Search

The development of oil and gas fields in the arctic brings to the table several challenges in the use of structural steels, particularly concerning their low-temperature properties. Among others, also fatigue behavior needs to be accounted for when using structural steels for arctic applications. As for static fracture, ferritic steels experience a fatigue ductile to brittle transition (FDBT) when temperature is decreased below a certain temperature. This may result in higher crack growth rate and, consequently, unpredicted fatigue-related failure. In order to shed some more light on this phenomenon, fatigue crack growth tests have been performed on a 420 MPa structural steel weld simulated coarse grained heat affected zone (CGHAZ) at different temperatures: room temperature, -30, -60. -90 and -120 °C, with -60 °C considered as a possible design temperature relevant for the most extreme arctic areas. Post-mortem fracture surface investigations have been also conducted in order to confirm the expected switch in fatigue crack growth mechanisms as temperature is lowered below the FDBT temperature. Finally, two analytical equations, valid for temperature ranges above the FDBT. were established based on the experimental results to relate yield strength and temperature variation of the Paris law constants . These are used to quantify the temperature impact on the designed fatigue life, and the results are compared to the actual design rules (BS 9710). [ABSTRACT FROM AUTHOR]

For steel structures to be installed in the Arctic region, the risk of brittle fracture represents a primary concern due to the ductile to brittle usually transition taking place at sub-zero temperatures. Therefore, the present investigation addressed the heat affected zone and weld metal toughness of two extra low carbon steels of 420 MPa yield strength grade, supplied in 20 and 50 mm thickness. The testing included tensile, Charpy V and CTOD. The results obtained showed that the Charpy V toughness was relatively high at -60°C, but that some low values may occur for the fusion line position. The fracture toughness at -60°C, based on SENB05 (a/t=0.5) geometry, appeared to be low for both weld metal and fusion line positions. More specific measures may be taken into account in welding procedure qualification of the current steels, such as using lower crack length (e.g., a/t=0.2), tension instead of bending (SENT testing) or a full engineering critical assessment. [ABSTRACT FROM AUTHOR]

The article discusses research which examined the tensile properties of 420 MPa steel exposed at low temperature. Topics discussed include the dependency of yield stress, tensile strength and strain hardening on temperature, proposed correction of yield stress and Lüders band development at low temperature and effect of temperature dependent material properties on brittle fracture.

The article discusses research which examined the properties in submerged arc welding of X80 plate in Arctic areas. Topics discussed include the increase in ultimate strength of the base metal and weld metal yield with falling temperature, weld thermal simulation, testing and characterization for welds, weld macros and hardness and fracture toughness.

The article discusses research which examined the metallurgical changes in welding clad X60/X65 pipelines. Topics discussed include the investigation of welded samples by light optical microscope, electron microscope analysis and microhardness measurements and the presence of a nickel (Ni)-interlayer preventing the carbon diffusion across the base metal (BM)-clad interface during exposure to elevated temperatures.

The article discusses research which evaluated the ferritic weld metal toughness based on the use of commercial wires. Topics discussed include some problems associated with the structural steel applications in the Arctic environments, materials and experimental procedure, microstructure characterization and quantification and gas cutting preparation for welding.

The article discusses research which investigated a data management system for material assessment at low temperature. Topics discussed include the proposed generic database platform for efficient access to material data, analysis of various materials including steels/weldments and aluminium alloys and improved design guideline for materials requirements in Arctic conditions.

The article discusses research which examined the fatigue crack growth rate tests performed on a structural steel at low temperature. Topics discussed include the effect of low temperature on fatigue crack growth, chemical composition and mechanical properties of steel and improvement of all the stages of the fatigue crack growth as the testing temperature is lowered from room temperature.

The article discusses research which examined the potential use of instrumented charpy testing for steels used by the oil and gas industry in the Arctic region. Topics discussed include the material and experimental procedure and the basic charpy test data, possible use of crack arrest for Artic materials.