Q: What does "O.D." and "Nominal Pipe Size" (NPS) refer to?
A: O.D. is the outside diameter. NPS is a standardized dimensionless designator for pipe size. For NPS ≥14, the O.D. equals the NPS in inches. For smaller sizes, O.D. is fixed but not equal to NPS.
Q: How does wall thickness typically relate to pressure rating?
A: For a given material and diameter, a thicker wall increases the pipe's pressure rating (hoop stress capability).
Q: What is a major global standard for pipelines competing with API 5L?
A: ISO 3183, which is largely harmonized with API 5L but has some regional (e.g., ISO 3183-3 for Arctic conditions) variants.
Q: What is the main challenge when welding high-strength grades like X80 or X100?
A: Achieving a weld and HAZ with matching strength and, more critically, sufficient toughness and resistance to hydrogen cracking, often requiring specific consumables and procedures.
Q: What is "clad or lined pipe," and why is it used?
A: A carbon steel pipe with a thin inner layer of corrosion-resistant alloy (stainless steel, nickel alloy) welded or bonded inside. It provides corrosion resistance at a lower cost than solid alloy pipe.
