Vineet Jha

Optimized Hybrid Composite Flexible Pipe for Ultra-Deepwater Applications

Different hybrid composite pipe solutions have been proposed and evaluated for use in ultra-deepwater applications. This includes composite and hybrid composite/metallic pipe designs made from both a thermoplastic and thermosetting matrix. Each of these designs target a proportion of the future deep sea market and will require a leveraging of present logistics and infrastructure or new developments for deployment. These design concepts primarily focus on deepwater (hence, a higher collapse load) in combination with higher pressure and/or sour service requirements. A section of this hybrid composite pipe design targets the larger diameter high through-put (low or high pressure) FLNG market.GE Oil & Gas has proposed hybrid metallic/composite pipelines which use composite layers for both hoop and tensile loads. This paper discusses and compares several different design concepts i.e. bonded composite pressure armor, composite tensile armor and both. Although the use of composite pipe will reduce the overall weight, consideration should be given to the buoyancy versus drag requirements of each composite pipe design. Further, consideration needs to be given to manufacturing, reeling, transportation and installation for each of these different design concepts. Acceptability of these individual designs by the end customer requires detailed FMECA, qualification and testing. This paper therefore compares detailed advantages of each composite pipe design for ultra-deepwater applications, presents the latest developments and compares future applications.Considerations have been given to development of continuous quality control procedures for the manufacture of these composite pipelines and working prototypes. In addition, the latest results are discussed. The possibilities of defects correction and repair mechanism are also explored. This paper aims to show an appreciation of various composite pipe design concepts and addresses key concerns from both a manufacturing and customer acceptability point of view.Copyright

In Situ Investigation of Microstructural Changes in Thermoplastic Composite Pipe Under Compressive Load

Thermoplastic composite materials are very advantageous as component layers in subsea risers due to their inherent properties such as high strength, low density, fatigue and chemical resistance. However, response of composite materials to applied loading is complex and three-dimensional in nature. The heterogeneous structure of the composite material induces irregular distribution of stress/strain over the cross-section and thus, it is essential for design to use analytical methods capable of determining the stress-strain relationship in three-dimensional space. Currently, most methods rely upon one-dimensional or two-dimensional data collection techniques with macro scale stress / strain observations for experimental validation. In order to ascertain the correct load to the failure, a complete understanding of the material failure at the micro-scale is essential.In this work, X-ray computed tomography is employed for the in situ observation of micromechanical failure of the composite material under a compressive load. The observed results are compared and validated with the traditional stress-strain data and finite element analysis. It is observed that the damage in the composite material initiates by delamination which grows as the loading progresses. Moreover, the properties and failure modes are highly dependent on the manufacturing process. By gaining further understanding of the failure modes using these methods, the findings can be utilized in optimizing the design of composite riser structures.© 2014 ASME

In Situ and Real Time X-Ray Computed Tomography for the Micromechanics Based Constitutive Modelling of the Unbonded Flexible Riser

The failure mechanism of the composite flexible riser, comprising a pipe with melt fused carbon fiber tape or pultruded composite rods, is not well understood. As there is change in the configuration of the composite layers and its manufacturing methods, so the bulk material property also changes significantly. To capture the correct material model for global FE analysis, real time x-ray computed tomography was performed while the flexible pipe was being compressed. For developing a constitutive model for the composites, a time series of 3D volume images were analyzed quantifying the local strains responsible for the debonding of the layers and the crack development. These values were then used to understand the inter-layer adhesion leading to correlation between the FE global modelling and experiments capable of capturing the progressive delamination. The resulting global modelling was used to determine the area under compressive loading. The effect of global sea conditions and cumulative damage was noted. A correlation between the global model and experiments can be used to optimize riser performance. This method hopes to capture the overall behavior of flexible pipe under compressive loading.Copyright

Integrated self-healing of the composite offshore structures

The self-repairing composite materials integrated with sensing is way forward to reduce maintenance cost and increase consumer safety. In this work, the novel self-healing carbon fibre reinforced unidirectional bulk tape of simple architecture is prepared using nanocomposite film. The bulk material tape was prepared using nanocomposite film of low melting temperature polymer sandwiched between two carbon fibre reinforced unidirectional tapes. First, the nanocomposite polyamide 6 (PA 6) tape with iron oxide nanoparticle was prepared using in-situ polymerization and mixing method. The iron oxide nanoparticle was silane coated suing tri-phasic reverse emulsion method to achieve better dispersion in PA 6 matrix. The nanocomposite was characterized using FTIR, XRD, DSC and TEM. Result shows that the proposed method of preparing self-healing bulk tape material has potential to be used for self-healing composite structure.

Flexible Fiber-reinforced Pipe for 10,000-foot Water Depths: Performance Assessments and Future Challenges

The primary aim of the present composite development program is to enhance access to deepwater fields in the Gulf of Mexico, Brazil, and West Africa. To accomplish that goal, composite materials are being incorporated in unbonded flexible pipelines to lower mass and enhance the overall system performance to expand the operational design envelope. In addition, the use of composite materials will allow a significant improvement in pipe operating pressure (>70 MPa), pipe operating temperature (>125C) and due to increased CO2 and H2S resistance, will improve sour service performance and lifespan. Composite materials are well known for their low density and high specific strength, stiffness and fatigue performance. These properties are desirable and will certainly enhance pipe performance, but the overall performance of the pipe during all stages of manufacture and deployment must be considered, as well as a conservative approach to introducing these new materials. Some of the key factors that need to be assessed are material failure modes under varied pipe loadings, dynamic interactions and exposure to severe oil field environments. There are several individual standards, specifications and joint industry projects (JIPs) focused on composite pipes that address some of these issues, but there is also a general lack of consensus with regard to testing standards and understanding of the long-term performance. As flexible pipe suppliers, the industry must aim to provide performance assessments and address all key challenges to allow the flexible pipe industry to build confidence in the new and enabling composite pipe technologies. In a previous paper, we presented design concepts and a toolbox approach to construct different composite pipe solutions to meet all the aforementioned performance parameters. The present paper selectively highlights important failure modes and design considerations, demonstrates an understanding of behavior in the matrix and fiber phases, and addresses concerns related to the chemical performance of composite materials. The present paper also highlights and addresses some of the concerns of composite pipes and focuses on areas for future development and testing. These results will support the selection and standardization of analysis tools and testing methods across the industry. Bespoke testing capabilities to address the relevant failure mechanisms and installation strategies for composite pipes will also be discussed.