1. Q: Why is "Drop Weight Tear Testing" (DWTT) critical for Arctic-grade pipes like X65 or X70?
A: For pipelines operating in low-temperature environments, ductile fracture propagation is a major concern. DWTT determines the shear Area Percentage (SA%) at the design temperature. A high SA% (e.g., >85% at -40°C) ensures the pipe will arrest a running ductile fracture, which is a key safety requirement for Arctic service.
2. Q: Why does welding P91/P92 pipe require a specific Post-Weld Heat Treatment (PWHT) cycle?
A: P91/P92's high strength comes from a specific tempered martensitic structure. Welding creates a soft HAZ. A precise PWHT (e.g., 760°C ± 10°C for P91) is mandatory to retemper the HAZ, restore toughness, relieve stresses, and homogenize the microstructure to achieve the required creep strength in the weld region.
3. Q: What is "Galvanic Corrosion" risk when connecting a CS (A106B) pipe to a 316L stainless pipe, and how is it mitigated?
A: The carbon steel, being anodic to stainless steel, will corrode preferentially. Mitigation includes: using insulating flange kits, applying protective coatings on the CS pipe extending from the joint, or using a sacrificial anode. Cathodic protection must be carefully designed to avoid over-protection and hydrogen charging of the SS.
4. Q: What is "Erosion-Corrosion" and which pipe grades are most susceptible?
A: It's material loss due to combined mechanical erosion (from sand, droplets, turbulence) and electrochemical corrosion. Soft materials (e.g., copper-nickels) and thin passive films (on carbon steel) are susceptible. For severe service (e.g., sand-producing wells), hard CRAs like Duplex, Inconel 625, or internally clad pipes are specified.
5. Q: What are "Risers" and why are they often a different grade/material than the flowline?
A: Risers are vertical pipes connecting seabed flowlines to the surface facility. They experience dynamic fatigue from waves/vessel motion, higher temperatures/pressures, and are critical safety components. They often use higher grades (X80, special QT steels), thicker walls, or fatigue-resistant materials (e.g., clad pipe, flexible pipe with Alloy 625 layers) compared to static flowlines.
