The demand for energy is steadily increasing and, at least for the coming decades, the world has to rely on oil and gas to address this need. Most of the easiest accessible offshore petroleum reservoirs have been discovered and a great part developed over the last six decades. Thus, development of new oil and gas fields faces a lot of challenges as most of them are in remote areas, in deep waters and/or in areas with extreme environments like the Arctic region. One of the major trends in the offshore petroleum industry points towards deeper waters (e.g. outside West Africa, the Brazilian Pre-Salt developments and in the Gulf of Mexico). This trend also includes increased use of subsea installations instead of platforms, more subsea processing and increased use of pipelines to transport the hydrocarbons to shore or into a pipeline grid. This paper addresses some of the challenges pipeline design, installation and operation may face in deep and ultra-deep waters. The main design challenge is related to the high external pressure that may cause collapse of the pipeline. This potential failure mode is normally dealt with by increasing the pipe wall thickness, but at ultra-deep water depths this may require a very thick walled pipe that becomes very costly, difficult to manufacture and hard to install due to its weight. One approach to overcome this is to improve some of the parameters that determine the collapse resistance by an improved manufacturing process. Other approaches are to ensure a minimum internal pressure is maintained in the pipeline during all phases, or to install a buoyant pipeline that is anchored at a moderate water depth rather that laying on the sea bed.

The reel-lay method is a fast and cost efficient alternative to the S-lay and J-lay installation methods for steel pipelines up to 20″ in diameter. The quality of the pipeline construction is high due to onshore welding under controlled conditions. However, reeled pipelines are subject to plastic straining (up to approx. 2.3%) during installation. It is therefore common practice to specify a minimum required wall thickness to avoid on-reel buckling. For a given pipe outside diameter and bending radius, formulae developed for pipes under pure bending are generally used. In addition, to ensure the integrity of pipelines during reeling, a minimum spooling-on tension is specified and tolerances on pipe properties, such as wall thickness and yield strength, are constrained. Tolerance limits are specified to reduce the likelihood of spooling two consecutive pipe joints, which have a significant difference in plastic moment capacity (mismatch). It has been shown previously that high levels of mismatch can trigger an on-reel buckle [1]. The reliability of the reeling process is indeed related to the uniformity of pipe properties. It can therefore be supposed that more uniform pipe properties may allow reeling of thinner-walled pipes, while achieving the same level of reliability. This issue has been investigated as part of a wider evaluation of reeling mechanics and the development of procedures for optimized assessment of the process, including such aspects as the effect of the geometry of pipelay equipment [2]. This paper explores methods that can be used to evaluate the reliability of reeling a given pipe onto a given vessel. Particular focus is given on the selection of appropriate material variation parameter for the assessment. The concept of an averaging factor is introduced as a means to relate variations in individual wall thickness and yield strength measurements to the variation in pipeline cross-section, which determines the likelihood of buckling. It is suggested that, in the future, this factor could be used as a method for optimizing design for reeling when using higher quality pipe.

The reel-lay method is a fast and efficient rigid pipeline installation method for infield flowlines and smaller export lines (up to 20″). However, reeling operations induce significant bending strain in the pipeline. To avoid pipe buckling during reeling, it is a common practice to limit pipe yield strength and wall thickness variations in addition to ensuring an adequate wall thickness. Simple formulas in design standards, based on the assumption of pure bending, are often used to determine the minimum reelable wall thickness. It is, however, known that the mechanics of reeling process differs from pure moment bending. Therefore, the likelihood of pipe buckling during reeling may depend on factors that are not captured by these simple formulae. A more refined procedure for establishing the minimum reelable wall thickness and the associated probability of failure has been developed. This procedure involves the combination of finite-element and statistical analyses. It is aligned with the methodology which is regularly used by Technip to demonstrate the on-reel integrity of non-standard pipeline configurations such as thick coated pipelines with soft field joint coating or transitions between pipelines with different nominal sizes or material grades. This paper outlines the procedure, which can be used to determine the level of safety associated with the simple formulae for the minimum wall thickness in the design standards. The reeling parameter studies carried out in this work have shown that it is not only the maximum bending strain, pipe outer diameter and the statistical variations of wall thickness and yield strength that affect the reliability of the reeling process, but also the arrangement of the reeling equipment.

Whereas the wall thickness for most pipelines is governed by internal pressure, the wall thickness of pipelines at very deep waters may be governed by external pressure and the failure mode is collapse. This paper will firstly summarise the work performed in the early 90ties in the SUPERB project that constitutes the basis for the collapse equation adopted in DNV Rules for Submarine Pipeline Systems. This work documented a comparison between various expressions for collapse prediction (Timoshenco, Murphy and Langner (Shell) and Haugsmaa (BSI)) to available experimental results. This work made it possible to select the formulation deemed to be most appropriate as a design equation as well as calibrating safety factors. Secondly, the paper will discuss the well documented detrimental effect that pipe forming can have on the compressive yield strength in the hoop direction and thus the collapse capacity of pipes. This effect led to the introduction of the so-called fabrication factor in DNV-OS-F101 that reduces the compressive yield strength by 7–15 per cent for pipes manufactured using cold forming. However, DNV-OS-F101 states “The fabrication factor may be improved through heat treatment or external cold sizing (compression), if documented” and the paper will summarise various published work, experimental and analyses, that has, during the last 15 years, been performed in several pipeline projects to document the beneficial effect that mainly light heat treatment but also optimised forming in the UOE process have on the compressive yield stress and collapse capacity.

The paper describes activities and critical issues in relation to the preparations, qualifications, reeling and installation of two 10" Steel Catenary Risers (SCR's) on behalf of Petrobras on the Roncador field, offshore Brazil, in 1360 m of water. A combined installation technique with J-lay of the critical touchdown area and traditional reeling for the remaining flowline/riser part was applied. The operations related to reeling the pipe sections onto the reel, reeling off, welding on site (J-lay sections) and transfer to P-36 have been outlined. The paper describes in more detail the analyses performed to evaluate the effects of using the reeling method for installation of the risers. The following issues are addressed: riser torsional effects due to residual curvature, effects of residual stresses, ovalisation, strain concentrations, variability in yield strength, riser analyses, reeling analyses, fatigue aspects, hoop buckling and propagating buckling.