| 1. What is a major corrosion concern for welded X65/X70 carbon steel pipelines in CO2-containing environments? | Preferential Weld Corrosion (PWC), where the weld metal (WM) and heat-affected zone (HAZ) corrode faster than the parent metal due to galvanic differences-7. |
| 2. What primarily drives Preferential Weld Corrosion (PWC)? | PWC is generated by a galvanic corrosion mechanism due to dissimilarities in composition and microstructure between the parent metal, weld metal, and HAZ-7. |
| 3. What is the most dangerous type of defect in a pipeline girth weld? | Cracks are the most dangerous defects as they act as stress concentrators and can lead to catastrophic failure-8. |
| 4. What are the main factors influencing the formation of welding cold cracks in high-strength steels like X70? | The three main factors are: the hardenability of the steel, the amount of diffusible hydrogen in the weld, and the level of restraint stress-8. |
| 5. What is "knife-line" attack in the context of stainless steel welds? | It is a form of localized corrosion that can occur in the very narrow zone immediately adjacent to the weld fusion line in stabilized grades (e.g., 321, 347), typically after exposure to high temperatures-10. |
