1. What Is ASME Section IX?

ASME Boiler and Pressure Vessel Code (BPVC) Section IX is the governing standard that establishes qualification requirements for welders, welding operators, brazers, brazing operators, and fusion operators, along with the procedures they use to join metals and plastics. Published by the American Society of Mechanical Engineers (ASME), this code is foundational to the pressure equipment, piping, and power generation industries worldwide.

In practical terms, Section IX ensures that every weld made on a pressure vessel, boiler, or pressure piping system has been produced using a tested and documented procedure, by a person who has demonstrated the skill to execute it correctly. Without this structured qualification system, the integrity of safety-critical equipment could not be reliably assured.

2. Scope and Application

Section IX applies to the qualification of procedures and personnel involved in welding, brazing, and plastic fusing, in accordance with both the ASME Boiler and Pressure Vessel Code and ASME B31 Code for Pressure Piping, as well as other referencing standards and specifications.

The code covers three core metal-joining technologies:

• Welding – fusion processes including SMAW, GTAW, GMAW, SAW, FCAW, PAW, and more
• Brazing – joining metals using a filler metal at temperatures above 450 °C (840 °F) without melting the base metal
• Plastic fusing – heat-fusion joining of thermoplastic piping and components

3. Referencing Construction Codes

Section IX is a qualification standard, not a standalone construction code. It is invoked — or “referenced” — by numerous other codes that govern the actual construction of pressure equipment and piping. When a project is built to one of these referencing codes, the welding and brazing qualification requirements of Section IX must be met.

Common construction codes that reference ASME Section IX include:

• ASME BPVC Section I – Power Boilers
• ASME BPVC Section III – Nuclear Power Plant Components
• ASME BPVC Section IV – Heating Boilers
• ASME BPVC Section VIII (Divisions 1, 2 & 3) – Pressure Vessels
• ASME BPVC Section XI – In-service Inspection of Nuclear Components
• ASME BPVC Section XII – Transport Tanks
• ASME B31.1 – Power Piping
• ASME B31.3 – Process Piping
• API 510 – Pressure Vessel Inspection
• API 570 – Piping Inspection

Each referencing code applies to specific types of fabrication and may impose additional requirements beyond those stated in Section IX. Whenever a referencing code’s requirements differ from Section IX, the referencing code takes precedence.

4. Organization of Section IX

Section IX is divided into four major parts, each dedicated to a specific material-joining process. This structured approach allows engineers and inspectors to navigate directly to the requirements relevant to their work.

5. Part QG – General Requirements

Part QG establishes the foundational requirements that apply uniformly across all joining processes addressed in Section IX. It introduces key definitions, outlines the responsibilities of the manufacturer or contractor, and describes how qualification records must be maintained.

Notable requirements in Part QG include:

• The manufacturer or contractor is responsible for the welding or brazing performed by their organization.
• Qualification records (PQRs, WPQs, BPQRs) must be certified and retained as long as they are in use.
• Qualification is not transferable between employers; re-qualification is required when a welder changes organizations.

6. Part QW – Welding Qualifications

Part QW is the most widely used section of the code. It contains all requirements for qualifying both welding procedures (how a weld is to be made) and welding personnel (who is authorized to make it). Part QW is organized into five articles:

Article I – Welding General Requirements

Article I sets out the general framework for welding qualification, explaining the purpose and relationships between the three primary qualification documents:

• Welding Procedure Specification (WPS) – A written document providing the required welding parameters (variables) and their permitted ranges for a given application. The WPS is the instruction document used by the welder in production.
• Procedure Qualification Record (PQR) – The test record that supports a WPS. It documents the actual welding variables used to weld a test coupon and the results of the mechanical tests performed on that coupon.
• Welder/Welding Operator Performance Qualification (WPQ) – The record demonstrating that an individual welder or welding operator has the skill to produce an acceptable weld using a qualified procedure.

This article also addresses how multiple WPSs can be derived from a single PQR, and how a single WPS can be supported by multiple PQRs when combining different variables.

Article II – Welding Procedure Qualifications

Article II contains the detailed requirements for qualifying a Welding Procedure Specification. It covers:

• The mechanical tests required for PQR qualification (tension tests, guided bend tests, impact tests where applicable)
• Thickness qualification ranges for groove welds, fillet welds, partial-penetration groove welds, stud welds, and tube-to-tubesheet joints
• Qualification criteria for repair welds and dissimilar-thickness joints
• Test coupon dimensions for each welding process and special processes such as weld overlay and hybrid welding

Welding variables for each process are addressed starting at QW-250, where they are categorized as essential, supplementary essential, or non-essential. Clauses QW-252 through QW-267 address the specific variables applicable to each covered welding process.

Article III – Welder Performance Qualifications

Article III defines the requirements for qualifying individual welders and welding operators. A qualified welder is one who has successfully met the testing requirements of Section IX and possesses the skill to produce sound, acceptable welds.

Key topics covered in Article III include:

• Test coupon requirements for each welding process
• Qualification by visual examination, bend testing, or volumetric NDE (radiographic or ultrasonic examination)
• Positions qualified and the limits of qualification (e.g., a welder qualified in the 6G pipe position qualifies for all positions)
• Re-qualification requirements when a welder has not used a specific process for six months or longer

When qualifying by volumetric NDE, a minimum weld length of 150 mm must be examined, covering the entire weld circumference. For smaller-diameter pipes where 150 mm cannot be achieved from a single coupon, up to four coupons may be combined. Welding operators may also be qualified over a production weld, in which case the minimum examination length is 1 metre.

Article IV – Welding Data

Article IV is a data repository containing the supporting tables, figures, and reference information used throughout Part QW. This includes:

• P-Number groupings – Base materials are organized into P-Numbers (and Group Numbers) based on their chemical and mechanical properties, so that a single PQR can qualify welding on a range of similar materials.
• F-Numbers – Filler metals are grouped by F-Number to allow one welder performance qualification to cover a range of similar electrodes.
• A-Numbers – Weld metal chemical composition groupings used for procedure qualification.
• Welding positions, joint designs, test specimen dimensions, and acceptance criteria for mechanical tests.

Article V – Standard Welding Procedure Specifications (SWPSs)

Article V addresses Standard Welding Procedure Specifications (SWPSs), which are pre-qualified WPSs published by the American Welding Society (AWS). SWPSs allow manufacturers and contractors to use documented welding procedures without conducting their own PQR testing, subject to the usage limitations defined in this article.

The use of SWPSs must be explicitly permitted by the referencing construction code. Not all codes allow their use, and when they are permitted, any additional restrictions imposed by the referencing code must be observed.

7. Part QB – Brazing Qualifications

Part QB mirrors the structure of Part QW, but is dedicated entirely to brazing processes. It sets out requirements for:

• Brazing Procedure Specification (BPS) development and qualification
• Brazing Procedure Qualification Records (BPQRs)
• Brazer and brazing operator performance qualification
• Essential and non-essential variables specific to brazing (e.g., base metal, brazing filler metal, flux, torch type, joint design)

Brazing is used extensively in heat exchangers, HVAC systems, and certain pressure vessels where the lower heat input and capillary-action joint formation of brazing are more appropriate than fusion welding.

8. Part QF – Plastic Fusing Qualifications

Part QF covers the qualification of procedures and operators for plastic fusion joining, used primarily in thermoplastic piping systems. The processes addressed include butt fusion, socket fusion, and electrofusion. This part is particularly relevant to water, gas distribution, and chemical piping constructed from materials such as polyethylene (PE) and polypropylene (PP).

9. Understanding Welding Variables

Section IX defines variables for each welding process. A variable is any parameter that can influence the outcome of a weld. For procedure qualification, variables are those factors that affect the mechanical properties of the weld. For performance qualification, variables are those that affect the ability of the welder to produce a sound joint.

Variables are classified into three categories:

10. WPS, PQR, and WPQ – The Core Documents

Understanding the distinction and relationship between the three primary qualification documents is essential for anyone working with Section IX.

Welding Procedure Specification (WPS)

A WPS is a written document that provides the parameters and allowed ranges for each welding variable applicable to a given application. It serves as the instruction set for the welder at the job site. A WPS must be supported by one or more PQRs that demonstrate the procedure produces welds with acceptable mechanical properties. A single WPS can be used as the basis for multiple production welds, and multiple WPSs can be derived from a single PQR.

Procedure Qualification Record (PQR)

The PQR documents the actual welding variables used when welding a test coupon, as well as the results of the mechanical tests performed on that coupon. The PQR is the evidence that the welding procedure produces welds meeting the minimum mechanical property requirements specified by Section IX and the applicable construction code. The PQR must be certified by the manufacturer and retained for the life of the WPS it supports.

Welder/Welding Operator Performance Qualification (WPQ)

The WPQ records that a specific individual has demonstrated the ability to produce a sound weld using a defined process and within defined limits (position, thickness range, diameter range, etc.). The welder qualification is tied to the employer — if a welder changes organizations, re-qualification is required. A welder’s qualification may also lapse if they have not welded with a specific process for a period of six months or more.

11. Conclusion

ASME BPVC Section IX is the cornerstone qualification standard for welding, brazing, and plastic fusion in the pressure equipment and piping industries. Its structured approach — through WPSs, PQRs, and WPQs — ensures that both the procedures and the people executing them meet a documented and tested standard of quality.

For fabricators, contractors, and inspection professionals, understanding the organization of Section IX and the relationships between its parts and articles is essential. Whether you are qualifying a new welding procedure for a pressure vessel, certifying a welder for a critical piping project, or auditing a manufacturer’s quality system, Section IX provides the framework to do so consistently and reliably.

If you would like us to publish a deeper dive into any specific part or article of Section IX — such as supplementary essential variables, mechanical testing requirements, or P-Number groupings — please let us know in the comments below.