Evaluation of the Use of 6Al-4V ELI TSJ (Grade F23) in Gas Export Risers in the SEAP Field

Abstract The Sergipe Águas Profundas (SEAP) field, stands out as one of the newest production frontiers in deep waters in Brazil. Located in the Sergipe-Alagoas Basin, 100 km from the coast and at depths reaching 3000 m, it poses several technological challenges for the development of the field. Divided into two modules, the field is planned to have several Steel Lazy Wave Risers (SLWR), including two for Gas Export associated with a trunk line linking two FPSO to shore. Due to the low level of contaminants present in the transported gas, and the possibility of wet park these risers empty in an ultra-deep-water depth, which may be challenging for Flexible Joints, a comprehensive study for the use of TSJ in-stead, as top termination of these Gas Export SLWRs, was carried out. Although the use of Titanium Stress Joint is widespread throughout the world, especially in the Gulf of Mexico, the application in spread mooring FPSO (as SEAP) is still limited, and costly. On the other hand, the Stress Joint option can be a more reliable alternative than the Flexible Joints, due to the properties of titanium and the absence of structural elastomeric supports, making it resistant to prolonged operation at high temperature and pressure and less susceptible to pressure cycles during their service life. Several numerical simulations (global analyzes) are performed to verify the technical viability of the Titanium Stress Joint and the riser configuration for the intended use, and the opportunity to use the Ti-6Al-4V ELI alloy (grade F23), which has lower cost and greater availability on the market, is investigated. Advantages of the Stress Joints over the Flexible Joints in the specific scenario of pre-lay of the Gas Export risers for a long period without the need of special tools, and the possibility of reducing diving inspections for integrity management of the riser’s top termination throughout the operational life are also discussed in this article.