1. Q: When is Super Duplex Stainless Steel (e.g., UNS S32750) pipe necessary?
A: Super Duplex (25Cr-7Ni-4Mo-N) is specified for even more aggressive environments: higher chloride content, higher temperatures, or the presence of H₂S (sour service). It has a higher Pitting Resistance Equivalent Number (PREN > 40) and strength than standard duplex, used in demanding subsea systems and deepwater developments.
2. Q: Why is Alloy 625 (UNS N06625) a preferred CRA for deepwater flexible pipes, jumpers, and clad liners?
A: Alloy 625 offers outstanding, broad-spectrum corrosion resistance (excellent pitting, crevice, SCC resistance), high strength, and excellent fatigue performance. It maintains these properties in sour, high-chloride, and high-temperature environments encountered in deepwater oil and gas production.
3. Q: What is the risk with using standard Austenitic 316L pipe in stagnant, chloride-containing, oxygenated water?
A: It is highly susceptible to Microbiologically Influenced Corrosion (MIC) and crevice/pitting corrosion under deposits. For such services (e.g., treated seawater injection systems), a more resistant grade like 6Mo austenitic (UNS S31254) or Duplex is often chosen.
4. Q: What is the "Quench and Temper" (Q&T) process, and which grades require it?
A: Q&T is a heat treatment where the steel is austenitized, rapidly quenched to form martensite, and then tempered to achieve a fine-grained microstructure with high strength and good toughness. All high-strength API 5L PSL2 pipes (X70 and above) and alloy steels like A335 P91/P92 are Q&T.
5. Q: What does a "Sour Service" qualification test package typically include for an X65 pipe?
A: It goes beyond standard tests and includes: 1) HIC Test (NACE TM0284 Solution A, B, or C), 2) SSC Test (NACE TM0177 Method A tensile test or Method C four-point bend on stressed coupons), 3) Hardness Survey (to ensure HAZ hardness is below NACE MR0175/ISO 15156 limits, typically 250 HV10), and 4) Detailed chemistry control (low S, Ca treatment).
