The testing is done using a universal testing machine for a tensile load. From the experiment, specimen with full welding has shown as a good result with an ultimate load of 13.37 kN and reported having 35.41% when compared with normal specimen without any of connection methods. Furthermore, the experimental result is distinguished by using Eurocode 3. The failure of a full welding specimen is due to breaking at the welding location. Additionally, all specimens with either full weld or spot weld or combination failed due to breaking on weld connection, but specimen with flange plate and self-drilling screw failed due to tilting and bearing. Finally, the full welding specimen is chosen as a good connection to perform the strengthening method of CFCCS section.

Impact of Weld Locations of TWBs of Different Thickness Ratios on Dissimilar Steels on its Bulging Formability

This study aimed to analyze the impact of the weld location of TWBs of different thickness ratios on dissimilar steels, particularly on its height, which is known as the rigid hemispherical punch bulging formability. Laser welding was conducted on St12 (0.8 mm) and St16 (1.2 mm) samples using three different width ratios (1:2, 1:1, and 2:1). Then, the microstructure and microhardness of the TWBs and welded joints were tested. Finally, a rigid hemispherical punch bulging formability test was conducted to obtain the bulging formability of the TWBs for the study. Further, the results were compared to the bulging formability of the parent metal. The results show that the microstructure of welds contain all types of ferrites, bainites and lath martensites. The hardness on both sides of the weld is different, and it appears to be an asymmetric distribution. The hardness of the weld seam and heat-affected zone is much higher than the parent metal. The limit dome of the TWBs is lower for each side of the parent metal. When the weld location is parallel to the direction of the principal strain, the bulging formability of TWBs of different thickness ratios is much better. Under certain combinations of material and thickness, the thicker the plate is, the better the bulging formability of the different thickness TWBs is.

Measuring Residual Stresses in Orthotropic Steel Decks Using the Incremental Hole-Drilling Technique

Manufacturing processes such as welding cause residual stresses which exist in most steel civil structures, causing plastic deformations without any external loads. This type of stress is often overlooked during design. Nevertheless, residual stresses can have serious influence on the material strength and the fatigue life of the construction. This is also true for orthotropic steel decks which have many complex welding details. Since little is known about the distribution of residual stresses due to welding, a semi-destructive experimental test setup is developed for a stiffener-to-deck plate connection of an orthotropic steel deck. In particular, hole-drilling is used. The test procedure has been optimized to reduce measurement errors. The most important influencing factors on measurement accuracy are the surface preparation and the precision of the determination of the zero-depth. Once these measurement errors are optimized using proper grinding and visual inspection tools, a clear residual stress pattern becomes visible. The results confirmed the theoretical assumption of high tensile yield stresses near the weld location. However, at small distance from the weld, the residual stresses tend to decrease to almost zero.

Vibration-Based Method for Damage Detection at Welded Beams and Rods

In this work, a vibration-based method for damage detection at welded beams and rods is presented. The model of the structural element includes the effect of the added inertia due to the welding process. Two methods of solution, analytically and by means of the Finite Element Method (FEM), are presented. From the results obtained it can be asseverated that the method can be a useful tool to detect degradation of welded structures. In contrast to other existing methods for cracks detection, it is shown that several frequencies have to be taken into consideration to determine the wear characteristics of the welded elements, since depending on the location of welding, some frequencies can be very little sensitive to the reduction of rigidity at the welded section. The results presented show similar tendency to those obtained by other investigations for cracks detection when added inertia was not included.

Fatigue crack behavior in power plant residual heat removal system piping including weld residual stress effects

The piping in some residual heat removal (RHR) systems in nuclear power plants, made of 304L stainless steel, is subjected to a multiaxial cyclic stress state in the cold/hot water mixing zone due to thermal fluctuations. In addition, residual stresses produced by welds and/or surface treatments can be large in magnitude and be tensile or compressive, depending on the proximity to the weld location. Crack networks have been observed to nucleate and grow under these stress states. Prominent cracks originating from micro-cracks on the order of grain size continue to grow to a length of about 2.5mm. The thermal fluctuation is such that crack growth is in the high cycle fatigue regime. In this paper, the plane orientation and growth direction of these cracks with respect to the cyclic and mean stress states and their gradients are analyzed. The roles and interactions of shear, tensile, and compressive stresses with regards to the direction and orientation of the cracks are also discussed. Weld residual stresses (WRS) are decomposed into a local effect in tension near the weld and a structure effect in compression farther away, which also help explain some crack configurations in RHR systems. Moreover, a dependence of WRS field on spatial second derivative of weld temperature field is shown, which can have an important impact for comparison of measured and simulated WRS. Crack growth was also simulated with XFEM in the presence of WRS, with the principal hypothesis that mean stress acts only on crack opening.

Use of modified electrode caps for surface quality welds in resistance spot welding

Surface quality of resistance spot welds is important in many applications. The surface quality of welds made with a modified electrode cap on the face side of the weld was investigated and compared with welds made using a copper backing bar and standard electrode caps. The surface features of the spot welds were evaluated and compared using laser surface scanning technology. The results indicate that the welds made with the modified electrode caps are equivalent to the welds made using copper backing bars in regards to the surface quality. The weld lobes were determined for resistance spot welding using combinations of standard electrode caps, an Asian T-16-D type, and the modified electrode caps T-16-D-10 plus the T-16-D type, on the face and bottom side of the weld. The weld lobes made using the latter combination of caps are shifted towards higher currents compared to those welded with standard electrode caps. Metallographic examination was carried out to compare the weld nugget sizes and locations within the welded steel sheets for various welding parameters. Use of the modified electrode caps instead of the copper backing bars can increase flexibility of the welding process and significantly reduce cost of the fixtures utilised in the production lines.

Energy absorption behavior of tailor-welded tapered tubes under axial impact loading using coupled FEM/SPH method

Thin-walled tubes are widely used as energy absorbers. In this study, we evaluated the energy absorbing behavior of empty and aluminum metal foam-filled tubes with different taper angles (0°, 5°, 10°, and 15°) by using the Finite Element Method (FEM)/Smooth Particle Hydrodynamics (SPH) with the Feed forward Neural Network (FNN). Within the scope of the study, tubes composed of AL6061 and AISI1018 materials were designed by using three different weld locations (L0/L=0.25, L0/L=0.50, and L0/L=0.75). In the welded tubes, the thickness of the lower part (AISI1018) was held constant (1.5mm), while the thickness of the upper part (AL6061) and the foam density of the filler material were variable (0.5–2.5mm and 100–800kg/m3, respectively). Based on the analysis of the study results, it was determined that empty and foam-filled tubes with a 5° taper angle exhibited the best energy absorbing behavior. In addition, we also determined the optimum upper part thickness and foam density for obtaining the minimum peak force (Fpeak) and maximum specific energy absorption (SEA) values.

Test study on residual stress distribution of hybrid steel u-rib stiffened plates

Orthotropic steel bridges were found to experience early fatigue failures of several welded connections in the steel deck plate. The welding process inevitably produces welding residual stresses and deformations that should be evaluated and considered to better understand the fatigue life of steel bridges. Aiming to study the residual stress distribution of hybrid steel u-rib stiffened plates, the blind hole method was applied. Various parameters, including the plate widths, the ratio of the u-rib thickness to the motherboard thickness, and the steel strength of the combination of the u-rib with the motherboard, were considered, and nine specimens were subjected to experimental tests. The results indicate that strain release factors have great impact on the calculated residual stress: as the value of strain release factor increases, the calculated residual stress in absolute term increases accordingly. However, due to experimental errors, as the ratio of the motherboard to the u-rib thickness varies from 1:2 to 1:2.5 and the u-rib spacing increases from 120mm to 160mm, the residual stress value and the distribution change are not obvious; when different steel strengths were used in the specimens, as the material yield strength of the motherboard (u-rib) increases, the residual tensile stress peaks of the motherboard (u-rib) increase, while the residual tensile stress distribution of the u-rib (motherboard) remains essentially the same. Based on the comparison between the cutting method and the blind hole method, the values from residual stress test points appear to be similar; from the perspective of measuring points' distribution and the directions of the tested residual stress, the cutting method cannot test the weld location, and the residual stress at the measuring point can only be obtained along the cutting direction because the blind hole method can test the weld location residual stress, and the residual stress of the measuring point can be obtained in any direction.