Rita G. Toscano

Experimental/numerical analysis of the collapse behavior of steel pipes

The production of steel pipes with guaranteed external collapse pressure (e.g. high collapse casings for oil wells) requires the implementation of an accurate process control. To develop that process control it is necessary to investigate how different parameters affect the external collapse pressure of the pipes. Experimental/numerical techniques implemented to investigate the collapse behavior of steel pipes are presented. The discussion of the experimental techniques includes the description of the facilities for performing external pressure collapse tests and the description of an imperfections measuring system. The numerical techniques include 2D and 3D finite element models. The effects on the value of the pipes’ external collapse pressure of their shape, residual stresses and material properties are discussed.

Performance of the QMITC element in two-dimensional elasto-plastic analyses

A detailed study of the performance of the two-dimensional element QMITC in elasto-plastic analyses is presented. Standard benchmark problems and involved industrial applications are considered. The conclusion is that the QMITC element is reliable and efficient enough to be used for actual engineering applications.

Finite element models in the steel industry. Part II: Analyses of tubular products performance

In this paper we discuss the finite element models that we developed for simulating the service performance of the tubular steel products used in the oil industry. These tubular products include the oil country tubular goods, that is to say the tubular products used in the oil wells, and the pipes used in pipeline applications.

DETERMINATION OF THE COLLAPSE AND PROPAGATION PRESSURE OF ULTRA-DEEPWATER PIPELINES

In the design of ultra-deepwater steel pipelines, it is important to be able to determine the pipe behaviour while subjected to external pressure and bending. In many cases, the ultra-deepwater lay process, where these high loads exist, governs the structural design of the pipeline. Much work has been performed in this area, and it is generally recognized that there is a lack of test data on full-scale samples of line pipe from which analyses can be accurately benchmarked. This paper presents the results of a nil-scale test program and finite element analyses performed on seamless steel line pipe samples intended for ultra-deepwater applications. The work involved obtaining full-scale test data and further enhancing existing finite element analysis models to accurately predict the collapse and post-collapse response of ultra-deepwater pipelines. The work and results represent a continuing effort aimed at understanding the behaviour of pipes subjected to external pressure and bending, accounting for the numerous variables influencing pipeline collapse, and predicting collapse and post-collapse behaviour with increasing confidence. The test program was performed at C-FER Technologies (C-FER), Canada, with the analyses undertaken by the Center for Industrial Research (CINI), Argentina. The results of this work have demonstrated very good agreement between the finite element predictions and the laboratory observations. This allows increased confidence in using the finite element models to predict collapse and post-collapse behaviour of pipelines subject to external pressure and bending.Copyright

A shell element for finite strain analyses: hyperelastic material models

Purpose – This paper aims to develop a simple and efficient shell element for large strains hyper‐elastic analyses.Design/methodology/approach – Based on the classical MITC4 shell element formulation a 3D shell element with finite strain kinematics is developed. The new quadrilateral shell element has five dof per node and two global dof to model the thickness stretching. The shell element is implemented for hyperelastic material models and the application of different hyperelastic constitutive relations is discussed.Findings – The results obtained considering three of the hyperelastic material models available in the literature are quite different when the developed strains are relatively high; this indicates that, for analyzing actual engineering examples, experimental data should be used to decide on the most suitable constitutive relation.Originality/value – The 3D version of the MITC4 element was developed.

Premium and Semi-Premium Connections Design Optimization for Varied Drilling-With-Casing Applications

As high resistance to fatigue loading together with high overtorque and compression capacities are at the top of a list of required features for connections to be used in new drilling and completion techniques such as casing drilling, then special connections with enhanced performance need to be developed. On the other hand, a cost-effective solution should be chosen to balance the performance when considering low-demanding shallow wells for which sophisticated premium connections could be uneconomical. This paper describes the development and evaluation of premium and semi-premium connections for tubing/casing which were developed to stand cyclic loads and reach an extended number of cycles under such conditions. The development process of an integral connection for casing sizes targetting very demanding applications comprised Finite Element Analysis (FEA) and Full Scale Fatigue Test (FSFT) showing Stress Concentration Factors (SCF) lower than 2. In addition, during the development of the semi-premium connection to cover less demanding applications, some of these techniques were used to optimize the results until getting SCF lower than 3, good enough when low doglegs are present. The results of the tests are plotted in S-N (Alternating Stress vs Number of cycles to failure) curve with a standard curve as a reference. As per the results, both types of connections achieved the objective set at the beginning of the development process now being suitable alternatives for low and high demanding drilling/completion operations.

Modeling the UOE Pipe Manufacturing Process

It has been demonstrated in previous work that, for deepwater applications, the cold forming processes involved in UOE pipe manufacturing significantly reduces pipe collapse strength. To improve the understanding of these manufacturing effects, Tenaris has embarked on a program to model the phases of the UOE manufacturing process using finite element analysis simulations. Phase 1 of this work, presented previously in the literature [1], formulated the basis for the model development and described the 2D approach taken to model the various steps of manufacture. This paper presents the results of the Phase 2 work, and includes a description of the enhancements made to the modeling approach, a summary of the full-scale collapse testing performed at C-FER, and a comparison of the model predictions to the test results. Variations are made to the simulated manufacturing process in order to evaluate the sensitivity of collapse strength to key parameters. Based on the modeling approach taken, the findings of the Phase 2 work have shown that the deterioration of the collapse pressure diminishes with increasing O-press compression. The residual stress value is the most sensitive parameter when the strain hardening varies. It increases with the compression ratio and with the strain hardening value. In addition, given the assumed compression ratio of the test pipes, predictive behavior of the test results was found to be acceptable.Copyright

Effects of internal/external pressure on the global buckling of pipelines

The global buckling (Euler buckling) of slender cylindrical pipes under internal=external pressure and axial compression is analyzed. For perfectly straight elastic pipes an approximate analytical expression for the bifurcation load is developed. For constructing the nonlinear paths of imperfect (non straight) elasto-plastic pipes a finite element model is developed. It is demonstrated that the limit loads evaluated via the nonlinear paths tend to the approximate analytical bifurcation loads when these limit loads are inside the elastic range and the imperfections size tends to zero.

Experimental validation of a finite element model that simulates the collapse and post-collapse behavior of steel pipes

In previous publications CINI presented finite element models that simulated the collapse and post-collapse behavior of steel pipes under external pressure and bending. Those finite element models were used to analyze the effect of different imperfections on the collapse pressure and collapse propagation pressure of the steel pipes. Laboratory tests were carried out at CFER (Edmonton, Canada) in order to obtain experimental results that could be used to validate the numerical models. In this paper we compare the numerical and experimental results for the case of external pressure without bending.

Shell Element Formulations for General Nonlinear Analysis. Modeling Techniques

In 1970, Ahmad et al. [1] presented a shell element formulation that after many years still constitutes the basis for modern finite element analysis of shell structures. The original formulation was afterwards extended to material and geometric nonlinear analysis under the constraint of the infinitesimal strains assumption [2–4].