Q245R straight seam steel pipe production method: double-sided submerged arc welded steel pipe, implementation standard: GB/T150.2 pressure vessel;
(1) Chemical composition: carbon content: ≤0.20, silicon content: ≤0.35, manganese content: 0.50-1.00, steel plate phosphorus content: ≤0.025, steel plate sulfur content: ≤0.015, aluminum content: ≥0.020
(2) Mechanical properties: tensile strength σb (MPa): 380-520MPa, yield strength σ0.2 (MPa): 185-245MPa, elongation after fracture δ5 (%): ≥35, impact test temperature: -20℃, impact absorption energy KV/J: ≥25J.
The use regulations of steel plates in CB/T3274-2007 “Hot-rolled thick steel plates and strips of carbon cable structural steel and low alloy structural steel” are as follows:
a) The chemical composition (melting analysis) of the steel shall comply with the provisions of GB/T7002006 “Carbon cable structural steel”, but the phosphorus and sulfur content in the steel plate quality certificate shall comply with the requirements of P≤0.035% and S≤0.035%.
b) Steel plates with a thickness of 6mm or more shall be subjected to impact tests, and the test results shall comply with the provisions of GB/T700. For Q235C boiler plates used at a temperature below 20℃ to 0℃ and a thickness of 6mm or more, the container manufacturing unit shall additionally conduct an 0℃ impact test on the transverse specimen, and the average impact energy of 3 standard impact specimens KV.≥27J. The minimum impact energy value of 1 specimen and the impact energy value of the small-sized impact specimen shall comply with the corresponding provisions of GB/T700.
e) The steel plate shall be subjected to a cold bending test, and the cold bending qualification standard shall comply with the provisions of GB/T700.
d) The design pressure of the container is less than 1.6MPa.
e) The service temperature of the steel plate: 20℃～300℃ for the steel plate; 0℃～300℃ for the Q235C steel plate.
The thickness of the steel plate used for the container shell: Q235B and Q235C are not more than 16mm. The thickness of the steel plate used for other pressure-bearing components: Q235B is not more than 30mm, and Q235C is not more than 40mm. It shall not be used for extremely or highly toxic media.
First, the production process and quality control of Q245R straight seam welded steel pipe
1. The manufacturing process of Q245R straight seam welded steel pipe:
(1) Milling and forming: adopt a 45° groove angle and a 4.8mm blunt edge design to ensure that the weld is fully penetrated.
(2) JCO forming: For steel pipes with a diameter of 711mm and a wall thickness of 10mm, they are stamped into a “J-C-O” shape in steps, with a single press of 185mm to control the rebound and roundness.
2. Welding process of Q245R straight seam welded steel pipe:
(1) Internal welding: three-wire submerged arc welding, the first wire is DC reverse connection (current 540-660A), the second and third wires are AC (current 405-550A), welding speed 1.4-1.8 m/min, line energy 19.5-23.5 KJ/cm.
(2) External welding: similar parameters but higher current (first wire 720-880A), line energy 21.1-25.7 KJ/cm, to ensure weld penetration and morphology.
(3) Diameter expansion and heat treatment: mechanical diameter expansion rate 0.5%-1.2%, local heat treatment after welding (580-620℃ insulation for 50 minutes) to release stress and refine grains.
3. Quality inspection of Q245R straight seam welded steel pipe:
(1) Nondestructive testing: ultrasonic testing (detecting defects in welds and heat-affected zones), X-ray inspection (100% weld coverage), water pressure test (pressure is 90%-100% of yield strength).
(2) Appearance control: ovality, straightness, and weld excess height must comply with GB150 standards.
Second, the performance advantages and application areas of Q245R straight seam welded steel pipe
1. Performance characteristics of Q245R straight seam welded steel pipe
(1) Low-temperature resistance: suitable for -20℃ environment, meeting the low temperature requirements of natural gas processing plants in the northwest region.
(2) Corrosion resistance: by controlling sulfur and phosphorus content and post-weld treatment, the corrosion risk in the H₂S environment is reduced.
(3) High toughness structure: the weld is mainly composed of acicular ferrite and bainite, the grains in the heat-affected zone are fine, and the crack resistance is improved.
2. Main applications of Q245R straight seam welded steel pipes
(1) Natural gas engineering: used for low-temperature vent pipes to handle exhaust gas combustion emissions containing H₂S.
(2) Pressure vessels: boiler gas bags, reactor shells, etc., with a design pressure of ≤1.6 MPa and a temperature range of -20℃~300℃.
(3) Construction and infrastructure: large-diameter steel casings (such as piling and bridge support), with a wall thickness of up to 50mm and a diameter of up to 2 meters.
Third, installation and use precautions for Q245R straight seam welded steel pipes
(1) Welding specifications: multi-layer welding requires control of interlayer temperature to avoid overheating; thick plates (≥25mm) need to be preheated to above 125℃.
(2) Stress control: post-weld heat treatment can reduce residual stress and prevent crack propagation.
(3) Medium restrictions: not suitable for extremely or highly toxic media.
Post time: May-16-2025