First, the material characteristics and standard specifications of Q345QC longitudinally welded steel pipe.
Q345QC is a low-alloy, high-strength steel specified in the GB/T 1591 standard. The “C” designation indicates that the material meets the 0°C impact test requirements. Its chemical composition keeps the carbon content below 0.2%. The addition of alloying elements such as manganese and silicon enhances strength, while microalloying elements such as niobium and vanadium refine the grain size. Its yield strength is ≥345 MPa, tensile strength is 470-630 MPa, elongation is ≥22%, and impact energy at -20°C is ≥34 J. These performance characteristics are significantly superior to those of ordinary Q235 steel. Compared to standard Q345, Q345QC offers the following advantages:
1. Low-temperature toughness: Strictly controlled phosphorus and sulfur content (both ≤ 0.025%) and the addition of nickel ensure resistance to brittle fracture in low-temperature environments.
2. Z-axis performance: Reduction of area through thickness ≥ 30%, effectively preventing lamellar tearing.
3. Weldability: Carbon equivalent (CEV) ≤ 0.45%, requiring a low preheating temperature (typically 100-150°C).
Second, key control points in the production process for Q345QC straight seam welded steel pipe.
The production process for straight seam welded steel pipe includes steel plate pretreatment → coiling → high-frequency welding → weld seam treatment → sizing and straightening → non-destructive testing.
1. Plate Pretreatment:
- Utilizes the Controlled Rolling and Controlled Cooling Process (TMCP) to ensure microstructure uniformity.
- Ultrasonic testing detects internal defects and eliminates substandard plates with delamination, inclusions, and other defects.
2. Welding Process:
- Utilizes high-frequency resistance welding (HFW) or submerged arc welding (SAW).
- Controls weld energy within the range of 15-25 kJ/cm2.
- Performs immediate post-weld heat treatment to eliminate residual weld stress.
3. Quality Inspection:
- 100% eddy current testing to verify weld continuity.
- Hydrostatic testing (Hydraulic pressure testing) is performed on samples from each batch (test pressure is 1.5 times the operating pressure).
- Charpy impact testing at -20°C to verify low-temperature toughness.
Third, Analysis of Typical Application Scenarios for Q345QC Longitudinal Welded Steel Pipe.
1. Energy Transportation:
- Oil and gas gathering and transportation pipelines: Common specifications range from 219 to 610 mm in diameter, with wall thicknesses of 6 to 20 mm.
- In western oil and gas field projects, Q345QC welded steel pipe can replace some imported pipes, reducing costs by 15-20%.
2. Engineering Machinery Structures:
- Critical load-bearing components such as crane booms and excavator chassis.
- Tests by a heavy machinery manufacturer show that replacing Q345B with Q345QC can reduce equipment weight by 8% while also increasing fatigue life.
3. Special Environment Applications:
- Polar research station building support structures.
- Offshore wind turbine conductors, with an anti-corrosion coating, can achieve a service life of 25 years.
Fourth, Market Status and Selection Considerations for Q345QC Straight Seam Welded Steel Pipe.
- Industrial Grade: Conforms to GB/T 3091 standard, priced approximately 5,000-6,000 yuan/ton.
- High-Pressure Fluid Grade: Complies with GB/T 9711 requirements, with a 20-30% price increase.
- Custom Grade: For example, nuclear power pipes require additional -40°C impact testing.
Key Considerations When Purchasing:
1. Actual chemical composition and mechanical property data in the warranty
2. Third-party inspection report (especially impact test curves)
3. Pipe end bevel processing accuracy (affects on-site welding quality)
4. Anti-corrosion solutions (commonly available include 3PE anti-corrosion and epoxy powder coating)
Fifth, Technical Development Trends of Q345QC Straight Seam Welded Steel Pipe
1. Material Upgrade: Some companies have developed Q420QC-grade welded steel pipe, increasing yield strength by 20%.
2. Smart Production: Some leading companies have introduced AI-powered visual inspection systems, achieving a 99.7% accuracy rate for weld defect detection.
3. Green Manufacturing: Using induction heating instead of gas heating reduces energy consumption by 40%.
According to industry forecasts, with the accelerated construction of oil and gas pipeline networks during the 14th Five-Year Plan period, annual demand for Q345QC welded steel pipe will exceed 3 million tons by 2025. When selecting a pipe, users should consider the specific operating conditions and focus on the pipe’s low-temperature toughness and welding procedure qualification report. If necessary, suppliers can be requested to provide performance verification data under simulated service conditions. Through reasonable material selection and standardized use, this high-performance welded steel pipe can provide reliable protection for various demanding projects.
Post time: Sep-26-2025