In typical insulated Pipe-in-pipe (PIP) systems, both extremities of the outer jacket pipe are swaged down close to the inner pipe and are welded directly to the outer surface of the inner pipe. This full penetration weld (hereafter called swaged weld) works as a structure connection between the inner and outer pipes and seals the annulus between the two pipes. The integrity of this swaged weld ensures the structure integrity of whole PIP as well as its thermal properties. The non standard geometry of this swaged weld presents a real challenge for its Non Destructive Examination (NDE). Despite of its long existence and its importance, the inspection of this swaged weld has always been performed by Manual Ultrasonic Testing (MUT) or Semi Automated Ultrasonic Testing. This paper presents an Automated Ultrasonic Testing (AUT) system recently developed to inspect this type of weld more efficiently and more completely. The principle of this system and its Det Norske Veritas (DNV) qualified performance in term of defect detection capability and sizing accuracy will be described. To enhance the integrity of the inspected welds, fitness-for-purpose acceptance criteria have to be developed for this AUT system. Due to the range in weld geometry, the analytic approach conventionally employed for girth welds is no longer applicable. A Finite Element Analysis (FEA) based on Engineering Critical Assessment (ECA) approach has to be applied and this approach will be presented. In a recent West African SURF project, this AUT system coupled with fitness-for-purpose acceptance criteria has been applied with success. 1. Introduction Developments of the high temperature high pressure (HTHP) field bring on stage more strict requirements on thermal insulation of the pipelines. Conventional wet thermal insulation such as 5-layer polypropylene foam (5LPP foam) or 5-layer syntactic polypropylene (5L syntactic PP) turns out to be limited both in terms of the insulation efficiency (U value over 1.5W/ m2.K or 0,264BTU/hr.ft2.°F) and the maximum service temperature (approximately 130°C or 166°F). The Pipe-in-pipe (PIP) system presents a good alternative where conventional wet thermal insulation is not applicable. A typical PIP system can provide U value down to 0.5W/ m2.K or 0.09BTU/hr.ft2.°F, which extends the cooling down time of the pipelines and reduces the risk of hydrate formation and waxing during shutdowns and start ups. PIP systems were introduced to the fields inWest Africa more than a decade ago. The first typical PIP system was installed in Tchibeli field; one PIP production line, with a length of 25km, was installed in 1999. More recently such system was installed in several other fields such as Bonga and Kizomba Satellite.

Recent years have seen the first uses of steel catenary risers with spread moored FPSOs for deep water field developments in West Africa. Acergy have been in charge of the design and installation of more than 20 Steel Catenary Risers (SCRs) on FPSOs in this area. The design, fabrication and installation of these risers have required many significant challenges to be overcome for the first time. Innovative solutions have been developed and implemented to overcome these challenges particularly in the areas of design, welding and installation. This paper presents some of these challenges and solutions with the applications of SCRs attaching to mono-hull floating production units. Strength and fatigue analysis, on bottom stability, interface with the FPSO, and fabrication issues are described in detail. Lessons learnt from previous projects as well as results of new developments /1/ to extend the suitability of Steel Catenary Risers to deeper developments and to turret-moored FPSOs are also presented. Introduction A steel catenary riser is a seemingly relatively simple system, when comparing to others, where the riser is in continuity with the flowline and is made up from welding a number of rigid steel pipe joints of standard length. The catenary riser is generally connected to a floating platform with a flexible joint, steel or Titanium stress joint to absorb the potentially large angular movement of the platform. The bottom end of the riser pipe rests on the seabed as a beam on elastic foundation. The main concerns for the design of steel catenary risers described in the following sections are:Interface management with the floater,Impact of as-built uncertainties on the static configuration of the riser,Dynamic behavior of the catenary riser,Welding requirements,Installation aids for the final transfer and pulling of the riser on the FPSO /2/. The last section presents some results of new analyses performed by Acergy to improve the dynamic behavior of SCR's with the aim of using them for turret moored FPSO's in West Africa. Interface with the floating vessel Design of the SCR is strongly linked with the characteristics of the floater. Main interfaces are:Location of the hang-off point alongside the hull,Flexible joints designed to sustain great temperaturesStiffness of the floater mooring system and maximum excursion,1st and 2nd order motions of the floater,maximum heel, yaw and pitch in extreme, damage and survival conditions,local structural detail design of hang-off supports and hull reinforcements,Integration of installation aids including transfer and pulling winches,Space and lifting equipment available for precommissioning activities. This list is not exhaustive and a huge number of pieces of information have to be exchanged all along the design phase of the SCR and of the floater /3/. Clear definition of all these needs and requests with associated schedule, open relationship between Contractors and support of the Company when necessary are the key drivers for success of the project. Some of the main lessons learnt are the following /4/:

Ten years back the choice between turret-moored FPSO and spread-moored FPSOs was primarily dictated by local met ocean conditions: spread moored FPSO in West Africa, soft-(DICAS) mooring FPSO in Brazil, and turret-moored FPSO elsewhere. Over the recent years West Africa is turning to turret-moored FPSOs (internal and external), and Brazil has installed spread-moored FPSOs. Whereas spread moored FPSOs prevail in larger sizes (about 2MB), new built, turret-moored, FPSOs are usually smaller in size (1MB) with external-turret offering cost and schedule benefits to the operators over internal-turrets. This paper presents the impact of this new trend in FPSO mooring on the design of the flow lines and risers and related impact to field layout. The orientation of a spread-mooring is governed by the local met ocean conditions and may not be optimal for the routing of the flowlines; also compromises may have to be done with regards to flow assurance constraints. Turret-moored FPSO allow possibly a better use of the seafloor space especially in deeper water where the seafloor slope is gentler, and result in shorter flowlines. Risers for spread-moored FPSOs are decoupled unless they can be a small number and limited to the central part of the hull. For turret-moored FPSO, decoupled risers allow larger FPSO offset movements and are compatible with both internal and external turret. In the case of SHR or HRT, safety rules impose a significantly longer jumper lines to protect the FPSO from accidental buoyancy tank release. SCRs may also be feasible but highly insulated risers are very light and prone to fatigue in-service. Examples are being provided to evaluate the impact of the various FPSO mooring options.

Bundles arrangements are currently used in the design of riser towers or oilexport lines. Some of them are characterized by a non-circular cross section[6] and therefore may be prone to plunge instability, so-called galloping orplunge instability when exposed to strong current. It is important to be ableto assess, at conceptual design stage, their likelihood of being subject tothis phenomenon. Galloping is taking place in the low frequency range compared to VIV, but withlarger amplitude, up to several diameters, which could be critical in term ofglobal motion. Galloping occurrence is related to the dissymmetry of the crosssection and then there is a risk for non-circular geometries, such as riserbundles, buoyancy tanks and floater columns. Instability can also occur intorsion or rotation by a coupling effect between transverse oscillations. Riser Vortex-Induced-Vibrations have been studied for decades, and numerousexperiments have been performed both in-situ and in model test facilities tounderstand and predict the response of a slender cylindrical structure in acurrent. The main reason is the influence of VIV on riser fatigue life. If galloping and fluttering are well known in aerodynamics [10], no largespecific experiment/study exists for hydrodynamic flows [1], [9]. So it is notevident to assess whether or not galloping may occur for a given riser bundledesign, and, in case of expected galloping, whether there is a potential riskof damage to the individual pipes in the bundle. Until recently, only theBlevins criteria [1] are available to predict the risk of instability but thereare limitations. Based on recent examples of riser tower, experimental and numericalinvestigations have been done within the CITEPH Gallopan project, with the goalto propose guidelines to help designing a bundle cross section in a way toavoid or reduce the risk of galloping. Two cross section shapes supported the investigations, the academic squarecross section, for which previous studies have been done [1], and a tokenbundle cross section expected to be subject to galloping. Model tests have beenperformed in two steps:Captive tests and transverse forced oscillation tests in steady current toderive hydrodynamic coefficients (using a multi-DoF motions generator), to beused to check the Blevins instability criteria.Free oscillations in steady current to identify the instability domain inrelation to the reduced velocity and to estimate galloping amplitudes. Aspecific experimental arrangement, based on a vertical pendulum system, hasbeen designed and set-up for this step. A methodology has been proposed to assess the risk and consequence of gallopinginstability using standard riser numerical tools in which hydrodynamiccoefficients are issued from model tests. This paper presents the main resultsof the Gallopan project in term of methodology based on model tests to analysegalloping occurrence and response for non-circular slender geometries. Usingthese results, it is now possible to develop a galloping-free riser bundledesign.

A new riser concept is proposed by Subsea 7 for field development in deep and ultradeep waters: the Tethered Catenary Riser (TCR)-patent pending. The concept consists of a number of steel catenary risers supported by a subsurface buoy which is tethered down to sea-bed by means of a single pipe tendon and anchored by means of a suction pile; flexible jumpers are used to make the connection between the Floating production Unit (FPU) and the buoy. Umbilicals run without interruption from the FPU to their subsea end while being supported by the buoy. The system has all the advantages of de-coupled riser arrangements: flexible jumpers effectively absorb platform motions, thereby the rigid risers and tendon have very small dynamic excitation. The system can be installed before FPU arrival on site, which improves the time before first oil. Analyses have shown that, with adequate geometry of the buoy, the latter is sufficient stable to induce acceptable tilt and twist when different arrangements of SCRs and flexible jumpers are installed, and under accidental scenarios during the in-place life. The riser system is best designed for a number of risers between 4 and 8, in addition to a number of umbilicals, thus convenient for one or two drilling centers. Results of the basic engineering work on the TCR clearly indicate that it is possible to have a robust design using presently qualified materials and technology. The components used in the TCR are all field proven as they are commonly used in existing riser systems. As a result of installation studies, a method very similar to the one commonly used by Subea7 for Single Hybrid Risers (SHRs) has been selected for the buoy and tether system. Placement of rigid risers, jumpers and umbilicals is as done by Subsea 7 for the BSRs. This method is well adapted for installation by the new Subsea 7 flagship vessel Seven Borealis which is able to perform heavy lift and pipe laying. The Tether Catenary Riser is a credible option for use in deep water developments all over the world. Since all the components, design methods and installation procedures are fully qualified and familiar to Subsea 7, the concept is cost effective and ready for project application. Introduction A lot of well proven riser concepts have been used in deepwater for different environments, in particular, steel or flexible risers in catenary or lazy-wave shape, and single or bundle Hybrid Riser Towers (HRTs). Nevertheless, for some application new concepts are deemed more attractive and selected, as the Buoy Supporting Riser (BSR) for ultra-deep water offshore Brazil. But other ideas of riser concept emerge from the review and comparison of pros and cons of existing riser systems, trying to take the better of each one. The TCR is an adaptation of the BSR, but with a simpler tether arrangement and easier installation method. It can also be seen as a SHR with a number of SCRs attached to the buoyancy tank. The concept is described below as well as design methodology, application example and installation outline procedures.