1. **What is the difference between P22 and P91?**
P22 is a chromium-molybdenum alloy steel containing about 2.25% chromium and 1% molybdenum. It offers good high-temperature strength and oxidation resistance compared to carbon steel. P91 is a higher-grade chromium-molybdenum-vanadium alloy steel containing about 9% chromium and 1% molybdenum, with additions of vanadium and niobium. P91 offers significantly higher strength, creep resistance, and oxidation resistance at elevated temperatures compared to P22. This allows for thinner walls in high-pressure/high-temperature piping systems. P91 also requires much stricter control during welding and heat treatment.
2. **What is the difference between A335 and SA335?**
There is essentially no technical difference in the material requirements between ASTM A335 and ASME SA335. ASTM A335 is the material specification developed by ASTM International for seamless ferritic alloy-steel pipe for high-temperature service. ASME SA335 is the ASME Boiler and Pressure Vessel Code (BPVC) adoption of the ASTM A335 specification. SA335 includes all the requirements of A335 but is published within the ASME code system and is the version *mandated* for use in ASME code stamped pressure equipment (like boilers and pressure vessels).
3. **What is the difference between A53 and A500 pipe?**
A53 pipe (ASTM A53) is a standard specification for black and hot-dipped galvanized welded and seamless steel pipe, commonly used for mechanical and pressure applications (like conveying fluids, steam, air, water, gas) and structural support. A500 pipe (ASTM A500) is a standard specification for cold-formed welded and seamless carbon steel structural tubing in various shapes (round, square, rectangular, etc.). It is specifically designed for structural applications (like building frames, bridges, columns) where high strength-to-weight ratio is important, but it is *not* intended for pressure piping applications.
4. **What is the thickness of P91 pipe?**
There is no single standard thickness for P91 pipe. The thickness of a P91 pipe is determined by the design requirements of the specific piping system it is used in. Design engineers calculate the required wall thickness based on factors like the internal pressure, temperature, pipe diameter, material allowable stress (which is high for P91), corrosion allowance, and applicable design codes (like ASME B31.1 or B31.3). P91 pipe is manufactured in standard pipe schedules (like Sch 40, 80, 160, XXS) or to specific custom wall thicknesses.
5. **What is the pressure rating of A500 pipe?**
ASTM A500 structural tubing **does not have a standard pressure rating**. It is designed and manufactured for structural applications, not for containing internal pressure. While the material itself has strength properties, the specification does not provide pressure ratings or hydrostatic test requirements for pressure service. Using A500 for pressure piping is **not recommended and can be unsafe**. For pressurized systems, pipes conforming to specifications like ASTM A53, A106, or A333 (depending on service) should be used, as they are designed, tested, and rated for pressure.
