钒：改造未来

The Effect of Vanadium on the Properties of Thick Wall API 5Lx65-70 Linepipe

Abstract:

To investigate the possibility of manufacturing grade API 5LX-65 linepipe for sour service, in wall thicknesses up to 40mm, three laboratory heats (0.033%C, 0.31 %Si, 1.3%Mn, 0.04%Nb) with different vanadium contents (<0.002%, 0.061 % 0.0120%), were investigated. The heats were thermomechanically rolled in three rolling stages, following the same rolling schedule in all cases. The finish rolling temperature was 710°C. Rolling was followed by accelerated cooling, with a cooling rate of about 10°C/s, down to 450-500°C, after which the plates were air cooled to room temperature.

Strength levels were improved by increasing the vanadium content and it is considered desirable to include an addition of 0.04% V to ensure achievement of API 5LX65 strength requirements. In the case of API 5LX70, a vanadium addition of at least 0.08% is indicated as being necessary to achieve strength requirements.

Both Charpy vee-notch impact and Battelle drop weight transition temperatures exhibited a small deterioration with increasing vanadium level. However, with impact energies of 3501, or more, at -20°C and 85% shear at -5°C, these can be considered to be good for thick wall, sour service, plates. The microstructures reflected the processing conditions and were similar in all three cases. They consisted of 95-97% elongated ferrite and 3-5% bainite.

Keywords:

vanadium, linepipe steel.

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