Advances in Deepwater Steel Catenary Riser Technology State-of-the-Art: Part I — Design

Abstract

Steel Catenary Riser (SCR) concept offers great advantages over others and has been widely deployed worldwide. The first deepwater SCR was installed in the Gulf of Mexico in 1994. Since then, more than 100 SCRs have been installed for many types of deepwater floaters (SPAR, TLP, SEMI, and FPSO) in the deepwater fields of West of Africa, Gulf of Mexico, and Offshore Brazil. This paper presents the state-of-the-art of the design methodology of deepwater SCRs. First of all, the design procedure is discussed and is also illustrated in a flowchart. Material selection is discussed in terms of weldability, corrosion resistance, and effect on riser performance. Different wall thickness sizing criteria and design codes are compared. The three most commonly used types of SCR hang off system (flex joint, stress joint, and pull tube) are presented and their application limitations are discussed. Strakes and fairings are discussed and compared as the vortex induced vibration (VIV) suppression devices. Focus is given to the design of SCR global configuration and riser routing. Effect of different floaters on the global configuration design is discussed and illustrated through examples. Thermal performance requirements versus riser global response are traded off. Corrosion, thermal insulation, and anti-abrasion coating materials available for deepwater SCRs are summarized. SCR cathodic protection design methodology is summarized and a design guideline is given. The number one challenge of deepwater SCR design is fatigue. Selection of SN curve, effect of sweet and sour service on fatigue performance, stress concentration factor (SCF) calculation, full scale fatigue testing requirements, application of fracture mechanics to engineering criticality assessment (ECA) is discussed. Fatigue mitigation design is also explored supported by examples. Design of the SCR subsea interface to flowline and pipeline is presented.

Vessel relocation strategy for multiple steel catenary riser fatigue damage mitigation

“…For an existing field (brownfield) SCR, if the remaining or residue fatigue life of the SCR is 𝑇 𝑟𝑒𝑚 , then the life extension, 𝑇 𝑒𝑥𝑡 , of the SCR is expressed in equation (6).…”

“…Steel catenary riser (SCR) systems are used to transport hydrocarbon production-related materials between the seabed and the host floating platform. SCRs are the most attractive riser solution likely because of their simplicity, robustness, and lower procurement costs [1][2][3][4][5][6]. A significant challenge with SCR application is the high stress and fatigue damage incurred around its critical sections: the hang off (HO) and the TDZ [5,[7][8][9], which are depicted in Figure 1.…”

“…As a result of the vessel movement, the active seabed sections of the six SCRs will experience different degrees of spatial variation compared to the nominal configuration. The six SCR TDP offsets from their nominal position when the vessel is relocated towards the vessel portside for relocation axes (1,2,3,5,6) and towards the stern (axis 4) are presented in Figure 3 (a). Similarly, the six SCR TDP offsets from their nominal position when the vessel is relocated towards the vessel starboard for relocation axes (1,2,3,5,6) and towards the bow (axis 4) are presented in Figure 3 (b).…”

“…The six SCR TDP offsets from their nominal position when the vessel is relocated towards the vessel portside for relocation axes (1,2,3,5,6) and towards the stern (axis 4) are presented in Figure 3 (a). Similarly, the six SCR TDP offsets from their nominal position when the vessel is relocated towards the vessel starboard for relocation axes (1,2,3,5,6) and towards the bow (axis 4) are presented in Figure 3 (b). For both sets of vessel relocation directions, it is observed that if the axis of relocation relative to a given riser is in the riser far direction, a longer section of the riser will be hanging, meaning the TDP arc length position will be longer than the nominal TDP arc length.…”

Floating catenary riser system concept for brownfield application

“…Steel catenary risers (SCRs) are widely favoured for greenfield deepwater oil and gas development [1], in environmental conditions that are relatively mild. This attraction to SCR may be attributed to its simplicity and lower cost of procurement compared with other riser types [2].…”