1. **What is ASME SA 335 grade P22?**
ASME SA-335 Grade P22 is a specification for seamless ferritic alloy-steel pipe intended for high-temperature service. It designates pipes made from a chromium-molybdenum alloy steel with a nominal composition of 2.25% Chromium and 1% Molybdenum. This grade is commonly used in power generation boilers, refineries, petrochemical plants, and other applications involving elevated temperatures and pressures. The "SA" prefix indicates it's an ASME specification, adopted from the base ASTM standard (A335) and incorporating additional ASME Boiler and Pressure Vessel Code (BPVC) requirements.
2. **What is a P22 pipe?**
A P22 pipe is a seamless pipe manufactured to meet the requirements of specifications like ASME SA-335 or ASTM A335 Grade P22. It is made from a specific chromium-molybdenum alloy steel (nominal 2.25% Cr, 1% Mo) chosen for its strength and resistance to oxidation and creep at elevated temperatures. P22 pipes are primarily used in critical high-temperature and high-pressure applications, such as steam lines, superheaters, reheaters, and headers in power plants, refineries, and process industries.
3. **What does grade P22 mean?**
The "Grade P22" designation refers to a specific alloy composition and set of mechanical properties within the A335/SA-335 specification. The "P" stands for "Pipe", differentiating it from tube grades (which would use "T", like T22). The number "22" historically corresponds to the nominal chromium content (approximately 2.25%) and the molybdenum content (approximately 1%) in the alloy. So, Grade P22 specifically identifies a low-alloy steel pipe containing about 2.25% Chromium and 1% Molybdenum, designed for high-temperature service.
4. **What is the allowable stress for A335 P22 pipe?**
The allowable stress for A335 P22 pipe is not a single fixed value; it varies significantly depending on the metal temperature. This stress is defined in the ASME Boiler and Pressure Vessel Code, Section II, Part D (Materials, Properties), specifically in the tables for Maximum Allowable Stress Values for Ferrous Materials. For example (illustrative ranges based on typical BPVC data):
* At room temperature (100°F / 38°C), it's approximately **17.9 ksi (123 MPa)**.
* At 800°F (427°C), it's approximately **7.8 ksi (54 MPa)**.
* At 1000°F (538°C), it's approximately **3.8 ksi (26 MPa)**.
* At 1100°F (593°C), it's approximately **2.0 ksi (14 MPa)**.
* At 1200°F (649°C), it's approximately **1.1 ksi (7.6 MPa)**.
**Critical Note:** For actual design, you MUST consult the latest edition of ASME BPVC Section II, Part D, Table 1A for the precise, code-mandated allowable stress values corresponding to the specific design temperature. Values change with code revisions and material heat treatment.
5. **What is ASTM A335 material specification?**
ASTM A335 is the base standard specification for seamless ferritic alloy-steel pipe designed for high-temperature service. It defines the chemical composition, mechanical properties (tensile strength, yield strength, elongation), heat treatment requirements (normalize and temper for P22), dimensions, tolerances, testing methods (hydrostatic, nondestructive electric test), and marking requirements for various grades of alloy steel pipes, including P5, P9, P11, P22, P91, etc. ASME SA-335 adopts this ASTM standard but includes additional requirements to make it acceptable for use in ASME Boiler and Pressure Vessel Code construction. Pipes conforming to ASTM A335 are primarily used in power plants, refineries, and chemical plants for critical high-temperature/pressure applications.
