The installation of Floating Production Storage and Offloading (FPSO) vessels has become a common means of decreasing 'time to first oil' on marginal and deepwater offshore oil fields.
There are three types of FPSO design: new build, conversion of an oil tanker under construction, and conversion of existing oil tankers. FPSOs will face sea load conditions never experienced by an oil tanker, especially when loading and offloading products. Whatever the option chosen by the industry, many structural problems can be avoided during design and construction.
The FPSO needs to be designed to avoid major structural failure for a minimum of 20 years (oil tankers require typically five to 10 years).
TWI has been involved with design, construction and assessment of FPSOs since the first one was commissioned in the UK, working with operators, regulators and classification authorities that need support.
TWI was recently called as a consultant on a fitness-for-service and repair methodology of defective turret welds for a major oil company in the southern hemisphere. The joints assessed presented manufacturing defects not identified during the construction inspection.
The investigation involved a multidisciplinary team at TWI including NDE engineers in advanced techniques (TOFD and phased array, among others) for defect sizing and characterisation. Fracture and fatigue engineers assessed the mechanical properties and likelihood of failure, while materials engineers investigated welding parameters adopted during construction. TWI's welding engineers have also been involved in the development of full-scale 'mock-up' welded joints, representative of the turret welds, and to develop suitable repair procedures in case repair became an option after the structural assessments.
TWI was subsequently able to demonstrate to the satisfaction of the operator and their classification authority that the turret was fit for service. This outcome saved the operator the costs of the repair estimated to be over US$5M.
If you would like to know more about how TWI's engineers can help you with regard to FPSOs, contact Marcos Pereira. E-mail: firstname.lastname@example.org.