Shell Weld Research Articles

Research on welding defect examination technique based on phased array ultrasonic for high voltage transformer oil tank welds

Oil tank of high voltage transformer plates. During welding and operation, defects such as incomplete fusion, incomplete penetration , air holes and cracks may be produced which influence the integrity and density of the welds and the whole tank. In order to test the integrity of the shell weld of high-pressure transformer box and ensure no leakage of transformer oil, the phased array testing technology is used to detect the defects of the butt weld of the transformer oil tank. The characteristics of weld defect detection under the condition of incomplete penetration were studied, and the sound beam accessibility, process selection principle and probe selection principle were theoretically analyzed. The test tests were carried out on the artificial samples of the butt weld of the transformer oil tank plate. The results show that the phased array can effectively detect the defects in the weld of transformer tank shell under the condition of incomplete welding, and the imaging results are intuitive and easy to judge, which can effectively evaluate the integrity of transformer tank weld. During the process selection, the probe-wedge combination with appropriate front distance and detection Angle should be selected according to the wall thickness, weld penetration depth and crown width of the transformer oil tank. During defects judgment, the interference of structure echo wave and incomplete penetration area should be considered. The assistant defect positioning analysis based on incomplete penetration is also suggested.

Application of Distributed Fiber Optic Strain Sensors to LMQXFA Cold Mass Welding

The future High Luminosity upgrade of the Large Hadron Collider (HL-LHC) at CERN will include the low-beta inner triplets (Q1, Q2a/b, Q3) for two LHC insertion regions. The Q1, Q3 components consist of eight 10 m-long LMQXFA cryo-assemblies fabricated by the HL-LHC Accelerator Upgrade Project. Each LMQXFA Cold mass contains two Nb3Sn magnets connected in series. A stainless-steel shell is welded around the two magnets before the insertion into the cryostat. There is a limit on how much coil preload increase induced by the shell welding is allowed. Distributed Rayleigh backscattering fiber optics sensors were used for the first time to obtain a strain map over a wide area of a Nb3Sn magnet cold mass shell. Data were collected during welding of the first LMQXFA cold mass and the results confirm that the increase of the coil pole azimuthal pre-stress after welding do not exceed requirements.

Production of blanks for flexible waveguide sections of the spacecraft by laser weld-ing

Currently, JSC ISS named after Academician M. F. Reshetnev is working on the development of the production of billets of flexible waveguide sections (DHW) with sections from 2010 to 7030, with a wall thickness of 0.1 mm made of BrB2 copper alloy. The maximum deviation of the size of the inner channel is not more than 0.1 mm. Such methods of manufacturing DHW blanks by pressure, such as rolling and drawing, take up to 20 working shifts and include a large number of cycles (from 6 to 8), require heat treatment and etching of parts after each cycle. In this regard, the task was set to reduce the complexity of the production of DHW blanks. The solution to the problem can be welding of shells from sheet blanks on a forming device, followed by the execution of a longitudinal seam. As part of the solution of the task, the calculation of the amount of energy required to melt the edges of the part was carried out, the analysis of the possibility of assembly by various welding methods for welding thin-walled shells with exact dimensions was carried out. The analysis of the material showed that welding should be carried out in inert media. The following methods were chosen for welding the samples: arc welding in the environment of argon protective gas with a non-melting electrode, microplasma and laser welding. In the course of the work, 30 samples of 100200 were welded, showing that 70 % of the samples are defective during arc welding and microplasma welding, while only 5 % are formed during laser welding. The following conclusions are obtained: with arc welding methods of small thicknesses, unacceptable defects occur due to the instability of the arc, whereas when using laser welding, uniform formation of the weld is observed. Metallographic studies and tensile tests were carried out on samples welded by laser welding, showing the specific strength of the weld metal at least 90 % of the strength of the base metal and the absence of defects in the cross section of the weld metal.

Three-Dimension Crack Propagation Behavior of Conical-Cylindrical Shell

The conical-cylindrical shell is prone to stress concentration in the convex cone position under the action of deep-sea pressures. This results in unidirectional or bidirectional positive tensile stresses on the surfaces of the shell. The conical-cylindrical shell is a large, welded structure. Welding residual stress was generated at the cone-column joint position, resulting in high-stress concentration at this location. Under both the residual stress of welding and seawater pressure, cracks easily form and propagate on the shell weld toe, leading to fatigue damage and even structural failure. In this paper, based on the seawater’s alternating load and the residual stress of welding, the three-dimensional crack propagation process was studied for the submarine conical-cylindrical shell. The effects of crack depth and shape ratio on crack propagation trend and fatigue life were analyzed. The results can provide references for predicting the crack propagation trend, assessing the remaining life and evaluating the structural safety of the submarine conical-cylindrical shell.

HDPE@UHMWPE Powders for Power Bed Fusion Based Additive Manufacturing

AbstractCommercial UHMWPE powder of 60 µm size (d50) embossed with 2–5 wt% of nanosilica is used as a support for the preparation of core–shell HDPE@silica@UHMWPE particles. The HDPE shell is generated by polymerization of ethylene in toluene slurry after treatment of the silica@UHMWPE with a methyl aluminoxane activated bisimine pyridine iron complex. Heat pressing the powder gives a solid material with identifiable original UHMWPE particles and a layer from fusion of UHMWPE and the surrounding HDPE shell; the properties match those of the UHMWPE base material. The powder flow properties of the HDPE@silica@UHMWPE are insufficient for a powder bed fusion process, a value for the flow function between 2 and 3 is measured in a ring shear tester. Additivation with nanosilica helps to overcome the insufficient flowability and allows the material to be recoated in a power bed fusion system. Laser sintering gives evidence for a substantial mixing and welding of the HDPE shells and UHMWPE. Caking at the surface of the built parts hinders the manufacturing of isolated parts. Further additivation with carbon black reduces the caking; however, the welding within the HDPE@silica@UHMWPE material is much less strong.

Strategy for D-shape assembly of ITER vacuum vessel sector #06 as applying 3D metrology

The first sector of the ITER vacuum vessel (VV) has been delivered to the ITER Organization. One of the critical manufacturing steps is d-shape assembly. The manufactured four poloidal segments (PS 1, 2, 3, 4) are assembled, and then form the d-shape structure with a height of 11.4 m. Each PS is a complex and heavy double-wall structure with an inner shell and outer shell, poloidal and toroidal ribs, and in-wall shielding blocks are filled inside of the double wall as radiation shield. Thus, it is quite difficult to handle for assembly in keeping with the segment final dimensional status, so that it is necessary to set a practical plan. Before conducting actual assembly, the d-shape is virtually fitted using all results of final 3D metrology on each PS. In detail, each inner shell as-built result on four interfaces, plus a margin for welding shrinkage and gap for welding are considered to set the d-shape fit-up reference. To set each PS in the right position as comparing the fit-up reference, the fiducial posts (FPs) on each PS are measured using a 3D metrology system. After done the fit-up on the assembly plate, whole FPs (55 ea.) are checked as verification. As a result, the PS2 and PS4 are shifted Avg 7.4 mm and Avg 7 mm to the poloidal way, respectively. After finished inner shell welding, the whole FPs are also measured. The PS2 and PS4 are still shifted Avg 1.4 mm and Avg 0.8 mm to poloidal way, respectively. Eventually, the as-built dimension on the important part is evaluated with given tolerance as a preliminary prediction of the final d-shape result.

Pressure Welding of Shells with Creep and Plasticity

An approach to calculating the pressure welding of shells is proposed. Expressions are obtained for states of plasticity, creep, and creep–plasticity in pressure welding.

Research on Station Balance of Robot Production Line Based on Improved Double Population Genetic Algorithm

Aim to solve the balance problem of robot production line, an improved double population genetic algorithm is proposed. The priority relation of production process is treated as the constraint condition, the selection function of crossover probability and mutation probability is designed according to the individual fitness of the population. Then the beat optimization algorithm is used to optimize the production rhythm of a switch shell welding line. The simulation result show that the balance rate of this robot welding line is improved and the production rhythm is optimized.

Welded joint permissible defects influence on the resource of a vertical steel tank under low-cycle loading

This paper is devoted to the VST determining the residual life issues by the shell welds low-cycle fatigue criterion with permissible defects, taking into account a typical stress concentrator, which has not been fully studied. The fatigue tests results analysis for materials made of low-alloy steel, taking into account welded joints, is given. The Ansys software package has built a model and calculated the stress-strain a vertical steel tank lower belt state for storing oil and oil products VST 20000 with a branch pipe. It is shown that the VST design most dangerous point is in the branch pipe upper part. The maximum stresses and stress amplitudes were obtained in the stub pipe zone and the wornom seam. The cycles to failure performed calculations number showed that the lower VST belt without welded joints wall area withstands 2.4 times more loading cycles than the area with a welded seam and 9.3 times more than the dangerous point in the nozzle stub area.

Pressure welding of shells under creep-plastic compression

A calculation scheme for pressure welding of shells is proposed. Analytical expressions are obtained for the material in the states of plasticity, creep and creep-plasticity during pressure welding. Keywords: pressure welding, plasticity, creep, time, relaxation. mpf-tula@rambler.ru, vladimir-chudin@yandex.ru

Non-Destructive Detection of GIS Aluminum Alloy Shell Weld Based on Oblique Incidence Full Focus Method

In this paper, a new ultrasonic phased array full focus imaging method based on oblique incidence is proposed to solve the problem of the non-destructive testing of the internal defects in the GIS (gas insulated switchgear) shell welds. By using wedge coupling, the measured weld is far away from the near-field range of the transducer, and the detection angle range can be increased by changing the propagation direction of the acoustic beam. Based on Snell's law, the propagation characteristics of the ultrasonic wave in the interface are studied. On the basis of the conventional ultrasonic array matrix and the full focus imaging algorithm, by introducing the energy attenuation calibration coefficient of the acoustic wave propagation through the wedge, the correction amplitude of the specific focus point p(x, z) is obtained, The non-destructive testing of weld defects of GIS shell in the spot is carried out, and the test results show that the qualitative and quantitative detection of the weld defects can be well realized by using this method.

Mechanical and fracture properties of aluminium cylinders manufactured by orbital friction stir welding

AbstractButt welding of AA6063 aluminium cylindrical shells was performed using the orbital friction stir welding (FSW) method. Tool rotation speed and orbital speed (i.e., traverse speed of rotating cylinder during welding) were considered as variable, and the strength and the mechanical properties including tensile strength, microhardness, mode I fracture energy and mode I crack growth behaviour of manufactured cylinders were investigated experimentally. A novel and subsized test specimen was designed and manufactured for fracture testing of specimens extracted from both base metal and weld zone region of cylinders. The initial precrack was introduced along (i) the tool penetration through the pipe thickness (i.e., T‐direction) and (ii) along the tool travelling direction (i.e., L‐direction). It was found that the crack growth resistance and fracture energy values of FSW samples are greater than the corresponding values of base aluminium material along both “L”‐ and “T”‐directions. Also, the fracture resistance value in T‐direction was higher than the L‐direction for the whole tested FSW samples with different welding speeds.

Demonstration of Structural Integrity of Boiling Water Reactor Pressure Vessels Under Ultimate Response Guideline Operation

In recent years, the compound beyond-design-basis accident (BDBA), which combines earthquake, tsunami, or some other severe events to impact a nuclear power plant (NPP), has received more attention. After the Fukushima nuclear disaster, the licensee of NPPs in Taiwan established the ultimate response guideline (URG) that instructs operators to perform reactor depressurization, low-pressure water injection, and containment venting to prevent core meltdown and hydrogen explosion once long-term loss-of-power and water-supply events occur. In this paper, we employed the probabilistic fracture mechanics (PFM) method to evaluate the structural integrity of boiling water reactor (BWR) pressure vessels under URG operation. At first, models of the beltline shell welds for BWR vessels associated with the Pressure Vessel Research Users Facility-Exponential flaw distribution were built for the PFM Fracture Analysis of Vessels–Oak Ridge (FAVOR) code. Then, the thermal-hydraulic data of URG transients for Taiwan domestic BWRs were imposed as the loading conditions. The analysis results demonstrate that performing URG operation will not cause significant fracture probability even at extreme embrittlement conditions. If long-term station blackout occurs due to a compound BDBA, the URG procedures can prevent core damage and hydrogen explosion, while maintaining the structural integrity of the reactor pressure vessels.

Failure analysis of an exploded large-capacity liquid storage tank using finite element analysis

In case of liquid storage tank has been designed regardless of international standards and there is little interest with its operating conditions, it may lead to fully or partially failure. This paper has studied a failure of Toluene storage tanks with different capacities. Toluene is a liquid aromatic hydrocarbon C7H8 which is toxic, flammable and may cause boiled liquid expanded vapor explosions (BLEVE). Failure analysis was performed to determine the root causes of toluene storage tank failure as well as corrosion influence. Axisymmetric finite Element analysis (FEA) was performed for fillet welding of tank roof and top shell zone to develop a relation between weld electrode size and tank diameter at each type of weld electrode to determine the main framework of roof to top shell welding process. Also, to develop a relation between tank diameter and maximum stresses that resulted at every amount of vapor pressure according to maximum von-Mises stress theory. The optimum roof to top shell welding size is obtained through the circumference welding path. The results of analysis allowed us to redesign the tank according to API 650 and to express the recommendations for toluene storage tanks operation.

Failure Analysis of an Exploded Large-Capacity Liquid Storage Tank Using Finite Element Analysis

In case of liquid storage tank has been designed regardless of international standards and there is little interest with its operating conditions, it may lead to fully or partially failure. This paper has studied a failure of Toluene storage tanks with different capacities. Toluene is a liquid aromatic hydrocarbon C7H8 which is toxic, flammable and may cause boiled liquid expanded vapor explosions (BLEVE). Failure analysis was performed to determine the root causes of toluene storage tank failure as well as corrosion influence. Axisymmetric finite Element analysis (FEA) was performed for fillet welding of tank roof and top shell zone to develop a relation between weld electrode size and tank diameter at each type of weld electrode to determine the main framework of roof to top shell welding process. Also, to develop a relation between tank diameter and maximum stresses that resulted at every amount of vapor pressure according to maximum von-Mises stress theory. The optimum roof to top shell welding size is obtained through the circumference welding path. The results of analysis allowed us to redesign the tank according to API 650 and to express the recommendations for toluene storage tanks operation.

ANALYSIS OF DEFORMED CONDITION OF SHUTTERS LOCATED ON ROLLER-PROOFERS

When assembling the shells of cylindrical vessels and apparatus, there are increased requirements for deviations of geometrical parameters and for the accuracy of installation of internal devices. The requirements for deviations of the shape and size of the shells of cylindrical vessels and apparatus, the maximum allowable values of the displacement of the edges during welding of shells were considered. The study of deformations will allow to understand their structure, which, in turn, will increase the accuracy in the manufacture of vessel shells and apparatus. Most of the cylindrical shells are assembled in a horizontal position when the shells lie on the roller supports. The article presents an analysis of the deformations arising under the action of gravity in the shells located on the roller supports. A simulation of the deformations occurring in the shells located on the roller bearings due to the action of gravity was carried out using the finite element method. The simulation was carried out in the ANSYS software package, in the Mechanical APDL module. The dependences of the magnitude of the maximum strain as a function of the angle of the rollers were studied. The dependence of the deviation of the conventional axis of the apparatus on the real from the distance between the pairs of rollers was also investigated. Methods for controlling the geometric parameters of the shells, such as a mechanical profilograph and an automatic system for controlling geometric parameters using modern laser technologies, were considered. The results of the study showed that gravity did not significantly affect the deformation of the shells. The studies did not take into account the residual welding stresses, stresses and strains that occur during the assembly of the shells. The obtained value of the optimal angle of location of the rollers is 140o. It is necessary to establish the maximum angle of location of the roller, if they can not be located at an angle of 70o. The deviation of the real axis of the apparatus from the conditional is within 0.5 mm, which does not significantly affect the accuracy of production. The resulting ovality of the end and central sections under the influence of gravity on the body does not exceed 0.1 %, which is within the limits of acceptable values.

Hot pressure welding of hemispherical shells

The process and methods of calculating the conditions of pressure welding of hemispherical shells in local deformation are proposed. It is assumed that the material is viscoplastic. An energy method for calculating the parameters of the process is proposed. The results are presented and components and spherical containers made of a titanium alloy are described.

Ultrasonic high-frequency guided waves for the inspection of shell weld in core support structure of fast breeder reactors

This article reports an ultrasonic high-frequency guided wave based methodology for inspection of shell weld of core support structure of the main vessel in 500-MWe sodium-cooled prototype fast breeder reactor. The high-frequency guided waves are generated in 30-mm-thick plate of core support structure at 2 MHz (frequency–thickness product of ∼60 MHz-mm). These wave modes are fairly nondispersive over considerable distance of propagation through the material. In order to understand the generation and propagation characteristics of these high-frequency guided waves, a series of two-dimensional plane strain finite element models are developed using explicit scheme. The optimum transducer placement for generating efficient high-frequency guided wave is achieved by sweeping the transducer position along the curvature of the main vessel plate with respect to the centerline of the vertical shell support plate. The generated high-frequency guided waves are analyzed and identified with the help of dispersion curves and time–frequency analysis. The simulation results are found to capture the features observed in the experimental measurements rather well, and the time of flight of the reflected waves in the simulation is found to be in excellent agreement with the experimental results. The optimum transducer locations for inspection of a general T-joint configuration with different angles between the web and the base have been studied in detail using finite element simulations. With optimum transducer position, the high-frequency guided waves are also used to inspect the artificially introduced defects in the connecting weld of shell support plate. It has been demonstrated that the high-frequency guided wave could detect defects of 20% wall thickness (6 mm) in the connecting shell weld.

Sub-surface stress measurement of cross welds in a dissimilar welded pressure vessel

Manufacturing process of pressure vessels used in high-temperature applications normally needs employing dissimilar metal welds (DMWs) between austenitic and ferritic steel. However, high amount of thermal stresses at the welds are induced due to differences in coefficient of thermal expansion between the types of steel. This study investigates the evaluation of welding residual stresses in a pressure vessel manufactured by DMW of 316 L stainless steel shell to A106 carbon steel caps as well as similar welding of stainless steel shells. By using longitudinal critically refracted (LCR) ultrasonic waves, the residual stresses are experimentally measured. The ultrasonic method is based on acoustoelasticity law by which the ultrasonic wave velocity could be connected to the material stress. By changing the frequency in which the ultrasonic transducers are working, the LCR waves are able to penetrate in various depths of the material in order to measure the sub-surface residual stresses. Hence, four main aspects are considered in this study: (I) stress evaluation of the DMW; (II) sub-surface stress measurement; (III) stress evaluation of longitudinal weld and (IV) stress measurement in cross weld. It is demonstrated that the residual stresses of the DMW pressure vessel could be comprehensively evaluated by using the LCR method.

Fabrication of full-size mock-up for 10° section of ITER vacuum vessel thermal shield

In this paper, a full-scale prototype fabrication for vacuum vessel thermal shield (VVTS) of ITER tokamak is described and test results are reported. All the manufacturing processes except for silver coating were performed in the fabrication of 10° section of VVTS. Pre-qualification test was conducted to compare the vertical and the horizontal welding positions. After shell welding, shell distortion was measured and adjusted. Shell thickness change was also measured after buffing process. Specially, VVTS ports need large bending and complex welding of shell and flange. Bending method for the complex and long cooling tube layout especially for the VVTS ports was developed in detail. Dimensional inspection of the fabricated mock-up was performed with a 3D laser scanner and the scanning data was analyzed.