Q: Why is post-weld heat treatment (PWHT) performed on some alloy steel pipes?
A: To relieve residual stresses, improve toughness in the HAZ, and enhance resistance to stress corrosion cracking.
Q: What is the typical maximum service temperature for carbon steel pipes like ASTM A106 Grade B?
A: Approximately 425°C (800°F) for continuous service. Above this, oxidation and loss of strength become significant.
Q: What property does a "G" suffix indicate in API 5L grades (e.g., X52 G)?
A: The "G" denotes "Grade," but in the context of ordering, it's part of the standard grade designation.
Q: What causes "weld line corrosion" in some welded pipes, and how is it mitigated?
A: It's caused by microstructural differences in the HAZ. Mitigation includes using low-carbon grades (e.g., 316L), solution annealing, or using corrosion-resistant weld overlays.
Q: What is the main advantage of using thermo-mechanically controlled processed (TMCP) steel for line pipe?
A: It provides high strength and good toughness without requiring high alloy content, improving weldability and reducing costs.
