Molybdenum for creep strength
Molybdenum keeps strength at temperature, so ½Mo and 1Mo steels carry steam and hot hydrocarbons where carbon steel would creep. Carbon steel is normally limited to about 425 °C in long-term service.
Alloy Steel
Chrome-moly alloy steels carry high-temperature, high-pressure steam and hydrocarbons in power plants and refineries. One chemistry appears under different letters in each product specification: P (pipe, A335), T (tube, A213), Grade (plate, A387), F (forgings, A182) and WP (fittings, A234). Bright Tubes supplies the complete P1–P91 family in all of those forms.
Alloy Steel grades
- P1 / T1 (C-½Mo)P1 / T1 is a carbon-½% molybdenum steel, the simplest of the ASTM A335/A213 creep-resistant grades, used for moderate-temperature pressure piping and tubes.
- P5 / T5 / Grade 5 (5Cr-½Mo)P5 / T5 is a 5% chromium, ½% molybdenum alloy steel for refinery and petrochemical service where high-temperature sulphidation and hydrogen attack must be resisted.
- P9 / T9 / Grade 9 (9Cr-1Mo)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.
- P11 / T11 / Grade 11 (1¼Cr-½Mo)P11 / T11 is a 1¼% chromium, ½% molybdenum alloy steel, one of the most widely used grades for steam piping, boiler tubes and refinery equipment operating up to about 550 °C.
- P22 / T22 / Grade 22 (2¼Cr-1Mo)P22 / T22 is a 2¼% chromium, 1% molybdenum alloy steel with higher creep strength than P11, widely used for high-temperature steam piping, headers and hydroprocessing reactors.
- P91 / T91 / Grade 91 (9Cr-1Mo-V)P91 / T91 is a modified 9% chromium, 1% molybdenum steel with vanadium, niobium and nitrogen, giving creep strength far above P22
One chemistry, five designations
Chrome-moly steels change their name with the product form. P91 pipe, T91 tube, F91 forgings, WP91 fittings and A387 Grade 91 plate are the same 9Cr-1Mo-V-Nb chemistry, each made to its own specification. Order every component of a line by its own designation.
| Chemistry | Pipe (A335) | Tube (A213) | Plate (A387) | Forgings (A182) | Fittings (A234) |
|---|---|---|---|---|---|
| P1 Carbon-½ molybdenum | A335 P1 | A213 T1 | — | A182 F1 | A234 WP1 |
| P5 5% chromium-½% molybdenum | A335 P5 | A213 T5 | A387 Grade 5 | A182 F5 | A234 WP5 |
| P9 9% chromium-1% molybdenum | A335 P9 | A213 T9 | A387 Grade 9 | A182 F9 | A234 WP9 |
| P11 1¼% chromium-½% molybdenum | A335 P11 | A213 T11 | A387 Grade 11 | A182 F11 | A234 WP11 |
| P22 2¼% chromium-1% molybdenum | A335 P22 | A213 T22 | A387 Grade 22 | A182 F22 | A234 WP22 |
| P91 Modified 9% chromium-1% molybdenum-vanadium | A335 P91 | A213 T91 | A387 Grade 91 | A182 F91 | A234 WP91 |
Why chromium and molybdenum, and how far they go
Chromium for oxidation and hydrogen
Chromium raises oxidation resistance and resistance to high-temperature hydrogen attack. Refinery hydrogen service is designed with the Nelson curves in API RP 941, which is why 1¼Cr, 2¼Cr and higher grades appear in hydroprocessing units.
From P11 to P91
As temperature and pressure rise, designers move from P11 and P22 to P91. P91's vanadium and niobium give much higher creep strength, so walls can be thinner in modern supercritical boilers.
Fabrication discipline
All Cr-Mo grades need preheat, interpass control and post-weld heat treatment. P91 is the least forgiving: wrong tempering or weld heat input leaves soft or brittle zones, so hardness checks after PWHT are routine.
What to put on an alloy steel order
- Designation per itemA335 P22 pipe, A234 WP22 fittings and A182 F22 flanges, not just "P22".
- Heat treatmentNormalised and tempered, with temperatures on the certificate; A387 Class 1 or 2 for plate.
- IBR or code stampIBR certification for Indian boilers; ASME code requirements for export.
- TestsPMI on every piece, hardness, and impact or step-cooling where the project calls for it.
Alloy Steel products by form
Alloy Steel: comparisons, charts & tools
Frequently asked questions
What is the difference between P11, P22 and P91?
They rise in creep strength: P11 (1¼Cr-½Mo) for moderate temperatures, P22 (2¼Cr-1Mo) for higher temperatures and hydrogen service, and P91 (9Cr-1Mo-V) for supercritical steam.
Is P91 the same as T91?
Same chemistry, different product specification: P91 is pipe (A335), T91 is tube (A213).
How many alloy steel grades do you supply?
6 grades and products, in 5 product forms: pipes, tubes, plates, fittings, flanges.
Which standards apply to alloy steel?
Do you export worldwide?
Yes: to the GCC, Southeast Asia, Europe, the USA, the UK and beyond, with export packing and documentation.
Looking for alloy steel?
Tell us the grade, form, specification, size, quantity and destination.