Abstract
Large-diameter pipelines are increasingly used in deep-water offshore applications. In this context, reliable predictions of the mechanical properties and the collapse pressure of the line pipe product constitute important challenges towards optimization of line pipe fabrication process. The JCO-E line pipe fabrication process, from a flat plate to a circular pipe, is a cost effective method regarding the required forming force tooling [1]. The present study focuses on the numerical modelling of JCO-E process, using information from the fabrication process directly from the pipe mill. The validity of the proposed numerical model is verified by comparing numerical results with actual measurements from JCO-E pipes. Following the modelling of manufacturing process, the collapse performance of as-fabricated JCO-E line pipe is investigated.In the first part of the PhD thesis, the finite element simulation of JCO-E line pipe fabrication process is presented using a numerical model, developed ...
Large-diameter pipelines are increasingly used in deep-water offshore applications. In this context, reliable predictions of the mechanical properties and the collapse pressure of the line pipe product constitute important challenges towards optimization of line pipe fabrication process. The JCO-E line pipe fabrication process, from a flat plate to a circular pipe, is a cost effective method regarding the required forming force tooling [1]. The present study focuses on the numerical modelling of JCO-E process, using information from the fabrication process directly from the pipe mill. The validity of the proposed numerical model is verified by comparing numerical results with actual measurements from JCO-E pipes. Following the modelling of manufacturing process, the collapse performance of as-fabricated JCO-E line pipe is investigated.In the first part of the PhD thesis, the finite element simulation of JCO-E line pipe fabrication process is presented using a numerical model, developed for the purposes of the present study. The deformation and stresses induced by manufacturing process, namely the edge crimping, the JCO forming, the LSAW welding, and the expansion (E) operation are calculated utilizing finite element simulation tools. In addition to numerical modelling, strip specimens are extracted from the steel plate (raw material) and subjected to monotonic and cyclic uniaxial loading to measure the material properties. Using stress-strain curves obtained from the experiments, an efficient constitutive model is calibrated and incorporated in the finite element model, as a material user subroutine. The elastic-plastic behavior of the steel plate is described by a (combined) kinematic/isotropic hardening plasticity model, which can also takes into account the anisotropy of plate. Once the numerical analysis of JCO-E process is completed, the predicted material properties of JCO-E pipe are compared with experimental results from strip specimens extracted from the final line pipe aimed at validation of the numerical model. Following the simulation of the fabrication process, and using the same finite element model, the analysis is continued, so that the mechanical response of JCO-E pipe under external pressure is obtained, and its collapse pressure is calculated for different values of the manufacturing parameters.Considering the parameters provided by Corinth Pipeworks S.A., the above methodology is applied on the JCO-E process of (a) a 26-inch-diameter X65 “relatively thin-walled” line pipe and (b) a 30-inch-diameter X60 “thick-walled” line pipe, which are candidates for offshore pipeline applications. The first pipe is used in moderately deep water applications, whereas the latter pipe is candidate for deep-water applications that may exceed 2,000 meters of water depth. Using the finite element model, comparisons of numerical results with geometric characteristics of the pipe, provided by the pipe mill, and material properties of the “actual” pipe are presented, in order to validate the model. The simulation of JCO-E process enables the prediction of ultimate external pressure capacity of the corresponding as-fabricated JCO-E pipe taking into account different values of the manufacturing parameters. In particular, the expansion level and the displacement size of the JCO press are the main parameters under consideration. In the first application of finite element analysis (relatively thin-walled pipe), it was found that the residual stresses induced by welding stage are eliminated after the expansion process, and have minor effect on collapse pressure. Hence, in the second application of finite element analysis, the welding process is modeled through a “simple” no-slip condition activated, after JCO steps, and upon contact of the plate edges. A main conclusion of the above finite element analyzes is that the expansion process reduces ovalization and residual stresses in the pipe. Furthermore, there is an optimum level of expansion corresponding to maximum collapse pressure; beyond that level, the collapse pressure is reduced primarily because of the degradation of circumferential compressive strength, due to Bauschinger effect.The last part of the PhD thesis presents the development of a simplified semi-analytical methodology of JCO-E forming process, based on plate kinematics and the constitutive model adopted above. This numerical modelling is aimed at better understanding of the forming process and offers a simple and efficient prediction of geometry, residual stresses, mechanical properties, and collapse pressure of JCO-E pipe with respect to the corresponding predictions obtained from finite element modelling.
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