1. Q: In what aggressive service is ASTM A335 P92 used?
A: P92 (9Cr-0.5Mo-1.8W-V-Nb) is an advanced CSEF steel with tungsten addition. It is used for the hottest sections of ultra-supercritical (USC) power plants, with steam temperatures exceeding 620°C (1148°F), where it provides the highest creep rupture strength among commercially available ferritic alloys.
2. Q: What is the primary limitation of standard A335 grades like P5 or P9 in modern refining?
A: Standard P5 (5Cr-0.5Mo) and P9 (9Cr-1Mo) have lower resistance to high-temperature sulfidation corrosion compared to higher chromium austenitic steels or modified alloys. They may be inadequate for certain high-sulfur crude processing units, where stainless-clad or solid 300-series stainless pipes are used.
3. Q: What is the difference between ASTM A106 Grade B and ASTM A53 Grade B?
A: Both are common carbon steel process pipes. A106 is seamless and is mandated for high-temperature service (e.g., refinery process lines). A53 can be seamless or welded (ERW/FBW) and is generally for lower temperature/pressure applications (e.g., utilities, water lines). A106 has stricter chemistry and tensile requirements, making it more suitable for critical service.
4. Q: When would you select ASTM A106 Grade C over Grade B?
A: Select Grade C for higher pressure applications where a higher minimum yield strength (40,000 psi vs. 35,000 psi for Grade B) allows for a thinner wall (per ASME B31.3 code calculations), reducing weight and cost, provided the increased carbon content doesn't adversely affect weldability for the specific fabrication.
5. Q: What is the key application driver for using Duplex Stainless Steel (e.g., UNS S31803/S32205) pipe?
A: Duplex pipes are used for handling chlorides. They combine high strength (about 2x 316L) with excellent resistance to chloride stress corrosion cracking (SCC), pitting, and erosion-corrosion. Common applications include offshore seawater systems, subsea flowlines with high CO₂/Cl⁻, and topside process piping.
