Ilson P. Pasqualino

Strength Analyses of Sandwich Pipes for Ultra Deepwaters

Design requirements for pipelines regarding both ultimate strength and flow assurance in ultra deepwater scenarios motivated the development of a new sandwich pipe which is able to combine high structural and thermal insulation properties. In this concept, the annulus is filled with low cost materials with adequate thermal insulation properties and good mechanical resistance. The aim of this research work is to perform small-scale laboratorial tests and to develop a finite element model to evaluate the structural performance of such sandwich pipes with two different options of core material. After calibrated in view of the experimental results, a three-dimensional finite element model incorporating nonlinear geometric and material behavior is employed to perform strength analyses of sandwich pipes under combined external pressure and longitudinal bending. Ultimate strength envelopes for sandwich pipes are compared with those generated for single-wall steel pipes with equivalent collapse pressures. The study shows that sandwich pipe systems with either cement or polypropylene cores are feasible options for ultra deepwater applications.

Fatigue analysis of aluminum drill pipes

An experimental program was performed to investigate the fundamental fatigue mechanisms of aluminum drill pipes. Initially, the fatigue properties were determined through small-scale tests performed in an optic-mechanical fatigue apparatus. Additionally, full-scale fatigue tests were carried out with three aluminum drill pipe specimens under combined loading of cyclic bending and constant axial tension. Finally, a finite element model was developed to simulate the stress field along the aluminum drill pipe during the fatigue tests and to estimate the stress concentration factors inside the tool joints. By this way, it was possible to estimate the stress values in regions not monitored during the fatigue tests.

Numerical-Analytical Prediction of the Collapse of Flexible Pipes Under Bending and External Pressure

This work gathers the phenomena indicated through the available literature and industry standards as determinant in the evaluation of the collapse of flexible pipes under combined bending and external pressure. It also proposes a complete analytical formulation to assess the collapse strength. The effects of dimensional variations and added ovalization due to bending are combined to evaluate the final collapse pressure. Numerical models are generated for comparison purposes and experimental results are used to validate the formulation proposed. The good agreement obtained between numerical and analytical predictions show that is possible to determine the curve collapse of flexible pipes through analytical approaches.Copyright

Stress Concentration Factors of Dented Pipelines

A nonlinear finite element model was developed to assess stress concentration factors induced by plain dents on steel pipelines subjected to cyclic internal pressure. The numerical model comprised small strain plasticity and large rotations. Six small-scale experimental tests were carried out to determine the strain behavior of steel pipe models during denting simulation followed by the application of cyclic internal pressure. The finite element model developed was validated through a correlation between numerical and experimental results. A parametric study was accomplished, with the aid of the numerical model, to evaluate stress concentration factors as function of the pipe and dent geometries. Finally, an analytical formulation to estimate stress concentration factors of dented pipelines under internal pressure was proposed. These stress concentration factors can be used in a high cycle fatigue evaluation through S-N curves.Copyright

The Effect of the Reeling Laying Method on the Collapse Pressure of Steel Pipes for Deepwater

This work deals with a numerical and experimental investigation on the effect of the reeling installation process on the collapse pressure of API X steel pipes. A three-dimensional nonlinear finite element model was first developed to simulate the bending and straightening process as it occurs during installation. The model is then used to determine the collapse pressures of both intact and plastically strained pipes. In addition, experimental tests on full-scale models were carried out in order to calibrate the numerical model. Pipe specimens are bent on a rigid circular die and then straightened with the aid of a custom-made test facility. Subsequently, the specimens are tested quasi-statically under external pressure until collapse in a pressure vessel. Unreeled specimens were also tested to complete the database for calibrating the numerical model. The numerical model is finally used to generate collapse envelopes of reeled and unreeled pipes with different geometry and material.Copyright

COMPARATIVE STRUCTURAL ANALYSES BETWEEN SANDWICH AND STEEL PIPELINES FOR ULTRA-DEEP WATER

Pipe-in-pipe systems are usually composed of two concentric metal pipes with or without an insulation material in the annulus region. Design requirements for ultra-deep water pipelines motivated the development of a new pipe-in-pipe conception in which the annulus is filled with materials that combine low cost, adequate thermal insulation properties and good mechanical resistance. The aim of this ongoing research project is to evaluate the structural performance of sandwich pipes with two different options of core material. Because of their wide availability and relatively low costs, the materials considered in this study were cement and polypropylene for the annulus, with pipes made of API X-60 grade steel. In this paper, a three-dimensional finite element model considering material and geometric nonlinear behavior was developed. This numerical model was used to perform a parametric study to determine the collapse envelopes of different pipe-in-pipe configurations under combined bending and external pressure. The collapse envelopes were compared with others obtained for steel pipelines of equivalent collapse pressure. The study showed that the pipe-in-pipe systems with either cement or polypropylene cores are feasible options to ultra-deep water pipelines fulfilling concomitantly both the requirements of structural resistance and thermal insulation.Copyright

Response of marine bacteria to oil contamination and to high pressure and low temperature deep sea conditions

The effect of pressure and temperature on microbial communities of marine environments contaminated with petroleum hydrocarbons is understudied. This study aims to reveal the responses of marine bacterial communities to low temperature, high pressure, and contamination with petroleum hydrocarbons using seawater samples collected near an offshore Brazilian platform. Microcosms containing only seawater and those containing seawater contaminated with 1% crude oil were subjected to three different treatments of temperature and pressure as follows: (1) 22°C/0.1 MPa; (2) 4°C/0.1 MPa; and (3) 4°C/22 MPa. The effect of depressurization followed by repressurization on bacterial communities was also evaluated (4°C/22 MPaD). The structure and composition of the bacterial communities in the different microcosms were analyzed by PCR‐DGGE and DNA sequencing, respectively. Contamination with oil influenced the structure of the bacterial communities in microcosms incubated either at 4°C or 22°C and at low pressure. Incubation at low temperature and high pressure greatly influenced the structure of bacterial communities even in the absence of oil contamination. The 4°C/22 MPa and 4°C/22 MPaD treatments resulted in similar DGGE profiles. DNA sequencing (after 40 days of incubation) revealed that the diversity and relative abundance of bacterial genera were related to the presence or absence of oil contamination in the nonpressurized treatments. In contrast, the variation in the relative abundances of bacterial genera in the 4°C/22 MPa‐microcosms either contaminated or not with crude oil was less evident. The highest relative abundance of the phylum Bacteroidetes was observed in the 4°C/22 MPa treatment.

High Cycle Fatigue of Pipelines With Plain Dents: Simulations, Experiments and Assessment

The objective of this work is to propose a methodology for assessing the fatigue life of dented pipelines according to the current high cycle fatigue theory. The proposed methodology employs S-N curves obtained from tensile test material properties and includes an expression to estimate stress concentration factors for spherical dents. Finite element analyses are carried out to determine stress concentration factors for different pipe and dent geometries. Using the numerical results, an expression to estimate stress concentration factors of dented pipelines is developed. Additionally, fatigue tests are conducted with the application of cyclic internal pressure on small-scale dented steel pipe models. Different pressure levels are employed, resulting in failures ranging from around 6000 to more than 106 cycles, enabling the determination of the endurance limit and of the finite life behavior of dented pipes. Furthermore, the Goodman and Gerber criteria to account for the mean stress are evaluated in view of the experimental results. The fatigue test results are used to validate the proposed assessment methodology for the analyzed conditions.Copyright

Materials Selection for Sandwich Pipes Under the Combined Effect of Pressure, Bending and Temperature

Recent researches point to the great potential of the sandwich pipe conception for ultra deepwater exploitation and production of oil and natural gas. Its configuration is very simple and comprises two concentric metallic pipes with a core material, polymeric or ceramic, in the annulus. The main functions of the annular layer are: to provide satisfactory thermal insulation so as to avoid the formation of wax and hydrates along the pipeline during production shutdown; to improve the overall structural strength of the system. Polypropylene and cement have been recently proposed for these applications. The reason for the choice of these materials was the low cost and the extensive availability in industry. Here a systematic material selection approach is employed in order to assess the applicability of other polymeric materials. The attributes of materials needed to meet the design specification are thoroughly studied. The list of possible materials was enlarged and the modified digital logic approach is used with the purpose to define a top group of materials for further numerical comparative study. Finite element analyses are carried out to assess the structural strength of the sandwich pipe under pure external pressure or longitudinal bending and combined external pressure and bending. Additionally, the effect of thermal gradient is included to the numerical analyses to evaluate each pre-selected material of the top group. Results indicate that other potential materials such as PEEK and polycarbonate can improve the structural performance of the sandwich pipe conception and yet meet other several design criteria.Copyright

Core Material Performance on the Propagation Pressure of Sandwich Pipes

Due to their insulative nature and ability to withstand high hydrostatic pressures, sandwich pipes have been considered feasible for use in ultra deepwater pipelines. As defined here, sandwich pipes consist of an inner and outer metallic pipe with a suitable core material in the annulus. In this paper, a non linear three-dimensional finite element model, previously presented and compared with experiments, is used in an extensive parametric study of the quasi-static propagation of buckles in sandwich pipes. The primary purpose of this study is to investigate the actual contribution of the core material to the propagation pressure. Parameters addresses include bonding condition (no adherence, perfect adherence), metallic pipe thickness, and core material thickness.Copyright