Details of Q345R straight seam welded steel pipe in industrial projects

First, the introduction of Q345R straight seam welded steel pipe

(1) Q345R straight seam welded steel pipe is made of rolled steel plate.

(2) The implementation standard of Q345R straight seam welded steel pipe: GB/T151.2 Pressure vessel part 2 materials.

(3) The chemical composition of Q345R straight seam welded steel pipe: carbon: ≤0.20, silicon: ≤0.55, manganese: 1.20-1.70, phosphorus: ≤0.025, sulfur: ≤0.010, copper: ≤0.30, nickel: ≤0.30, chromium: ≤0.30, molybdenum: ≤0.08, niobium: ≤0.050, vanadium: ≤0.050, titanium: ≤0.030, aluminum: ≥0.020, other copper + nickel + chromium + molybdenum ≤0.70.

(4) Mechanical properties of Q345R straight seam welded steel pipe: Steel plate thickness ≤ 16mm: yield strength: ≥345, Steel plate thickness 16~36mm: yield strength ≥325, Steel plate thickness 36~60mm: yield strength ≥315, Steel plate thickness 60~100mm: yield strength: ≥305, Steel plate thickness 100~150mm: yield strength: ≥285, Steel plate thickness 150~200mm: yield strength ≥265.

(5) Tensile strength of Q345R straight seam welded steel pipe: 470-640mpa.

(6) Impact test of Q345R straight seam welded steel pipe: Temperature: 0℃: ≥34.

(7) Elongation of Q345R straight seam welded steel pipe: ≥21.

(8) High-temperature mechanical properties of Q345R straight seam welded steel pipe: Temperature: 500℃: 20-36: Yield ≥ 180.

When the steel pipe in GB/T21833 is used for heat exchange tubes, cold-drawn or cold-rolled steel pipes should be used. The dimensional accuracy of the steel pipe should be selected with high precision. Class I and Class W steel pipes in GB/T 12771 are allowed to be used, but they shall not be used for heat exchange tubes. The selected boiler tube category shall be indicated on the drawing. The allowable stress of Class 1 steel pipe can be selected from the allowable stress of the seamless steel pipe with the rough steel grade in CB/T14976. The use regulations of Class II and Class W steel pipes are as follows!

The design pressure is less than 10.0MPa; it shall not be used for media with extremely or highly toxic levels. The use regulations of steel pipes in CB/T24593 are as follows: steel pipes shall be tested for eddy currents one by one, and the artificial defects of the comparison sample pipes shall comply with the provisions of acceptance level B in GB/T7735: design pressure is less than 10.0MPa; it shall not be used for medium with extremely or highly toxic degree. Class I and Class II steel pipes in GB/T21832 are allowed to be used, but shall not be used for heat exchange tubes. The selected steel pipe category shall be indicated on the drawing. The allowable stress of Class I steel pipes can be selected from the allowable stress of seamless steel pipes with corresponding steel grades in GB/T21833. Class I steel pipes in GB/T21832 are only used for heat exchange tubes. The steel pipe category (Class I) shall be indicated on the drawing. The allowable deviation of the outer diameter of the steel pipe shall be delivered according to high precision. The use regulations of this type of steel pipe are as follows: steel pipes shall be tested for eddy currents one by one, and the artificial defects of the comparison sample pipes shall comply with the provisions of acceptance level B in GB/T7735:

Design pressure is less than 10.0MPa; it shall not be used for medium with extremely or highly toxic degrees.

The lower limit of the use temperature of steel pipes shall comply with the following provisions: -20℃ for steel pipes of various steel grades in GB/T21832 and GB/T21833; and 3.7.2 for steel pipes of various steel grades in GB13296., GB/T14976, GB/T12771 and GB/T24593.

The wall thickness of the pipe shall not exceed 8mm, and it shall be used in the state of solid solution (or stabilization) treatment: the allowable stress of each steel grade steel pipe can be selected from the allowable stress of the corresponding steel grade in GB/T 14976: the lower limit of the use temperature of each steel grade pipe shall be by the provisions of 3.7.2: the hardness (or tensile) test and non-destructive testing requirements of the pipe shall be specified in the design documents.

Second, the production process and quality control of Q345R straight seam welded steel pipe

1. The process flow of Q345R straight seam welded steel pipe

Including raw material uncoiling, forming, welding (straight seam double-sided submerged arc welding), internal and external weld bead removal, pre-correction, heat treatment, sizing and straightening, non-destructive testing (such as ultrasonic, magnetic flaw detection), pickling and water pressure testing.

(1) Welding process: butt joints are preferred to reduce stress concentration; the flux must meet high toughness requirements (-45℃ impact absorption energy ≥28J).

2. Quality inspection of Q345R straight seam welded steel pipe

(1) Nondestructive testing: including magnetic testing (detecting surface and near-surface defects) and penetration testing (coloring or fluorescence method).

(2) Ultrasonic testing: testing each steel plate, and the standard is implemented according to the contract requirements.

(3) Hardness control: Brinell hardness ≤200 HB to ensure material toughness.

Third, the performance advantages and application areas of Q345R straight seam welded steel pipe

1. Performance characteristics of Q345R straight seam welded steel pipe

(1) High strength and toughness: It has both high yield strength (340-450 MPa) and good low-temperature impact toughness (-20℃ impact energy ≥34J).

(2) Fatigue resistance and corrosion resistance: It is suitable for acidic environments (such as oil and gas pipelines containing hydrogen sulfide).

(3) Excellent weldability: Post-weld heat treatment (such as normalizing) can refine the grains and improve the performance of the weld (grain size reaches 5-8 levels).

2. Application fields of Q345R straight seam welded steel pipe

(1) Energy transportation: oil and natural gas pipelines, high-voltage transmission lines, nuclear power plant evaporator heat transfer tubes, etc.

(2) Pressure vessels: boiler gas bags, reactors, liquefied gas tanks, etc.

(3) Large projects: such as pressure steel pipes in hydropower projects (diameter can reach 6.2 meters).

Fourth, installation and use requirements of Q345R straight seam welded steel pipe

1. Installation specifications of Q345R straight seam welded steel pipe

(1) The deviation per meter is less than 3 mm when installed vertically, and the deviation is less than 1 mm when installed horizontally.

(2) Avoid welding branches at the weld, and there should be no weld in the bending area.

2. Post-weld treatment of Q345R straight seam welded steel pipe

(1) Heat treatment process: high-frequency induction heating (850-900℃ insulation for 20-60 seconds, air cooling), significantly refines the weld structure and increases the elongation to 31%-36%.

(2) Stress control: multi-layer welding needs to control preheating and post-heating to prevent reheating cracks (especially in the range of 380-550℃)

In summary, Q345R straight seam welded steel pipe has become the preferred material in key engineering fields due to its high strength, corrosion resistance, and excellent welding performance. In practical applications, it is necessary to strictly follow the production, testing, and installation specifications, and combine new heat treatment processes to improve performance.