Welded Pipe Joints Research Articles

Crack growth analysis and remaining life prediction of dissimilar metal pipe weld joint with circumferential crack under cyclic loading

Fatigue crack growth model has been developed for dissimilar metal weld joints of a piping component under cyclic loading, where in the crack is located at the center of the weld in the circumferential direction. The fracture parameter, Stress Intensity Factor (SIF) has been computed by using principle of superposition as KH + KM. KH is evaluated by assuming that, the complete specimen is made of the material containing the notch location. In second stage, the stress field ahead of the crack tip, accounting for the strength mismatch, the applied load and geometry has been characterized to evaluate SIF (KM). For each incremental crack depth, stress field ahead of the crack tip has been quantified by using J-integral (elastic), mismatch ratio, plastic interaction factor and stress parallel to the crack surface. The associated constants for evaluation of KM have been computed by using the quantified stress field with respect to the distance from the crack tip. Net SIF (KH + KM) computed, has been used for the crack growth analysis and remaining life prediction by Paris crack growth model. To validate the model, SIF and remaining life has been predicted for a pipe made up of (i) SA312 Type 304LN austenitic stainless steel and SA508 Gr. 3 Cl. 1. Low alloy carbon steel (ii) welded SA312 Type 304LN austenitic stainless-steel pipe. From the studies, it is observed that the model could predict the remaining life of DMWJ piping components with a maximum difference of 15% compared to experimental observations.

Effect of plastic pre-strain on the fatigue properties of welded joints of X80 LSAW pipes

The fatigue properties of the original, 1%, 2%, and 3% plastic pre-strained welded joints of X80 pipeline steels were tested to find the effect of plastic deformation on the service of pipelines. Results showed that the fatigue cracks growth period remarkably decreased with the increasing plastic pre-straining extent, reducing the safety of pipeline transportation. The decrease was caused by the cleavage fractures generated by dislocation synthesis reactions during the fatigue process. The results reveal the effects of dislocation distribution on fatigue property of the welded pipe after plastic deformation and provide a reference for the safety design of pipelines.

Evaluation of friction welded dissimilar pipe joints between AISI 4140 and ASTM A 106 Grade B steels used in deep exploration drilling

In the present research work, a detailed evaluation of dissimilar friction welded joints between the hot rolled ASTM A106 Grade B (carbon steel) pipes and hot rolled AISI 4140 (low alloy steel) pipes in the as-received (AR) condition and quenched and tempered (QT) condition has been carried out. All the specimens were subjected to stress relief annealing after welding. Optical and scanning electron microscopy on the AISI 4140 steel side revealed dynamically recrystallized grains, consisting of a mixture of ferrite and martensite in the friction welded AR-condition joints and mixture of ferrite and tempered martensite in the friction welded QT-condition joints. On the ASTM A 106 Grade B steel side the material showed ferrite and pearlite microstructure. SEM analysis did not reveal any intermixing between AISI 4140 and ASTM A106 Grade B steels at the weld interface in both the conditions. The region adjacent to the weld interface on AISI 4140 steel side consistently showed higher hardness in the QT-condition compared to AR-condition due to the presence of fine-grained microstructure in QT-condition. The dissimilar welded pipe joints in the present study have shown slightly higher tensile properties than that of ASTM A106 Grade B steel but significantly lower than that of AISI 4140 steel. The friction welded dissimilar pipe joint specimens have shown substantially lower impact toughness values compared to either ASTM A 106 Grade B steel or AISI 4140 steel in both AR and QT-conditions due to the presence of carbides at the weld interface.

The use of sprayed powders to create coatings in the welds of oilfield pipelines

The most damaged elements of oil field pipelines are welded joints, the life of which often does not exceed one or two years. The problem of anticorrosive protection of internal surfaces of welded pipe joints has not been solved to date. In this paper, the possibility of applying powder protective stainless coatings to the inner edges of the pipe adjacent to the annular weld is considered. The research of corrosion resistance and mechanical properties of pipe welded joints is presented.

Simulation of the residual stress in a multi-pass oil and gas pipe weld joint

In this paper, a welding simulation procedure is developed using the FE software MSC Marc to predict the residual stresses.Numerical simulation was used to predict the thermal, mechanical and residual stresses behaviour in dissimilar material welded pipes which were found to be in good concurrence with experiments. Both two-dimensional FE model (2D) and three-dimensional FE model (3D) models are used to simulate the residual stressesin different directions in several regions of the weld zone under the same welding conditions. The 2D modelwas used toreduce the time and cost of numerical simulation.The aimof the present work is to understand the evolution of residual stresses (axial, radial and hoop stresses) in weldments. The results of thesimulationreveal that the hoop and the axial residual stresses around the weld region arenoticeablyvarying from those in the steady range.

Investigation of the welded joints of siphon pipes of the underwater crossing of main oil pipeline

The article investigates the welded joints of siphon pipes of the underwater crossing of the main oil pipeline manufactured from 09G2 steel. The diameter of the welded pipes is 1220 mm, the wall thickness is 29 mm. The manufacturing of steel pipes involves thermal strengthening during accelerated cooling. The studies were performed both in the field and in the laboratory. The following studies are described: hardness measurement, its distribution along the fusion line and heat affected zone, measuring the distribution of residual welding stresses, and tensile testing of samples at room temperature. Distributions of residual welded stresses are determined from both the outer and inner walls of the oil pipeline siphon. Destructive and non-destructive direct methods were used to determine the mechanical properties of the metal on standard samples of the welded joint and heat affected zone of the pipeline. Tensile strength, yield strength, and relative elongation are determined. The mechanical properties of the pipeline metal were calculated concerning the hardness. It has been established that the mechanical properties and structure of the welded joint of the pipeline metal comply with the regulatory documents, certificates, and specifications for pipelines. Analysis of the results shows that there is a tendency toward hardening of heat affected zone during multilayer welding and a decrease in ductility.

Determination of high-gradient components of residual stress by data of test hole drilling method

The article discusses a modified method for the determination of residual stress in a deformable solid. The general approach is based on a combination of test hole drilling method and speckle pattern interferometry as a tool for deformation response registration. A feature of the proposed procedure for processing experimental data is that it directly takes into account possible high stress gradients at the stage of theoretical model building. The applicability of this technique is illustrated by the example of the residual stresses components measuring at a welded pipe joint.

On mechanical and morphological investigations of tungsten inert gas welded SS 304 thin pipe joints

Tungsten inert gas welding is one of the established joining processes for stainless steel. But hitherto very little has been reported on induced residual stresses in circular thin pipe joints during tungsten inert gas welding of SS 304. This paper reports the effect of welding parameters such as welding speed, welding current and shielding gas flow rate of tungsten inert gas welding on micro-hardness, width of the heat-affected zone, residual stresses and microstructural properties of SS 304 thin pipe joints. The results indicate that the welding current and the welding speed have a significant effect on micro-hardness of weld bead and width of the heat-affected zone. Further changes in the microstructure of the joints were studied in terms of dendrite formation. It has been observed that there is proportional increase in depth/width of the heat-affected zone with the heat input during the joining process, resulting in a decrease of micro-hardness. The results are also supported by radiographic analysis and X-ray diffraction data to understand the nature of residual stresses which was observed as compressive at the weld bead and tensile along the axis of thin welded pipe joints. Finally, the process capability analysis based on Cp and Cpk values of ≥1 suggests that the process can be gainfully used for mass production.

Методы определения локальных напряжений в сварных соединениях труб (Обзор)

Методы определения локальных напряжений в сварных соединениях труб (Обзор)

Methods for determination of local stresses in welded pipe joints (Review)

Methods for determination of local stresses in welded pipe joints (Review)

Mechanical properties of electro and butt fusion welded high-density polyethylene pipes

Abstract Electrofusion welding and butt fusion welding are common methods for joining polyethylene pipes used for water and gas distribution. Because of the wide use of these two methods in infrastructure engineering, welded pipe joints and pipe materials should be examined with the intent of reducing errors in projects. The purpose of this study is to increase knowledge of electrofusion and butt fusion welding methods and examine them in order to establish which offers the best performance for a specific engineering service project. Tensile and hydrostatic pressure tests are performed on un-welded and welded pipes for high-density polyethylene pipes. Additionally, a numerical analysis of the experimental results is conducted by employing the ANSYS program for tensile test samples. In tensile tests, according to the maximum average load, electrofusion welding values are larger than those of butt fusion welding and the elongations of the un-welded pipe at the fracture in butt fusion welding are greater than in electrofusion welding. For short-term hydrostatic pressure tests, the resistance in butt fusion welding for defects of roundness and alignment is better than that of electrofusion welding.

A Deep Artificial Immune System to Detect Weld Defects in DWDI Radiographic Images of Petroleum Pipes

In recent years, research focused on (semi)automatic radiographic inspection methods has gained more attention. The present work proposes a method for detecting defects in radiographic images of welded joints of oil pipes. Real condition images obtained by the double wall double image (DWDI) technique usually present a lower quality when compared with images traditionally considered in many studies reported in the literature. First, the proposed approach detects discontinuities in DWDI radiographic images of welded joints, and then, based on a hybrid paradigm encompassing artificial immune systems (AIS) and deep learning (DL), it classifies each discontinuity as `defect' and `non-defect'. The proposed method performs two phases in the AIS module: early classification (based on negative selection) and evolving classification (based on clonal selection). In both phases, the pattern recognition task is performed using a set of features extracted from each discontinuity through a detector genetically encoded into immune cells. As an attempt to improve the classification performance, DL models (AlexNet and autoencoders) are incorporated aiming to increase the number of extracted features. Experiments performed on a set of 727 discontinuities show that the proposed approach achieves an Fscore of 70.7%, outperforming each of its modules running by themselves: AlexNet with Fscore = 64.86% and AIS with Fscore = 66%. Considering the challenges imposed by real conditions on image acquisition - and the low rates of false negatives -, results demonstrate that the proposed approach can be used to assist in inspection works when dealing with DWDI images.

Rotary Friction Welding versus Fusion Butt Welding of Plastic Pipes – Feasibility and Energy Perspective

Abstract According to the Plastics Pipe Institute, butt fusion is the most widely used method for joining lengths of PE pipe and pipe to PE fittings “by heat fusion” (https://plasticpipe.org/pdf/chapter09.pdf). However, butt-welding is not energy-cognizant from the point of view of a phase-change fabrication method. This is because the source of heating is external (heater plate). The initial heating and subsequent maintenance at relatively high temperature (above 200 C for welding of high-density polyethylene pipe) is energy intensive. Rotary friction welding, on the other hand focuses the energy where and when as needed because it uses electric motor to generate mechanical (spinning) motion that is converted to heat. This work will make the case for friction heating as energy efficient. An initial feasibility study will also be introduced to demonstrate that the resulting welded pipe joints may be of comparable quality to those produced by butt fusion and to virgin PE material.

Effect of Residual Stress on the Destruction of Field Joints of Gas Pipelines Operating in Conditions of the North

Welding residual stresses are determined by algebraic summation of stresses by the effect of external loading and can have a significant impact on the performance of welded joints. The present article examines the effect of residual welding stress on the destruction of circumferential butt welds of the gas pipeline sections. The features of the distribution of the welding residual stresses of annular welded pipe joints are considered. It has been established that thin-walled tubes are formed in the inner layers of the sealing elements with growing tension pins forming inside. Analysis of destruction of ring welded joints of the underground and underwater sections of the pipeline was carried out. The welding residual stresses were investigated with X-ray diffraction technique. It is shown that the initiation and growth of macrocracks in the field joints of thin-walled main gas pipelines occur in the heat-affected zone from the interior face of the pipe wall in the zone of high tensile residual welding stress. Analysis of the destruction of real welded joints of gas pipelines has proved that the residual welding stress is the main factor that influences the development of brittle and fatigue cracks in them.

A New Design of MFL Sensors for Self-Driving NDT Robot to Avoid Getting Stuck in Curved Underground Pipelines

The magnetic flux leakage (MFL) type pipeline inspection gauge (PIG) is commonly used to detect defects on the underground pipelines as one of the nondestructive testing instruments. Although it is effective for the inter-city scale large size pipeline, it is hard to detect defects for the small size pipeline installed inside the city. So, it is necessary to adopt self-driving robot system to drive PIG module because the small gas pressure inside a small size pipeline is not enough to push PIG module. Even though it is enough to pass in straight line, when this module passes through bent pipe or welded pipe joint, the magnetic force between pipe and inspection module is increased sharply so that the PIG module could be stuck eventually. This paper proposed a new design structure of MFL system to decrease stuck forces on the pipe wall. All structural parameters for MFL sensors based on the magnetic field theory were designed to minimize the magnetic force and maximize the detection sensitivity of defect signals. The performance of the proposed system was verified by simulation results using 3-D finite-element method and experimental measured ones.

Взаимосвязь трещиностойкости и структуры зоны термического влияния сварных соединений труб

Взаимосвязь трещиностойкости и структуры зоны термического влияния сварных соединений труб

Combined strengthening treatment of welded joints of metal pipes of large diameter

This article describes a method and device for the combined hardening treatment of welded joints of large diameter metal pipes, which allow to increase their strength and corrosion resistance due to the wave effect on the weld joint of the hardening tool and feeding the suspension into the working area without disturbing the overall process of welding pipes.

Structural heterogeneities of tube steels taken into account in the development of contactless magnetometry of pipeline systems

One of the problems facing gas and oil pumping companies is the aging of pipelines, whose service life is rapidly approaching, or even exceeding, the resource planned during design. The only possible way to evaluate the possibility of further safe operation and residual life of pipelines is to conduct studies of the actual state of the parent metal and welded pipe joints. However, the direct investigation of metal pipes is practically impossible due to the linear dimensions of objects and their position. The analysis of the state of the pipeline system can only be made with the help of contactless, most often magnetic methods. Interpretation of magnetograms and detection of defects that are dangerous for the operation of pipes is one of the most difficult problems facing defectoscopists, which can be solved only by creating a library of structures and defects. This paper presents the results of a structural analysis of the metal of pipes, which must be taken into account when interpreting the results of magnetograms. These results constitute a part of the library of defects in pipeline systems developed in SPbPU.

Low‐Cycle Fatigue Properties of the X70 High‐Frequency Electric‐Resistant Welded Pipes

The strength, toughness, corrosion, and fatigue resistance are the main requirements for evaluating the integrity of a pipeline. In this study, the tensile strength, impact toughness, and fatigue properties of the pipe body and weld joint of an X70 high‐frequency electric‐resistant welded (HFW) pipe were measured and the effects of microstructure and surface defects at weld joint on properties were discussed. Results show the appearance of a weakened zone at the weld joint of the X70 HFW pipe. Nevertheless, all mechanical properties, including strength and impact energy, were superior to the specified values of the API specifications for the X70 line pipe. The reduced strength, toughness, and resistance to S‐N fatigue of the weld joint caused the microstructural coarsening at the weld junction zone. However, for the specimens without surface finishing, the resistance to S‐N fatigue for the weld joint was further reduced. This phenomenon was mainly attributed to the burring defects and microstructural coarsening at the heat‐affected zone (HAZ). Therefore, to improve the quality of the X70 HFW pipe, refining the microstructure of weld joint and reducing the deburring defects by optimizing the postweld heat treatment (PWHT) and deburring processes should be firstly considered in the future research works.

Investigation of Friction Welding Conditions and Thickness of Friction Welded Pipe Joint between A5052 and SUS304

Investigation of Friction Welding Conditions and Thickness of Friction Welded Pipe Joint between A5052 and SUS304