UOE Pipe Research Articles

Robust Optimization of UOE Forming Process Considering Inhomogeneity of Material Properties

Abstract The properties inhomogeneity of steel plates will result in uncertainty of forming quality of large diameter UOE oil pipes and increase the risk of pipeline failure. In this paper, a robust design method for UOE forming process based on support vector machine and sequential response surface modeling and considering the variation of steel plates′ properties is proposed. A hundred of mechanical experiments are first carried out and the variation of X80 steel's properties is statistically evaluated. The varied properties are assigned to partitioned steel segments and taken as the noise factor in process design. The ovality of the UOE pipe is employed as the optimization objective, and the forming quality indicators including convex amount, mean outside diameter, yield strengths and Ys/Uts7, O-forming gap, the width of the U-shaped plate, inclined angle of straight arm of the U-shaped plate, etc., are taken as the constraints. Based on the semi-analytical computation of C-, U- and O-forming processes and finite element simulation of expanding process, a sequential response surface model is established by using the support vector machine method. Finally, a Monte Carlo sampling is performed to demonstrate the effectiveness of the proposed method. Compared to conventional optimization method, the robust optimization performs obviously better in reducing the ovality and increasing the robustness of UOE forming process.

Characterization of Anisotropic Mechanical Properties of X70 Spiral Welded Steel Pipes

Abstract Anisotropic tensile and compressive properties of base metals and girth welds of two API X70 spiral welded pipes have been investigated in this study. Spiral welded pipes exhibit different characteristics of anisotropy from UOE pipes, as the anisotropic property is determined by the thermo-mechanical rolling process of plates and coils produced for pipes. Spiral pipe steels have the lowest strengths in the pipe's transverse direction, contrary to UOE pipes with high strengths in the transverse direction. Yield strengths measured from tensile and compressive tests and their anisotropic characteristics are comparable, although tensile yield strengths are somewhat greater. The results of compressive tests also indicate an anisotropy in the pipe's through-thickness orientation as well as in the longitudinal orientation; yield strengths are highest in the through-thickness direction for both base metals and girth welds of the two pipes.

Non-linear Analysis of the Expanding Stage in the UOE Pipe Manufacturing Process

Non-linear Analysis of the Expanding Stage in the UOE Pipe Manufacturing Process

Yield strength estimation of X65 and X70 steel pipe with relatively low t/D ratio

During the pipe forming process, a steel plate undergoes inelastic behavior multiple times under a load condition repeating tension and compression in the circumferential direction. It derives local reduction or increase of yield strength within the thickness of steel pipes by the plastic hardening and Bauschinger effect. In this study, a combined hardening model is proposed to effectively predict variations of yield strength in the circumferential direction of API-X65 and X70 steel pipes with relatively low t/D ratio during the forming process, which is expected to experience accumulated plastic strain of 2~3%, the typical Luder band range in a low-carbon steel. Cyclic tensile tests of API-X65 and X70 steels were performed, and the parameters of the proposed model for the steels were calibrated using the test results. Bending–flattening tests to simulate repeated tension and compression during pipe forming were followed for API-X65 and X70 steels, and the results were compared with those by the proposed model and Zou et al. (2016), in order to verify the process of material model calibration based on tension–compression cyclic test, and the accuracy of the proposed model. Finally, parametric analysis for the yield strength of the steel plate in the circumferential direction of UOE pipe was conducted to investigate the effects of t/D and expansion ratios after O-forming on the yield strength. The results confirmed that the model by Zou et al. (2016) underestimated the yield strength of steel pipe with relatively low t/D ratio, and the parametric analysis showed that the t/D and expansion ratio have a significant impact on the strength of steel pipe.

The research on pipe structural behavior of 3D UOE manufacturing process

A 3D UOE manufacturing process is established by ABAQUS software in this study with the consideration of detailed boundary conditions. From two aspects of geometric profile and material distribution, the effects of each forming step are determined from three directions: circumferential direction, radial direction and longitudinal direction. As for the geometric profile of the 3D UOE model, the radius distribution of X70 is more concentrate around the nominal value than X80 pipe. As the longitudinal deformation in O forming and expansion step is not uniform, greater compression ratio and expansion ratio are needed for reducing section ovality. Under the effect of twice expansion steps, the ovality in the overlapping area is smaller than that in the region subjected to one-step calibration. As for the structural behavior of UOE pipe, the weakest position of the pipe after UOE manufacturing process is determined according to the principle of Bauschinger effect. Different with 2D model, 3D UOE pipe has a stronger collapse resistance under the effect of low ovality and the supporting of neighboring sections. Comparing with the offshore standard DNV-OS-F101, the accuracy of 3D UOE model is verified whose resistance to the external pressure is more sensitive with the expansion ratio than the internal pressure.

Yield strength tracking of UOE pipe considering various thickness-to-diameter ratios

Abundant literature was dedicated to the numerical tracking of the yield strength of cold formed pipes throughout their forming process. However, the flattening process conducted on straps sampled from the formed pipe for tensile test as well as the residual stress developed after each stage were not considered in most studies. Therefore, a simulation-based finite element analysis program was developed to replicate the UOE forming of steel pipes and track the yield strength throughout the forming process and final flattening considering the residual stress. The accuracy of the simulation was validated through comparison with experimental data for API 5L X70 steel pipe. In this study, the program is employed to examine the causes leading to the change in the yield strength at each forming stage. In addition, the effect of the thickness-to-diameter ratio (t/D) on the yield strength is evaluated. The consideration of the residual stress in the simulation enabled to find the existence of a critical range for t/D beyond which further improvement of the yield strength cannot be achieved.

Yield Strength Prediction of UOE Pipes: From Forming to Flattening

Yield Strength Prediction of UOE Pipes: From Forming to Flattening

Effects of manufacturing plastic prestrains found on calendered and UOE pipes and pressure vessels on structural integrity assessments regarding fatigue crack growth and LBB

High responsibility components operating under cyclic loading can have their resistance against initiation and growth of fatigue cracks highly influenced by previous thermomechanical processing. Within the interest of the present work, different manufacturing processes (such as the fabrication of pipes using UOE) or installation procedures (such as pipe reeling) can lead to nonuniform plastic prestrain fields thus affecting lifetime and safety. Previous studies conducted by the authors revealed that prestraining up to 14% considerably reduced fatigue crack growth rates (da/dN-ΔK) for a hot-rolled (1/2”) ASTM-A36 steel as a result of strain hardening and its effects on plastic zone sizes. In addition, results also revealed two interesting trends: i) the larger is the imposed prestrain, the greater is the growth rate reduction in a nonlinear asymptotic relationship; ii) the larger is imposed ΔK, the more pronounced is the effect of prestraining. Within this scenario, this work explores the effects of those results on more realistic lifetime predictions applicable to pipelines and pressure vessels. First, a nonlinear model based on the experimental results was developed to predict crack growth rates (da/dN) as a function of ΔK and varying plastic prestrain levels. Second, refined nonlinear FE models were developed to quantify plastic prestrain fields caused by manufacturing sequence of the studied pressure vessels and pipes. Such fields proved to be remarkably nonuniform, in accordance to the literature. Finally, considering an idealized cyclic internal pressure and the obtained fields, a MatLab algorithm was implemented to predict fatigue crack growth rates until LBB (Leak Before Break) condition takes place. Best practices for implementing such evaluations are presented and results revealed that effects of plastic prestrains are not negligible and should be taken into account on recommended practices and structural integrity assessments to avoid excessive conservatism or lack of safety in applications.

UOE pipe strains measurement during manufacturing process using digital image correlation

UOE pipe manufacturing processes influence directly on pipeline resilience and operation capacity. At present, most spread pipe manufacturing method is UOE. This kind of manufacturing process is based on cold forming principle. To avoid appearance of unwanted effects, the need to know the level of strains resulted after every technological step appeared. For this case a manufacturing process by using special designed equipment is simulated. The experimental simulation presented in this paper is performed for L 415MB (X60) steel plate with 7.9 mm thickness and a width of 1250 mm. As a result a DN 400 (16 inch) pipe is obtained. Manufacturing process is monitored by Digital 3D Image Correlation System Q-400 and the principle of operation is based on Digital Image Correlation.

UOE Pipe Numerical Model: Manufacturing Process And Von Mises Residual Stresses Resulted After Each Technological Step

AbstractFluid transportation from production areas to final customer is effectuated by pipelines. For oil and gas industry, pipeline safety and reliability represents a priority. From this reason, pipe quality guarantee directly influence pipeline designed life, but first of all protects environment. A significant number of longitudinally welded pipes, for onshore/offshore pipelines, are manufactured by UOE method. This method is based on cold forming. In present study, using finite element method is modeled UOE pipe manufacturing process and is obtained von Mises stresses for each step. Numerical simulation is performed for L415 MB (X60) steel plate with 7,9 mm thickness, length 30 mm and width 1250mm, as result it is obtained a DN 400 pipe.

UOE Pipe Manufacturing Process Simulation: Equipment Designing and Construction

Abstract UOE pipe manufacturing process influence directly on pipeline resilience and operation capacity. At present most spreaded pipe manufacturing method is UOE. This method is based on cold forming. After each technological step appears a certain stress and strain level. For pipe stress strain study is designed and constructed special equipment that simulate entire technological process.UOE pipe equipment is dedicated for manufacturing of longitudinally submerged arc welded DN 400 (16 inch) steel pipe.

Strain aging on the yield strength to tensile strength ratio of UOE pipe

ABSTRACTStrain aging of microalloyed steel pipe can occur at the relatively low temperatures associated with the pipe coating process and/or during long-term storage. A Box–Behnken statistical design was used to determine the significant strain aging variables that affect the longitudinal yield strength to tensile strength (Y/TS) ratio for three uncoated X70 UOE pipes. The strain aging variables examined include time, temperature, steel composition/microstructure (vis-a-vis the C/Nb ratio) and position through the pipe wall thickness. Metallographic and electron backscattered diffraction examinations were undertaken to determine the grain size and phase percentages of the as-received pipe steel. Both position in the pipe and the C/Nb ratio were found to have a statistically significant effect on the yield strength to tensile strength ratio.

Effects of the Initial Geometric Imperfections on the Buckling Behavior of High-Strength UOE Manufactured Steel Pipes

The effects of the initial geometric imperfections on the buckling response of grade X-100 UOE manufactured pipes are studied through finite element analysis (FEA). The initial geometric imperfections had been previously measured and quantified in terms of deviations in outside radius (OR) and wall thickness. The measurement results are used to develop imperfection models to be incorporated into buckling analysis. The OR deviation is seen to have insignificant effects on the buckling behavior, while the effects of thickness deviation are seen to be profound for both unpressurized and pressurized pipes. The geometric imperfection models are further investigated through a sensitivity study to isolate the most influential imperfection aspects on the buckling resistance of UOE pipes. A parametric study is carried out using these models and shows that excluding geometric imperfections will always result in overprediction of buckling capacity irrespective of D/t ratios.

Finite element analysis of UOE manufacturing process and its effect on mechanical behavior of offshore pipes

• We simulate the UOE forming process, using finite elements and an advanced plasticity model. • We present results for geometrical imperfections and anisotropy induced by the UOE forming process. • We investigate the effect of cold-forming on the performance of UOE pipes under external pressure, tension and bending. • We compare the structural performance of UOE pipes with the performance of seamless pipes. • We examine the efficiency of a simplified methodology for determining the structural capacity of a UOE pipe. Thick-walled steel pipes during their installation in deep-water are subjected to a combination of loading in terms of external pressure, bending and axial tension, which may trigger structural instability due to excessive pipe ovalization. The resistance of offshore pipes against this instability depends on imperfections and residual stresses due to the line pipe manufacturing process. The present study examines the effect of UOE line pipe manufacturing process on the structural response and resistance of offshore pipes during the installation process using advanced finite element simulation tools. The cold bending induced by the UOE process is simulated rigorously and, subsequently, the application of external pressure and structural loading (bending or axial force) is modeled, until structural instability is reached. A parametric analysis is conducted, focusing on the effects of line pipe expansion on the structural capacity of the pipe. The results show that there exists an optimum expansion at which the highest pressure capacity is achieved. The effect of the axial tension on the pressure capacity of the pipe is examined as well. The influence of the line pipe expansion on bending capacity in the presence of external pressure is also identified. Finally, a simplified methodology is employed, accounting for the material anisotropy induced by the manufacturing process, capable of determining the structural capacity of a UOE pipe in a simple and efficient manner with good accuracy, using more conventional modeling tools.

Mechanical and Metallurgical Properties of Heavy Wall Grade X80 High Strain Line Pipe Steel

Mechanical and metallurgical properties of a 27mm thick Grade X80 steel plate and its UOE pipe are described in this paper. The steel is economically designed for its chemical compositions. Steel plates were produced by Thermal-mechanical processing (TMCP) with attentive reduction control during hot rolling stage. The microstructure is composed of multi-phases in which polygonal ferrite and granular bainite are the principal constituents. Line pipes of 1219mm outer diameter, which has strain based design for long distance natural gas transportation over the permafrost and seismic areas, were manufactured by the UOE process under a 0.8% expanding ratio on the pipe. Mechanical properties of the pipe and in the girth weld joints comply well with the pipeline construction requirement. Precipitation behaviors were analyzed in the steel materials, and a strengthening contribution at about 45.6 MPa is disclosed. Dislocation hardening in the pipe base materials after the simulating coating gives rise to 44.9 MPa.

Yield strength development from high strength steel plate to UOE pipe

The yield strength of the UOE pipe is different from raw steel plate and inhomogeneously distributed on pipe body, because of the Bauschinger effect and work hardening during UOE forming process. The yield strength development of high-strength pipeline steels from raw plate to UOE pipe is investigated by using a modified Chaboche hardening model that incorporates the Bauschinger effect and yield plateau of X70, X80 and X90 steels. The final yield strength of pipe is evaluated by finite element simulation of uniaxial tension of a pipe specimen and an empirical equation. The influences of UOE process parameters on yield strength development are discussed. The results show the modified hardening model can predict the yield stress with good accuracy. The circumferential variation of yield stresses for X80 and X90 pipes are about two times more than that for X70 pipe due to their stronger Bauschinger effect. In UOE forming, C-, U- and O-forming reduce tensile yield stress, and expansion increases and homogenizes yield stress. Fattening operation reduces the measured yield stress, which should be considered in expansion ratio design especially for high strength steels. The yield strength increases logarithmically with t/D ratio and linearly with expansion ratio.

A numerical method for predicting O-forming gap in UOE pipe manufacturing

Large diameter welded pipes used in oil and gas pipelines are primarily manufactured by the UOE process, which consists of U-forming, O-forming, and expansion procedures. The formation of O-forming gap in the O-forming stage is a key processing factor and it involves complex plastic deformation and springback of the steel plate. In this paper, a numerical method is proposed for predicting geometric configuration and O-forming gap of steel plate after C–U–O-forming. A combined hardening model for characterizing the loading–unloading–reverse loading deformation of pipe steels is developed based on the Chaboche hardening model. The yield plateau phenomenon and the variation of elastic modulus with the increase of pre-strain are incorporated. Industrial experiments are carried out, and the proposed method is validated through comparison between experimental and calculated results. Furthermore, the influence of material and processing parameters on O-forming gap is numerically investigated. The results reveal that U-forming radius is the most important factor in C- and U-forming stages to determine O-forming gap, and the opening gap width increases with increasing of compression ratio in O-forming stage. Finally, the established numerical method is combined with a genetic algorithm and applied to optimize UOE process parameters for obtaining an ideal opening gap. The proposed method provides an effective and efficient tool for UOE process design.

Robust Design of UOE Forming Process Based on Support Vector Machine

Fluctuations in material properties of the incoming steel for UOE forming process are widespread. According to the statistics, the fluctuation range of the yield strength of the same grade pipeline steel is around 80MPa. Robust optimization methods have been widely applied in sheet metal forming area. In this paper, experiments were conducted to investigate how a stochastic material behavior of noise factors affected UOE forming quality. Robust design models integrated with response surface method for UOE forming process were established to minimize impact of the variations and improve the qualified rate of UOE pipe ovality. Support vector machine in both classification and regression was adopted to map the relation between input process parameters and forming qualities. The deterministic and robust optimization results are presented and compared, demonstrating increased process robustness and decreased number of product rejects by application of the robust optimization approach.

Numerical study on the X80 UOE pipe forming process

The UOE process is an effective approach for manufacturing large-diameter submerged-arc welding pipes used in oil and gas pipelines. A UOE process comprises the successive procedures of crimping, U-forming, O-forming, joining, welding, and expanding. In this study, a two-dimensional finite element model of UOE forming process is established and all the forming stages of an X80 high strength steel pipe are numerically studied. A kinematic hardening model is incorporated in FEM to describe the Bauschinger effect of X80 steel. The formation mechanism of O-forming open-seam is unveiled based on analysis of the complex deformation and springback behaviors of plate under loading–unloading–reverse loading condition. The validity of the model established is demonstrated by comparing the calculated result and practical measurement. Furthermore, the influence of processing parameters, friction coefficient and material properties on open-seam and ovality are numerically investigated.

Analysis and Simulation of the UOE Pipe Production Processing by Finite Element Method

Large-diameter pipes used in offshore applications are commonly manufactured through the UOE process. The plate is crimped along its edges, formed into a U-shape and then pressed into an O-shape between two semicircular dies. The pipe is welded closed and then circumferentially expanded to obtain a highly circular shape. In this study, the two-dimensional finite element model of the whole processing of the UOE pipe production has been established, including large deformation and complex contact. The deformed geometries of different steps and distribution of the equivalent plastic strain and variation in load are analyzed. This research is helpful in UOE forming process design and evaluating the capability of the pipe mill.