Power Generation Alloy Steel ASTM A335 P91 Pipe Seamless
ASTM A335 P91 Seamless Alloy Steel Pipe For Power Generation
Specification
ASTM A335 P91 Alloy Steel Pipe is a seamless, ferritic alloy steel pipe designed for severe high-temperature and high-pressure service, featuring high strength, creep resistance, and oxidation resistance due to its composition of ~9% Chromium, ~1% Molybdenum, plus Vanadium and Niobium, making it ideal for power plants (supercritical boilers), refineries, and petrochemical facilities. It's a highly refined material produced by precise heat treatments (normalizing and tempering) for superior performance in demanding environments, outperforming older grades like P22.
| American Standard | Standard Name |
| A335 / A335M | Standard Specification for Seamless Ferritic Alloy-Steel Pipe for High-Temperature Service |
ASTM A335 P91 Alloy Steel Pipe Chemical Composition
Sources American Standard A335 / A335M TABLE 1 Chemical Requirements
| ASTM A335 Grades |
UNS Designation |
C | Mn | P | S | Si | Cr | Mo | Others |
| P91 Type 1 | K90901 | 0.08-0.12 | 0.30-0.60 | 0.02 | 0.01 | 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 Nb F 0.06-0.10 Ti 0.01 max Zr 0.01 max |
| P91 Type 2 Heat | K90901 | 0.08-0.12 | 0.3-0.5 D | 0.020 D | 0.005 D | 0.20-0.40 D | 8.0-9.50 D | 0.85-1.05 | V Heat 0.18-0.25 Ni 0.20 max D Al 0.020 max D N 0.035-0.070 D N/Al ratio ≥4.0 Nb F Heat 0.06-0.10 Ti 0.01 max D Zr 0.01 max D Sn 0.010 max D Sb 0.003 max D As 0.010 max D B 0.001 max D W 0.05 max D Cu 0.10 max D |
| P91 Type 2 Product | K90901 | 0.07-0.13 | 0.3-0.5 D | 0.020 D | 0.005 D | 0.20-0.40 D | 8.0-9.50 D | 0.80-1.05 | V Product 0.16-0 27 Ni 0.20 max D Al 0.020 max D N 0.035-0.070 D N/Al ratio ≥4.0 Nb F Product 0.05-0.11Ti 0.01 max D Zr 0.01 max D Sn 0.010 max D Sb 0.003 max D As 0.010 max D B 0.001 max D W 0.05 max D Cu 0.10 max D |
| A New designation established in accordance with Practice E527 and SAE J1086, Practice for Numbering Metals and Alloys (UNS). B Grade P5c shall have a titanium content of not less than 4 times the carbon content and not more than 0.70 %; or a niobium content of 8 to 10 times the carbon content. C Alternatively, in lieu of this ratio minimum, the material shall have a minimum hardness of 275 HV in the hardened condition, defined as after austenitizing and cooling to room temperature but prior to tempering. Hardness testing shall be performed at mid-thickness of the product. Hardness test frequency shall be two samples of product per heat treatment lot and the hardness testing results shall be reported on the material test report. D Applies to both heat and product analyses. E Chromium-Nickel Balance is defined as CNB = (Cr + 6Si + 4Mo + 1.5W + 11V + 5Nb + 9Ti + 12Al) – (40C + 30N + 4Ni + 2Mn + 1CU). F The terms Niobium (Nb) and Columbium (Cb) are alternate names for the same element. |
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ASTM A335 P91 Alloy Steel Pipe Mechanical Properties
Sources American Standard A335 / A335M TABLE 3 Tensile Requirements
| ASTM A335 Grade |
UNS Designation |
Yield strength, Min:ksi/MPa |
Tensile strength, Min:ksi/MPa |
Elongation Requirements % (Min) | Hardness Requirements (Max) | ||
| Brinell | Vickers | Rockwell | |||||
| P91 Type 1 and Type 2 | K91560 | 60/415 | 85/585 | 20 | 190 to 250 HBW | 196 to 265 HV | 91 HRBW to 25 HRC |
ASTM A335 P91 Alloy Steel Pipe Heat Treatment
Sources American Standard A335 / A335M TABLE 2 Heat Treatment Requirements A
| ASTM A335 Grade | Heat Treatment Type | Normalizing Temperature Range F [C] | Cooling Media | Subcritical Annealing or Tempering Temperature,min or range“F[°C] |
| P91 Type 1 and Type 2 | normalize and temper or | 1900-1975 [1040 - 1080] | - | 1350-1470 [730 - 800] C |
| quench and Temper | 1900-1975 [1040 - 1080] | - | 1350-1470 [730 - 800] | |
| A Where ellipses (_) appear in this table there is no requirement. B Alternatively, Grade P36, Class 2 shalbe cooled from the austenitizing temperature by accelerated cooling in air or by liquid quenching. C Except when Supplementary Requirement S7 is specified by the purchaser. D Accelerated cooling from the normalizing temperature shall be permited for section thicknesses greater than 3 in. [75 mm). |
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ASTM A335 P91 Alloy Steel Pipe Permissible Variations in Outside Diameter
Sources American Standard A335 / A335M TABLE 7 Permissible Variations in Outside Diameter
| NPS [DN] Designator | Over | Under | ||
| in. | mm | in. | mm | |
| 1/8 to 1 1/2 [6 to 40], incl. | 1/64 (0.015) | 0.4 | 1/64 (0.015) | 0.4 |
| Over 1 1/2 to 4 [40 to 100], incl. | 1/32 (0.031) | 0.79 | 1/32 (0.031) | 0.79 |
| Over 4 to 8 [100 to 200], incl. | 1/16 (0.062) | 1.59 | 1/32 (0.031) | 0.79 |
| Over 8 to 12 [200 to 300], incl. | 3/32 (0.093) | 2.38 | 1/32 (0.031) | 0.79 |
| Over 12 [300] | +/- 1% of the specified outside diameter | |||
ASTM A335 P91 Alloy Steel Pipe Permitted Variations in Wall Thickness
Sources American Standard A335 / A335M TABLE 8 Permitted Variations in Wall Thickness
| NPS [DN] Designator | Tolerance, % from Specified | |
| Over | Under | |
| 1/8 to 2 1/2 [6 to 65] incl., all t/D ratios | 20.00% | 12.50% |
| Above 2 1/2 [65], t/D < or = 5% | 22.50% | 12.50% |
| Above 2 1/2 [65], t/D > 5% | 15.00% | 12.50% |
| (t = Specified Wall Thickness; D = Specified Outside Diameter) | ||
ASTM A335 P91 Alloy Steel Pipe Manufacturing Proces
ASTM A335 P91 Alloy Steel Pipe Application
- Power Generation
- High-temperature and high-pressure steam lines power plants
- Main steam pipes and hot reheat steam pipes
- Boiler superheater and reheater headers and connecting pipes.
- Turbine bypass systems and other critical high-energy piping.
- Petrochemical & Refining Industries
- Transfer lines in fluid catalytic cracking (FCC) units.
- High-temperature piping in hydrocracking
- Steam methane reformer manifolds and outlet headers.
- High-temperature heat exchanger piping.
- Industrial Heating & Process Piping:
- Piping systems in high-temperature industrial
- High-temperature process gas and steam transfer lines
ASTM A335 P91 Alloy Steel Pipe Packing & Loading
a. 1/2"-2"Plain end with black oil paint, caps both ends, bundles with loading belt.
b. 2"-4"Beveled end with black oil paint, caps both ends, bundles with loading belt.
c. 10"-20"Beveled end with black oil paint, caps both ends, loose packed in to container.
→Alloy Steel Pipes is transported in containers
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