ASME Section IX — Welding and Brazing Qualification Standard
ASME Section IX is the welding qualification standard within the ASME Boiler and Pressure Vessel Code. It governs procedure qualification through PQRs and welder performance qualification through WPQs for pressure vessels, boilers, and piping systems regulated by ASME construction codes including Section VIII and B31.3.
Key distinction: Unlike AWS D1.1 which allows prequalified WPSs under Clause 5 with no testing required, ASME Section IX requires every welding procedure to be qualified by testing and documented on a PQR. There is no prequalified exemption in ASME IX.
What Is ASME Section IX?
ASME Boiler and Pressure Vessel Code Section IX governs welding and brazing qualification for pressure equipment. Unlike D1.1, ASME IX has no prequalified WPS path — every procedure requires qualification by testing with a PQR. Section IX uses P-numbers for base metals and F-numbers for filler metals to organize qualification ranges.
ASME Section IX — formally titled “Qualification Standard for Welding, Brazing, and Fusing Procedures; Welders; Brazers; and Welding, Brazing, and Fusing Operators” — is one of twelve sections of the ASME Boiler and Pressure Vessel Code (BPVC). It establishes the requirements for qualifying welding procedures and the personnel who perform welding on pressure-retaining equipment. The standard is also commonly referred to as ASME IX, ASME Section 9, or simply Section IX.
Section IX does not specify when welding is required or what acceptance criteria apply to production welds. Those requirements come from the referencing construction code — Section I for power boilers, Section VIII Division 1 or 2 for pressure vessels, B31.1 for power piping, or B31.3 for process piping. Section IX provides the framework for demonstrating that a welding procedure produces sound welds and that the welder or welding operator can execute it competently.
The standard is organized into four parts. Part QW covers welding, Part QB covers brazing, Part QF covers plastic fusing, and a mandatory appendix provides definitions and supplemental requirements. Part QW is the section most fabricators and inspectors reference daily. It contains the rules for procedure qualification (Article II), performance qualification (Article III), and the welding data tables (Article IV) that define essential, nonessential, and supplementary essential variables for each welding process.
Procedure Qualification Under ASME IX
ASME IX requires every WPS to be supported by a Procedure Qualification Record (PQR). The fabricator produces a test weld, extracts specimens for destructive testing (bend tests, tensile tests, impact tests if required), and documents the results. Essential, supplementary essential, and nonessential variables determine when re-qualification is required.
Every welding procedure specification used under ASME IX must be supported by at least one procedure qualification record. The qualification process requires producing a test coupon using the WPS parameters, then performing mechanical tests — typically tension tests and guided bend tests — to demonstrate the procedure produces welds with adequate strength and ductility.
The WPS specifies the welding parameters within ranges that cover the intended production application. The PQR records the actual parameters used during the test weld and the test results. Once qualified, the WPS can be used for production welding within the ranges of the essential variables established by the PQR. A single PQR can support multiple WPSs, and a single WPS can reference multiple PQRs.
ASME IX classifies welding variables into three categories that control when re-qualification is required:
- Essential variables
- Parameters that, if changed beyond the qualified range, require a new PQR. Examples include changes in base metal P-number, filler metal F-number, welding process, or thickness range. A change in any essential variable invalidates the existing qualification for the affected range.
- Supplementary essential variables
- Parameters that become essential only when the referencing construction code requires impact (toughness) testing. When impact testing is not required, these variables are treated as nonessential. Examples include changes in heat input, preheat reduction, and PWHT conditions. This dual classification is unique to ASME IX.
- Nonessential variables
- Parameters that can be changed in the WPS without re-qualification. Examples include changes from stringer to weave beads, changes in electrode diameter within a group, or changes in joint design details within the qualified range. The WPS must still document these variables, but changing them does not require a new PQR.
P-Numbers and F-Numbers
ASME IX assigns P-numbers to base metals and F-numbers to filler metals to simplify qualification ranges. P-Number 1 covers carbon steels (SA-36, SA-516 Gr.70). P-Number 8 covers austenitic stainless steels (304, 316). F-Number 4 covers low-hydrogen SMAW electrodes (E7018). Qualification on one material qualifies a range of similar materials within the same P-number.
ASME IX groups base metals and filler metals using numerical classification systems that simplify qualification ranges and reduce the number of PQRs required.
P-Numbers (Base Metal Groups)
P-numbers group base metals by composition, mechanical properties, and weldability characteristics. Materials within the same P-number group have similar welding behavior, so a procedure qualified on one material in the group generally qualifies for other materials in the same group. The major P-number assignments include P-Number 1 for carbon steels (SA-36, SA-516 Gr.70, SA-106 Gr.B), P-Number 8 for austenitic stainless steels (304, 316, 321), P-Number 5A and 5B for chromium-molybdenum steels (SA-387 series), and P-Number 11 for quenched-and-tempered high-strength steels.
P-numbers are further divided into Group Numbers that distinguish materials within a P-number based on composition ranges and strength levels. For example, P-Number 1 Group 1 covers lower-carbon steels (SA-36, SA-283) while P-Number 1 Group 2 covers higher-strength carbon steels (SA-516 Gr.70). The group number subdivision becomes an essential variable only when impact testing is required.
F-Numbers (Filler Metal Groups)
F-numbers group filler metals by usability characteristics. Electrodes and filler wires that handle similarly during welding are assigned the same F-number, regardless of their tensile strength classification. F-Number 4 covers low-hydrogen SMAW electrodes (E7018, E7016, E7028), F-Number 6 covers carbon steel solid wires (ER70S-6, ER70S-3), and F-Number 36 covers flux-cored wires (E71T-1, E71T-8). Changing F-number is an essential variable that requires re-qualification. The A-number, which classifies weld metal chemical composition, must also be considered when evaluating qualification ranges.
How ASME IX Compares to Other Welding Codes
ASME IX governs pressure equipment qualification while D1.1 governs structural steel. The fundamental difference: ASME IX requires a PQR for every WPS with no prequalified exemption. D1.1 Clause 5 allows prequalified WPSs without testing. ASME IX uses P-numbers and F-numbers; D1.1 uses Table 5.6 categories and A5.x matching.
ASME IX vs AWS D1.1
The most significant structural difference is that D1.1 provides a prequalified path under Clause 5 that requires no procedure qualification testing, while ASME IX requires testing for every procedure. D1.1 uses Table 5.6 base metal groups (I through V) rather than P-numbers. D1.1 applies to structural steel, while ASME IX applies to pressure equipment. D1.1 Table 5.11 provides preheat requirements directly, while ASME IX defers preheat to the WPS and the construction code. Both standards use WPS and PQR documents, but the variable classifications and qualification ranges differ significantly.
ASME IX vs API 1104
API 1104 is specific to pipeline welding and uses its own qualification framework independent of both ASME IX and D1.1. API 1104 classifies base metals into material groups based on SMYS (specified minimum yield strength) rather than P-numbers. API 1104 qualification ranges for thickness and diameter are more restrictive than ASME IX. Both standards require procedure qualification testing, but the test methods and acceptance criteria differ — API 1104 uses nick-break and root/face bend tests rather than ASME IX guided bend and tension tests.
ASME IX vs CSA W47.1 / CSA W59
The Canadian standards use a different framework. CSA W47.1 governs company certification and welder qualification, while CSA W59 specifies welded steel construction requirements (analogous to D1.1). ASME IX is accepted in Canada for pressure equipment, and many Canadian fabricators maintain both CSA and ASME qualifications depending on the application.
| Aspect | ASME IX | AWS D1.1 | API 1104 | CSA W59 |
|---|---|---|---|---|
| Scope | Pressure equipment | Structural steel | Pipelines | Structural steel (Canada) |
| Prequalified WPS? | No — all require PQR | Yes (Clause 5) | No | Yes (Clause 5) |
| Base metal grouping | P-numbers | Table 5.6 categories | Groups I–IV | 4 grade groups |
| Filler metal grouping | F-numbers | AWS A5.x matching | AWS A5.x | CSA W48 |
| Preheat method | Per WPS/PQR | Table 5.11 | Per WPS | Table 5.3 |
| Edition | 2025 | 2025 (25th) | 2021 (22nd) | 2018/2024 |
Welder Performance Qualification (WPQ)
ASME IX Clause QW-300 requires welders to demonstrate their ability to produce sound welds by testing. The welder produces a test coupon that passes either mechanical testing (bend tests) or volumetric examination (radiography). Qualification ranges depend on the welding process, base metal thickness, position, and filler metal F-number.
In addition to procedure qualification, ASME IX requires welders and welding operators to demonstrate their ability to produce sound welds following a qualified WPS. The welder performance qualification test requires the welder to produce a test coupon that passes either mechanical testing (bend tests) or volumetric examination (radiography or ultrasonic testing).
Performance qualification is specific to the welding process, position, base metal P-number range, filler metal F-number, electrode diameter range, and backing conditions. A welder qualified in the 6G position (inclined at 45 degrees) qualifies for all positions for groove welds. Performance qualifications must be maintained through continued use of the qualified process — if a welder goes more than six months without using a specific process, the qualification for that process expires.
The WPQ record documents the test variables, the test results, and the ranges for which the welder is qualified. Unlike the PQR which demonstrates the procedure works, the WPQ demonstrates that a specific individual can execute the procedure to produce acceptable welds.
Related Standards Guides
Frequently Asked Questions
ASME Section IX is the welding, brazing, and fusing qualification standard within the ASME Boiler and Pressure Vessel Code (BPVC). It establishes the rules for qualifying welding procedures (WPS supported by PQR) and welders or welding operators (WPQ). Unlike AWS D1.1 which allows prequalified WPSs, ASME IX requires every welding procedure to be qualified by testing. Section IX is referenced by construction codes including ASME Section I (power boilers), Section VIII (pressure vessels), and B31.3 (process piping).
The most significant difference is that ASME Section IX requires procedure qualification testing (PQR) for every WPS, while D1.1 allows prequalified WPSs under Clause 5 with no testing required. ASME IX uses P-numbers to group base metals by composition and weldability, while D1.1 uses Table 5.6 base metal groups (I through V). ASME IX applies to pressure equipment (vessels, boilers, piping), while D1.1 applies to structural steel. ASME IX covers all welding processes, while D1.1 prequalifies only SMAW, SAW, GMAW (except short-circuit), and FCAW.
P-numbers are ASME Section IX base metal groupings that classify materials by chemical composition, mechanical properties, and weldability characteristics. P-Number 1 covers carbon steels (SA-36, SA-516 Gr.70), P-Number 8 covers austenitic stainless steels (304, 316), and P-Number 11 covers quenched-and-tempered high-strength steels. Materials within the same P-number group can generally be welded using the same qualified procedure, reducing the number of PQRs a fabricator must maintain.
Yes. ASME Section IX requires every welding procedure specification to be supported by a procedure qualification record demonstrating acceptable test results. There is no prequalified exemption in ASME IX. Each WPS must reference at least one PQR that covers the essential, nonessential, and supplementary essential variables specified in the WPS. This is one of the key structural differences between ASME IX and AWS D1.1, where prequalified WPSs under Clause 5 require no PQR.
Essential variables are welding parameters that, if changed beyond the qualified range, require re-qualification of the procedure with a new PQR. Nonessential variables can be changed in the WPS without re-qualification. Supplementary essential variables become essential only when impact (toughness) testing is required by the construction code. For example, changing base metal P-number is an essential variable requiring a new PQR, while changing from stringer to weave bead technique is typically a nonessential variable.