1. Q: What are the main cost drivers when purchasing Q235 vs. Q345 pipes?
A: The main drivers are raw material cost (Q345 is more expensive due to alloys), manufacturing process (seamless is more costly than welded), dimensions, quantity, surface coating, and testing/certification requirements. Q345 typically commands a 10-30% price premium over Q235.
2. Q: Can Q345B pipe be used in low-temperature environments?
A: Q345B has an impact test requirement at 20°C. It is suitable for general use but not specifically designed for low temperatures. For environments below 0°C, grades with better low-temperature toughness like Q345D (tested at -20°C) or Q345E (tested at -40°C) should be specified.
3. Q: How does the machinability of these two steels compare?
A: Q235, being softer and with lower tensile strength, generally has better machinability (easier cutting, drilling) than Q345. Machining Q345 may require more powerful equipment and can result in faster tool wear.
4. Q: What is the role of heat treatment for Q345 pipes?
A: Q345 pipes, especially seamless ones, are often supplied in a normalized (N) condition. Normalization refines the grain structure, improves mechanical property uniformity, enhances toughness, and relieves internal stresses from the forming process, making the pipe more suitable for critical applications.
5. Q: How does the performance of these pipes in fire conditions differ?
A: Both will lose strength at elevated temperatures. As a higher strength steel, Q345 may retain a higher absolute load capacity at a given elevated temperature, but its percentage strength retention relative to room-temperature strength is similar to Q235. Fire protection (e.g., intumescent coating, concrete encasement) is crucial for structural applications of both grades.
