What ASTM A335 Covers
ASTM A335 governs seamless pipe made from ferritic chrome-moly alloy steel for service where carbon steel would lose strength or scale. The specification, often cited as A335/A335M, fixes the chemistry, mechanical properties, heat treatment, dimensions, and testing for each grade. The grade designation starts with the letter P, for "pipe," followed by a number that echoes the alloy content: a higher number generally means more chromium.
These pipes are produced seamless, with no longitudinal weld, which suits the high pressures and thermal cycling of boiler and steam-header duty. Material is supplied in a heat-treated condition, typically annealed, normalized and tempered, or subcritical annealed depending on the grade, so that the microstructure is set for creep service before the pipe leaves the mill.
A335 pipe is the pressure-piping backbone of power generation and refining. For the stock itself, see our alloy steel pipe range, part of the wider industrial pipe program.
ASTM A335 Grades
The chrome-moly family runs from the lean 0.5% molybdenum P1 up to the 9% chromium creep-strength-enhanced P91. The chromium builds a protective oxide scale and the molybdenum resists creep, the slow deformation that carbon steel suffers under sustained load and heat. The table below summarizes the common A335 grades Nandini Steel stocks and their nominal chemistry.
| A335 Grade | Family | Nominal chemistry | Matching plate / forging | Typical service |
|---|---|---|---|---|
| P1 | Cr-Mo alloy steel | 0.5% Mo (carbon-moly) | A182 F1 | Moderate-temperature steam and oil lines |
| P11 | Cr-Mo alloy steel | 1.25% Cr, 0.5% Mo | A387 Gr 11 / A182 F11 | Boiler superheaters, hydrocarbon heaters |
| P12 | Cr-Mo alloy steel | 1% Cr, 0.5% Mo | A182 F12 | Steam piping, elevated-temperature lines |
| P22 | Cr-Mo alloy steel | 2.25% Cr, 1% Mo | A387 Gr 22 / A182 F22 | High-temperature steam headers, reformers |
| P5 | Cr-Mo alloy steel | 5% Cr, 0.5% Mo | A182 F5 | Refinery service with sulfur at temperature |
| P9 | Cr-Mo alloy steel | 9% Cr, 1% Mo | A182 F9 | High-sulfur, high-temperature refinery duty |
| P91 | Creep-strength Cr-Mo alloy steel | 9% Cr, 1% Mo, V-Nb-N | A182 F91 | Supercritical boiler and main steam lines |
For the companion plate grades, see ASTM A387 chrome-moly pressure-vessel plate and the SA387 Grade 11 and 22 hub. The wider alloy-steel catalog and grade logic sit on the alloy steel grades overview, and the family distinction is explained in carbon vs stainless vs alloy steel.
Why Chromium and Molybdenum Matter
At high temperature, two things defeat plain carbon steel: oxidation and creep. Chromium forms a tight oxide scale that slows attack, so the 5% and 9% chromium grades hold up in hot, sulfur-bearing refinery streams where lower grades would waste away. Molybdenum raises the creep rupture strength, letting the pipe carry pressure for years at temperature without stretching. The P91 grade adds vanadium, niobium, and nitrogen to form fine carbonitrides that pin the microstructure, pushing creep strength well above the older P22 for the same wall thickness.
Heat Treatment and Welding
Chrome-moly pipe is only as good as its heat treatment. A335 specifies the delivered condition per grade, and field welding almost always requires preheat and post-weld heat treatment (PWHT) to temper the hardened heat-affected zone and relieve residual stress. The higher the chromium, the more critical the thermal control: P91 in particular demands tight preheat, interpass, and PWHT windows, because an out-of-range cycle can leave the weld brittle or soft.
| Grade | Typical delivered condition | Welding note |
|---|---|---|
| P11 / P12 | Annealed or normalized and tempered | Preheat and PWHT per procedure |
| P22 | Annealed or normalized and tempered | Higher preheat, mandatory PWHT |
| P5 / P9 | Annealed | High preheat, matching filler, PWHT |
| P91 | Normalized and tempered | Strict preheat, interpass, and PWHT control |
Testing and Certification
A335 requires each length to pass a hydrostatic test, or an approved nondestructive electric test, before shipment. The mill verifies chemistry and mechanical properties against the grade, and hardness is commonly checked to confirm the heat treatment. Every order from Nandini Steel ships with an EN 10204 3.1 or 3.2 mill test certificate giving heat number, chemistry, and mechanical results for full traceability. See MTC, NDT and PMI testing and the EN 10204 certificate standard for what each document records.
| Requirement | ASTM A335 provision |
|---|---|
| Product form | Seamless pipe only |
| Pressure test | Hydrostatic test, or approved nondestructive electric test |
| Heat treatment | Per grade, annealed or normalized and tempered, verified |
| Chemistry and mechanicals | Per grade, reported on the mill test certificate |
| Documentation | EN 10204 3.1 / 3.2 MTC with every order |
Related Standards for a Complete System
A chrome-moly piping system rarely uses pipe alone. A335 pipe mates with buttweld fittings to ASTM A234 carbon and alloy steel buttweld fittings, dimensioned to ASME B16.9, and with forged flanges and valve parts to ASTM A182 forged alloy components and ASME B16.5 flanges. The matching high-temperature bolting is covered by ASTM A193 / A194. Where the service is corrosive rather than purely high-temperature, the austenitic stainless companion pipe spec is ASTM A312.
Applications
A335 chrome-moly pipe serves pressure vessels and boilers, oil and gas processing, and petrochemical plants. It carries high-pressure steam in power stations and hot hydrocarbon streams in refinery heaters and reformers, where strength at temperature and oxidation resistance decide the grade. For the fitting and flange side of the same chemistry, see our alloy steel pipe fittings, forged fittings, and flanges.
FAQ
What grades does ASTM A335 cover?
Is ASTM A335 pipe always seamless?
What is the difference between A335 P11 and P22?
Does ASTM A335 pipe need post-weld heat treatment?
What is A335 P91 used for?
Request a Quote
Nandini Steel holds ASTM A335 chrome-moly alloy steel pipe ex-stock for immediate dispatch, with an EN 10204 3.1/3.2 mill test certificate on every order. Send your grade, size, schedule, and quantity to reachus@nandinisteel.com or WhatsApp +91 99202 09184 for live pricing.