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What is P9 Alloy Steel (9% chromium-1% molybdenum)?
Quick answer
- Definition
- P9 / T9 is a 9% chromium, 1% molybdenum alloy steel with higher oxidation and sulphidation resistance than 5Cr, used for refinery heater tubes and high-temperature process piping.
- Family
- Chromium-molybdenum alloy steel
- Key strength
- 8–10% Cr, 1% Mo
- Main forms
- Pipes, Tubes, Plates, Fittings, Flanges
- Typical uses
- Fired heater and furnace tubes; Refinery high-temperature process piping; Hydrocracker and reformer lines
With 8–10% chromium and about 1% molybdenum, 9Cr-1Mo resists high-temperature oxidation, sulphidation and hydrogen attack better than 5Cr-½Mo, and has good strength at temperature. It's widely used for fired heater tubes and furnace piping in refineries.
It's air-hardening, so welding needs careful preheat, interpass control and PWHT. Where creep strength is the priority, the vanadium-niobium-modified P91 has largely replaced P9 in power plants.
Key characteristics
- 8–10% Cr, 1% Mo
- Good resistance to sulphidation and hydrogen attack
- Air-hardening: strict welding procedures
- Refinery heater tubes and furnace piping
What are the specifications and equivalents of P9?
| Product form | Specification / designation | Product page |
|---|---|---|
| Pipes | ASTM A335 P9 | P9 pipes → |
| Tubes | ASTM A213 T9 | P9 tubes → |
| Plates | ASTM A387 Grade 9 | P9 plates → |
| Fittings | ASTM A234 WP9 | P9 fittings → |
| Flanges | ASTM A182 F9 | P9 flanges → |
Standards: ASTM A213, ASTM A387, ASTM A182, ASTM A234, ASTM A335.
What is the chemical composition of P9?
| Element | Limit (%) |
|---|---|
| C | 0.15 max |
| Mn | 0.30 – 0.60 |
| P | 0.025 max |
| S | 0.025 max |
| Si | 0.25 – 1.00 |
| Cr | 8.00 – 10.00 |
| Mo | 0.90 – 1.10 |
What are the mechanical properties of P9?
| Property | Value |
|---|---|
| Tensile strength | 415 MPa (60 ksi) |
| Yield strength (0.2% offset) | 205 MPa (30 ksi) |
| Elongation | 30% (longitudinal) |
Physical properties and service temperature
| Property | Value |
|---|---|
| Density (typical) | 7.8 g/cm³ (7800 kg/m³) |
| Magnetism | Magnetic (ferritic/martensitic). |
| Heat treatment | Supplied annealed, or normalised and tempered, per specification. |
| Service temperature | Designed for elevated-temperature pressure service. |
How is P9 welded and fabricated?
Requires preheat, interpass control and post-weld heat treatment.
Always follow a qualified welding procedure (for example ASME Section IX) and the filler-metal recommendations for P9. Verify incoming material by PMI and check the mill test certificate against the specification.
Which P9 products do we supply?
P9 Alloy Steel (9% chromium-1% molybdenum) is available in 5 product forms, from ready stock or mill-sourced to your specification, with EN 10204 3.1 mill test certificates (3.2 with third-party inspection on request).
P9 TubesASTM A213 T9Specification & sizes
How it's madeSeamless tubes are hot-extruded or pierced and then cold-drawn or pilgered to size. Welded tubes are formed from strip, welded (TIG/laser/HF), bead-worked and drawn or sized. Heat-exchanger and boiler tubes are annealed after final forming, and U-tubes are bent and stress-relieved as required.
- Specification
- ASTM A213 T9
- Size range
- OD 3 mm to about 127 mm (¼" to 5") typical, wall 0.5 mm to 12 mm; BWG or mm; straight lengths up to about 30 m, U-bent to drawing
- Finish
- Annealed & pickled, bright annealed (BA), polished (sanitary), cold-drawn
- Ends
- Plain square-cut, deburred; U-bends with stress-relieved bends on request
Testing & documents
- Eddy-current and/or ultrasonic testing on each tube
- Hydrostatic or pneumatic test
- Flattening, flaring and flange tests
- Grain size (H grades), IGC and hardness when specified
- Surface roughness (Ra) for sanitary and instrumentation tube
- EN 10204 3.1 certificate; 3.2 with third-party inspection
P9 PlatesASTM A387 Grade 9Specification & sizes
How it's madeSlabs are hot-rolled on a reversing plate mill (or a Steckel/hot-strip mill for thinner plate), then heat treated (annealed, normalised, or quenched and tempered, depending on material), descaled and pickled or shot-blasted. Plates are cut to size by plasma, oxy-fuel, waterjet or shearing.
- Specification
- ASTM A387 Grade 9
- Size range
- Thickness about 3 – 150 mm (and heavier on request), widths 1,000 – 3,000 mm, lengths 2,000 – 12,000 mm; cut-to-size and profile-cut parts
- Finish
- No.1 (hot-rolled, annealed and pickled) for stainless; shot-blasted, mill scale or primed for carbon steel
- Ends
- Mill edge, sheared, plasma or waterjet cut, profile cut to drawing
Testing & documents
- Chemical analysis and tensile tests (per plate or heat)
- Impact tests for low-temperature and pressure-vessel plates
- Ultrasonic testing (e.g. ASTM A435 / A578) when specified
- IGC, HIC and simulated PWHT tests as required
- Flatness and dimensional inspection
- EN 10204 3.1 certificate; 3.2 with third-party inspection
P9 FittingsASTM A234 WP9Specification & sizes
How it's madeButt-weld fittings are formed from seamless or welded pipe or plate by hot or cold forming (mandrel bending, hydraulic bulging, pressing), then heat treated, bevelled and finished. Socket-weld and threaded fittings are machined from forgings or bar.
- Specification
- ASTM A234 WP9
- Size range
- Butt-weld ½" – 48" (larger fabricated to order) in schedules matching the pipe; socket-weld and threaded ⅛" – 4" in Class 2000, 3000, 6000 and 9000
- Finish
- Annealed & pickled, shot-blasted, black painted or galvanised (by material)
- Ends
- Bevelled (butt-weld), socket-weld, threaded NPT/BSP
Testing & documents
- Chemical and mechanical tests of the starting material
- Dimensional inspection to B16.9 / B16.11
- Radiography of welded fittings (seamed WPW/WX)
- Hardness, IGC and impact tests as specified
- EN 10204 3.1 certificate; 3.2 with third-party inspection
P9 FlangesASTM A182 F9Specification & sizes
How it's madeFlanges are forged from billets (or cut from plate for some blind and plate flanges), heat treated to the material specification, and machined: bore, face, raised face or ring groove, bolt holes and hub bevel.
- Specification
- ASTM A182 F9
- Size range
- NPS ½" – 24" (B16.5), 26" – 60" (B16.47 Series A/B); Class 150, 300, 600, 900, 1500, 2500; EN 1092-1 PN 6 – PN 100 on request
- Finish
- Raised face (RF), flat face (FF) or ring-type joint (RTJ); serrated spiral or concentric face finish (typically 3.2 – 6.3 µm Ra)
- Ends
- Weld-neck bevel matched to pipe schedule; socket bore; threaded
Testing & documents
- Chemical and mechanical tests of the forging
- Dimensional inspection to ASME B16.5 / B16.47
- Hardness, impact and IGC tests as specified
- Ultrasonic testing of forgings on request
- EN 10204 3.1 certificate; 3.2 with third-party inspection
Where is P9 used?
Typical applications
- Fired heater and furnace tubes
- Refinery high-temperature process piping
- Hydrocracker and reformer lines
- Heat exchangers for hot oil
Where do we supply P9?
P9 is regularly requested for projects in these markets:
What should you specify when buying P9?
- Grade and specification, e.g. ASTM A335 P9
- Product form, size and tolerance
- Heat treatment / condition and surface finish
- Quantity, delivery location and required date
- Tests: PMI, hydro/NDT, IGC, impact or hardness as required
- Certificate type (EN 10204 3.1 / 3.2) and third-party inspection
See our RFQ checklist guide and what drives metal prices.
Explore more on P9
Comparisons & articles
Related grades
Frequently asked questions
What is the difference between P9 and P91?
P91 is a modified 9Cr-1Mo steel with vanadium, niobium and nitrogen, giving much higher creep strength. P9 is the older, unmodified grade used mainly in refinery heaters.
What is P9 used for?
Fired heater and furnace tubes, Refinery high-temperature process piping, Hydrocracker and reformer lines, Heat exchangers for hot oil. It's used across Oil & Gas, Petrochemical & Refining, Power Generation.
What is the UNS number of P9 / T9 / Grade 9 (9Cr-1Mo)?
P9 / T9 / Grade 9 (9Cr-1Mo) has no UNS designation. See the specification notes above.
Which product forms is P9 available in?
Pipes, Tubes, Plates, Fittings, Flanges, to ASTM A335 P9, ASTM A213 T9, ASTM A387 Grade 9 and related specifications.
What is the density of P9 / T9 / Grade 9 (9Cr-1Mo)?
About 7.8 g/cm³ (7800 kg/m³), used for weight calculations.
Is P9 / T9 / Grade 9 (9Cr-1Mo) magnetic?
Magnetic (ferritic/martensitic).
What temperature can P9 withstand?
Designed for elevated-temperature pressure service.