16.5 P-Numbers, Group Numbers, F-Numbers & A-Numbers

16.3 P-Numbers, F-Numbers, A-Numbers & Mechanical Test Coupons

Quick Answer: ASME Section IX categorizes base metals into P-Numbers based on composition and weldability (e.g., P-No 1 carbon steels, P-No 8 austenitic stainless steels) and further subdivides them into Group Numbers when impact testing is required by construction codes. Filler metals are categorized by F-Numbers (QW-432) according to usability and slag system (F-1 through F-6 for steels) and by A-Numbers (QW-442) according to deposited ferrous weld metal chemical analysis (A-1 through A-12). Procedure qualification per QW-202 and Table QW-451.1 requires two transverse tension specimens and four guided bend specimens (or two root and two face bends for thin plate). Tension specimens must reach the specified minimum tensile strength (SMTS), but QW-153.1(d) accepts specimens failing in the base metal outside the weld at no more than 5% below SMTS. Guided bends evaluated per QW-163 reject any open discontinuity exceeding 1/8 in (3.2 mm). Charpy V-notch tests per QW-170 require specific notch placement across the weld metal centerline and HAZ.

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Base Metal Grouping Taxonomy: P-Numbers & Group Numbers (QW/QB-422)

To avoid the unsustainable burden of qualifying individual procedures for thousands of distinct commercial metal alloys, ASME Section IX establishes the P-Number base metal grouping system in Table QW/QB-422. Metals are grouped based on comparable chemical composition, weldability, mechanical properties, and metallurgical transformation behavior.

                                ASME SECTION IX BASE METAL P-NUMBERS

    P-NO 1                P-NO 3 / 4 / 5            P-NO 8                P-NO 9 / 10H
  Carbon Steels         Cr-Mo Alloy Steels        Austenitic SS        Cryogenic Ni & Duplex
  - SA-36               - P-No 3: 0.5 Mo          - SA-240 Type 304    - P-No 9A/B: 2-3.5% Ni
  - SA-106 Gr B         - P-No 4: 1.25Cr-0.5Mo    - SA-240 Type 316    - P-No 9C: 9% Ni
  - SA-516 Gr 70        - P-No 5A: 2.25Cr-1Mo     - SA-240 Type 321    - P-No 10H: 2205 Duplex
                        - P-No 5B: 5Cr to 9Cr     - SA-240 Type 347    - P-No 10I: 2507 Super Duplex
                        - P-No 5C: P91/P92 CSEF

Primary P-Number Designations

• P-No 1: Carbon-manganese construction and pressure vessel steels (e.g., SA-36, SA-106 Gr B, SA-516 Gr 60/70, SA-53).
• P-No 3: Carbon-molybdenum (0.5% Mo) low-alloy steels (e.g., SA-335 Gr P1, SA-209).
• P-No 4: 1.25% Cr – 0.5% Mo creep-resisting low-alloy steels (e.g., SA-387 Gr 11, SA-335 Gr P11).
• P-No 5A, 5B, 5C: 2.25% Cr through 9% Cr alloys. P-No 5A includes 2.25Cr-1Mo (SA-335 P22); P-No 5B includes 5Cr and 9Cr (SA-335 P5, P9); P-No 5C governs Creep Strength Enhanced Ferritic (CSEF) martensitic steels like Grade 91 (SA-335 P91) and Grade 92.
• P-No 6: High-chromium martensitic stainless steels (e.g., Type 410).
• P-No 7: Ferritic stainless steels (e.g., Type 405, Type 430).
• P-No 8: Chromium-nickel austenitic stainless steels (e.g., Type 304, 304L, 316, 316L, 321, 347).
• P-No 9A, 9B, 9C: Nickel alloy steels for cryogenic service (2.25% to 9% Ni steels, SA-333 Gr 3, SA-553).
• P-No 10H: Duplex and super duplex stainless steels (e.g., UNS S31803, S32205, S32750).
• P-No 21 through 26: Aluminum and aluminum-base alloys.
• P-No 41 through 49: Nickel and nickel-base alloys (Inconel 600, 625, Incoloy 800H, Hastelloy C-276).
• P-No 51 through 53: Titanium and titanium-base alloys.

Group Numbers and Notch Toughness Rules (QW-403.5)

Within ferrous P-Numbers (P-No 1, 3, 4, 5, 9, 10, 11), base metals are further divided into Group Numbers assigned primarily according to tensile strength and deoxidation practice:

• P-No 1 Group 1: Steels with minimum specified tensile strength < 70 ksi (e.g., SA-516 Gr 60, SA-106 Gr B).
• P-No 1 Group 2: Steels with minimum specified tensile strength >= 70 ksi (e.g., SA-516 Gr 70, SA-537 Cl 1).

+---------------------------------------------------------------------------------------------------------+
|                              P-NUMBER VS. GROUP NUMBER QUALIFICATION SCOPE                              |
+------------------------------------+----------------------------------+---------------------------------+
| Toughness Requirement Status       | Procedure Qualification Coupon   | Qualified Base Metal Range      |
+------------------------------------+----------------------------------+---------------------------------+
| NOT MANDATORY                      | Welded on P-No 1 Group 1         | Qualifies ALL P-No 1            |
| (Standard Article II Qualification)| (e.g., SA-516 Gr 60)             | (Group 1, Group 2, Group 3)     |
+------------------------------------+----------------------------------+---------------------------------+
| MANDATORY (CVN Impact Required)    | Welded on P-No 1 Group 1         | Qualifies ONLY P-No 1 Group 1   |
| (Supplementary Essential QW-403.5) | (e.g., SA-516 Gr 60)             | (DOES NOT qualify Group 2)      |
+------------------------------------+----------------------------------+---------------------------------+
| MANDATORY (CVN Impact Required)    | Welded on P-No 1 Group 2         | Qualifies ONLY P-No 1 Group 2   |
| (Supplementary Essential QW-403.5) | (e.g., SA-516 Gr 70)             | (DOES NOT qualify Group 1)      |
+------------------------------------+----------------------------------+---------------------------------+

Core Engineering Principle: The Group Number Toughness Barrier When notch toughness is not required by the construction code, qualification on any material in a P-Number qualifies all materials within that P-Number (QW-403.1). However, under supplementary essential variable QW-403.5, when impact testing is required, qualification of a procedure on one Group Number qualifies only that specific Group Number. It does not qualify other Group Numbers within the same P-Number, nor does it qualify combinations unless specifically tested.

Unassigned Base Metals

Base metals not listed in Table QW/QB-422 (such as proprietary alloys or non-ASME specifications) are designated as unassigned metals. An unassigned metal must be qualified independently. Qualification of an unassigned metal qualifies only that specific specification, type, and grade.

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Filler Metal Grouping: F-Numbers (QW-432) & A-Numbers (QW-442)

ASME Section IX classifies filler metals using two independent parameters: F-Numbers (which evaluate usability and operator manipulation characteristics) and A-Numbers (which evaluate the chemical composition of the deposited ferrous weld metal).

F-Numbers (Table QW-432)

F-Numbers group welding electrodes and rods based on their operational characteristics, coating formulation, and slag chemistry, significantly reducing procedure and performance qualification requirements.

+-------------+---------------------------------------+---------------------------------------------------+
| F-Number    | Electrode Description & Flux System   | Representative AWS Classifications                |
+-------------+---------------------------------------+---------------------------------------------------+
| **F-1**     | High-deposition, heavy iron-powder    | EXX20, EXX24, EXX27, EXX28                        |
| **F-2**     | Rutile coatings, general purpose      | EXX12, EXX13, EXX14                               |
| **F-3**     | Cellulosic coatings, deep penetration | EXX10, EXX11 (E6010, E7010)                       |
| **F-4**     | Basic low-hydrogen coatings           | EXX15, EXX16, EXX18, EXX18M (E7018, E8018)        |
| **F-5**     | Stainless steel covered electrodes    | E3XX, E4XX series (E308L-16, E316L-16)            |
| **F-6**     | Solid wires, cored wires, bare rods   | All carbon & low-alloy GTAW/GMAW/FCAW/SAW wires   |
|             |                                       | (ER70S-6, E71T-1M, F7A2-EM12K)                    |
| **F-41-46** | Nickel and nickel-alloy consumables   | ERNiCr-3 (Inconel 82), ENiCrMo-3 (Inconel 625)    |
+-------------+---------------------------------------+---------------------------------------------------+

Under QW-404.4, changing from one F-Number to another F-Number (e.g., qualifying with an F-3 E6010 electrode and switching to an F-4 E7018 electrode) is an essential variable for procedure qualification that mandates a new PQR.

A-Numbers (Table QW-442)

A-Numbers classify the chemical analysis of the deposited weld metal for ferrous alloys. They do not apply to nonferrous metals (nickel, aluminum, copper).

+-------------+---------------------------------------+---------------------------------------------------+
| A-Number    | Weld Metal Deposit Type               | Nominal Chemical Composition (Weight %)           |
+-------------+---------------------------------------+---------------------------------------------------+
| **A-1**     | Mild Carbon Steel                     | C: 0.15% max, Cr: ---, Mo: ---, Ni: ---, Mn: 1.6% |
| **A-2**     | Carbon-Molybdenum (C-Mo)              | C: 0.15%, Mo: 0.40–0.65%                          |
| **A-3**     | Chromium-Molybdenum (0.5Cr-0.5Mo)     | Cr: 0.40–1.25%, Mo: 0.40–0.65%                    |
| **A-4**     | Chromium-Molybdenum (2Cr-1Mo)         | Cr: 1.75–3.00%, Mo: 0.40–1.50%                    |
| **A-5**     | High Cr-Mo (5Cr to 10Cr)              | Cr: 4.00–10.5%, Mo: 0.40–1.50%                    |
| **A-8**     | Chromium-Nickel Austenitic (18Cr-8Ni) | Cr: 14.5–30.0%, Ni: 7.5–15.0% (308, 316)          |
| **A-9**     | Chromium-Nickel Austenitic (High Cr)  | Cr: 19.0–30.0%, Ni: 15.0–37.0% (309, 310)         |
+-------------+---------------------------------------+---------------------------------------------------+

Per QW-404.5, a change in the weld metal chemical composition from one A-Number to any other A-Number is an essential variable. The A-Number may be determined by chemical analysis of the test coupon weld deposit or from the filler metal manufacturer's certified material test report (CMTR) matching the AWS specification.

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