During subsea offshore drilling operations, the floating vessel is connected to the wellhead through a series of equipment assemblies. The riser is exposed to dynamic loads from currents, waves, and drilling platform motions. Therefore, a dynamic analysis of the riser system is required to obtain forces and moments in the wellhead. It is even more important in dynamic positioning (DP) operations, where the knowledge of boundary conditions for a safe emergency disconnection is highly relevant. The objective of this paper is to calculate the effects of changing the light and older BOP (typically with 4 rams) for newer and heavier BOPs (after Macondo accident, with 6 rams) on the Emergency Disconnect Sequence (EDS) time and on wellhead equipment strength. A typical scenario of drilling is proposed, in which the marine riser system considers the drilling string, the lower flex-joint, the marine riser, the kill and choke lines and the tensioners. Tensioners are used to top tension the marine riser and to compensate relative heave motion between the riser and the floating vessel. Riser systems were designed using the API RP 16Q and simulated using Orcaflex software. Vessel dynamic motions were calculated according to the response amplitude operator (RAO) data from a typical offshore drilling semi-submersible. The vessel motion is superimposed by a drift-off motion, which consists of a horizontal displacement along time in the direction of the propagating waves. It is employed to simulate the condition of vessel position loss due to thruster and or control system failure. Results indicate that the use of heavier BOPs reduces significantly the available time for initiating the EDS. Results are worse if older generation of wellhead equipment is used, where a smaller drift-off is necessary to safely disconnect the riser before potential equipment and environmental damage occurs.

Sandwich Pipes (SP) can be an effective solution for the ultra-deepwater submarine pipeline, combining high structural resistance with thermal insulation. Besides polymer, strain hardening cementitious composites (SHCC), a micromechanically designed material with the characteristic of high tensile ductility, can be another choice for the annular material. The purpose of this work is to investigate numerically the limit strength of SP with SHCC under external pressure and longitudinal bending. The mechanical behaviour of SHCC is simulated using a Concrete Damaged Plasticity (CDP) model provided by Abaqus/Standard. The finite element (FE) model is employed to better understand the structural behaviour of SP in different conditions of geometry, adhesion and loading. The pressure-curvature (P – K) failure envelopes for SP with unbonded and fully bonded interface conditions are presented. The results show that the resistance of the annulus layer has a great contribution for the overall structural behaviour. The interface condition and the thickness of the annulus are important influence factors on the overall structural behaviour. Besides, the lateral confinement effect on SHCC caused by the inner and outer steel tubes and the ultra high ductility of the SHCC have strong influence on the results for the pressure-curvature collapse envelopes.

Sandwich pipes (SP) can be an effective solution for the ultra-deepwater submarine pipeline, combining high structural resistance with thermal insulation capability. Besides polymer, steel fiber reinforced concrete (SFRC) can be an another choice for the annular material, based on the characteristics of high fracture toughness and good adhesion with metal. The purpose of this work was to investigate numerically the ultimate strength of SP filled with SFRC under external pressure and longitudinal bending. The mechanical behaviour of SFRC was simulated using a Concrete Damaged Plasticity (CDP) model whose parameters were estimated by uniaxial tension, compression and four-point bending tests. The applicability of the parameters obtained was verified by simulating the compression and four-point bending tests, where the results showed good correlation between measured and predicted numerical values. Pressure–curvature ultimate strength for SP with perfect adhesion and no adhesion interface condition was obtained. Besides, a parametric study was performed to investigate the effect of the thickness of each layer on the pressure–curvature collapse envelope of SP. It was found that the adhesion between layers and the lateral confinement effect on SFRC play a dominant role in the ultimate strength behaviour of SP, which lead to the non-monotonicity of the collapse envelope.

Sandwich Pipes (SP) can be an effective solution for the ultra-deepwater submarine pipeline, combining high structural resistance with thermal insulation. Besides polymer, strain hardening cementitious composites (SHCC), a micromechanically designed material with the characteristic of high tensile ductility, can be another choice for the annular material. The purpose of this work is to investigate numerically the limit strength of SP with SHCC under external pressure and longitudinal bending,. The mechanical behaviors of SHCC are simulated usine, a damaged plasticity model whose parameters are estimated by the tension and compression tests. The pressure-curvature (P - K) failure envelopes for SP with unbonded and fully bonded interface conditions are presented. The results show that the interface condition and the thickness of the annulus are the main influence factors on the overall structural behaviour. Besides, the lateral confinement effect caused by the inner and outer tubes and the ultra high ductility of SHCC itself lead to the new observations of the pressure-curvature collapse envelops.

Oil&gas production on deep and ultra deepwater scenarios require very thick walled steel pipelines or heavy Pipe-in-Pipe systems, which are expensive and difficult to install. Sandwich Pipe is a new pipeline concept composed of two concentric steel pipes separated by and bonded to a polymeric annulus that provide the adequate combination of structural strength and thermal insulation. In later works, Sandwich Pipes have been analyzed regarding to the structural strength and results have indicated good relation between steel weight and external pressure resistance, mainly when compared to the Pipe-in-Pipe system. To fulfill the thermal insulation requirements, an adequate polymer for the annular layer should be selected, combining both insulation requirements and good bonding strength to steel, which are determinant for the adequate performance. Sandwich Pipes with typical inner diameters of those employed in the offshore production are analyzed numerically to evaluate the ultimate strength under external pressure. Polyurethane based materials with different mechanical and thermal properties are selected. Experimental tests are performed to evaluate adhesion strength to steel, which are used as input for the numerical models. Non-linear geometry, material and contact properties are included, as well as temperature effect on polymer stiffness. To estimate the insulation capacity for each option the global heat transfer coefficient is calculated and a maximum “U value” is considered for all systems. Also, both numerical and analytical analyses are employed to design a PIP system for a hypothetical offshore field. Similar conditions to the newly discovered sub-salt fields offshore Brazil are adopted, i.e. 2500 m water depth and 80°C produced fluid temperature. API 5L specifications table are used for thickness and diameter selection and API RP1111 is employed to design PIP inner pipe. Results indicate that Sandwich Pipes with adequate strength and insulating annular material can generate significant advantages in relation to the PIP system. In addition to the sandwich structure benefit, the initial out-of-roundness maximum diameter directions between inner and outer pipes have a secondary role that produces additional strength for the collapse pressure resistance. Lower steel weight is calculated in all cases, even when the outer pipe is larger. All cases yielded lower submerged weight, which is an important parameter for installation purposes, because less expensive lay vessels may be required.

There were investigated geometrical distortions of two steel plates jointed by metal inert gas welding. The distributions of residual stresses in this welded joint were measured by X-ray diffraction method. The measured residual stress distributions were compared with residual stress state obtained by means of finite element analysis with using of ABAQUS software. A good agreement was obtained between experimental and analytical data.

Surface residual stress evaluation for double-electrode welding was studied. The stresses were monitored after each operational step: positioning, implementing of constraints, welding and constraints removal. The measurements were performed at the deposited metal, heat affected zone, base metal close to the weld joint and along the plate using the X-ray diffraction method. It was observed differences in the stress evaluations for double-electrode welding which resulted in lower bending distortions and higher values of surface residual stresses, compared with single-electrode welding. This behavior is associated with the stress distribution just after the welding processes in both heat affected zone and base metal close to the fillet for double-electrode welding. The main results from the laboratorial tests indicated lower values of the bending distortions for double-electrode welding compared with the single-electrode. In relation to the residual stress, the double-electrode welding generated, in general, higher stress values in both longitudinal and transversal directions.

Ultra deepwater scenarios, related to water depths beyond 1,500 m, require very thick walled steel pipelines or pipe-in-pipe systems, which are expensive and difficult to install due to excessive weight. Sandwich pipe is a new concept composed of two concentric steel pipes separated by and bonded to a polymeric annulus that provide the combination of high structural strength with thermal insulation. Previous results indicate that collapse pressure is strongly dependent on the polymer stiffness. The adhesion property is also important and can affect significantly the pipeline external pressure resistance due to the relative displacement between layers. Sandwich pipes can minimize steel costs and facilitate the ultra deepwater installation, with thermal and structural performance close to pipe-in-pipe systems. In this work, experimental tests and numerical models are employed to verify the influence of the inter-layer adhesion on the ultimate strength under external pressure and longitudinal bending of a sandwich pipe prototype. The maximum shear stress obtained from sandwich pipe specimens bonded by a particular adhesive indicated the adhesion levels to be adopted in the numerical simulations. Contact model combined with non-linear springs that connect the steel pipes to the polymer layer was employed to analyze both bonding and slipping conditions. As expected for a sandwich structure, the strength is strongly dependent on the interface stickiness. The analyzed geometry is able to withstand a water depth up to 3,000 meters with a bonding strength corresponding to only 10% of the idealized perfect adhesion condition. Finally, sandwich pipes with typical inner diameters of those employed in the offshore production are analyzed numerically to evaluate the ultimate strength under external pressure. The annular material must have both adequate mechanical strength and low thermal conductivity properties to satisfy the operational requirements. Some polymeric materials with different properties are selected. The global heat transfer coefficient is determined in each case to attend the thermal insulation requirements of an oil field. Introduction New concepts for submarine pipelines and risers have been proposed recently in order to achieve flow assurance in deepwater environment. It is the case of both pipe-in-pipe (PIP) and sandwich pipe (SP). PIP is composed of two concentrically mounted steel pipes with the annular space filled with either circulating hot water or materials with known thermal insulation properties. The objective of this type of pipe is to increase the thermal insulation capacity to prevent blockage of the line caused by dropping fluid temperature below that required to form paraffin or hydrate. One of the advantages of PIP system is the possibility of using materials with excellent thermal properties, considering that the structural integrity is provided independently by the outer and inner steel layers, Grealish and Roddy (2002). In the case of SP, object of this study, the annular layer characteristics differ from PIP by satisfying simultaneously mechanical and thermal requirements. Therefore, greater structural strength combined with adequate flow assurance can be obtained. Sandwich structures are a particular kind of composite characterized by the combination of different materials bonded together, contributing with their single properties to the global structural performance. Usually, the sandwich structure is divided in three layers: two external thin and stiff and a central thick and flexible core. The external layers are bonded to the core to allow the load transfer between the components. Numerical and experimental studies have been carried out to obtain data about the mechanical behavior of this kind of structure not very well understood so far, as done by Borselino et.al. (2004) and Sokolinsky et.al. (2002). Sandwich structures, i.e. light and stiff panels, have been employed in the naval industry mainly, searching the advantages associated with weight reduction, fuel economy, stability during navigation and corrosion resistance, as mentioned by Mouring (1999). Several multilayered applications are found with thermal insulation purpose for submarine pipelines and equipment in the offshore industry, but the benefit of the structural performance of this kind of structure has not been yet pursued for deepwater pipelines and risers, as it is the case of the present work.

Sandwich pipes composed of two steel layers separated by a polypropylene annular can be used for deepwater oil&gas transportation. They combine high structural strength to resist external pressure with thermal insulation to prevent blockage by paraffin and hydrate.In this work, experimental tests and numerical models were employed to verify the influence of the inter-layer adhesion on the ultimate strength under external pressure and longitudinal bending of a sandwich pipe prototype. The maximum shear stress obtained from sandwich pipe specimens bonded with a specific adhesive indicated the adhesion levels to be adopted in the numerical simulations. Two contact models were employed to simulate the bonding and slipping conditions between layers, one adopting a friction model and the other including non-linear springs between metal and polymer nodes. The latter is an adapted solution to simulate both tension and shear loads. As expected for a sandwich structure, the structural strength is strongly dependent on the interface stickiness. The analyzed geometry is able to withstand a water depth up to 3,000 meters with a bonding strength corresponding to only 10% of the idealized perfect adhesion condition.

Sandwich pipes composed of two steel layers separated by a polypropylene annular can be used for deepwater oil and gas transportation, combining high structural resistance with thermal insulation in order to prevent paraffin and hydrates formation. In this work, sandwich pipes with typical inner diameters of those employed in the offshore production are analyzed numerically regarding to the influence of the inter-layer adhesion between steel and polymer on the ultimate strength under external pressure and longitudinal bending. The effect of the reeling method of installation is also simulated. The maximum shear stress of the metal–polymer interface is obtained by experimental tests. Numerical simulation of the adhesion is modeled by contact surfaces adopting a maximum shear stress value to allow the relative displacement between the layers. It was observed that the ultimate strength of the sandwich pipe is strongly dependent on the shear stress acting at the interface.

Sandwich pipes composed of two steel layers separated by a polypropylene annulus can be used for the transport of oil&gas in deepwaters, combining high structural resistance with thermal insulation in order to prevent blockage by paraffin and hydrates. In this work, sandwich pipes with typical inner diameters of those employed in the offshore production are analyzed numerically to evaluate the ultimate strength under external pressure and longitudinal bending as well as the effect of the reeling installation method on the collapse pressure. Numerical models were developed using the commercial finite element software ABAQUS. The validation was based on experimental results. The analyses for combined loading were performed using symmetry conditions and the pipe was reduced to a ring with unitary length. The analysis of bending under a rigid surface was simulated numerically according to the experiments performed using a bending apparatus especially built for full scale tests. Symmetry conditions were employed in order to reduce the analysis to a quarter of a pipe. Mesh sensitivity studies were performed to obtain an adequate mesh refinement in both analyses. The collapse pressure was simulated numerically either for the pre or post reeling process. Bauschinger effect was included by using kinematic hardening plasticity models. The influences of plasticity and out-of-roundness on the collapse pressure have been confirmed.

The stress state analysis of welded plates is presented. Two different methods of welding with single and double wire were applied. The evolution of the stress state was monitored in each operational step: plates positioning, implementing of boundary and inner restrictions, welding, partial and full restrictions removal. The measurements were performed at the deposited metal, heat affected zone (HAZ), base metal next to the weld joint and along the plate. The X-ray diffraction method with the RAYSTRESS ® portable equipment was used for stress measurements. Differences were observed in the residual stress distribution as well as established typical residual stress distribution profile for both single and double wire welding.