ASME Section II Part A — Ferrous Material Specifications: Complete Reference Guide

ASME Section II Part A, formally titled BPVC Section II — Materials, Part A: Ferrous Material Specifications, is the material reference backbone of the entire ASME Boiler and Pressure Vessel Code. Every carbon steel plate, alloy steel pipe, stainless steel tube, iron casting, and forged fitting used in ASME Code construction must conform to a specification listed in this document. Section II Part A is published in two volumes — covering SA-specifications from SA-6 through to SA-1058M — and is updated with every biennial ASME BPVC edition. The current edition is ASME BPVC 2025; the 2023 edition remains widely used on projects that specified it at contract time.

Unlike the construction code sections (Section VIII for pressure vessels, Section III for nuclear, or B31.3 for process piping), Section II Part A does not tell you how to design or fabricate. It is a service section: a library of approved material specifications that the construction codes draw from by reference. When ASME Section VIII Division 1 clause UG-4 states that pressure vessel materials must conform to specifications listed in Section II Part A, it is pointing directly at this document. Understanding how Section II Part A is structured, how to read an SA specification, how the SA numbering system maps to ASTM, and how materials are assigned P-Numbers under Section IX is fundamental knowledge for any pressure vessel engineer, quality inspector, or fabrication engineer working within the ASME code framework.

This guide covers the full structure of Section II Part A, the SA-number system, key material categories and their most important specifications, the general requirements documents, material certification requirements under UG-93, and practical guidance on selecting the right ASME material for common pressure equipment applications. Whether you are selecting shell plate for a carbon steel process vessel, specifying high-temperature Cr-Mo alloy steel pipe, or verifying a Mill Test Certificate against code requirements, this reference will give you the technical grounding you need.

What Is ASME Section II Part A?

ASME BPVC Section II Part A is the authoritative collection of ferrous material specifications approved for use in ASME Code pressure equipment construction. It is a two-volume document containing over 150 individual specifications, each covering a specific material type, product form, and application. The specifications are designated with an SA-number prefix (SA standing for “ASME adopted”), and in most cases mirror an underlying ASTM A-number specification with the same technical requirements plus any ASME-specific additions.

Section II Part A is described by ASME as a “service section” — meaning it exists solely to be referenced by, and to serve, the construction code sections. A Section II Part A specification on its own carries no legal weight in a fabrication contract. It becomes mandatory when a construction code invokes it by reference. For example, ASME Section VIII Division 1 UG-4(a) states that pressure parts shall be made from materials conforming to SA or SB specifications listed in Section II. That single reference makes the entirety of Section II Part A mandatory for all pressure-containing parts in an ASME Section VIII vessel.

The SA-Number System: How ASME Adopts ASTM Specifications

The dominant feature of Section II Part A is the SA-number system. ASME does not, in general, write its own material specifications from scratch. Instead, the ASME Committee on Materials works alongside ASTM committees to adopt ASTM ferrous specifications into the BPVC. When ASME adopts an ASTM specification, it assigns an equivalent SA-number and publishes the full specification text in Section II Part A. In the majority of cases, the SA-specification is technically identical to the corresponding ASTM specification at the time of adoption.

SA vs A: The Key Differences

While the chemistry and mechanical property requirements are usually identical, ASME may add supplementary requirements or modify certain elements of the ASTM specification to suit pressure equipment construction. Common ASME-specific additions include:

• Mandatory impact testing — Some SA-specifications require Charpy V-notch impact tests as mandatory requirements where the underlying ASTM specification makes them supplementary or optional only. For example, low-temperature service specifications such as SA-333 (low-temperature pipe) and SA-350 (low-temperature forgings) mandate Charpy testing as a base requirement.
• Certification requirements — ASME requires that material test reports (MTRs or MTCs) certify compliance with SA requirements specifically, not just ASTM requirements. The certified mill test report must identify the SA specification number and edition.
• Restricted supplementary requirements — ASME periodically restricts which ASTM supplementary requirements may or may not be invoked on ASME Code materials, to ensure consistency in Code construction.
• Edition alignment — ASME adopts ASTM specifications as of a specific ASTM edition. The SA-specification text in a given BPVC edition reflects the ASTM edition current at the time ASME adopted it, which may lag behind the current ASTM edition.

Structure of Section II Part A

Section II Part A is organised as a collection of individual specifications, each identified by its SA-number and title. At the front of each volume there is a cross-reference index listing all specifications by product form category — plates, pipes, tubes, forgings, castings, bars, bolting, and so on — as well as a specification removal list noting specifications that have been withdrawn from the Code in recent editions. Within each individual specification, the typical structure is:

1. Scope — defines the material, product form, size range, and any applicable restrictions
2. Referenced documents — lists standards for testing methods, tolerances, and ancillary requirements
3. Ordering information — designators required on purchase orders
4. Materials and manufacture — melting practice, heat treatment, forming method restrictions
5. Chemical requirements — heat analysis and product analysis limits
6. Mechanical requirements — tensile, yield, elongation, hardness, and where applicable, impact energy requirements
7. Dimensions, mass, and permissible variations — tolerances on thickness, diameter, width, straightness, etc.
8. Workmanship, finish, and appearance
9. Marking — required identification markings on each piece
10. Certification — MTC / test report requirements
11. Supplementary requirements — additional tests or restrictions that may be specified by the purchaser

General Requirements Specifications

Several SA-specifications function as “umbrella” general requirements documents that apply to an entire class of products. These are referenced by individual material specifications and need not be separately ordered — compliance is automatic when ordering a material to its individual SA-specification. Key general requirements specifications include:

Material Categories in Section II Part A

The specifications in Section II Part A cover a broad range of ferrous materials. For practical engineering use they are best understood by material category and intended service, as the construction codes reference specific material types for specific applications.

Carbon Steel Specifications — Key Materials

Carbon steels with a maximum specified carbon content not exceeding 0.30% are generally assigned P-Number 1 under ASME Section IX and represent the most common material family in pressure vessel fabrication. The dominant specifications are discussed below.

SA-516 — Pressure Vessel Plates, Carbon Steel, for Moderate and Lower Temperature Service

SA-516 is the single most widely used plate material in ASME pressure vessel fabrication. It is supplied in four grades based on minimum tensile strength:

SA-516 Grade 70 is the de facto standard for carbon steel pressure vessel shells, heads, and nozzle reinforcing pads operating at moderate temperatures (typically up to 400°C / 750°F) and at design temperatures above -29°C / -20°F without impact testing in many thickness ranges. Above 38 mm (1.5 in.) thickness, Charpy impact testing per UCS-66 and UG-84 may be required depending on the minimum design temperature and joint efficiency. It is weldable with any of the common welding processes and responds well to normalising and post-weld heat treatment. For an in-depth explanation of when SA-516 Grade 70 plate requires Charpy impact testing under UG-84, see our dedicated guide on that topic.

SA-515 — Pressure Vessel Plates, Carbon Steel, for Intermediate and Higher Temperature Service

SA-515 is similar to SA-516 in grade structure (Grades 55, 60, 65, 70) but is optimised for elevated temperature service. Compared to SA-516, SA-515 allows a higher carbon content, which improves high-temperature tensile strength at the cost of reduced low-temperature notch toughness. SA-515 Grade 70 is selected when the design temperature exceeds the range where SA-516 Grade 70’s allowable stress values remain competitive, particularly in the range 370–450°C (700–840°F).

SA-106 — Seamless Carbon Steel Pipe for High-Temperature Service

SA-106 is the standard specification for seamless carbon steel pipe intended for use at elevated temperatures. Three grades are covered:

SA-106 Grade B is the workhorse of carbon steel process piping for ASME B31.3 applications. Its combination of mechanical properties, weldability (P-No. 1, carbon equivalent values typically 0.35–0.40), and widespread availability make it the default choice for plant piping up to approximately 425°C (800°F). Above this temperature, the allowable stress values in Section II Part D begin to favour alloy steel alternatives.

SA-105 and SA-266 — Carbon Steel Forgings

SA-105 covers carbon steel forgings for piping applications, including flanges, fittings, valves, and pressure parts. It is one of the most commonly specified forging specifications and is used for weld-neck flanges, slip-on flanges, socket-weld fittings, and nozzle forgings in carbon steel piping systems. SA-266 covers larger carbon steel forgings specifically for pressure vessel components such as nozzle necks, shell courses, heads, and vessel heads forged from thick plate. Both are P-No. 1 materials and weld directly to SA-106 pipe and SA-516 plate without preheat in most thickness ranges.

Chromium-Molybdenum Alloy Steel Specifications

For high-temperature pressure service above the carbon steel creep range (approximately 370°C / 700°F for carbon steel), Cr-Mo alloy steels offer superior elevated-temperature tensile strength, creep resistance, and oxidation resistance. Section II Part A covers the full range of conventional and advanced Cr-Mo grades.

SA-387 — Pressure Vessel Plates, Alloy Steel, Chromium-Molybdenum

SA-387 is the primary plate specification for Cr-Mo alloy steel pressure vessels. The most important grades and their P-Number assignments are:

SA-335 — Seamless Ferritic Alloy Steel Pipe for High-Temperature Service

SA-335 is the seamless alloy steel pipe equivalent of SA-106. It covers the complete range of ferritic Cr-Mo grades for high-temperature piping service and is one of the most referenced specifications in power generation and refinery construction. Major grades include:

• P1 — C-Mo (0.5Mo), P-No. 3, for temperatures up to 510°C
• P5 — 5Cr-0.5Mo, P-No. 5B, for refinery and petrochemical high-temperature service
• P9 — 9Cr-1Mo, P-No. 5B, predecessor to P91, still used in some applications
• P11 — 1.25Cr-0.5Mo, P-No. 4, widely used in superheater headers and steam piping
• P22 — 2.25Cr-1Mo, P-No. 5A, standard for hydrogen service piping and reactor piping
• P91 — 9Cr-1Mo-V, P-No. 15E, the modern high-strength creep-resistant grade for advanced power plant steam systems
• P92 — 9Cr-1.8W-0.5Mo-V-Nb, P-No. 15E, even higher creep strength than P91 for ultra-supercritical steam conditions

SA-213 — Seamless Ferritic and Austenitic Alloy Steel Boiler, Superheater, and Heat Exchanger Tubes

SA-213 is the tube counterpart to SA-335, covering both ferritic (Cr-Mo) grades (T5, T9, T11, T22, T91, T92) and austenitic stainless steel grades (TP304, TP316, TP321, TP347). It is the dominant specification for heat exchanger and boiler tubing in high-temperature service. The T-grade designators correspond directly to the P-grade pipe designators in SA-335: T11 pipe has the same composition as P11, and T22 corresponds to P22.

Stainless Steel Specifications

Austenitic stainless steels are assigned P-Number 8 under Section IX, duplex stainless steels are generally P-No. 10H, and ferritic and martensitic stainless steels are P-Nos. 6 and 7 respectively. Section II Part A covers all of these families. For more on the metallurgy and welding of stainless steels see our guides on duplex stainless steel and stainless steel weld decay.

SA-240 — Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip for Pressure Vessels

SA-240 is the primary stainless steel plate specification for pressure vessels. It covers the full range of austenitic (Types 304, 304L, 316, 316L, 317, 317L, 321, 347, 309, 310), ferritic (Types 405, 409, 430), martensitic (Types 403, 410, 416), and duplex (2205, 2507) grades. The four-digit UNS designation (e.g., S31600 for Type 316) or the three-digit type number is used to identify the grade on purchase orders and MTCs.

SA-312 — Seamless, Welded, and Heavily Cold Worked Austenitic Stainless Steel Pipes

SA-312 is the standard specification for austenitic stainless steel pipe in pressure service. Grades mirror SA-240 (TP304, TP304L, TP316, TP316L, TP317L, TP321, TP347, etc.). Seamless and welded pipe are covered in the same specification, with welded pipe identified by the “W” suffix on the tube identification. ASME B31.3 Table A-1 lists both seamless and welded SA-312 pipe with different joint quality factors (E = 1.0 for seamless, E = 0.85 for welded unless 100% RT is performed, in which case E = 1.0).

Bolting Specifications

Pressure vessel and flange bolting requires materials listed in Section II Part A with specific mechanical properties for the temperature range. Two specifications cover virtually all Code bolting requirements:

P-Number Assignments for Section II Part A Materials

ASME Section IX assigns P-Numbers to the base metals listed in Section II (and other code sections) to group materials with similar composition, weldability, and mechanical properties. A welding procedure qualification on one material in a P-Number group qualifies the welding procedure for all materials within the same group (with some exceptions for impact-tested applications). Understanding P-Numbers is essential for reading and writing WPS/PQR documentation — see our full guide on P-Numbers, F-Numbers, and A-Numbers for a complete explanation. The most important P-Number groups drawn from Section II Part A materials are:

Material Certification Requirements — UG-93 and MTC Content

ASME Section VIII Division 1 clause UG-93 establishes the material documentation requirements for all pressure-containing parts. The key requirements are:

What the MTC Must Include

• The SA-specification number and revision (edition) to which the material was produced
• Grade, class, type, or condition as applicable
• Heat number (the unique identifier for the melt from which the material was produced)
• Product analysis results where the specification requires or where the purchaser has invoked Supplementary Requirement S1
• Heat analysis (ladle analysis) results — elemental breakdown by percentage for each required element
• Mechanical test results: tensile strength, yield strength, elongation, reduction of area, and Charpy energy as applicable
• Heat treatment condition: as-rolled (AR), normalised (N), normalised and tempered (NT), quenched and tempered (QT), annealed (A), solution annealed (SA) as required by the specification
• Dimensional conformance statement or dimensional test results as required
• The manufacturer’s name and the certifying signature or electronic equivalent

Traceability and Marking

Each piece of Section II Part A material must be marked with the specification number, grade, heat number, and required size information. For plates, this is typically stencilled or stamped on the plate surface. For pipe and tube, it appears on the pipe itself at defined intervals. ASME UG-77 requires that material identification (heat number) be traceable from the material itself to the MTC throughout the fabrication process. Quality control procedures for ASME Code vessels must include a system for maintaining this traceability — any material that loses traceability to its MTC must be either reidentified (if the heat number can be recovered) or treated as unidentified and not used for Code construction without retesting.

Practical Material Selection Guide for Common ASME Applications

The following table summarises material selection logic for the most common ASME pressure vessel and piping application categories:

Recommended Books on ASME Section II and Pressure Vessel Materials

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FAQ — ASME Section II Part A Ferrous Material Specifications

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