1. Q: What standards govern the production of Q235 and Q345 pipes in China?
A: Common Chinese National Standards (GB/T) include:
For welded pipes: GB/T 3091 (for fluid transmission), GB/T 13793 (for structural purposes).
For seamless pipes: GB/T 8162 (structural), GB/T 8163 (for fluid service).
The material grades themselves are defined under GB/T 700 (Q235) and GB/T 1591 (Q345).
2. Q: How does the ductility and toughness of Q345 compare to Q235?
A: Q345 generally offers good ductility and significantly better low-temperature toughness than Q235 due to its alloying. Grades like Q345D or E are specifically designed for low-temperature service.
3. Q: What does the "Q" and the following letter (A, B, C, D, E) mean in these grades?
A: "Q" stands for Yield Strength ("Qu" in Chinese). The subsequent letters (A, B, C, D, E) denote the impact toughness grade and deoxidation process. 'A' has no impact requirement, while B, C, D, and E require Charpy V-notch tests at +20°C, 0°C, -20°C, and -40°C, respectively. 'E' also indicates fine grain practice.
4. Q: What are the main quality defects to inspect for in these pipes?
A: Common defects include surface imperfections (cracks, scarring, laminations), dimensional deviations (OD, wall thickness, ovality), weld defects (in welded pipes like lack of fusion, porosity), and improper heat treatment affecting mechanical properties.
5. Q: In the construction industry, how are these pipes connected?
A: Connection methods include welding (most common for structural joints), flange connections (for piping systems), threaded couplings (for smaller diameter pipes), and mechanical couplings like Victaulic®-style grooved systems.
