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- Akselsen, Odd M., et al.
(författare)
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Effects of phase transformations on residual stresses in welding of stainless steels
- 2007
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Ingår i: International Journal of Offshore and Polar Engineering. - 1053-5381. ; 17:2, s. 145-151
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Tidskriftsartikel (refereegranskat)abstract
- In this investigation, we investigate the effects of solid state phase transformation on residual stresses in welding super-martensitic stainless steels, using the Satoh experimental test approach. The results obtained clearly demonstrate that the austenite-to-martensite phase transformation has remarkable effects on the final tensile residual stress level, and stresses as low as 70 to 170 MPa were found, depending on the weld thermal program. These results may imply that unnecessary conservatism is often used when assuming residual stresses to be of the same order as the base metal yield strength.
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- Akselsen, O. M., et al.
(författare)
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Root bead profiles in hyperbaric GTAW of X70 pipeline
- 2006
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Ingår i: International Journal of Offshore and Polar Engineering. - 1053-5381. ; 16:2, s. 123-127
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Tidskriftsartikel (refereegranskat)abstract
- This investigation began with the goal of studying the root bead penetration profiles in hyperbaric GTAW welding of X70 pipelines. Such profiles may vary substantially depending on the wire and base metal chemical composition. Root beads were deposited with a pressure corresponding to 75-m seawater depth, and with a systematic increase of 10 A in the pulse current until burnthrough took place. The results obtained showed that the penetration profiles were different between the 2 wires included in the welding program. The largest penetration width was found for wire B with the highest sulphur content (0.013% S), with a maximum width of about 8-mm width on the pipe inside for 160 A. At pulse current levels of 120 to 170 A, the difference between the 2 wires was about 1 mm. With current beyond 180 A, the profiles approached similar values, followed by burnthroughs for both wires at 190 A. However, the welding parameters were already too hot at 180 A. These results are probably caused by a Marangoni convection in the weld pool. A high content of surface active elements (e.g., sulphur) is known to shift the How pattern, providing deeper penetration. In practice, small variations in the bead penetration profile may have large consequences during offshore tie-in welding. Cost-increasing repair operations may be required if nondestructive inspection later reveals poor root bead quality. Such actions require mobilisation of huge resources.
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- Akselsen, Odd M., et al.
(författare)
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Weld metal mechanical properties in hyperbaric GTAW of X70 pipeline
- 2006
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Ingår i: International Journal of Offshore and Polar Engineering. - 1053-5381. ; 16:3, s. 233-240
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Tidskriftsartikel (refereegranskat)abstract
- In the present investigation, 2 different wires for hyperbaric (underwater) GTA (gas tungsten arc) welding of X70 pipelines have been tested with respect to their weld metal mechanical properties. Welding of full coupons at different pressures (seawater depths of 16, 75 and 200 msw) was done with subsequent weld metal chemical analyses, hardness measurements, tensile testing and Charpy V notch testing as well as microstructure characterization. It is shown that both wires satisfied strength requirements set to X70 grade, representing a weld metal overmatch situation. Both wires gave sufficient impact toughness, but the toughness of the Ni-Mo containing weld was reduced with increasing seawater depth. This observation was strongly linked to the positioning of the Charpy V notch, and crack growth in a brittle, partially transformed region as a consequence of reheating by subsequent stringer beads. The embrittling microstructure consisted of high carbon MA (martensite-austenite constituents islands) decorating prior austenite grain boundaries. This microstructure was less pronounced when welding with the high Ni wire, which may explain why no similar toughness drop was found.
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- Aune, Ragnhild E., et al.
(författare)
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Measurement of Thermophysical Properties of Liquid Metallic Alloys in a Ground- and Microgravity Based Research Programme - the ThermoLab Project
- 2005
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Ingår i: Microgravity, science and technology. - 0938-0108 .- 1875-0494. ; 16:1-4, s. 7-10
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Tidskriftsartikel (refereegranskat)abstract
- The ThermoLab project is concerned with the measurement of the thermophysical properties of industrial alloys in the liquid phase. The project combines long and short duration microgravity measurements based on containerless processing with an electromagnetic levitation device and a ground based experimental programme using conventional and containerless processing techniques. An overview of the project and representative results from the ground based experimental programme are given. Alloys investigated included Ni-based, Fe-based, a Cu-Sn-Mg alloy and a gamma-TiAl alloy.
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- Aune, Ragnhild E., et al.
(författare)
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Surface Tension and Viscosity of Industrial Alloys from Parabolic Flight Experiments : Results of the ThermoLab Project
- 2005
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Ingår i: Microgravity, science and technology. - 0938-0108 .- 1875-0494. ; 16:1-4, s. 11-14
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Tidskriftsartikel (refereegranskat)abstract
- The surface tension and the viscosity of a series of industrial alloys have been measured by the oscillating drop technique with an electromagnetic levitation device under reduced gravity conditions in several parabolic flights. It was demonstrated that the 20 seconds of reduced gravity available in a parabola were sufficient for melting, heating into the liquid phase, and cooling to solidification of typically 7 mm diameter metallic specimen. The surface tension and the viscosity were obtained from the frequency and the damping time constant of the oscillation which were evaluated from the temperature signal of a highresolution pyrometer. Alloys processed included steels, Ni-based superalloys, and Ti-alloys which were supplied by industrial partners to the project. Three to four parabolas were sufficient to obtain the surface tension and the viscosity over a large range in temperature.
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- Aune, Ragnhild E., et al.
(författare)
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Thermodynamic approach to physical properties of silicate melts
- 2005
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Ingår i: Ironmaking & steelmaking. - : Informa UK Limited. - 0301-9233 .- 1743-2812. ; 32:2, s. 141-150
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Tidskriftsartikel (refereegranskat)abstract
- The thermophysical properties of silicate melts are strongly structure dependent. It is well known that the viscosity of slags increases with increasing degree of polymerisation of the silicate anion. Even the thermodynamic properties of slags are dependent on the species type and population in the melt. Thus, a link between the thermophysical and thermochemical properties of silicate melts is logically expected. The present paper elucidates the salient features of Darken's excess stability approach to the Gibbs energy of solution as applied to the viscosities of silicate melts. It is demonstrated that the second derivatives of the viscosities of binary silicate melts with respect to composition indicate maxima corresponding to the existence of stable compounds in these systems. The concept has been successfully applied to the following systems: Al2O3-SiO2, CaO-SiO2, FeO-SiO2, MgO-SiO2 and MnO-SiO2. In all cases, the second derivative plots of viscosities with respect to composition show peaks corresponding to the metasilicates. The second derivatives of the activation energies of viscous flow with respect to temperature have earlier been shown to reflect the formation of associates/embryos in homogeneous silicate melts, indicating the readiness of the melt to separate a solid phase. Thermodynamic coupling of thermal diffusivities in the case of the CaO-Al2O3-SiO2 system from laser flash measurements of these slags, as a function of temperature, has been examined as part of the present study. Densities have been estimated from integral molar enthalpies in the case of silicate systems, and the results are presented.
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