Mechanical properties of X70 spiral submerged arc welded steel pipe:
Grade and Material: X70
Type and Type: 1016mm x 14.6mm spiral submerged arc welded steel pipe
Production requirements: API SPEC 5L X70 acicular ferrite, oxygen converter or electric furnace smelting, vacuum degassing, calcium and micro-titanium treatment, low carbon micro-alloy killed steel; TMCP production steel plate (roll), particle size 10 or more, non-metallic inclusions < 2.
Tensile properties:
Steel pipe: _s (_t 0.5) = 485-620 MPa_b (> 570 MPa) yield ratio (< 0.90)
Steel plate (roll): _s (_t 0.5) = 530-620 MPa_b (> 570 MPa) yield ratio (< 0.92)
According to API SPEC 5L, the elongation requirement is calculated to be more than 22%.
Weld b>570 MPa


Resilience:
DWTT: Steel plate (roll) (- 15 degree C) single SA%> 70 average SA%> 85
Steel Pipe: (- 5 degree C) Single SA%> 70 Average SA%> 85
Charpy impact: pipeline transverse (-20 degree C) single SA%>80 average SA%>90 single Cv>140 J average Cv>190J
Welding and Heat Affected Zone (-20 degrees C): Single SA%>30 Average SA%>40 Single Cv>60 J Average Cv>90


In addition to Nb, V, Ti and X70 pipeline steel, there are a small amount of Ni, Cr, Cu and Mo, which delays the formation of ferrite at a lower temperature, which is conducive to the formation of ferrite and lower bainite. The microstructure of X70 steel plate is mainly acicular ferrite. Adding a small amount of granular bainite, the banded structure is less than 2.0, and the grain size is fine, basically 11-12. Therefore, X70 pipeline steel is basically acicular ferrite high strength, high toughness pipeline steel.


The X70 coil is deformed and hardened because of its special structure. The influence degree is high, which greatly reduces the influence of Bauschinger effect, and the yield strength loss is only about 10 MPa.


Since the tensile strength mainly depends on the saturation value of work hardening, the tensile strength value increases slightly after the pipe is made, which makes the average yield ratio of the back pipe decrease, which means that the plastic deformation ability of the pipe is improved.