P11 Alloy Steel Pipe Supplier — ASTM A335 P11 (1.25Cr-0.5Mo)

ASTM A335 P11 is a 1.25% chromium, 0.5% molybdenum alloy steel seamless pipe designed for elevated temperature service in power generation and process industries. The primary applications include boiler headers and stub connections, economiser inlet and outlet piping, intermediate-pressure steam piping, HRSG evaporator and superheater headers, and process piping in refineries and chemical plants operating between 400-550°C. P11 is the most widely used Cr-Mo grade in Indian thermal power plants for IBR-certified boiler piping.

ASTM A335 P11 pipe has an ASME allowable stress up to 565°C (1050°F) for pressure design calculations per ASME B31.1 Power Piping. Above 565°C, the allowable stress drops significantly and higher grades like P22 (2.25Cr-1Mo) or P91 (9Cr-1Mo-V-Nb) should be considered. In practice, P11 is commonly used for headers and piping where metal temperature does not exceed 540°C. For cyclic service (frequent startups/shutdowns), many designers limit P11 to 510°C to ensure adequate fatigue life.

P11 (1.25Cr-0.5Mo) and P22 (2.25Cr-1Mo) differ in chromium content and temperature capability. P22 has nearly double the chromium of P11, providing better oxidation resistance and higher creep strength above 500°C. At 565°C, P22 has approximately 20% higher allowable stress than P11. P22 is preferred for main steam and hot reheat piping while P11 is used for lower-temperature headers, economiser piping and intermediate-pressure steam. P11 is easier to weld and has a simpler PWHT requirement (650-700°C vs 690-730°C for P22).

Yes, Creative Metal Industries maintains dedicated IBR-certified stock of ASTM A335 P11 seamless pipe specifically for boiler and pressure vessel applications under Indian Boiler Regulations. We supply P11 pipe with IBR Form III-C from approved mills including ISMT India, Maharashtra Seamless, Sumitomo Japan and Vallourec France. Our IBR stock covers sizes from 1/2 inch to 24 inches in SCH 40 through XXS. Each pipe is individually marked with IBR stamp, heat number and grade, with full documentation for boiler inspector approval.

P11 (1.25Cr-0.5Mo) requires preheat of 150-200°C minimum before welding. Interpass temperature should be maintained at 150-300°C. Recommended filler metals are ER80S-B2 (GTAW) and E8018-B2 (SMAW) matching the 1.25Cr-0.5Mo composition. Post-weld heat treatment is mandatory at 650-700°C for minimum 1 hour per 25mm wall thickness. Maximum hardness after PWHT is 225 HBW. P11 is considered the easiest Cr-Mo grade to weld among the common P-grades, making it suitable for field welding applications.

We maintain comprehensive stock of ASTM A335 P11 seamless pipe from 1/2 inch (15NB) to 24 inches (600NB) in schedules SCH 40, 60, 80, 100, 120, 140, 160 and XXS (extra extra strong). For boiler tube applications, we stock ASTM A213 T11 from 3/4 inch to 4 inch OD. Standard random lengths 5-7 metres. We hold heavy-wall P11 stock (SCH 120 and above) specifically for boiler header and high-pressure economiser applications in BHEL and Thermax boiler projects.