Flexibles Pipe Corrosion Monitoring

The number of flexible risers in the oil industry is steadily increasing. The failure rate for flexible pipes is high on the Norwegian continental shelf. Reporting and follow up of failures on the Norwegian continental shelf is good compared to other regions. Integrity management of flexible pipe is becoming increasingly important because failures will affect both reliability and costs. PSA Norway has expressed that the industry should give priority to activities related to integrity management of flexible pipe. 4Subsea is a specialist company in integrity management of flexible pipes. International success depends on 4Subsea possessing the best knowledge and tools for integrity assessment of such pipes. Shell, ExxonMobil, Statoil, BP and Petrobras have been industrial partners. The cooperation with these partners has been excellent and has given access to offshore experience with corroding flexible pipe. Research partner, IFE, has in the project period been involved in several flexible pipe corrosion investigations in addition to FPCM. Much of this work has been done for the industrial partners in FPCM project. Damage to the outer sheath is the most common damage to flexible risers. Subsequent corrosion has in some cases resulted in serious accidents, including the loss of life. However, there are other outer cover damages that have only given negligible corrosion. Offshore experience, IFE corrosion competence, laboratory tests and dissections have been used in the FPCM project. The experience database used in FPCM is the world largest database for such information, containing more than 310 different flexible pipes, more than 1466 annulus tests, more than 784 annulus gas composition analyses and dissection of more than 50 km of used flexible pipe. Experience, evaluation of critical corrosion processes, lab investigations and discussions in the Steering Committee have been the basis for armour wire testing and full-scale testing. The full-scale test was with a new pipe with an artificial damage, the test had extensive instrumentation and monitoring of important parameters like the inflow through the damage, fluid flow in the annulus, composition of vented gas, etc. The project has prepared a "Best Practice - Assessment of outer sheath damages and associated corrosion mechanisms" document which is planned for worldwide use. The Best Practice is calibrated with field experiences. Moreover, the project has tested measurement equipment offshore and contributed to improvements of the 4Subsea inspection tools. Several flexible pipes have failed because of brittle fracture in the steel reinforcement, possibly connected with sour annulus environment. FPCM has summarized all known experiences and has discussed with academic expertise on brittle fracture and corrosion in sour environment. Recently, new challenges related to the brittle fracture and corrosion of flexible pipe reinforcement in deep water offshore Brazil have been experienced. The effort to understand this will be continued in the IFE project " Environmental Cracking of Flexible Pipe Armour Wires" which is a KPN project supported by the Research Council of Norway and industrial sponsors. In the project period, new corrosion challenges with flexible pipe have been observed also in the North Sea. Work with improved understanding of these new phenomena in Brazil and the North Sea is planned continued in in a JIP project managed by 4Subsea with IFE as a research partner. Close cooperation is planned with the IFE KPN project on brittle fracture. The FPCM project has received significant international attention. In 2016, BP joined the project as a new partner, Petrobras joined in 2017. In addition to new foreign partners, the project has contributed to 4Subsea winning major contracts in Brazil, establishment of 4Subsea branch office in Brazil and enhancement of IFE expertise such that IFE is now considered the leading research institute for corrosion in flexible pipes.

There are knowledge and technology gaps preventing operators of flexible pipes from adequate identification of pipes at risk for corrosion and predicting the remaining service life of pipes with damage to the outer cover. 4Subsea has dissected more than 40 flexible risers and flow lines retrieved from service for different reasons by different operators. This has provided significant information and data related to: [1]conditions that load carrying armour wires are exposed to [2]cases of serious corrosion. It has been recognized that more insight can be gained by further assessment of available data. Combined with laboratory testing there is a good potential for developing monitoring and assessment services that will meet many of the needs within the industry. IFE has been chosen as partner for expertise on corrosion mechanisms and laboratory testing facilities. Shell, ExxonMobil and Statoil will be the industry Partners. The first Work Package (WP1) State of the Art, shall build the knowledge base from available data and information. This will cover assessment of results from dissection and monitoring performed by 4Subsea, information from partners and public domain. In WP2 Scenarios and Signatures, detailed features of relevant corrosion mechanisms will be identified for specification and design of testing and for selection of monitoring equipment to detect corrosion signatures. WP3 Laboratory Testing, starts with small scale testing leading on to mid-scale testing in relevant corrosion environments. CO2 and O2 environments will be replicated in short sections of flexible pipes. Investigations of H2S related corrosion issues will be covered in WP4. The final WP5 (Integrity Management Services) shall build on the results from WP2, WP3 and WP4 to develop new capabilities for monitoring and prediction of corrosion of armour wires in the annuli of flexible pipes. Guidelines and procedures for corrosion assessment will also be developed.