Steel catenary risers (SCR) have been a favored choice for recent ultra-deep waters field developments subjected to harsh environments and large floating production units (FPU) motions. The design of SCRs in such conditions is always a great challenge where the key issues are the fatigue near the hang-off and at the touch down point; clashing between lines, especially on fields with a large number of wells and high payloads on the production unit. This paper describes the solution provided by the Buoy Supporting Risers (BSR) concept which has recently been installed in the Santos basin offshore Brazil.Subsea7 detailed the original concept of BSR system, from the design to fabrication and installation. The BSR concept combines several benefits to overcome the challenges of installing SCRs on ultra-deep waters, such as: allowing decoupling between installation of risers/flowlines and the platform, reducing payload on the production unit, very small dynamics transmitted from production unit to the risers, resulting in significant less fatigue issues. Also, the BSR concept reduces the risks associated with clashing and interference due to the smaller dynamics when compared to traditional coupled solutions. Fabrication is also addressed to highlight main challenges associated to assembling and welding clad and lined pipelines.In this paper the key aspects of the design and qualification are presented. Due to sour and CO2 service requirements for the production and water injection risers, it was decided to use corrosion resistant alloy (CRA) mechanically lined pipe for the entire line, with the exception of the top and touch down sections, where metallurgical clad pipe was used. Considering its novelty, a significant amount of qualification and testing was demanded. Among the technological innovations part of the SCR package is the first successful application of a pressurized mechanically lined pipe by reel-lay method. The solution involved an extensive qualification program, including full scale tests on vessel. The methodology and rationale to allow the application of high strain levels during spooling mitigating potential risk of wrinkling within the internal liner, had to be addressed during the detailed design by extensive Finite Element Analysis and validation tests.The SCR itself, due to de-coupling of motions by the buoy, have negligible dynamic response from vessel motions, thereby behaving almost like a static system with robust fatigue performance. The only meaningful fatigue in SCRs is due to current induced VIV and is mitigated using strakes. There was negligible potential clashing with adjacent SCRs.This paper provides a summary of design and qualification work carried for SCRs lined pipes installed in the BSR system and a discussion regarding main outcomes.

Steel catenary risers (SCR) have been a favored choice for recent ultra-deep waters field developments subjected to harsh environments and large Floating Production Units (FPU) motions. The design of SCRs in such conditions is always a great challenge where the key issues are the fatigue near the hang-off and at the touch down point; clashing between lines, especially on fields with a large number of wells and high payloads on the production unit. This paper describes the solution provided by the Buoy Supporting Risers (BSR) concept which has recently been installed in the Santos basin offshore Brazil.Subsea7 detailed the original concept of BSR system, from the design to fabrication and installation. The BSR concept combines several benefits to overcome the challenges of installing SCRs on ultra-deep waters, such as: allowing decoupling between installation of risers/flowlines and the platform, reducing payload on the production unit, very small dynamics transmitted from production unit to the risers, resulting in significant less fatigue issues. Also, the BSR concept reduces the risks associated with clashing and interference due to the smaller dynamics when compared to traditional coupled solutions. Fabrication is also addressed to highlight main challenges associated to assembling and welding clad and lined pipelines.In order to install Corrosion Resistant Alloys (CRA) lined pipes with a Reel-Lay vessel, a novel methodology for water pressurized spooling and pipelay was developed to mitigate the risk of liner damage during installation. Full-scale pressurized spooling trials were done ahead of the pipelay campaign for testing and validation of this methodology. In addition, analyses were performed to evaluate the BSR system behaviour during SCRs installation and to minimize buoy de-ballasting interventions.The SCR itself, due to de-coupling of motions by the buoy, have negligible dynamic response from vessel motions, thereby behaving almost like a static system with robust fatigue performance. The only meaningful fatigue in SCRs is due to current induced VIV and is mitigated using strakes. There was negligible potential clashing with adjacent SCRs.This paper provides a summary of design and qualification work carried for SCRs installed in the BSR system the faced challenges and solutions engineered during fabrication and installation scopes.

In order to meet the growing demand for oil production in even deeper waters, new technologies have been developed, making the exploration of such fields possible. A system used as an alternative for the control of extreme operating conditions (high temperatures and pressures) of such exploration fields is the pipe-in-pipe system. This kind of system is extensively used in offshore applications in which exceptional thermal insulation capability is required, preventing hydrate/wax formation and maintaining the production temperature up to the arrival facilities. However, extreme operating conditions can cause the system to experience thermomechanical buckling, which can lead to a structural failure of the system. In order to control these thermomechanical loads and ensure that pipeline is within a safe operating margin, the potential buckling formation locations need to be assessed and may need to be mitigated. The key point in the thermomechanical design of offshore pipelines is to define whether the buckling phenomena should be controlled or not. The optimal solution may often involve addressing natural imperfections whilst establishing the required engineered mitigation measures. Design assumptions such as the pipeline as-laid lateral Out-Of-Straightness (OOS) and the pipe-soil interaction parameters are common input data uncertainties existent during design of HP/HT offshore pipeline systems. A robust design should be impervious to variations in the values of these design parameters, considering values that lie within reasonable and feasible limits, such that the project can proceed with reasonable certainty and within sensible cost limits. In this scenario full of uncertainties, reliability analysis has been implemented in the thermomechanical design of offshore pipeline systems. The purpose of reliability analysis is to reduce the design conservatism by quantifying the probability of failure associated with the pipeline system. This paper presents a novel and viable proposal for conducting probabilistic analysis associated with lateral buckling of a full length pipe-in-pipe system, through the application of detailed finite element analysis. The information contained in the paper can be used as guidance for future reliability evaluations of offshore pipeline systems.

Global buckling is a behavior observed on subsea pipelines operating under high pressure and high temperature conditions which can jeopardize its structural integrity if not properly controlled. The thermo-mechanical design of such pipelines shall be robust in order to manage some uncertainties, such as: out-of-straightness and pipe-soil interaction. Pipeline walking is another phenomenon observed in those pipelines which can lead to accumulated displacement and overstress on jumpers and spools. In addition, global buckling and pipeline walking can have strong interaction along the route of a pipeline on uneven and sloped seabed, increasing the challenges of thermo-mechanical design. The P-55 oil export pipeline has approximately 42km length and was designed to work under severe high pressure and high temperature conditions, on a very uneven seabed, including different soil types and wall thicknesses along the length and a significant number of crossings. Additionally, the pipeline is expected to have a high amount of partial and full shutdowns during operation, resulting in an increase in design complexity. During design, many challenges arose in order to “control” the lateral buckling behavior and excessive walking displacements, and finite element analysis was used to understand and assess the pipeline behavior in detail. This paper aims to provide an overview of the lateral buckling and walking design of the P-55 oil export pipeline and to present the solutions related to technical challenges faced during design due to high number of operational cycles. Long pipelines are usually characterized as having a low tendency to walking; however in this case, due to the seabed slope and the buckle sites interaction, a strong walking tendency has been identified. Thus, the main items of the design are discussed in this paper, as follows: lateral buckling triggering and “control” approach, walking in long pipelines and mitigate anchoring system, span correction and its impact on thermo-mechanical behavior.

Raven is the third stage of the West Nile Delta development (following Taurus / Libra and Giza / Fayoum) from two BP-operated offshore concession blocks, North Alexandria and West Mediterranean Deepwater. The Raven project included the design of various rigid pipelines, of which one specifically is the subject of this paper. The 16" RSM to RP in-field flowline is approximately 4.8 km long, connecting a manifold (RSM) to a PLEM (RP) through a route that crosses a prominent geological feature identified as the Rosetta Channel, a submerged canyon that extends for about 30 km. The Rosetta Channel is about 2.5 km wide at the location of the 16" flowline route crossing, with steep slopes going down for approx. 40m (in height) on the RSM side, and then climbing up approx. 150m (in height) towards the RP side. Although it is typically preferred to avoid very rough geophysical features, this is not always possible or practicable and it is not uncommon to come across challenging seabed features that demand complex engineering solutions in order to minimise risks and associated costs. This paper addresses the numerous technical challenges involved in the design of the 16" flowline that crosses the Rosetta Channel. Following close collaboration between all involved stakeholders, a robust, reliable and cost-effective solution was achieved after a detailed engineering process, where the final design required a unique combination of mitigations including seabed excavation, pre-lay rock carpets, post-lay rock berms, cable jetting, curve bollards and sleepers.