Steel Catenary Jumper for Single Hybrid Riser in Deepwater Applications

Abstract

Abstract The Single Hybrid Riser (SHR) concept has been used successfully in industry onfloaters such as Floating Production, Storage and Offloading (FPSO) vessels indeepwater applications. This concept is especially effective with floaters inareas where challenging metocean environments result in severe vessel motions. The flexible jumper connecting the vessel to the rigid steel riser effectivelyisolates the dynamic vessel motions from the top-tensioned steel riser section. This results in lower strength and fatigue demand in the steel pipe section ascompared to other riser concepts such as a Steel Catenary Riser (SCR). However, the SHR concept also reaches the design limits of the flexible jumper aspressure, temperature, and sour service operating conditions become moresevere. ExxonMobil has demonstrated the feasibility of using a Steel Catenary Jumper(SCJ) as an alternative to the flexible jumper for extending the operationallimits of the SHR concept. This paper presents the results and designconsiderations for a SHR with a SCJ in 10,000 ft. Water Depth (WD) andpressures up to 10 ksi. The SHR/SCJ configuration was determined iteratively byassessing its strength performance in response to wave and current loading, vessel offset, internal content and pressure. Satisfactory strength and fatigueperformance is achieved under harsh North Atlantic and West Africa environmentswith a predominant fatigue condition. As is the case for SHRs with flexiblejumpers in similar conditions, vessel heading control is required to maintainacceptable response during extreme and long term environmental loading. Installation of the SHR/SCJ concept is determined to be within the presentmarket capability of heavy lift vessels, new generation J-lay vessels and FPSOpull-in facilities. A fabrication and installation procedure for the SHR/SCJconfiguration is presented. Introduction The SCJ was investigated as an alternative to the conventional flexible jumperfor connecting a SHR to a turret moored FPSO vessel. The primary advantage ofusing a SCJ is higher pressure and temperature service limits. Increasedresistance to sour service can also be achieved using Corrosion Resistant Alloy(CRA) lined pipe. The SHR/SCJ configuration was adapted from an existing 9-inID flexible jumper SHR conceptual design sized for a design pressure of 10 ksiand 10,000 ft. WD. Modest increases to the air (buoyancy) can depth, jumper length and distancebetween the FPSO turret and SHR base were made to the flexible jumper SHRconfiguration to arrive at the nominal SHR/SCJ configuration. The SCJ wasconnected to the FPSO vessel and SHR using typical flexible joints with taperedextensions. The SHR comprises a buoyancy can, rigid structural tether, TopRiser Assembly (TRA) with goose neck, dual thickness riser section with taperedsteel stress joints at each end, offtake spool assembly and roto-latchassembly. Strength analyses were performed to North Atlantic extreme storm conditions andfatigue analyses were performed to both North Atlantic and West Africa motionresponses. The harsher North Atlantic environment required an internal turretwhile the milder West Africa environment permitted an external turret. Production, water injection and gas injection riser applications were assessedfor feasibility. The SCJ and SHR were designed to standards API-RP-2RD [1], API-RP-1111[2], and DnV RP-F109 [3].