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PETROMAKS2-Stort program petroleum

Knowledge basis for repair contingency of pipelines

Alternative title: Kunnskapsbase for reparasjon-beredskap av subsea rørledninger

Awarded: NOK 18.0 mill.

Steel pipelines represent the most important infrastructure for transport of oil and gas to onshore facilities in Norway and Europe. Pipelines with metallic layers inside for corrosion protection, so called clad and lined pipes, have in recent years been installed in several fields. When the project was initiated there was however no subsea repair contingency available for this kind of pipelines, and relevant knowledge was thus required. In addition, the OG21 strategy highlighted the technology gap concerning addressing the understanding and assessing the influence of degradation mechanisms. Therefore, this topic has been also an important part of the project. The following industrial partners have been part of the project: Equinor, Gassco, Technip, POSCO (Korea)and EDF Induction. The national reserach partners were SINTEF, NTNU and IFE. A central part of the project have been the understanding of the physics of the relevant cold metal transfer (CMT) method and the influence that welding has on the material properties of the bi-metallic joints of clad pipes. This is an essential basis for developing a sound repair welding procedure as well as models for the welding and the structural integrity of the welded joints. Both numerical modelling and experimental teqhniques have been applied. Through the education of one PhD, one Post Doc and Master candidates as well as the fundamental research performed at IFE and SINTEF, the experimental and numerical knowledge related to subsea repair welding modelling has increased and strengthened the national knowledge base. This is especially valuable in a situation where the O&G industry must reduce costs related to repair and maintenance. Furthermore, the knowledge built within welding and modelling is highly relevant for subsea structures in ocean wind turbines and for future hydrogen gas transport using natural gas pipelines. Some central results: 1) Models for weld arc physics, molten weld pool behavior, multi pass welding with the resulting microstructure as well as structural integrity including hydrogen diffusion and resistanse towards hydrogen induced fracture. 2) A novel fracture mechanics test method for toughness testing of the interface between clad and pipe material was developed. The testing has shown that pipes with a thin Nickel layer between the pipe-steel and the clad improves the fracture toughness of the interface in hydrogen charged conditions, both before and after welding. 3)The project has shown that it is possible to do subsea remote butt welding of pipes using the CMT and pulsed MIG method down to a water depth of 1500 m. This may save the industry for costly repair by avoiding/reducing production stops with loss of income and reduce risk of negative environmental influence whether the pipes are transporting present natural gas or future hydrogen gas.

The project has established that a Ni interlayer between the inner clad and the pipeline steel clearly is preferable with respect to the structural integrity of the pipe in general as in girth repair welding. This influences the requirements from the purchaser to the pipeline producers when ordering new clad pipelines for subsea conditions. The weld research activity has proven that the cold metal transfer weld method (CMT)is well suited for subsea pipeline root pass welding. The results show that remote butt welding of pipes using CMT in the root and pulsed MIG for the fillers up to 150 bar (i.e. a water depth of 1500 m) is feasible and gives acceptable mechanical properties. The method represents cost savings in subsea pipelines repair compared to today's sleeve repair welding method. The project has strengthened the existing collaboration between Kyushu University (Japan) and Norway through joint laboratory experiments and one joint publication.

Steel pipelines represent today the most important infrastructure for transport of oil and gas to onshore facilities in Norway and Europe. Both clad and lined pipes, including pipe-in-pipe, have already been installed (Stjerne-8.8" pipe, Tordis-9.4", Visu nd North-10", all clad pipes installed last year; while Tyrihans-16/18" and Aasta Hansteen-12" are lined pipes). Today, there is no repair contingency available for this kind of pipelines, and relevant knowledge must be built, as described in the research tasks of the present proposal. In parallel, the TTA 4 strategy highlights the technology gap concerning degradation ("Integrity management and risk reduction") with R&D priority addressing the understanding and assessing of degradation mechanisms (includ ing modelling). This is also an important part of the present project. It is recognised that the infrastructure is aging, and also that enhanced lifetime of existing oil and gas fields is targeted. For newly discovered fields, transport is provided by cou pling of new pipes with existing pipeline infrastructure, which means that existing pipelines may face internal flow of constituents they were never designed for, such as hydrogen sulfide or carbon dioxide. In order to maintain Norwegian industry's positi on in the technology front in the TTA 4 area, it is essential with a continuous national emphasis on R&D. To establish knowledge basis for weld repair of both existing and new pipelines, as well as their degradation behaviour is deemed necessary for: - In tegrity management and risk reduction - Enhanced lifetime of existing infrastructure - New fields in environmentally sensitive areas - Aging infrastructure The project structure consists of the following 4 workpackages (WPs): (WP1) Structural integrity, (WP2) Material and process modelling, (WP3) Technical solutions, and (WP4) Demonstrators. The project will address education of 2 PhDs, one related to the weld repair process and one within structural integrity.

Publications from Cristin

Funding scheme:

PETROMAKS2-Stort program petroleum