ASTM A335

USED FOR:

Seamless ferritic alloy steel pipe intended for high-temperature service.

A335 governs seamless ferritic alloy steel pipe for high-temperature service. It is commonly used for chromium-molybdenum alloy piping where elevated-temperature mechanical properties, including creep strength and oxidation resistance, are required beyond the capability of carbon steel.

RELATED STANDARDS:

• Sibling specs: ASTM A106 covers seamless carbon steel pipe for moderate-temperature service but lacks the chromium-molybdenum alloying needed once design temperatures push into creep-controlled territory (typically above roughly 425–450°C/800–850°F, service-dependent). ASTM A691 covers carbon and alloy steel pipe produced by electric-fusion welding, with different manufacturing and qualification requirements from ASTM A335. It may be selected where welded alloy steel pipe is acceptable according to the applicable design conditions and project requirements. ASTM A213 covers seamless ferritic and austenitic alloy steel tube for boiler, superheater, and heat exchanger applications. Although some alloy designations overlap with ASTM A335, the application, dimensional requirements, and product form are different.
• Design code that invokes it: ASME B31.1 (power piping) and ASME B31.3 (process piping) both reference A335 extensively for high-temperature alloy steel piping, and ASME Section I (power boilers) references it for piping connected to boiler systems; allowable stresses vary significantly by grade and are temperature-dependent per the ASME B31 stress tables.
• Dimensional standard that pairs with it: ASME B36.10M defines the OD and wall thickness/schedule series for A335 pipe, consistent with other carbon and alloy steel pipe dimensional conventions (as opposed to the “S” schedules used for stainless under B36.19M).

GRADE / TYPE RANGE:
A335 covers a series of “P-grades” ; P1, P2, P5, P9, P11, P12, P22, P91, P92, and others , differentiated primarily by chromium and molybdenum content, which increases progressively through the series.

P11 and P12 are common intermediate grades (roughly 1–1.25% Cr) used in moderately elevated temperature service;

P22 (2.25% Cr, 1% Mo) is one of the most widely specified grades for high-temperature power and refinery piping;

P91 and P92 are advanced 9% chromium grades with vanadium/niobium microalloying, offering substantially higher creep strength at elevated temperature than the older grades, allowing thinner wall sections for the same design pressure/temperature, a significant economic driver in modern high-temperature plant design.

As chromium content increases through the series, resistance to high-temperature oxidation, creep, and hydrogen attack improves, while some grades (particularly P91/P92) require very tightly controlled heat treatment to develop their strength, making them considerably less forgiving in fabrication than the lower-alloy grades.

Tensile strength differences across grades are secondary to the creep-rupture and temperature-service differentiation, which is the actual basis for grade selection.

DESCRIPTION:
A335 covers seamless pipe manufacture only, produced by hot working (and cold finishing for smaller sizes/thinner walls) followed by a mandatory heat treatment, normalizing and tempering, or annealing, depending on grade, that is essential to developing the correct microstructure for creep resistance.

The heat treatment condition is far more consequential here than in A106, and improper heat treatment is a known cause of premature failure in high-chrome grades.

Testing requirements include tensile testing and hydrostatic or nondestructive electric testing as required by ASTM A335. Hardness testing and additional examinations may be required by the applicable grade requirements, supplementary requirements, or project specification.

Chemical composition is controlled by heat analysis with tight alloying element limits, and grain size/microstructure verification is sometimes required for the advanced grades. Marking requirements identify manufacturer, grade, heat number, and heat treatment condition, with full heat traceability typically demanded on higher-grade material given the consequences of a heat-treatment or chemistry error in service.

TYPICAL INDUSTRY USE:
Standard material for high-temperature steam piping in power generation (main steam, hot reheat lines), high-temperature process piping in refineries and petrochemical plants, and any application where design temperature exceeds the practical service range of carbon steel.

IMPORTANT NOTES:

• We very frequently catch confusion between A335 (pipe) and A213 (tube) on the same grade designation, material designations using the “T” prefix are commonly associated with ASTM A213 tube grades, while “P” prefix designations are associated with ASTM A335 pipe grades. The applicable ASTM specification shall always be verified from the material requisition or project specification. mixing these up on a procurement phase is one of the most common material spec errors we see in the field.

• Supplementary requirements under A335 mainly relate to additional NDE (UT in lieu of or in addition to hydro), and for P91/P92 in particular, many project specs impose supplementary hardness testing and post-weld heat treatment (PWHT) verification requirements beyond the base standard, we always recommend confirming the exact hardness acceptance window against the project spec since P91/P92 pipe that’s slightly outside spec on hardness is a common receiving-inspection rejection.

• P91/P92 fabrication requires very specific preheat, interpass temperature control, and PWHT, we’ve seen numerous field problems arise not from the base material but from welding procedures that didn’t adequately account for these grades’ narrow processing windows; this is as much a fabrication risk as a material selection risk.
• NACE MR0175/ISO 15156 qualification is generally not the primary concern for A335 grades since they’re specified for high-temperature service rather than sour, lower-temperature environments, but where a line transitions between sour and high-temperature zones (common in refinery hydroprocessing units), hardness limits under NACE can still conflict with the as-heat-treated hardness of higher chrome grades, so this is worth checking on hydroprocessing unit piping specifically.

• Lead times and mill availability for P91/P92 are typically much longer than for P11/P22, and not all fabricators are qualified (via PQR) for welding P91/P92; we always mention this early in procurement planning since it can become a schedule-critical item on power and refinery projects.