1. Q: What is "cold expansion" of spiral pipe, and what is its purpose?
A: A mechanical process of slightly enlarging the pipe diameter after welding. It helps improve roundness, relieve residual stresses, and can increase yield strength.
2. Q: What is a key difference in the forming mechanics between spiral and longitudinal (LSAW) pipe?
A: Spiral forming induces a bending moment primarily in one direction along the strip, while LSAW (UOE) involves complex multi-step forming with different strain patterns.
3. Q: Can spiral pipe be produced to high-strength grades like X100?
A: Yes, it is technically possible, but it requires advanced steel and precise process control. X80 is more common; grades above X80 are less frequent for spiral weld.
4. Q: What is "lamellar tearing" risk, and how is it mitigated?
A: It's a cracking risk in the base metal under the weld due to through-thickness stresses and non-metallic inclusions. It's mitigated by using steel with good through-thickness ductility (low sulfur, calcium treatment for inclusion shape control).
5. Q: What role does the De-oxidizer (like Silicon, Aluminum) play in pipe steel chemistry?
A: They remove excess oxygen from the molten steel, improving soundness and toughness. Aluminum also helps refine the grain structure.
