TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Erha and Erha North field development in deepwater Nigeria consists of multiple subsea wells connected to a floating production, storage, and offloading vessel (FPSO) via flowlines and steel catenary risers (SCRs). Processed crude oil is exported through an oil offloading system (OLS), consisting of a catenary anchor leg mooring (CALM) buoy and dynamic offloading lines (OLLs).The SCRs were identified as a key technical issue due to high-fatigue performance requirements, especially under potential sour service conditions. In addition, the associated flexible joint performance in a relatively high-temperature environment also extended the design envelope for this critical component. Innovative clad overlay and clad welding technologies were developed within the Project timeframe and efficiently executed both onshore and offshore. A rigorous design and qualification effort, including the development of novel sour environment fatigue testing and ultrasonic inspection technologies, ensured system integrity.The OLS was also identified as a key technical challenge early in the Project. The innovative, U-shaped OLL design is a first in the industry. The OLLs presented performance challenges similar to those of the SCRs, but in addition, the complicated coupled buoy/mooring/OLL motion behavior posed a unique challenge for OLL fatigue design. A dedicated qualification and validation program was devised to confirm system integrity. The design and execution teams utilized new technology and lessons learned from past projects to ensure that the installed system would meet challenging acceptance criteria.This paper discusses challenging issues and resolutions for the SCR and OLL designs. The extensive qualification programs, including CALM buoy model tests, SCR cladding and welding qualification tests, and the flexible joint qualification, are also discussed.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe Erha and Erha North Project utilizes a steel catenary riser (SCR) system to connect the floating production, storage, and offloading vessel (FPSO) to the subsea infrastructure. The system is a hybrid, composed of both steel and clad corrosionresistant alloy (CRA) pipe, with the CRA clad pipes located in the touch-down and hang-off areas of the SCRs. The CRA clad pipe sections are required to obtain satisfactory fatigue life due to the presence of CO 2 and potential H 2 S in the production stream. In total, four production and two test lines were required, with a total of 1,120 m of CRA clad pipe installed.Ultrasonic inspection of the welds joining the CRA clad pipes proved to be technically challenging due to the bimetallic features of the weldment and the small flaw size allowable for this fatigue-dominant application. Further complicating this effort was the need for reliable flaw detection on a real-time basis to maintain the pipelay rate. To meet these challenges, Shaw Pipeline Services (SPS) was enlisted to develop an automatic ultrasonic testing (AUT) system capable of reliable inspection of the weldments. This paper discusses the AUT system qualification program, product implementation, and lessons learned. Included in these discussions are technological challenges and respective approaches for metallurgically bonded and weld overlaid clad girth weld ultrasonic inspection, as well as detailed sizing accuracy data on seeded (i.e., intentionally planted) defects during the qualification stage and sizing accuracy data on production welds with naturally occurring flaws.
In 1982, Exxon initiated an enhanced worldwide marine safety program for mobile offshore drilling units (MODUs) operating for the corporation's affiliates. A task force was commissioned to survey, from a marine operations standpoint, selected MODUs to identify ways to maximize the effective use of existing marine safety equipment, practices, and training for emergencies including vessel abandonment. The effort resulted in specific goals to reduce the likelihood of serious mishaps and to improve the crew's chances of survival in the event rig abandonment were necessary. The goals were to (1) develop and implement a set of safety guidelines for MODUs operating for Exxon, (2) work to help upgrade industry standards and practices, (3) assess marine safety systems as part of the initial rig selection process, and (4) conduct effective, comprehensive structural inspections on selected rigs. Marine safety guidelines were developed to address several main areas, including emergency response, rig abandonment, personnel qualifications, stability procedures, and fire protection. The guidelines have been used in over 90 marine safety surveys (assessments) to date. A comprehensive onboard safety school was developed emphasizing effective scenario emergency drills and offshore survival. Over 35 of these schools have been conducted in cooperation with the drilling contractors. The content of the marine safety guidelines and the schools have been used in efforts to upgrade industry standards through the American Petroleum Institute (API), United Kingdom Offshore Operators Association (UKOOA), the Oil Industry International Exploration and Production Forum (E&P Forum), International Maritime Organization (IMO), and the U. S. Coast Guard (USCG).
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