Unequal Wall Thickness Research Articles

Research on Strain of Unequal Wall Thickness Pipeline of the X80 Pipeline under Lateral Load

X80 steel is a material with high strength and good toughness, which is widely used in long-distance natural gas pipelines. Pipelines will have different wall thicknesses, depending on the safety level requirements of different regions. Two sections of pipes with different wall thickness form unequal wall thickness of pipeline (UWTP) that is joined together by welding. UWTP pass through some geohazard areas, such as landslides. The frequency of landslides is extremely high in mountainous areas, which can seriously affect the safe operation of UWTP. In this paper, a model of a 12.8 mm wall pipe section and a 15.6 mm wall pipe section are linked by girth welds. The strain between the pipe section and the weld was quantitatively analyzed. The results show that the strain at the girth weld in the 3 o’clock direction of the pipe increases sharply. The strain in the 9 o’clock direction of the pipe is generally lower than the strain in the 3 o’clock direction. The strain value of the 12.8mm wall thickness pipe section is generally greater than the strain value of the 15.6mm wall thickness pipe section.

Quantitative research on stress failure risk assessment for girth welds with unequal wall thickness of the X80 pipeline under lateral load

The cumulative length of the X80 steel pipeline extends to 17,000 km, with a predominant portion traversing mountainous terrains characterized by intricate geological formations. Recurrent geological hazards significantly impede the safe operation of oil and gas pipelines. Landslides can induce substantial axial forces on steel pipelines, significantly increasing the risk of pipeline failure. Moreover, as a result of sudden changes in mechanical structure, the pipeline's unequal wall thickness leads to local stress concentration, making it more vulnerable to external loads than the steel pipeline itself. Therefore, to analyze the mechanical response of steel pipelines under different working conditions, we establish a smooth particle hydrodynamics, finite element transverse landslide pipeline model for girth welds with unequal wall thickness and investigate a tearing accident caused by a lateral landslide in a section of the large-diameter natural gas pipeline. The landslide volume is found to be the main controlling factor for the failure of pipeline circumferential welds. According to the genetic algorithm backpropagation neural network, the von Mises stress of the most dangerous section of the pipeline is calculated based on pipeline and landslide parameters, and the error is 11.67 %. According to the API RP 581–2016 Risk-Based Inspection Methodology, a failure risk assessment matrix is established using the pipeline statute as an evaluation indicator to evaluate the landslide risk to pipelines in different regions. A variable-wall-thickness girth weld on the ZG pipeline was selected for application. This method has good applicability for evaluating the failure risk of circumferential welds with wall thicknesses of 12.8/15.3 mm under the action of small landslides.

Fiber–Based Model for Simulating Inelastic Interaction Buckling of Rectangular CFST Slender Columns with Unequal Wall Thickness

Rectangular concrete-filled steel tubular (RCFST) columns can be designed to have unequal wall thickness to maximize their resistance to combined axial and uniaxial bending loads. However, there is very little published research on their local–global interaction buckling behavior. This paper presents an efficient fiber-based simulation model for analyzing the inelastic interaction buckling of eccentrically loaded RCFST slender columns with unequal wall thickness. The model considers the progressive local–global interaction buckling, distributed plasticity, concrete cracking and crushing, second-order effects, and geometric imperfections. The mathematical model is programmed to compute not only the axial load–displacement responses but also the interaction curves of axial load and moment of slender RCFST columns. The simulation modeling is validated by experimentally measured data. The validated computer model is used to parametrically study the interaction local–global buckling responses of RCFST columns while the range analysis is conducted to identify the relative significance of key parameters. It is demonstrated that the proposed computer model accurately simulates experimentally measured responses. Hence, it can be used with confidence in practice to analyze and design RCFST slender columns fabricated with steel plates of unequal thickness. The existing design standard AS/NZS 2327:2017 provides acceptable strength predictions of RCFST slender columns and beam-columns while the procedure specified in Eurocode 4 overestimates their capacities.

Fracture behavior analysis of X80 pipelines welded joints with unequal wall thickness

Pipeline transportation is one of the main methods for transporting oil and natural gas worldwide. The structural safety of welded joints of large diameter pipes with cracks and unequal wall thickness has become a research focus due to discontinuous geometrical structure and cracks in weld seams. In this paper, the tensile experiment and analysis of specimens with unequal wall thickness across welding seam based on the digital image correlation technology are carried out. Moreover, the influence of transition length and transition form on fracture behavior of welded joints of unequal wall thickness pipeline is obtained. In addition, a three-dimensional finite element model of welded joint of unequal wall thickness pipe with oblique line transition form and circular arc transition form is established. and the accuracy of the full-scale pipeline finite element model modeling method is verified by small-scale experiment data. On this basis, the influence of geometrical parameters of the transition section and wall thickness ratio, pipe diameter, and weld strength matching coefficient on the crack driving force of welded joints with unequal wall thickness is obtained. From the perspective of strain-based design, a method for obtaining the minimum transition length section and avoiding girth weld fracture is proposed. The research results guide the design and safety evaluation of welded joints with unequal wall thickness.

Fracture Analysis of Butt Joint Girth Weld of Pipe and Flange

Duplex stainless steel has been widely applied to industry. In this paper, nondestructive testing, chemical composition analysis, metallographic analysis, hardness test, and scanning electron microscope were used to study the causes of the crack in the butt joint girth weld of pipe and flange. Both steel pipe and flange are duplex stainless steel S31803. Through analysis, it was judged that the crack was a crystalline crack, generated in the welding process, which was related to the welding process and the control of the welding installation gap between the steel pipe and the flange with unequal wall thickness.

Quantitative study on magnetic-based stress detection and risk evaluation for girth welds with unequal wall thickness of high-grade steel pipelines

The magnetic-based stress detection technology has a great application potential in the field of girth weld stress detection. However, this technology lacks an effective theoretical model as a scientific guide. Therefore, to investigate the quantitative relationship between the magnetic gradient signal and weld stress and quantitatively evaluate the stress status of girth welds. In this paper, a numerical simulation model of stress-induced magnetic signals of girth welds with unequal wall thickness (UWT) is first established. Then, the model is used to calculate and analyse the quantitative variation law of the magnetic gradient signal of the girth weld with stress and detection height. Moreover, a magnetic-based stress detection and risk evaluation method is established to assess the stress failure risk of girth welds with UWT, whose accuracy is experimentally validated. The results indicate that the residual strength ratio RSR exponentially reduces from 0.83 to 0.49 as the Gmax increases from 373 to 542 μT/m. Moreover, the goodness of fit of the experimental data based on this relationship mentioned above reaches 0.98. The magnetic signal also exhibits a decaying exponential trend with detection height (0.1 m–0.3 m) when the internal pressure varies within 3 MPa–9 MPa. The numerical range of the RSR of seven girth welds is 0.31–0.95, which shows good agreement with the contact inspection results.

Behaviour of rectangular concrete-filled steel tubular slender column with unequal wall thickness

Concrete-filled steel tubular (CFST) components have been widely adopted in engineering applications. Recently, an optimised configuration of rectangular CFST column, e.g., unequal-walled cross-section, has been proposed to replace the traditional section with an equal wall thickness under eccentrically compression. Application advantages of CFST column with unequal wall thickness in terms of load-bearing behaviour have been revealed by experimental and numerical studies. A series of compressive tests were carried out on rectangular CFST columns with varying slenderness, eccentricities and wall thicknesses. Test results show that the rectangular CFST column with unequal wall thickness possesses higher post-peak load ductility than the column with an equal wall thickness under the same configuration. Numerical simulations were proposed to predict the performance of the test specimens and a good agreement can be obtained between numerical and experimental results. Based on the validated numerical model, parametric studies were conducted to investigate the effect of the wall thickness, slenderness and eccentricity on the load-bearing capacity of the CFST column. It suggests that the ultimate load-bearing capacity of the unequal-walled columns can be optimised with proper flange thickness ratio and slenderness.

Failure analysis on girth weld cracking of underground tee pipe

Three girth weld cracking events were found by X-ray inspection in one natural gas station. To determine the failure cause, one of the three failure events was studied by visual inspection, nondestructive testing, microstructure examination, scanning electronic microscopy (SEM) coupled with energy dispersive spectrometry (EDS), blasting tests, finite element simulations and a series physical and chemical tests. The results revealed that the welding defects were original failure factor, and these welding defects led to crack initiation and propagation through the wall thickness under three aspects of stress concentration effects with internal pressure. The stress concentration effects were originated from the unqualified inner chamfering angle, unequal wall thickness, and inherent shape of tee pipe. The reason causing welding defects of girth weld is that the slag inclusions were not cleaned up timely, and then the slag inclusions led to the existence of welding defects.

Investigations into Structural Behavior of Concrete-Filled RHS Columns with Unequal Flange Thickness under Compressive Load.

Previous studies have shown that components with an unequal-walled concrete-filled rectangular hollow section (CFRHS) can achieve a greater resistance under bending than those with equal-walled CFRHS. However, the study on the compressive behavior of the CFRHS column is limited. Therefore, this paper investigates the performance of compressed CFRHS columns with unequal flange thickness, based on experimental and numerical approaches. In the test, the effects of slenderness and eccentricity on the compressive capacity of the CFRHS columns with unequal shell thickness are discussed. Numerical models based on the finite element method are established, to evaluate the resistance and failure pattern of each specimen in the test. Parametric studies are carried out based on the validated model, to investigate the effect of eccentricity, wall thickness, and steel and concrete material properties on the load-bearing capacity of the compressed CFRHS column. In addition, the analytical expressions of the resistance of CFRHS columns with unequal wall thickness are derived, and the prediction values are validated through comparing with the test results. It is found that eccentric compressed columns with unequal-walled CFRHS have a similar load-bearing capacity and better ductility when compared with the equal-walled CFRHS.

Failure Mechanisms of Equal and Unequal Wall Thickness Hybrid Maraging Steel-P20 Tubular Joints: Effects of Welding Residual Stresses

Abstract Joining an additively manufactured component to a forged or cast part through welding processes has recently attracted the attention of engineers and scientists. This technique integrates the technical benefits of additive manufacturing (AM) technology with conventional processes that may be more cost-efficient. In this paper, the effect of residual stresses on the mechanical performance of a hybrid welded pipe joint connecting an additively manufactured maraging steel (MS1) pipe segment with a conventional P20 steel tube having an equivalent outside diameter was studied. A sequentially coupled thermo-mechanical continuum finite element (FE) modeling procedure to predict the residual stress state on circumferential pipe hybrid MS1-P20 joints subjected to multi-axial loads was developed and validated. Available experimental data on a welded pipe joint with conventional stainless steel (SUS304) were used to calibrate the model. The FE modeling procedures were further validated for the hybrid MS1-P20 joint. The predicted residual stress state was mapped on the pipe joint with equal and unequal wall thickness joint transitions. The mechanical performance of these pipe joints was evaluated with the application of internal pressure, uniaxial tension, and flexural loads. The major contribution of this study was the proposition of a new concept of hybrid joints, where a significant transition of the load was expected. The new hybrid joint concept was presented to meet the existing design criteria requirements without sacrificing other parameters (e.g., component weight and manufacturing expense) and facilitate the production of hybrid components using AM techniques.

Adaptive and Pathological Reshuffling in the Venous Wall in Special Hemodynamic Conditions-Acquired Arteriovenous Fistula.

ABSTRACT: Hemodialysis and peritoneal dialysis are the two possible choices in chronic renal disease in the uremic stage. Native arteriovenous fistula is susceptible to complications, some posing vital risk and requiring prompt treatment. We present the case of a patient undergoing hemodialysis on native AVF. An aneurism developed progressively on the arterialized cephalic vein. The AVF was abolished by closing the arteriotomy with a venous patch and excising the aneurismal venous segment. The pathology exam of the surgical specimen showed unequal vessel wall thickness due to hyperplasia of the media and subintimal space, with calcifications within the hyperplastic media.

Study on rectangular concrete-filled steel tubes with unequal wall thickness

Rectangular concrete-filled steel tubular columns with unequal wall thickness were investigated in the paper. The physical centroid, the centroidal principal axes of inertia, and the section core were given. The generalized bending formula and the generalized eccentric compression formula were deduced, and the equation of the neutral axis was also provided. The two rectangular concrete-filled steel tubular stub specimens subjected to the compression load on the physical centroid and the geometric centroid respectively were tested to verify the theoretical formulas.

Failure analysis of corrosion at an inhomogeneous welded joint in a natural gas gathering pipeline considering the combined action of multiple factors

Abstract A gathering pipeline in a gas field in Northeast China transporting mainly natural gas and also some water and sands was welded using two 20G pipes with different wall thicknesses. The internal corrosion of this pipeline was inhomogeneous. The unequal wall thickness welded joint suffered more serious corrosion damage than did other parts of the pipe and was found to fail during routine maintenance. In this paper, the corrosion damage at this joint was studied based on inhomogeneity. Internal and external factors affecting corrosion, such as the mechanical and electrochemical properties of materials, stress distribution at the joint, and the flow condition in the pipe, and their combined action were investigated. Failure attribution was performed on this basis. Specifically, a hardness test was conducted on different zones of the joint, including the base metal (BM), heat-affected zone (HAZ) and weld metal (WM), to investigate the abrasive wear resistance at the joint. Microstructures of the three zones were characterized by optical microscopy. The morphology and composition of the corrosion film covering the inner surface of the welded joint were characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and X-ray powder diffraction (XRD). Potentiodynamic polarization experiments and electrochemical impedance spectroscopy (EIS) were conducted on samples from the three zones to investigate their electrochemical performances. Moreover, a computational fluid dynamics (CFD) analysis was performed to obtain the flow condition near the joint, and a finite element method (FEM) was used to calculate the stress distribution at the joint. The results showed that the internal corrosion mechanism of the pipeline was CO2 corrosion accelerated by detrimental Cl−. The geometric discontinuity of the welded joint was the main cause of the accelerated corrosion damage at the joint. The change in wall thickness of the welded pipe not only produced gas vortices but also led to stress concentration. Both of these conditions can further accelerate corrosion by destroying the protectiveness of the corrosion film. It is suggested that the corrosion can be prevented by eliminating the inhomogeneities of fluid flow and stress distribution.

Effects of blank dimension on forming characteristics during conical-section ring rolling of Inco718 alloy

For profile ring rolling of difficult-to-deform materials, geometry and dimensions of blank are critical for dimensional accuracy and thermomechanical parameters distribution of the formed ring. In this study, four blank design principles for conical-section ring rolling are presented based on analytical description of the volume distribution characteristic curve (VDCC), and then effects of all dimension factors of the four blanks are explored comprehensively by using 3D coupled thermomechanical FE model established based on FORGE. According to the comprehensive analysis, optimal blank design principle for conical-section ring rolling is determined. The results obtained show that: (1) Preparation stage of rolling process (PSRP) is an essential stage for slope forming without wall thickness reduction, and the essence of PSRP is the process that the metal in rolling cavity seeking for balanced pressure along axial direction. (2) Unequal slope and unequal wall thickness have obvious effects on stress distribution. (3) We can, through controlling local deformation in PSRP and shortening the time of PSRP, improve the strain and the temperature distribution.

두께가 다른 이종배관 용접부 면삭 각도 변화에 따른 하중지지능력 평가

두께가 다른 이종강도 배관 용접부에서 인장, 내압 및 굽힘응력에 대한 하중지지능력을 평가하였다. 1.22, 1.54, 및 1.89의 두께비를 갖는 API X65-API X80, API X42-API X65 및 API X42-API X80 배관 용접부를 유한요소해석을 통하여 하중지지능력을 평가하였다. 이종강도 배관의 두께비가 1.5 이하에서 인장강도와 최대모멘트는 면삭각도 변화에 큰 영향을 받지 않으나 두께비가 1.5 이상에서는 큰 영향을 받는다. 저강도 배관의 길이방향 면삭각도와 두께비 변화에 따라서는 내압에 의한 파열압력은 영향을 받지 않는다.

Comparison of Two Methods of Finite Element Modeling for Elbows with Unequal Wall Thickness

Abstract In Finite Element Stress Analysis of elbow, its unequal wall thickness can be obtained by two methods: eccentric circle method and multi-spot spline curve drawed according to wall thickness of elbow. In this work, an elbow with constant inner diameter was taken as an illustration and its simulation results based on these two modeling methods were compared under different ratios of central line bend radius to mean diameter of pipe R/D. It is found that modeling method has no effect on the stress analysis results of elbows. But eccentric circle method has the virtue of being easier to implement and can be used without restriction of R/D, so it is an ideal method of finite element modeling for unequal wall thickness elbows. Because the FEA results of equal thickness elbows are recognizably higher than those of elbows with unequal wall thickness, considering non-uniform thickness of elbows is necessary to set up a reasonable safety evaluation for elbows.