The number of flexible pipes in operation is increasing due to new field developments and the desire to extend the lifetime of existing fields. There have been many challenges with respect to long term operation of such pipes, in many cases with the need to replace or repair before the end of the initial design life. The number of identified failure mechanisms and observed failure events is also increasing. The present paper summarizes state of the art technology related to operation of flexible pipes and some recent research and development activities that contribute to resolving these issues. In particular, the following topics are addressed: • Fatigue testing of flexible pipes subjected to corrosion damage during operation • Development of improved numerical models and methods for assessment of the residual capacity of flexible pipes • Integrity assessment of flexible pipes also applying quantified risk and reliability assessment • Repair methods for damaged pipe sections In addition, an outline is given of a Handbook (ref. Handbook 2014) which addresses the various topics related to life-cycle design and operation of flexible pipes, see Appendix. Future prioritized research efforts with focus on some of the topical issues given in the list above are finally addressed.

Many oil companies presently work on plans for production of Liquefied Natural Gas on a Floating LNG Production and Offloading (FLPO) vessel. All these schemes require suitable systems for offloading of the LNG to a transport tanker. Safety and regularity are important issues in design of offshore LNG production and loading systems. In addition to the offloading operation the tanker approach, connect, disconnect and departure phases include critical operations which are weather dependant and may impose restrictions on operability and regularity. The OCL system is a stern to bow, crane and flexible pipe solution that is developed, based on extensive experience from tandem offloading operations of crude in the North Sea in harsh weather conditions. The system is well suited for LNG transfer where high regularity is required and a large number of cargoes are shipped every year. The LNG tankers are dedicated transport vessels with modifications in the bow to suit purpose built hawser and loading facilities. When offloading the LNG carrier in a harbor a conventional LNG manifold offloading system in the center of the LNG tanker is used. In offshore loading, the two vessels are moored together in a "crowfoot" hawser configuration reducing the relative movements between the crane tip on the FLPO and the bow of the tanker. The LNG carrier is operating on constant stern thrust to ensure the required stability of the offloading system in both calm and harsh weather conditions. Components and sub-systems are selected on basis of functional requirements. Critical components have been qualified in a step-by-step process. The qualification includes development of mathematical tools that have been verified through material testing, model testing and full scale testing. Verification includes design, manufacture and testing of the complete pull-in and connection system as well as full flow testing. Figure 1 - The OCL LNG transfer system(available in full paper) Vessel model testing is used both as verification and calibration of the mathematical models and it ensures accurate calculation of the two vessel's motions in the loading area and thus good prediction of the loads on the transfer system. The flexible pipe is the most critical part of the transfer system. The OCL system is based on a longitudinally welded, thin-wall stainless steel tube corrugated to provide the required bending flexibility. The finished flexible transfer pipe is a lightweight, double-wall construction with vacuum in-between the pipes as thermal insulation. The qualification process includes full-scale flow testing with both water and LNG. All tests and calculations show that the described solution will allow safe and economic transfer of LNG from a floating production vessel to a tanker. The OCL LNG transfer system will allow development of stranded gas reserves in areas with no infrastructure, or where a pipeline to a shore facility is not viable or economical.

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There have been many challenges with respect to long term operation of flexible pipes, in many cases with the need to replace or repair them before the end of the initial design life. The number of identified failure mechanisms and observed failure events is also increasing. In the present paper, some typical issues that arise during the process of integrity assessment and qualification for lifetime extension are outlined. More detailed considerations are illustrated in relation to a particular case study. This involves elaboration of the different steps which are required in order to be able to extend the lifetime of a flexible riser for the case of corrosive annulus environments. The particular case of an outer sheath damage is applied for the purpose of illustration.

Flexible pipes for large volume gas export and gas injection have been installed on several platforms offshore Europe. In some of these applications high frequency vibrations have been reported. Onset of the vibrations is related to flow rate. The vibration frequency is typically above 150Hz and structures with stresses above the fatigue limit will rapidly fail in fatigue. This paper covers the following: • Results from a measurement program performed at the Norsk Hydro Troll C platform. • Theoretical studies related to gas flow in flexible pipes. • Actions taken to control the flow induced vibrations at Troll C.