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ABSTRACT Materials for fixed and floating structures in arctic environment must be designed for low ambient temperature. The offshore operating environment is also including sea ice, marine ice accretion and snow. The materials strength, ductility and wear resistance are challenged. Structural steels and steel for piping and pressure vessels for operating temperatures down to -60°C are needed, and the steel industry has a challenge to meet such requirements. At the same time the testing and qualification procedures should be improved to open for utilisation of new materials and welding procedures. As operation in many cases is located in remote areas, the cost of maintenance and repair is more expensive, and the need for replacements, repair and maintenance should be minimised. Of particular importance is the corrosion protection by painting and cathodic protection. The integrity and performance of the process system depends upon a good control of the temperature in the production and utility fluids. Therefore, insulation and electrical heat tracing of piping and process equipment is essential. The material selection must therefore take into account that large temperature variations can take place and that the maximum temperature associated with localised heating can be higher than normal process temperature. Operation of gas production systems includes strict requirements to ventilation. Natural ventilation is not compatible with enclosed process systems unless very large ventilation systems are installed. Material selection for advanced heating, ventilation and air conditioning (HVAC) systems and combinations of natural and mechanical ventilation systems need to be developed for systems operating in arctic marine environment where sea spray, ice accretion and snow can cause problems. Ice repellent materials are attractive, but the long term performance of the materials is questioned. The lecture will review the state-of art on these items and propose some ideas on the way forward.
- Europe (0.47)
- North America (0.29)
- Well Completion > Well Integrity > Subsurface corrosion (tubing, casing, completion equipment, conductor) (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers > Materials and corrosion (1.00)
- Facilities Design, Construction and Operation > Offshore Facilities and Subsea Systems (0.89)
Robust Material Qualification For Arctic Applications
Horn, Agnes Marie (Det Norske Veritas, and SINTEF, and Statoil) | Østby, Erling (Det Norske Veritas, and SINTEF, and Statoil) | Hauge, Mons (Det Norske Veritas, and SINTEF, and Statoil) | Aubert, Jean-Michel (Det Norske Veritas, and SINTEF, and Statoil)
ABSTRACT Oil and gas exploration and production is moving into arctic areas. The reduction in ice-covered areas has rendered northern routes more advantages and in addition it is anticipated that as much as 25% of the undiscovered oil and gas resources can be found in the Arctic. There is a lack of rules and standards that provide guidelines for material selection and qualification of materials for offshore and onshore structures in Arctic areas. Some actions have been taken to develop new standards e.g. ISO19906 Arctic Structure, however the guideline does not specify material requirements except for the statement that material shall have adequate toughness in order to behave ductile at low temperature. Material related standards like EN10225, API 2W and Norsok are not developed for low temperature applications and are generally applied for service temperatures down to -10°C (Norsok covers down to -14°C). For lower temperature, it is up to the designer to show fit for purpose of the selected material. Hence, one major challenge for designers is to specify adequate toughness requirements at an early stage of the design process for low temperature applications. This paper will discuss factors that influence the required CTOD toughness value at an early stage of a design process by discussing the following topics: required qualification and testing, utilization/robustness of a structure, weld defect size, residual stress, constraint effect and tensile properties. INTRODUCTION There is a lack of rules and standards that provide guidelines for material selection and qualification of materials for offshore and onshore structures in Arctic areas. Most of the offshore construction steels are purchased according to EN 10225 "Weldable structural steels for fixed offshore structures technical delivery conditions" which only provide requirements for Charpy values. No guidelines on CTOD toughness values are provided. For designers it can be challenging to decide the adequate CTOD requirements at an early stage when material is ordered, since limited design analyses have been carried out.
Comparison of Fracture Toughness In Real Weld And Thermally Simulated CGHAZ of a 420 MPa Rolled Plate
Østby, Erling (SINTEF Materials and Chemistry) | Kolstad, Gaute T. (NTNU (Norwegian University of Science and Technology)) | Thaulow, Christian (NTNU (Norwegian University of Science and Technology)) | Akselsen, Odd M. (SINTEF Materials and Chemistry, and NTNU (Norwegian University of Science and Technology)) | Hauge, Mons (NTNU (Norwegian University of Science and Technology), and Statoil ASA)
ABSTRACT Establishing the fracture toughness of real HAZ can be challenging due to the small extension of the potentially brittle zones. Application of testing of weld thermal simulated HAZ microstructures can provide an alternative approach to establish fracture properties of the more brittle microstructures. In this paper CTOD values measured in real and simulated CGHAZ of a 420 MPa steel are compared at -60 and -30ºC. It is shown that for the lower temperature, where the fracture toughness is very low, similar CTOD values are obtained in both the real and simulated HAZ. At the higher temperature the fracture toughness increases more in the real HAZ compared to the simulated one. FE analyses are used to propose an explanation for this behaviour. The results present an interesting first step in the direction of use of weld thermal simulated samples for obtaining relevant CTOD values for used in assessment of real HAZ. INTRODUCTION The low temperatures encountered in the Arctic poses a special challenge with regards to the use of steel structures. The risk of brittle behaviour in steels and their weldments must be controlled in order to have acceptable structural integrity. Especially weld metal and heat affected zone (HAZ) could be subject to low toughness. These are also areas where defects are most likely to occur. A challenge associated with the characterization of brittle fracture is the large scatter in fracture toughness test results. Application of statistics is necessary to obtain reliable estimates of the toughness. General approaches in this respect have been developed by Beremin (1983) and Wallin (2002), and examples of statistical methods applied to characterize scatter in HAZ fracture can be found in Hauge (1990). Determination of fracture toughness in the HAZ represents a special challenge. The brittle zones may be of limited size and there could be a large gradient of toughness acting over small distances in the material.
- Energy > Oil & Gas (1.00)
- Materials > Metals & Mining > Steel (0.48)