Pipeline Welding Research Articles

Numerical Simulations of temperature for the in-service welding of gas pipeline

Finite element (FE) method is employed to simulate the temperature field of the in-service welding on a single bead-on-pipeline. The methane gas was introduced as a cooling media to investigate the temperature field of the heat affected zone (HAZ) based on the validation of the numerical models. The heat transfer coefficient is significantly influenced by the pressure and flow rate of the gas and wall thickness of pipeline, which leads to the magnitude of cooling time, horizontal and vertical sizes of HAZ and peak temperature at inner wall were reduced. While, the t8/1 increases first and then decreases with the variable wall thickness and it get the maximum value about 208.42s at wall thickness of 8mm. It indicates that the effect of the gas and wall thickness on the temperature field of in-service welding need to be concerned.

Root stability in hybrid laser welding

Hybrid laser welding offers promising advantages over the traditional arc-based welding processes. The high penetration ability of lasers and the filler wire delivery of gas metal arc welding enable joining of thick section materials without the need of multipass. The output power of modern solid state lasers provides enough energy to penetrate thicknesses exceeding 20 mm in steel. However, the high aspect ratio fusion zone with the rapid solidification does not always provide beneficial conditions for achieving good weld profiles. Distribution of the liquid metal between the top and root sides of a joint, and hence the weld profile, is determined by a complex balance between the vaporization pressure of a laser, the electromagnetic force of an arc, and the surface tension of a meltpool. In this work, the stability of the root profile and all the aspects related to the achievement of acceptable roots in pipeline welding have been investigated. It has been found that in order to achieve a smooth root profile in deep penetration hybrid laser welding, not only a sufficient penetration force but also a certain amount of energy need to be provided. This is required to maintain the keyhole fully developed with a steady state pressure balance throughout the thickness. It is also important to achieve sufficient temperature in the root and to provide appropriate wetting between the liquid metal and the back surface of the material. Depending on the power density and energy used, different regimes were identified with sagging of the root in the initial stage, followed by good quality root profiles and then ending on excessive melt expulsion with a further increase in power density. The results suggest that if operated in the right regime, the process is very tolerant, in terms of energy, and power density required for acceptable root profiles and good quality joints can be achieved.

Research on the Mechanical Performance and Crack Defects Assessment of X65 Marine Pipeline Welding Joint

In order to study the influence of different types of weld defects, such as slag inclusion, porosity, incomplete fusion, incomplete fusion, burn through, crack on the mechanical performance of X65 marine pipe welding joint (Φ323.9 x 16 mm), the test on the mechanical properties of static tensile, fracture toughness CTOD and fatigue life were carried out to achieve the maximal defect tolerance size allowed in this paper. Research shows that the existence of crack defects would significantly reduce the fracture strength and the fatigue life of welded joint, the application of the maximal defect tolerance size allowed based on crack defects assessment can provide referential basis for the safe and stable operation of marine pipelines.

Collisional vibration of PIGs (pipeline inspection gauges) passing through girth welds in pipelines

The continuous collision between a running PIG (pipeline inspection gauge) and girth welds in a pipeline can induce significant vibrations on the PIG, which can harm its mechanical structure. The vibration response caused by the collision between a running PIG and a girth weld was studied both experimentally and theoretically. A two-dimensional dynamic model of the PIG is introduced to explain and understand the collisional vibration. Our results demonstrate that the girth weld, which can be regarded as an obstacle, can greatly affect the dynamic behaviour of a running PIG. The instantaneous acceleration when the PIG passed over the girth weld is larger than that of the PIG that collided with the girth weld. The distinct and regular vibration response signal of a PIG passing through a girth weld can be used to identify the obstacles inside a pipe to calculate and correct the pigging mileages with the help of a special algorithm based on the function of odometers during the pigging or inspection process.

Research on weld cracking of TP321H stainless steel pipeline under elevated temperature

The failure of pipeline which adopted material type TP321H austenitic stainless steel and occurred cracking after servicing at elevated temperature for less than two years had been investigated. The cracks were appeared repeatedly although they had been repaired for several times. The pipeline stress analysis was conducted to determine stress levels of cracking positions by finite element analysis software ABAQUS. The mechanical properties of base metals and welds including tensile and charpy impact tests were carried out. The test results showed that ductility of welds cut from the serviced pipeline was very poor. The microstructure investigations suggested that it was intergranular crack located in the HAZ near fusion line. It could be determined that it was reheat cracking based on some other works such as metallographic inspection, SEM, X-ray diffraction, etc. Welds analysis results showed that the welding of pipeline had not been in accord with right qualification of welding procedure leading to poor welding quality. The cracking reasons and preventive measures were discussed. Several suggestions were proposed to help extend service lifetime of the stainless steel pipeline under elevated temperature condition.

Numerical simulation of ductile crack growth in medium wide plate specimens using 3-D computational cells

This work examines the applicability of a local damage method based on the computational cell methodology, incorporating the Gurson-Tvergaard (GT) yielding model, to predict ductile crack extension of circumferential crack-like defects in Medium Wide Plates (MWP) specimens, extracted from girth welds of pipelines, using standard single edge bend SE(B) specimen and recently standardized clamped single edge tension SE(T) specimens to obtain model parameters. Laboratory testing of SE(B) and SE(T) specimens at room temperature provides necessary and sufficient information to calibrate the parameters of the GT yielding law. After the model parameters have been defined using small specimens, predictions of crack growth behavior can be carried out for other geometries and loading modes. Therefore, parameter transferability between different specimens can be investigated and comparative studies of predicted crack driving forces can be performed. In this study, the simulated tearing resistance curves are compared to experimental data of MWP specimens, where the former is obtained by the cell model calibrated using either SE(T) or SE(B) specimens and the latter is obtained by large-scale experiments. Overall, a good agreement between numerical and experimental δ-Δa curves was observed demonstrating that the cell methodology can be considered as a valid engineering tool for studying the integrity of structural components.

О физической природе возникновения дефектов типа «матовые пятна» при контактной сварке магистральных трубопроводов из феррито-перлитных сталей

О физической природе возникновения дефектов типа «матовые пятна» при контактной сварке магистральных трубопроводов из феррито-перлитных сталей

3D finite element modeling of in-service sleeve repair welding of gas pipelines

The present work investigates the influence of welding sequence and scheme on residual stresses induced during in-service sleeve repair welding of gas pipelines. For this purpose, a 3D thermo-mechanical FE analysis is conducted on an 8″-Schedule-20, API 5L-X65 steel pipe. Two welding sequences for the sleeve-pipe circumferential fillet welds are compared in the present study: sequential welding in which one side of the sleeve is welded first and then the other side is welded by the same welder, and simultaneous welding in which both sides of the sleeve are welded concurrently by two welders. Within the simultaneous welding sequence, four different welding schemes, designed to investigate the influence of the number of welders and welding directions on residual stresses, are investigated. The results show that the sequential welding sequence induces less residual stresses and distortions. Within the simultaneous welding sequence, the back-step welding scheme is found to induce the least average residual stresses as compared to other welding schemes.

Research on Full-Scale Hydrostatic Burst Testing of Different Pipeline Girth Weld Defects

Recently incidents related to cracking of girth welds in oil and gas pipelines occurred frequently. With highly concentrated stresses, girth weld defects may significantly reduce bearing capacity of pipelines. Many girth weld defects were detected in the in-line inspection and excavated verification. How to assess the severity of these defects to avoid the excessive and unnecessary repair was a technical challenge. Four different kinds of girth weld defects were manufactured in the 32-inch pipeline and full-scale hydrostatic burst testing were carried out to assess the pressure performance of these defects. Many fitness-for-purpose assessment methods were applied to verify the accuracy of experimental results. After the testing, pipelines with failure defects were cut out to carry out the microanalysis. The research results make us understanding the severity of these defects and avoid the excessive and unnecessary repair of these defects to ensure the pipeline safety.

Design and analysis of a novel ship pipeline welding auxiliary device

Nowadays ship pipelines alignment and welding process play a dominant role in ensuring the assembly speed in shipbuilding processes and the operation reliability in ship commissioning processes. However, the pipeline welding quality relies heavily on the experiences of personnel of the shipyard, which further hinders the improvement of welding efficiency and accuracy. This paper develops a novel ship pipeline welding auxiliary device(SPWAD). It is driven by hydraulic cylinder and equipped with the wedge force amplifier mechanism and able to align, center and lock two welding pipelines more conveniently and reliably. The capability of the SPWAD in resisting welding stress was analyzed by finite element analysis in ANSYS Workbench, and the results shows that the SPWAD is capable of resisting the certain welding stress in extreme condition A series of shipyard experiments were conducted, which demonstrated that the maximum concentricity and non-parallelism of the welding pipeline is 0.481mm and 2.615mm respectively by using the SPWAD, and its practicability was also verified. The efficiency of ship pipeline welding with the SPWAD is estimated up to increase by about 5 times.

Structural integrity of corroded girth welds in vintage steel pipelines

Girth welds of old steel pipelines and their surrounding heat affected zones are susceptible to corrosion attack. The resulting reduction in wall thickness may reduce the axial load or internal pressure bearing capacity to an unsafe level. Since standards provide limited guidance on weld corrosion assessment, the authors have executed an extensive experimental program to evaluate the axial load bearing capacity of corroded girth welds. To this end, curved wide plate tests have been executed and were analyzed by means of 3D digital image correlation. This paper discusses key influence factors related to weld geometry and material (strength and toughness). Then, the results are used to develop an assessment approach, based on Annex G of BS 7910:2013 and modified to account for the elastic–plastic stress–strain concentration resulting from weld misalignment.

A framework for fracture assessments of dissimilar girth welds in offshore pipelines under bending

This work describes the development of a framework for structural integrity assessments of dissimilar girth welds in clad and lined pipes subjected to high levels of bending load for a wide range of pipe geometries, crack configurations, weld grooves and weld strength mismatch levels based upon an EPRI estimation scheme for crack driving forces coupled with a weld groove simplification procedure and the equivalent stress–strain relationship. Systematic validation of the method is provided and the crack driving force estimation accuracy is demonstrated through comparisons with numerical tools and 3-D finite element analyses for reeled pipelines.

Engineering Critical Assessment of nickel-based clad pipeline girth welds in a wet H2S-containing environment

Specimens from nickel-based clad pipeline girth welds were tested in H2S solution. The results of the fatigue crack growth rate curve at higher ΔK values were about 4 times higher than the in-air values. The rate at 180°C was generally higher than the in-air data for flaw assessments found in the British Standard BS7910 by a factor of up to 3 times. From the analyses of the diffusible hydrogen, the backing steel of such pipelines are predominantly protected from the sour environment by the corrosion-resistant alloy clad layer. The results from this study are relevant for desktop Engineering Critical Assessment of girth welds of such pipelines.

Dynamic simulation and experimental research on the motion of odometer passing over the weld

Odometer wheel system, designed to measure the traveled distance and the instantaneous velocity of the intelligent inspection pig in operation, is an important part of the pig to define the position of pipeline defects. High accuracy positioning of pipeline defects can greatly improve the pipeline maintenance efficiency and highly reduce the costs. However, due to the peculiarity of its construction, the odometer is prone to unbounded accumulative errors and pipeline weld is the main reason. As a result, research on the motion and accuracy of odometer system is essential. In this paper, the motion of the odometer passing over the weld was investigated. Mathematical and simulation models were presented to describe and analyze the errors of the odometer, which was verified by the experiment. Research results indicate that the error of the measured distance can be divided into two conditions. At low velocity, the measured distance is larger than the actual distance, while the measured distance is smaller than the actual distance at high velocity. The results in this paper can provide better understanding of the accumulative errors of the odometer, and contribute to find a way to improve the accuracy of the odometer wheel system.

The Investigation of Structure Heterogeneous Joint Welds in Pipelines

Welding joints of dissimilar steels don’t withstand design life. One of the important causes of premature destructions can be the acceleration of steel structural degradation due to cyclic mechanical and thermal gradients. Two zones of tube from steel 12H18N9T, exhibiting the structural instability at early stages of the decomposition of a supersaturated solid austenite solution, were subjected to investigation. Methods of x-ray spectral and structure analysis, micro hardnessmetry were applied for the research. Made the following conclusions, inside and outside tube wall surfaces of hazardous zones in welding joint have different technological and resource characteristics. The microhardness very sensitive to changes of metal structure and can be regarded as integral characteristic of strength and ductility. The welding processes are responsible for the further fibering of tube wall structure, they impact to the characteristics of hot-resistance and long-term strength due to development of ring cracks in the welding joint of pipeline. The monitoring of microhardness and structural phase conversions can be used for control by changes of mechanical properties in result of post welding and reductive heat treatment of welding joints.

Поведение участков концентрации напряжений в околошовной зоне магистрального газопровод а при эксплуатации. Практическое исследование

Поведение участков концентрации напряжений в околошовной зоне магистрального газопровод а при эксплуатации. Практическое исследование

Failure Analysis of X80 Line Pipe’s Circumferential Weld

One 530mm X80 pipeline weld failed infrequently in service process. This paper gives a systematic analysis in consideration of both material quality and loading condition. Inspection was performed on chemical composition, mechanical performance, metallograghy and micro-morphology. The result shows that weld joint’s leakage failure accident is fatigue failure. Under the effect of tensile- tensile stress fatigue stress, fatigue crack originated from weld fusion line near the pipe body and developed along the weld. Porosity defect in the weld reduced its bearing capacity, and promoted the formation and development of the fatigue crack. Fatigue strength and fatigue life of the weld has great relationship with the size and distribution of porosity. The greater the porosity, the more close to surface, the decrease of fatigue life is more obvious.

INSPECTION BY ULTRASONIC TOMOGRAPHY (UT) LEADING TREND IN WELDING JOINT MONITORING

Welding work is a connection process between the structure and the materials. This process is used in the construction, maintenance and repair especially mechanical engineering. This study discusses the type of welding used in the industry, mainly involving the pipeline welds. On-demand need to every work process when finishing weld requires quality tests to ensure compliance to the standards required. Monitoring through the display image has long been used in Non-Destructive Testing (NDT). Various methods of monitoring used in NDT focused on Ultrasonic Tomography (UT) as a method used in NDT and as an option for the future. Previous imaging result was in two-dimensional (2D) and then upgraded to a three-dimensional image (3D). Besides, there is potential of 3D imaging beyond the existing limits in terms of size, material thickness, especially for welding steel pipes. Achievement through research of existing pipe size so far outside diameter of 200 mm and a thickness of 5.8 mm should be limited in view of the obstacles to enhanced image resolution is less effective when compared to other tomography methods.

Mathematical Approaching and Experimental Assembly to Evaluate the Risks of In-Service Welding in Hot Tapping

The welding onto in-service pipeline (operation condition) results in three possibilities of high risks: leaking and/or explosion by burn-through, chemical reactions to instability, or even explosion due to the heat on internal fluid and cracking in heat affected zone (HAZ). The numerical methods have a useful role in the assessment of welding conditions for the safe in-service welding of pipelines. Only limited published works have considered direct calculation of burn-through using a combination of thermal and stress analysis. The mathematical model of the heat source is the most important part of these numerical models, and actually the mathematical model which described better the heat distribution of the arc welding through gas-shielded tungsten arc welding (GTAW) process or shielded metal arc welding process is the double ellipsoidal heat source (DEHS) model of Goldak and Akhlaghi (2010, Computational Welding Mechanics, Springer Books, New York, pp. 32–35). However, that model has considered the heat source in rectilinear motion only, and it depends on three parameters (a, b, c) which are related with the weld bead size and shape to define the geometry and co-ordinates of heat source, and they are determined empirically or experimentally. Few researchers published works that could determine these parameters mathematically, from the welding data. The publication that best analytically addressed this issue was the work of Eagar and Tsai (1983, “Temperature Fields Produced by Traveling Distributed Heat Sources,” Weld. J., 62(12), pp. 346–355). First, this paper presents a new equation for heat source in double ellipsoid considering the circular motion, trying to develop a model closer to the physical situation of hot tapping onto pipeline. Second, a proposal for determination of the parameters a, b analytically from the Eagar model and Tsai (1983, “Temperature Fields Produced by Traveling Distributed Heat Sources,” Weld. J., 62(12), pp. 346–355), and third, an experimental facility to get the temperature field that was used to validate the numerical finite element models.

Variable Gain Super-Twisting Control of GMAW Process for Pipeline Welding

Quality control is the key issue that needs to be addressed in any gas metal arc welding (GMAW) system, especially in robotic pipeline welding system. This paper explores a second-order sliding mode control (SMC) strategy—a variable gain super-twisting control, to maximize the productivity, consistency in welding quality. This is achieved by the robust finite time output tracking of GMAW system. A nonlinear multi-input multi-output (MIMO) model of GMAW system has been considered here for the design of variable gain super-twisting (VGST) controller by which complete rejection of the bounded uncertainties/disturbances is possible and the adaptive characteristic of its gains help to use the control effort effectively. The stability of internal dynamics of the system is studied to establish the feasibility of solving the robust finite time output tracking problem. The stability of the overall system has been analyzed using Lyapunov stability criterion. The performance of the controller is demonstrated using the model of the system emulating the realistic conditions of operation. The simulation results are presented to illustrate the efficacy of the controller.