One of the main concerns regarding flexible pipe integrity is its annulus condition, as a flooded annulus can lead to excessive corrosion and reduce fatigue life of the armor layers. The current approach to address this is to periodically perform a vacuum or pressure test to check the annulus integrity and to measure its gas-filled volume, in order to detect an accumulation of condensation water, or the ingress of sea water (Bondevik, 2004). These measurements are sometimes complemented by a continuous measurement of the flow rate of gas escaping the flexible riser's vent ports (MCS International, October 2002). The vacuum or pressure test is a costly operation, performed intermittently, while the conventional vent-gas monitoring does not provide reliable information on gas diffusion rates or water vapor emissions. To address these issues, TOTAL and Schlumberger have developed the subC-racs* riser annulus condition surveillance system for continuous monitoring of flexible riser integrity, which eliminates the need for vacuum tests. The gas that permeates the riser pressure sheath is depressurized while measuring its pressure, temperature, and flow rate. As in a well production test, the pressure drawdown and buildup curves are analyzed to give detailed information about fluid content and connectivity. The instrument's resolution and accuracy allow frequent calculations of gas diffusion rate and of the volume of liquid that may have entered the annulus, weekly, daily, or more frequently, depending on gas diffusion rate and riser parameters. In this paper we describe the measurement principle and hardware, modeling of the gas diffusion in the annulus compared with experimental results, and field test results on various risers in a West Africa field. Emphasis is placed on the measurement results, but the implementation in hardware and real-time software for alarms and remote monitoring is also shown. Introduction Monitoring of flexible pipe integrity is a main concern for all offshore fields. It has become more significant as the number of flexible risers increases, and as they age. The main issues for flexible risers are the status of outer sheath and the presence of water in the annulus due either to condensation or by damage to the outer sheath (Figure 1).

Spread moored FPSO (Floating Production and Storage Offloading) vessels are generally used for the large West African oil fields. The oil is transferred from the FPSO to shuttle tankers via an Oil Loading Terminal (OLT). 2 to 3 large diameter flexible lines are connecting the FPSO to the OLT. The final connection between the OLT and the shuttle tanker is made by floating hoses. The single length of each flexible pipe can be typically 2,300 meters or higher, and the internal diameter is generally very large in the order of 15_23″ to minimize the pressure drop and the offloading time. Conventional flexible pipe is the most suitable solution for this application. However, its long length and large diameter require a large number of buoyancy modules which are necessary to support the substantial weight generated by the steel armor wires. An alternative to steel is Carbon Fiber Composite (CFC). This material is not only twice as strong and five times lighter than a high strength steel but it is also characterized by its exceptional performance in fatigue. As the weight of the composite armor flexible pipe is significantly reduced, the use of buoyancy is no longer necessary. The pipe can also be manufactured in a single length without intermediate connection. A qualification program based on a 19″ internal diameter prototype has been launched. This is the first time that a large internal prototype with Carbon Fiber Composite Armor (CFA) and end-fittings have been designed and manufactured. The main goals are to confirm the suitability of the CFA flexible pipe for oil offloading application in accordance with the design tools. The mechanical behavior responses of the CFA are monitored by strain gages when the flexible pipe is in straight and curved positions under internal pressure and bending cycles. The paper will present the main mechanical properties and the overall performance of the flexible pipe designed and tested. The economic viability will be demonstrated by showing how the CFC material cost is positively offset by the removal of the buoyancy modules and a faster offshore installation.

Subsea umbilical systems developed for deep offshore applications become more and more demanding regarding injection capacity, number of functionalities and water depth. Some applications, such as subsea boosting, subsea separation or gas lift are even more severe, leading to tube temperature, which can exceed, in some cases 70°C. These operating conditions and requirements are significantly impacting the performance of the main umbilical. The most common solution, to avoid such issues, is to design thicker tubes to improve the strength of the umbilical cross section. The positive effect of the wall thickness increase has to be opposed to major drawbacks, such as weight increase and fatigue performance degradation generating more issues than providing solutions. To face these challenges, Vallourec Umbilicals, with the technical support of TOTAL SA headquarter Technology Division, has developed a new manufacturing process for seam welded stainless steel tubes (SAF 2507), with higher mechanical properties and tighter wall thickness tolerances. The benefit of this innovation is to provide for a given application (i. e. pressure, water depth and temperature) thinner tubes able to meet severe operating conditions without impacting performances of the umbilical structure. This paper, after a description of the manufacturing process and product qualification protocol (that led to a Type Approval Certificate from Bureau Veritas in October 2012), presents the technical advantages brought by seam welded solution, compared to seamless super duplex tubes.

Umbilicals are important tubes assembly essentially used for subsea equipment controlling functions and fluid injection. Super duplex stainless steel 2507 (UNS 32750 / EN 1.4410) has been the historical grade used for its corrosion resistance and mechanical properties. The Oil and Gas industry is gradually working on the exploration and exploitation of offshore and deep offshore resources. These operating conditions lead to new philosophy in the design of subsea umbilicals, which are evolving to answer the needs of new functionalities. Recent years development supported by O&G operators, have seen innovative super duplex stainless seam welded tube solution being used for their high mechanical characteristics (YS0.2≥ 750 MPa; UTS≥ 900 MPa), tight dimension tolerances, and their ability to generate cost saving during installation. The specific metallurgical manufacturing route for the 2507 strip together with an efficient roll forming process and NDT control allows to obtained tubes for umbilicals which push the usual boundaries of utilization of this super duplex grades. In this paper, Hydrogen Induced Stress Cracking (HISC) behavior, possible failure mode of the super duplex stainless steel tubes exposed to cathodic protection in the termination unit, was extensively studied. A stress load of 110% YS0.2 was applied using a dead weight bench and the tubes performance was characterized after 500h of exposure in synthetic sea water under cathodic protection. Crevice corrosion is also a reported failure mode for umbilical tubes. Corrosion resistance of the 2507 seam welded tubes was also assessed in natural sea water in crevice conditions at open circuit potential (OCP). No failure was observed during the HISC testing in synthetic sea water after 500hours of exposure and no micro-crack was detected on the tubes after characterization. The metallurgical microstructure of the laser weld is not preferential initiation zone for crevice corrosion.

Offshore and deep offshore applications are coming more and more demanding regarding number of functionalities and water depth for umbilicals and especially regarding tubing. Oriented to new resources, the future developments (i.e. ultra deep offshore or abrupt margins) will be more difficult to operate leading to more and more stringent requirements for tubes. Thanks to its high mechanical properties and appropriate corrosion performances, super duplex stainless steel (SDSS) grade 2507 is already commonly adopted by main players of the O&G industry for a wide range of conditions. With a strong collaboration with one of the Majors, an innovative SDSS seam welded tube solution has been developed, exceeding the standards characteristics and opening new perspectives.An extensive program of qualification, here presented, has been built in collaboration between Oil Companies, Umbilical manufacturers and the tube supplier, to confirm the expected potentialities of the product. Based on more than 11000 results, this paper is presenting the performance of the product in terms of mechanical and corrosion properties. The associated innovative and robust process, here described, is able to guarantee tight manufacturing tolerances combined with a high quality level, offering attractive potential cost savings.