Challenges About Testing, Welding and NDT of CRA Pipelines in Brazilian Pre-Salt

Some new pre-salt fields at Santos Basin in Brazil are located in water depths as deep as 2200m and about 300 km away from the coast. There is variable level of contaminants in the produced fluid, mainly CO₂ that affects the material selection of the infield flowlines and risers. Based on these constraints, Petrobras has selected UNS N06625 clad or lined steel linepipes to develop the first fields in Pre-Salt area and also the module 3 of Roncador a post-salt field in Campos Basin. Several challenges have arisen during design, construction and installation of these facilities related to pipeline welding procedures, NDT inspection and Engineering Critical Assessment (ECA). Firstly weld overmatching condition may not be fully achieved due to differences in mechanical properties between UNS 06625 and API X65, and concern increases when reel-lay installation method is chosen. Another welding issue is the maximum interpass temperature of nickel alloys (DNV and PETROBRAS standards limit that to 100°C) and this impacts pipeline installation productivity. Thirdly, back purging characteristics and number of passes protected with purging gases affects the possibility of root oxidation. Also, the inspection of the weld overlay in the pipe end of lined linepipes is other point of great concern. As defect sizing is mandatory for ECA, lined pipes have been designed with a weld overlay length which allows the inspection of the final girth weld by AUT. However, AUT solutions are normally more efficient in rolled or extruded materials than in weld overlaid ones. Additionally, the ECA methodology for both girth welds and weld overlay has complexities that are not usually addressed in a regular ECA for carbon steel pipelines (e.g. internal misalignment of girth welds in risers has stringent requirements because of its effects on fatigue performance and, consequently, the ECA girth weld criteria). Also CRA clad/lined pipelines and risers qualification program may include additional testing when compared with usual carbon steel welding qualification process (namely pitting and intergranular corrosion, full scale fatigue, spooling trials of lined linepipes, segment testing for ECA, and others). Finally, the contribution of clad/lined layer in pipeline design strength is also discussed. This work presents challenges PETROBRAS has faced at design and construction phases of on-going Guaré and Lula-NE pre-salt fields and Roncador field projects, as well as the solutions proposed by the project team in order to overcome the issues raised during project execution.