The collapse strength of flexible pipes is a well known property and predicted by means of numerical or analytical modelling. However, recent oil field discoveries in the Brazilian pre-salt area, in water depths up to 2500m, are pushing the industry to evaluate the effects of flexible pipe curvature on its collapse resistance when the pipe is subjected to extreme levels of hydrostatic pressure such as that expected in the Brazilian pre-salt area. As part of Wellstream's R&D programme, a numerical model was specifically developed to predict flexible pipe collapse resistance when subjected to curvature to assess and quantify the effects of curvature on the flexible pipe collapse resistance. This paper summarizes the numerical modelling process and experimental calibration performed using five different pipe structures specifically designed for the pre-salt cluster. A total of 45 calibration tests were performed using samples taken from the same production run in order to eliminate variance in production machine setup and raw material batches. Regular production equipment, setups and quality control procedures were used to manufacture the test samples so that the collapse resistance of the pipes could be evaluated against conditions identical to commercial manufacturing. Of the five different pipe structures evaluated in this test programme, one of the pipe structures supplied for the TUPI EWT project development is already installed and operating at a water depth of 2140m. The test programme allowed the experimental assessment of the curvature effects on flexible pipe collapse behaviour, demonstrated the suitability of flexible pipe structures and model to predict the effects of curvature on collapse resistance.
Flexible riser systems are widely adopted by the industry as solutions to interconnect subsea equipment and pipelines to floating production units. Their unique ability to withstand motion and their ease of installation make flexible riser systems a favorable solution when compared to conventional rigid riser systems. Historically, the integrity of flexible risers has been an issue and it is therefore critical that risers are designed and qualified according to the current continually challenging operating conditions. Flexible riser integrity management and complex riser qualification processes have consequently become the main focus for major operators in guaranteeing the safety of offshore operations to reduce the risk of human, environmental and material losses. The industry has requested several qualification tests to verify the manufacture of the new flexible risers, e.g. a dynamic fatigue test, which is required to qualify the flexible pipe for deepwater installation. A means of monitoring the flexible riser response is also required in order to record the integrity of the riser and assist operators in identifying and implementing suitable remedial action, ranging from inspection plans through to riser replacement, as necessary. Based on these requirements, Pulse Structural Monitoring developed an armour wire failure monitoring system and, after extensive testing including offshore tests, validated the system through a full-scale dynamic test cycled to damage 1.0 (safety factor 10), performed by Wellstream. This test continued for more than one year and validated the monitoring system that was able to detect 100% of the wire breaks. This paper presents the results and conclusions from the blind test conducted to qualify the monitoring system. The results demonstrate that the monitoring system was able to detect the wire breaks caused during the full-scale dynamic test and would be a suitable solution to employ on flexible risers to detect failures in the field. Introduction Flexible risers are responsible for oil and gas transportation of approximately 80% of Brazilian offshore production and are mainly used in highly dynamic loaded environments, where outstanding fatigue performance is essential. Flexibles are commonly used in today's harsh ultra deepwater developments and play an outstanding role in deepwater offshore operations worldwide. Given that the depths are increasing where flexibles operate, environmental conditions are becoming ever more challenging, and the engineering challenges in designing and manufacturing risers are also increasing. There are more than 1,200 flexible risers currently in use offshore Brazil whilst over 1,000 flexible risers are operational in the North Sea. A complex engineering process takes place for the design and fabrication of flexible risers, based on presumptions about environmental loading conditions and the specific requirements of the application over its lifetime. As production expands into increasingly deeper water depths, more advanced riser designs and qualifications are required from offshore operators.
Flexible pipes are widely used in the exploration of oil at ultra-deepwater depths due to their properties of resistance to bending forces and ease of installation, compared to rigid pipe lines. For each specific service application, several tests are required to qualify the flexible pipe’s design. One of the most important is the dynamic tension to tension test, the purpose of which is to qualify the end fitting assembly procedure and evaluate the design methodology used to predict the pipe’s service life. During the development of the test, several sensors were fitted to the pipe sample to monitor the behavior of the armor wires. In order to monitor this test and identify any possible failure of the tensile armor wires, strain gauges were applied to all the wires of the external tensile armor layer in the area outside of the end fittings. Additionally, strain gauges were also applied to some of the internal and external tensile armor layer wires inside the end fittings. Other sensors, such as inclinometers and a tri-axial accelerometer were also applied to the pipe sample. Analyses of the signals from the test sample instrumentation enabled detection of rupture of the tensile armor wire while instrumentation redundancy confirmed the tensile armor wire’s failure. This paper presents the methodology used to identify the first 5 tension armor wire ruptures, which were identified by some of the sensors, i.e., the accelerometer, the inclinometer, and the strain gauges together with a comparison of the data of all the wire ruptures during the test.
The interface between the flexible risers and I tubes is being considered by the market as a critical region due to its geometric characteristics and high contact loads between the flexible risers and I tube interface equipment. During the past few years several instances of outer sheath damage were reported by the offshore industry. Such damage was a result of wear against steel parts and occurred in the regular design adopted by the industry, causing riser annulus flooding which significantly reduces service life. Some of the most severe riser failures reported indicate the rupture of the outermost tensile armour layer. Wellstream has designed and patented a new concept for riser interface equipment by adopting a split and replaceable polymeric insert designed to be in direct contact with the riser's outer sheath. Wellstream is currently performing a 12 month alternative dynamic test using a 9.13 inch gas export riser as part of the qualification programme; the interface between the outer sheath and the polymeric insert is under peer evaluation. As part of the test, the evaluation of the wear considers actual flexible riser service fatigue loads and actual relative displacement between the riser and polymeric insert in order to reproduce field service conditions. This paper presents the wear evaluation performed during the dynamic test, which also includes UT and laser scanning measurements to monitor and assess the wear on both the riser's outer sheath and the polymeric insert. The test results indicate that the proposed design, which adopts the polymeric insert, is capable of preserving the outer sheath throughout the riser's service life thus demonstrating that it resolves the problems reported by the industry. Introduction Floating production units used for offshore oil and gas exploration employ flexible pipe systems and may present two different kinds of configuration at the platform. In the first type, referred to as ‘direct’, the bend stiffeners and interface equipment are assembled directly onto the pipe's end fitting on the platform's riser balcony. This does not lend itself to wear-related problems since the distance between the end fitting and the interface equipment is so short that pipe axial deformation, due to service loads, may be considered negligible thus drastically reducing, or even eliminating, the possibility of damage to the pipe's outer sheath due to wearing.
It is known that the thermal exchange coefficient (TEC) of an insulated flexible pipe may be affected by both external pressure due to the operating water depth and by the annulus condition. International standards state that flexible pipe systems shall be designed considering the effects of these two environmental conditions. If not considered during the flexible pipe design phase, these factors may have an important impact in the production system by reducing the temperature and allowing hydrate and paraffin formation in the pipe bore. As part of Wellstream's research and qualification programme, a TEC test was performed to assess and quantify the effects of external pressure and the annulus condition during the flexible pipe system operation. The test was carried out using a 3m long sample taken from a 6 inch internal diameter production flowline designed to 1500m water depth and a maximum fluid temperature of 60°C with 276 bar internal pressure. Special end fittings were designed to reduce the pipe axial heat loss during the test. The tested pipe was designed in accordance with Wellstream methodology and design tools to provide a pipe structure with a TEC lower than a predicted value, even when subjected to external pressure due to the operating water depth, or in an annulus flooding event. The test was conducted in two different phases to separately evaluate the external pressure and annulus condition. The first phase of the test was conducted sequentially at four different levels of external pressure, these being 1, 50, 100 and 150 bar on a dry pipe annulus. The second phase of the test was carried out after flooding the annulus with water under an external pressure of 165 bar for 72 hours to soak the insulation tapes, which are responsible for the greatest part of the thermal exchange characteristics. After this period, the pipe TEC was measured sequentially at four different levels of external pressure. By the end of the test it was possible to determine thermal exchange characteristics when the pipe was subjected to environmental conditions representative of actual applications. The relationship between the external pressure and the TEC variation could also be assessed and furthermore, it was possible to evaluate the behaviour of the flexible pipe thermal properties after an annulus flooding event. The test also demonstrated that Wellstream's design methodology properly accounts for the effects that both the external pressure, due to the operating water depth, and the annulus condition has on the pipe's TEC.
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