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ASTM A335 Grade P91 is a premium-grade alloy steel pipe designed for high-pressure boiler applications. It is particularly well-suited for bending, flanging, and welding, making it a reliable choice for demanding operational environments. The steel material must strictly adhere to chemical composition, tensile properties, and hardness requirements to ensure performance and durability.
Super Steel Manufacturing Co.,Ltd is professional ASTM A335 P91 alloy steel pipe manufacturer, for more details, please contact:sales@super-steels.com
Specifications of ASTM A335 P91 Seamless Alloy Steel Pipes
Outer Diameter: 19.05mm – 114.3mm
Wall Thickness: 2.0mm – 14mm
Maximum Length: 16,000mm
Chemical Composition(%) of ASTM A335 P91 Pipe
|
Compositions |
Data |
|
UNS Designa-tion |
K91560 |
|
Carbon |
0.08-0.12 |
|
Manganese |
0.30-0.60 |
|
Phosphorus(max.) |
0.025 |
|
Sulfur(max.) |
0.025 |
|
Silicon(max.) |
0.50 |
|
Nickel |
… |
|
Chromium |
4.00-6.00 |
|
Molybdenum |
0.45-0.65 |
|
Other Elements |
… |
Chromium (Cr) – High-Temperature Strength & Oxidation Resistance
Chromium, commonly known as chrome, plays a critical role in enhancing high-temperature strength and oxidation resistance. It is indispensable in preventing oxidation at elevated temperatures. Additionally, chromium increases tensile strength, yield strength, and hardness at room temperature.
Molybdenum (Mo) – Strength & Creep Resistance
Molybdenum contributes to higher strength, improved wear resistance, and enhanced impact toughness. It also:
Increases hardenability and prevents grain growth.
Reduces softening and minimizes embrittlement in chromium steel.
Serves as the most effective element for improving high-temperature creep resistance.
Enhances corrosion resistance and prevents pitting in steel.
Nickel (Ni) & Manganese (Mn) – Hardenability Enhancement
Nickel and manganese, present in smaller amounts, help improve the hardenability of the steel, ensuring uniform strength throughout the material.
Vanadium (V), Columbium/Niobium (Cb/Nb), and Nitrogen (N) – Creep Strength Optimization
The controlled addition of vanadium, niobium (also known as columbium), and nitrogen plays a significant role in enhancing creep strength, making the steel more resilient under prolonged high-temperature exposure.
Heat Treatment Process – Key to Superior Creep Strength
Beyond alloy composition, the heat treatment process is crucial for achieving the exceptional properties of ASTM A335 P91 steel. The process includes:
Normalizing: Heating the steel to 1050°C, followed by air cooling to 200°C.
Tempering: Reheating the material to 760°C to refine its microstructure.
Mechanical Properties of ASTM A335 P91 Pipe
|
Properties |
Data |
|
Tensile strength, min, (MPa) |
415 Mpa |
|
Yield strength, min, (MPa) |
205 Mpa |
|
Elongation, min, (%), L/T |
30/20 |
ASTM A335 P91 pipes must undergo rigorous mechanical testing to ensure compliance with industry standards. The specified tests include:
Transverse or Longitudinal Tension Test
Flattening Test
Hardness Test
Bend Test
Testing Requirements Based on Heat Treatment Method
Batch-Type Furnace Treatment:
Testing must be conducted on 5% of the pipes from each heat-treated lot.
For small lots, a minimum of one pipe must be tested.
Continuous Process Heat Treatment:
A sufficient number of pipes must be tested to constitute 5% of the lot, with a minimum of two pipes tested per lot.
Bend Test Requirements
Pipes with a diameter exceeding NPS 25 and a diameter-to-wall thickness ratio of 7.0 or less must undergo the bend test instead of the flattening test.
Pipes with a diameter equal to or greater than NPS 10 may be tested using the bend test instead of the flattening test, subject to purchaser approval.
Bend Test Procedure:
The test specimen is bent 180° at room temperature.
The pipe must withstand the bending process without cracking on the outer surface of the bent area.
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