ASTM A335 P11 vs P22

Comparison of ASTM A335 P11 and P22 seamless alloy steel pipes:

ASTM A335 is the standard for seamless ferritic alloy steel pipes for high temperature use, including low alloy steel and high alloy steel, suitable for high temperature and high pressure environments such as power station boilers and petrochemicals. Among them, P11 and P22 are two common chromium-molybdenum alloy steels, which have significant differences in chemical composition, mechanical properties, temperature resistance and application fields. The following is a detailed comparison of the two:

1. Chemical composition comparison

Element	C	Mn	P	S	Si	Cr	Mo
P11(%)	≤0.15	0.30~0.60	≤0.025	≤0.025	0.50~1.00	1.00~1.50	0.44~0.65
P22(%)	≤0.15	0.30~0.60	≤0.025	≤0.025	0.50~1.00	1.90~2.60	0.87~1.13

Key differences:

Cr and Mo in P22 Higher content, making it more resistant to oxidation and creep at high temperatures.

P11 has a lower alloy content and lower cost, but its high temperature resistance is relatively weak.

2. Mechanical properties comparison

Performance	Tensile strength (MPa)	Yield strength (MPa)	Elongation (%)	Maximum operating temperature (℃)
P11	≥415	≥205	≥30	≤550
P22	≥415	≥205	≥30	≤600

Key differences:

P11 is suitable for medium temperature and high pressure environments, such as petrochemical pipelines. The maximum operating temperature is 540℃ (560℃ for a short time), and the endurance strength at 550℃ is not applicable (the design temperature is lower than 550℃) ‌
P22 has a higher applicable temperature and is more suitable for high temperature applications such as supercritical boilers. The maximum operating temperature is 580℃ (620℃ for a short time), and the endurance strength at 550℃ is not specified.

Heat treatment requirements:

Heat treatment process:
P11: Normalizing (900~950℃) + tempering (650~750℃)
Purpose: Optimize the structure and improve toughness.

P22: Normalizing (900~950℃) + tempering (680~750℃)
Purpose: Improve high temperature strength and creep resistance. The tempering temperature of P22 is slightly higher to ensure higher high temperature stability.

Application scenario:

‌P11‌: Widely used in subcritical boiler low temperature superheaters (<540℃), high temperature superheaters (540~560℃) in the power industry, low temperature steam pipelines in petrochemicals, atmospheric pressure heat exchangers, etc. Due to its good heat resistance and creep resistance, it is also suitable for high temperature hydrogenation reactor feed pipelines and cracking furnaces. Applicable to medium and high pressure environments of ≤550℃, more economical.

‌P22‌: Mainly used for superheaters, economizers (high temperature section tube bundles), headers and main steam ducts of high pressure, ultra-high pressure and subcritical power plant boilers in high temperature environments. Its high chromium and high molybdenum content gives it excellent tensile strength and corrosion resistance at high temperatures. Applicable to high temperature and high pressure environments of ≤600℃.

Corresponding domestic and foreign brands:

Grade	European brand (EN)	Chinese brand (GB 5310)	Japanese brand (JIS)
P11	13CrMo4-5	15CrMoG	STBA22
P22	10CrMo9-10	12Cr2MoG	STBA24

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P11‌ and P22: How to choose?

P11: Applicable to medium temperature and medium pressure environments of ≤550℃ (such as refineries, medium temperature boilers, chemical equipment), more economical.

P22: Suitable for high temperature and high pressure environment ≤600℃ (such as power station boilers, supercritical units), with better oxidation resistance and creep strength.

Read more: SA335-P91 VS SA335-P22 or ASTM A213 T22 Boiler Tube