Alloy Steel A335 P91 Seamless Pipe, ASME SA 335 Alloy Steel P91 Pipe

ASTM A335 Grade P91, also known as ASME SA335 Grade P91 Pipes, are ferritic chrome-moly alloy steel pipes primarily utilized in high-temperature applications. The UNS designation for Grade P91 is K91560.

The key components are Molybdenum (Moly) and Chromium (Chrome), imparting specific properties like improved corrosion resistance, increased strength, creep resistance, and wear resistance to the pipes. Additionally, P91 pipes contain small amounts of other alloys such as aluminum, columbium, nickel, nitrogen, titanium, vanadium, and zirconium. While these pipes adhere to the A335 standard, they can also fall under the A369 standard when forged or bored. With a minimum yield strength of 415 MPa and a minimum tensile strength of 585 MPa, these pipes have an elongation limit ranging from 20% to 30%. The enhanced creep strength and durability of ASTM A335 GR. P91 pipes are achieved through a heat treatment process involving normalization at 1500°C, air cooling at 200°C, and tempering by heat at 760°C.

These exceptional properties make P91 pipes well-suited for industrial plants, factories, and refineries where they are used to transport fluids and gases like water, oil, and steam at extremely high temperatures. Their high wear resistance ensures prolonged durability, making them highly cost-effective. These pipes can operate continuously at temperatures as high as 650°C.

Heat Treatment:

All pipes shall be reheated for heat treatment and heat-treated by the requirements of Table 1.

TABLE 1 Heat Treatment Requirements A

Grade	Heat Treat Type	Normalizing Temperature, min or range °F [°C]	Cooling Media	Subcritical Annealing or Tempering Temperature, min or range °F [°C]
P91 Type 1	normalize and temper or	1900–1975 [1040–1080]	—	1350–1470 [730–800]C
P91 Type 2	quench and temper	1900–1975 [1040–1080]	—	1350–1470 [730–800

A Where ellipses (–) appear in this table there is no requirement.

Chemical Composition of ASTM A335 Gr. P1 Pipes

Grade	UNS Designation A	Carbon	Manganese	Phosphorus, max	Sulfur, max	Silicon	Chromium	Molybdenum	Others
P91 Type 1	K21590	0.08-0.12	0.30–0.60	0.020	0.010	0.20-0.50	8.00-9.50	0.85-1.05	V 0.18–0.25 N 0.030–0.070 Ni 0.40 max Al 0.02 max Cb 0.06–0.10 Ti 0.01 max Zr 0.01 max
P91 Type 2	K21590	0.08-0.12 0.07-0.13	0.30–0.50D	0.020D	0.005D	0.20-0.40D	8.00-9.50D	0.85-1.05 0.80-1.05	V Heat 0.18–0.25 Product 0.16–0.27 Ni 0.20 maxD Al 0.020 maxD N 0.035–0.070D N/Al ratio $4.0 Cb Heat 0.06–0.10 Product 0.05–0.11 Ti 0.01 maxD Zr 0.01 maxD Sn 0.010 maxD Sb 0.003 maxD As 0.010 maxD B 0.001 maxD W 0.05 maxD Cu 0.10 maxD

A New designation established in accordance with Practice E527 and SAE J1086, Practice for Numbering Metals and Alloys (UNS).

Mechanical properties of ASTM A335 Gr. P1 Pipes

Grade	Tensile strength, min:		Yield strength, min:		Elongation Requirements
	KSI	MPa	KSI	MPa	Longitudinal	Transverse
P91 Type 1 and Type 2	85	585	60	415	20

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