Overview
ASTM A335/A335M-26 covers nominal- and minimum-wall seamless ferritic alloy-steel pipe intended for high-temperature service. Procurement requires the exact P grade, size and wall basis, heat treatment, forming/welding intent, mechanical and hardness evidence, hydrostatic or NDE acceptance and code-qualified design data.
Designation and acceptance
A335 applies to seamless low- and intermediate-alloy ferritic pipe containing defined P grades; it is not a specification for welded alloy pipe or every chromium-molybdenum component. Grade chemistry and heat treatment establish the mill product condition, while NPS, wall basis, examination, supplementary requirements and the governing construction code complete the purchasing identity.
Members and selection
| Designation | Selection context |
|---|---|
| P5 / P9 | Chromium-molybdenum branches requiring exact heat treatment and fabrication qualification. |
| P11 / P12 | Common lower-alloy high-temperature branches; confirm grade-specific condition and hardness. |
| P22 | 2.25Cr-1Mo family used in elevated-temperature equipment and piping. |
| P91 / P92 | Creep-strength-enhanced grades requiring strict heat treatment, welding and traceability control. |
Comparison framework
| Criterion | Decision context |
|---|---|
| A335 vs A106 | A335 covers ferritic alloy grades; A106 covers seamless carbon-steel high-temperature pipe. |
| P-grade vs component grade | Pipe grade does not qualify fittings, forgings or weld metal under their product standards. |
| Nominal vs minimum wall | The order must choose the wall basis used for dimensional and pressure acceptance. |
| Mill condition vs service allowables | Material properties do not replace construction-code allowable stresses or creep assessment. |
Performance
- Acceptance under ASTM A335 Alloy Steel Pipe depends on the ordered product branch, delivered condition, geometry and specified test basis rather than the standard number alone.
- Incorrect heat treatment, weld procedure or hardness can compromise toughness and long-term creep behavior.
- Service suitability remains an engineering decision: chemical similarity between grades or product forms does not establish code, welding or elevated-temperature equivalence.
Orderable product scope
- Seamless ferritic alloy-steel pipe by NPS and ordered wall.
- Plain-end, threaded where permitted, or bevelled pipe for qualified joining.
- Cut or random lengths with project marking and traceability.
Processing
- Qualify hot bending, forming and postweld heat treatment for the exact P grade and wall.
- Control preheat, interpass, consumables and hardness for creep-strength-enhanced grades.
- Keep heat-treatment and examination-lot identity through spool fabrication and field installation.
Applications
- Power and process piping at elevated temperature.
- Boiler and refinery services using the applicable P-grade design basis.
- High-temperature transfer lines where seamless ferritic alloy pipe is specified.
Selection
- Confirm that ASTM A335 Alloy Steel Pipe covers the required product form and manufacturing or coating route before comparing quotations.
- Select the grade, alloy, temper, coating or delivered condition from service, fabrication and the required acceptance evidence; never infer it from a trade name.
- Require a written technical comparison and responsible-engineer approval before substituting another standard, product route or condition.
Procurement
- State ASTM A335/A335M-26, exact P grade, unit system and nominal/minimum wall basis.
- State NPS/OD, schedule or wall, length, quantity, ends and dimensional tolerances.
- Define heat treatment, tensile/hardness tests, hydrostatic/NDE route and supplementary examinations.
- Require A999, material test report, heat/treatment-lot traceability, marking and protected capped shipment.