Pipe Welds Research Articles

Investigation on Weld Characteristic, Welding Position, Microstructure, and Mechanical Properties in Orbital Pulse Current Gas Tungsten Arc Welding of AISI 304L Stainless Steel Pipe

Orbital pipe welding is carried out in this study by Pulse Current Gas Tungsten Arc Welding (PC-GTAW) without metal filler (autogenous) of AISI 304L stainless steel pipe. The dimensions of the specimen are 114 mm outside diameter and the thickness of 3 mm. This study investigates the effect of pulse current parameters, weld position, and pulse width on the characteristics of weld geometry, mechanical properties, and microstructure. The welding method used in this study is the continuous current and pulse current. The mean current of each parameter is the same at 100 ± 0.5 Amperes, but in the pulse current, there are variations in peak current, base current, peak current time, and the base current time. The welding speed used is constant at 1.4 mm/s. The result of weld geometry on the outside of pipe has shown that the flat (0°) position is concave and the overhead (180°) position is convex due to the influence of gravity. The microstructure indicates that the fine cellular dendritic structures appear at PC-GTAW. The PC-GTAW can produce good mechanical properties such as the tensile strength and the micro-hardness. The tensile strength of the specimen is reduced 14.23 % from the base metal at parameter 65-B and the flat position.

Application of Metallographic Investigation in Development of Sub-Sized Specimen Testing Techniques

Currently, there is a growing interest in testing of mechanical properties using sub-sized samples. Using these methods, it is possible to measure the current mechanical properties of the component without the necessity of shutting down the device. This is advantageous in the cases, when the residual life (especially in the energy sector) needs to be evaluated. Another advantage of this method is that due to the very small dimensions of the extracted piece of material, only the local properties of the component are tested. Thus, the miniature samples can be extracted from areas that are critical for material failure, e.g. in the transition area of welded joints and thin-walled pipes, in a direction other than axial (for axial direction standard tensile test can be used). Another small specimen application can be found in the development of new materials. Modern materials (e.g. additively processed materials) are usually highly expensive, so miniature samples are an ideal solution. It was observed that the MTT results are fully comparable with the results on standard test pieces without the need for correlation. Mini-Charpy samples (3×4×27 mm) were used to determine transition temperature FATT. In this case a correlation relationship between the Mini- Charpy and standard sample Charpy (10×10×55 mm) constant C = 60 was successfully found

High-Temperature Ultrasound NDE Systems for Continuous Monitoring of Critical Points in Nuclear Power Plants Structures

High temperature pipe cracks are the root of a steam power failure in the EU typically every 4 years, resulting in loss of human life, serious accidents and massive financial losses. According to IAEA’s Reference Technology Database, such an event on a nuclear power plant has an average cost of €120 million, including outage costs, emergency repair costs, insurance and legal costs. Since only one growing crack is needed to cause a major failure, they have to be inspected and monitored thoroughly. Breakdowns at extreme conditions (e.g. 580°C, 400 bar) are a result of two major weld failure modes: a) creep cracks near pipe welds; b) fatigue cracks on pipe welds. Current maintenance practice is to proceed with repairs on a detected crack according to its severity. For cost reasons, cracks that are not judged as severe enough will not be repaired. Crack severity judgement is based on its probability to cause a failure and this probability is derived taking into account the crack size and operational lifetime. More variables such as operating temperature and vibrations may rarely be found in other studies. Recent data from fracture mechanics statistical studies shows this connection between the size of a crack on a nuclear power plant pipe and its probability to lead to a failure. To deal with the above problems two Structural Health Monitoring (SHM) systems have been developed and they are presented in this work. These systems are able to achieve continuous operation for an extended time period at operating temperatures of nuclear power plants. The developed systems employ novel phased array (PA) ultrasonic and ultrasound guided wave (UGW) probes able to withstand and continuously operate even up to 580 °C. The systems are designed to be permanently mounted on superheated steam pipes, at locations of known defects and to continuously monitor their size. However, this supposes that defects will have already been detected by a traditional method during an outage. The PA transducers are placed according to the Time-of- Flight Diffraction (TOFD) technique’s topology, thus creating a novel configuration, while the UGW transducers are placed on a stainless steel ring in a circular array configuration. These configurations can enable continuous tracking of cracks growth with high accuracy, enabling maintenance crews to estimate the severity directly and not through statistics.

Mechanical Properties Evaluation in Friction Stir Welding of Different Pipes

The friction stir welding is used for joining non-ferrous and ferrous materials whether tube-shaped sections or flat plates in several manufacturing applications like aerospace applications, transport land applications, and shipbuilding applications. This study is focused on friction stir welding joining for similar and dissimilar pipes as (AISI 316 Austenitic Stainless steel with API 5L carbon steels, 6063 aluminum alloy with API 5L carbon steels, 6063 aluminum alloy with C36000, 6063 aluminum alloy with C12200, 6063 aluminum alloy with 6082 aluminum alloy, AL 6063 alloy with AL 7022 alloy, 7022 aluminum alloy with C12200, 7022 aluminum alloy with C36000 and C36000 with C12200). The study was conduct for these joints to evaluate the mechanical properties by tensile test, visual inspection, and Microhardness test. In friction stir welding of these alloy systems, six welding parameters were used, rotation speed of (775, 1000, 1300 and 1525 rpm), welding speed of 1.7mm/min, axial force of 8.5KN, with a clockwise direction of rotation, and zero degree of tilt angle, using a tool with a threaded cone geometry pin. The results show that for (AL6063 with AL6082 weld joint cases the best case was case 19, AL6063 with AL7022 weld joint cases showed that the best case was case 21 and C36000 high-leaded brass with C12200 copper alloy showed that the best case was case 36).

Friction stir welds of aluminium alloy pipes: an investigation of defects and mechanical properties

ABSTRACT With the elimination of solidification defects, friction stir welding becomes the most effective process for joining flat and curved surfaces. Tool geometry (tool pin profile, shoulder diameter) and tool rotation speed mainly contribute to the overall weld quality. The study evaluates the simultaneous effect of tool geometry, rotational speed, base offset and double pass Friction Stir Welding (DP-FSW) on the defect formation and the mechanical properties. Micro-structure and macro-structure have been analysed for weld strength and hardness characterisation, and found, at high tool rotation speed maximum hardness is achieved in the Stir Zone (SZ). A small tunnel present near the middle proved to be more detrimental than the large one at the bottom. Grain refinement in the SZ was 87.2% while augmentation in hardness was 21.3 HV. Maximum tensile strength of approximately 103% with decent bead profile is obtained, using taper cylindrical tool at 710 rpm with 14 mm shoulder diameter. Fractography of the fractured surface revealed a pure ductile failure. It has been discovered that with base offset the strength of the weld is increased. However, reduction of 4.8% was obtained with DP-FSW. Better weld profile gives better strength. With DP-FSW, a significant improvement in bead surface is obtained.

Influence of welding sequences on induced residual stress and distortion in pipes

A three-dimensional (3D) finite element (FE) model based on thermal-elastic-plastic approach in SYSWELD® was employed to investigate the effects of welding sequences on induced residual stresses and radial distortion in AISI 316L stainless steel welded pipes. To mesh the model, the HYPERMESH® processor was utilized and the model was then exported to SYSWELD® for further thermo-mechanical analysis. The Goldak's double ellipsoidal moving heat source model was employed in SYSWELD® to obtain the volumetric heat flux density in the Gas Metal Arc Welding (GMAW) simulation process. A neural-network program was suitably trained and used to predict the parameters of Goldak's model. The obtained numerical models using predicted Goldak’s parameters were then successfully validated by experimental results in terms of size of welding pool and the temperature distribution. Four different welding sequences (concepts) were investigated and compared: three quarters and one full circumferential welding. These welding sequences were anticipated to create the least residual stress and distortion in pipe welding. The results demonstrate that the welding sequences significantly influence induced residual stresses and distortions in magnitude and in distribution. For the full circumferential welding concept, which was proposed in this study, the residual stresses and distortion present more uniform distribution along the circumferential direction than those in quarter welding sequences. The magnitude of welding distortion was also significantly lower in the full circumferential concept when compared to the quarter welding concepts. The FE results of residual stresses in the full circumferential welding sequences were accurately validated by experimental tests.

Mechanical and Microstructural Properties of HDPE Pipes Manufactured via Orbital Friction Stir Welding.

In recent decades, extensive research has been performed on the friction stir welding of flat-shaped materials while pipe welding, particularly polymer pipes, still encounters challenging issues. This work presents a feasible route for joining high-density polyethylene (HDPE) pipes using an orbital friction stir welding (OFSW) set-up properly designed with a retractable pin tool. Fully consolidated joints were achieved using a portable heating-assisted OFSW system suited for on-site pipeline welding. The obtained joined pipes were characterized by a high-quality weld surface and a lack of defects arising from the tool-pin hole. The samples welded with the optimum parameters presented comparable properties with the base materials and even a slight increase in the tensile strength. The highest tensile and impact strengths were 14.4 MPa and 2.45 kJ/m2, respectively, which is 105% and 89% of those of the base material. XRD, FTIR, and SEM were also applied to assess the property changes in the HDPE pipes after the FSW process. The morphological analysis evidenced that the crystalline structure of the welded sample was similar to that of the base material, proving the effectiveness of the proposed technology.

Automatic Calibration of the Adaptive 3D Scanner-Based Robot Welding System.

An advanced automatic calibration procedure and its versatile usage in the context of the adaptive robot welding technology are presented. The 3D scanner-based robot welding system calibration is composed of the measurement of the reference plate and numerical optimization of the hand-eye and intrinsic parameters by minimizing the deviation between the measured and reference plate. The measurements of the reference plate are acquired from various robot poses (typically 15). The shape features of the reference plate are then detected, and finally, the calculation of hand-eye and intrinsic parameters is performed using Powell’s optimization algorithm, where the merit function presents an average deviation between the measured and reference geometry. Validation experiments show appropriate system accuracy which is better than 0.06 mm perpendicular to the scanning direction. This calibration procedure’s important features are complete automation and fast execution times (approximately 90 s). This enables its implementation into a regular daily robot self-maintenance and monitoring plan. The universal use of such a robot welding system is demonstrated in multi-layer heavy-duty welding of thick pipes on cast machined hollow parts and in precise laser welding of thin sheet metal parts.

Failure analysis of welded joint leakage of TP321 pressure pipeline

Considering the continuity of production in petrochemical plants and the harmfulness of leakage, any slight defect in the system may lead to dramatic accidents. Therefore, we used systematic characterization methods to analyze the causes of leakage near the weld of outdoor pressure pipe in a petrochemical plant. It is found that the crack extends from the outside into the inside surface of the pipe wall, and there are massive corrosion products on the crack surface. Furthermore, the damaged parts observed of the external insulating layer are wet and accumulate chlorine, which from the corrosive environment to the pipe material. Finally, it is concluded that microcracks originate from pitting pits and gradually expand to the inner surface with the coaction of internal pressure of the pipe up to 12 MPa. The reason of pipe leakage is the interaction of pitting corrosion, transgranular corrosion, and stress corrosion cracking.

Numerical modelling of friction stir welding of pipes: Effect of tool shoulder on mechanical property and metallurgical characterization

One of the challenges during FSW of pipe is establishing sufficient contact between the tool shoulder and the pipes to be welded. With improper contact, the torque requirement increases, which thereby increases the power consumption. The present work focuses on the demonstration of a 3D thermo-mechanical model showing the influence of tool shoulder diameter on temperature rise, plastic strain development, spindle torque, material flow occurrence, and power consumption. The model showed a good correlation with experimentally observed temperature and maximum spindle torque for different rotational speeds. It was observed from the developed model that, an increase in the shoulder diameter increases the contact area and spread of maximum temperature resulting in a wider HAZ zone. Hence, optimization of the tool shoulder diameter was necessary, and it has been addressed considering its effect on contact area, heat generation, material flow, and spindle torque. The material flow behaviour has also been studied, and it was found that a larger shoulder diameter does not produce sufficient material stirring. The welded sample has been investigated by tensile strength and microstructure analysis. The optimum tool shoulder diameter of 16 mm resulted in joint strength efficiency of 90%.

Numerical Prediction of Strength of Socket Welded Pipes Taking into Account Computer Simulated Welding Stresses and Deformations.

The paper presents a numerical model based on the finite element method (FEM) to predict deformations and residual stresses in socket welding of different diameter stainless steel pipes made of X5CrNi18-10 steel. The next part of the paper concerns the determination of strength properties of a welded joint in terms of a shear test. A thermo-elastic–plastic numerical model is developed using Abaqus FEA software in order to determine the thermal and mechanical phenomena of the welded joint. This approach requires the implementation of moveable heat source power intensity distribution based on circumferentially moving Goldak’s heat source model. This model is implemented in the additional DFLUX subroutine, written in Fortran programming language. The correctness of the assumed model of thermal phenomena is confirmed by examinations of the shape and size of the melted zone. The strength of the welded joint subjected to shear is verified by performing a compression test of welded pipes as well as computer simulations with validation of the computational model using the Dantec 3D image correlation system.

Friction stir welding of AISI-316L steel pipes: Mechanical and metallurgical characterization of the joint

The present work attempts to develop a procedure for friction stir welding (FSW) of AISI-316L pipes. These pipes find applications across power, marine, food and chemical industries. Initially, welding is carried out in position control mode by setting parameters viz. spindle speed (RPM), transverse speed/feed rate (mm/min) and tool depth (mm) to get an idea about the welding process and to assess the effect of these parameters on the weldment. Based on the weld quality and the data recorded during the welding process, further welding is carried out in force control mode of the FSW setup. The welded joint at 300 rpm spindle speed and 35 kN force display greater strength (around 94%) compared to the base metal. The hardness of stir zone (SZ) as well as heat affected zone (HAZ) in welded samples was significantly higher compared to the base metal. The microstructural characterization revealed fine austenitic grain structures in SZ due to discontinuous dynamic recrystallization. In general, the weld is found to be consistent and the data obtained could be employed to produce high quality pipe welds.

Traditions, Current Innovations, Variations, and Deviations in the Control of Welding of Polymer Pipes

Traditions, Current Innovations, Variations, and Deviations in the Control of Welding of Polymer Pipes

Analysis and mitigation of the bending deformation in girth-welded slender pipes with numerical modelling and experimental measurement

Girth welded pipes are extensively used in the components of energy and chemical industries. The welding deformation modes depend on various influential factors, such as process schemes and geometric dimensions. The objective of this study is to investigate the characteristics and mechanism of the bending deformation generated in the girth welded slender pipes, and to develop mitigation schemes. Firstly, several 304-type stainless steel pipes were girth welded using four different welding schemes, and the 3D shape measuring system was employed to capture the basic welding deformation modes. Numerical models were developed to simulate the corresponding welding processes with experimental verification. And the mechanism of bending deformation was further clarified based on inherent strain theory. The results show that obvious bending was observed in the pipe of continuous full turn welding due to the non-uniform distribution of the axial residual plastic strain on the circumference. Welding of half turn tends to generate a bending from the weld starting position to the finish position besides the bending toward the weld side, which brings about the mutual elimination of the bending deformation with same direction half-turns and the superposition with reverse direction half-turns. Furthermore, a dual-torch scheme was proposed for girth welding of slender pipes and presented a great potential to mitigate the bending deformation with an improved welding efficiency.

Type IV creep crack initiation and propagation in mod.9Cr-1Mo steel welds

ABSTRACT The ratio of crack initiation and crack propagation life is important from the viewpoint of residual life prediction of mod. 9Cr-1Mo steel welds under Type IV creep damage. Both the creep void density distribution and the failure process with crack initiation/propagation/final failure are predicted for three types of welds in pipes and nozzles, which are compared with experimental results at 650°C. The ratio of crack initiation and final failure life depends on weld type and loading conditions; the ratio is about 0.95 in the cases where redistribution of stress occurs only in the thickness; the ratio is 0.59 ~ 0.65 in the cases where redistribution of stress occurs in both the thickness and circumferential directions of the pipe. Influence of stress ratio (axial vs. circumferential stress) is also predicted for circumferential welds subject to internal pressure/axial load and is compared with experimental results at 650°C.

Investigation of dynamic processes in the hydraulic system of clamping the staffs of the segment unwinder of the unit of aggregation of rolls pipe welding machine 20-114

In the technological line for the production of small diameter pipes used segment un-winder staffs with a cantilever drum and additional support. The experience of its operation has shown that one of its main shortcomings is the unsatisfactory operation of the hydraulic system clamping staffs. In the hydraulic clamping system of the staffs there are increased dynamic loads, which lead to the failure of components and elements of the hydraulic system. The layout of the hydraulic clamping system of the headquarters is made for design and technological rea-sons, without taking into account the influence of pipeline lengths on the nature of dynamic processes in the hydraulic system. In addition, the hydraulic system uses spool hydrodistributors with electro-hydraulic control, the operation time of which is practically not subject to regulation. Based on the analysis of known mathematical models for the study of dynamic processes in hydraulic systems, it was concluded that as a mathematical model that takes into account the design and operation of the hydraulic clamping system staffs finite-difference method in a sys-tem of ordinary differential equations with boundary conditions described by algebraic equations. A basic dynamic model has been created, which allows to analyze with high relia-bility the behavior of the hydraulic system of the clamping mechanism of the staff in the segment unwinder of the rolls, which is exposed to different nature in a wide range of mode parameters. Simulink MATLAB software environment was used to effectively solve this problem. During the implementation of the mathematical model, a study of the modes of operation of the hydraulic system of the clamping mechanism of the staff was performed. It was found that at the end of the working and reverse strokes of the clamping mechanism of the roll in the end posi-tions there are dynamic loads in the hydraulic system that reach the maximum allowable values. In addition, it was found that during the acceleration of the piston of the hydraulic cylinder during operation and reverse, although there are no dangerous loads, but there are rapid fluctuations in pressure in the cavities of the hydraulic cylinder. Theoretical studies of the modes of operation of the hydraulic clamping system of the staff in the segment unwinder with different operating times of the control valve. As a result of the study of transients in the unwinding hydraulic system with different operating times of the hydraulic distributor, its ra-tional operating time was recommended, which is 0.20 seconds when opening and 0.15 sec-onds when closing.

Stress Analysis of the Effect of Additional Load on the Butt Weld of Suspended Pipeline With Variable Wall Thickness

Under the special geological environment of the buried pipe, the ground is lost at the bottom of the pipe, which is created by various kinds of external factors. The pipe in the suspended state would be greatly deformed due to its own weight, internal pressure, and other factors, resulting in the failure of the pipeline. When a variable wall thickness weld occurs in the suspended section of the pipeline, the change of the pipeline stress will be more complicated and changeable. In this study, ABAQUS software is used to establish a pipe–soil model of variable wall thickness butt welds of suspended pipelines. The axial stress distribution with different affected factors in the pipe, the change of curvature, and Mises stress change of the entire pipe along the axial direction are obtained by analyzing the internal pressure, wall thickness ratio, suspended length, weld position, and cone length. The results show that the stress at the root of the weld changes significantly; therefore, the weld has a greater impact on the stress of the entire pipeline. The change of internal pressure has little effect on the stress at the pipe weld. As the suspended length increases, the change in stress at the weld is more obvious. When the weld seam is close to the soil, the support of the soil will gradually shift the maximum stress position of the pipe from the top of the pipe to the bottom of the pipe. With the increase in cone length, it will reduce the sudden change of pipe section and the change in stress effectively. The places where the curvature greatly changes along the axial direction are at the pipe–soil separation and the middle of the pipeline, while the stress reaches the maximum at the pipe–soil separation, and the place with the largest stress change is the weld in the middle of the pipeline.

Research on reduction of residual stress in girth welds of large-diameter natural gas pipes by ultrasonic

ABSTRACT Excessive residual stress of the girth weld in pipes will directly damage the pipe strength during its operation. Accurate measurement and effective reduction of the residual stress can ensure the safety of natural gas pipes during their service. In this paper, an X80-type large-diameter natural gas pipe section with girth welds is taken as the research object. The coercive force method is used to characterize the residual stress of the girth weld and its surroundings, and then the distribution law of the residual stress of the girth weld and its surroundings is obtained based on the measurement results of the Blind-hole method; the ultrasonic impact method was used to reduce the girth weld residual stress, and the effect of the ultrasonic impact method on the residual stress reduction was studied by comparing changes of the distribution characteristics of the coercive force in the girth weld and its surroundings before and after the residual stress reduction in the natural gas pipes. Lastly, the in-situ test specimen is made to carry out the uniaxial tensile test so as to study the effect of the ultrasonic impact method on the tensile mechanical properties of pipe welds. This study clarifies the influence law of the ultrasonic impact on the mechanical properties of weld toe materials, and provided technical theoretical guidance for the reduction of field residual stress in natural gas pipes.

FEATURES OF MICROSTRUCTURE FORMATION IN THE WELDED PIPE JOINTS DURING HIGH-FREQUENCY WELDING AND SUBSEQUENT LOCAL HEAT TREATMENT

The transience of heating and cooling processes during high-frequency welding (HFW) of pipes leads to the formation in the heat-affected zone (HAZ) of a coarse-grained strained bainitic and/or martensitic structure with high hardness. Local or volumetric heat treatment is used to correct the microstructure of the HAZ. The paper presents the results of a study of the structure and properties of welded pipe joints produced at the Vyksa Steel Works. It has been established that the microstructure of the welded joint of pipes made of low-carbon steels (not more than 0.07% C) is mainly bainite of lath morphology, and for steel with a high content of carbon (~0.3%) and manganese ‒ martensite. To estimate the temperature field in terms of the angle and thickness of the pipe wall during local heat treatment a finite element model was created. The paper shows that the use of the model made it possible to optimize the heating parameters during the local heat treatment of pipes of various sizes. The experiments on local heat treatment of pipes with a diameter of 325 mm, made from rolled products 8 mm thick of steel 09Г2С, showed a significant refinement of the initial microstructure of the HAZ, an increase in uniformity and the disappearanc of structural heat-affected zones. In medium carbon steels (~0.3% C) with a high manganese content, the thermal cycle of HFC welding leads to formation of martensite. The local heat treatment in the form of normalization does not allow one to exclude the formation of martensite in the segregation zones due to the high cooling rate. The local heat treatment of welded joints in pipes made of steel 30Г (Russian Standard) in the high tempering mode (650–700 °C), with preliminary cooling of the welded joint to a temperature below the completion of the martensitic transformation (in segregation zones ~50 °C), makes it possible to release the segregation martensite and form the microstructure of sorbitol there.

Peculiarities of manufacture of large diameter welding pipes and method of their heat treatment

Peculiarities of manufacture of large diameter welding pipes and method of their heat treatment