ASME Section IX explained

ASME Section IX is the qualification standard for welding and brazing within the ASME Boiler and Pressure Vessel Code. Anyone building pressure vessels, boilers or process piping to ASME qualifies procedures and welders to ASME IX in almost every case. It defines how to test a welding procedure, how to test welders and which variables set the range of each qualification. When qualification is required, and with what additional requirements, is left to the construction code.

ASME IX is used far beyond North America, in refineries, petrochemical plants and EPC projects worldwide. Its logic differs from the ISO system familiar in Europe. This article explains the structure, from P-numbers to the relationship with ASME B31.3 and Section VIII. For a direct comparison with the ISO route, see ASME IX versus ISO 15614-1.

1. How ASME IX is organised: QW, QB and QF

ASME IX has three parts: Part QW for welding, Part QB for brazing and Part QF for plastic fusing. For metal fabricators, QW is the core, divided into articles:

• Article I: general requirements, including test methods and specimens.
• Article II: welding procedure qualification, with variable tables per process in the QW-250 series.
• Article III: welder and welding operator performance qualification.
• Article IV: welding data, including variable definitions, P-numbers, F-numbers, A-numbers and positions.
• Article V: AWS Standard Welding Procedure Specifications (SWPS), usable without your own PQR under conditions.

2. P-numbers and F-numbers

To limit the number of qualifications, ASME IX groups materials. P-numbers group base metals by composition, weldability and mechanical properties: P-No. 1 for carbon and carbon-manganese steel, P-No. 4 and 5A for chromium-molybdenum steels, P-No. 8 for austenitic stainless steel, P-No. 10H for duplex, P-No. 21 to 26 for aluminium and P-No. 41 to 49 for nickel alloys. Ferrous P-numbers carry group numbers, which matter when notch toughness is required. Table QW/QB-422 lists ASTM and ASME materials and a number of European grades.

F-numbers group filler metals by usability for the welder: among covered electrodes, F-No. 3 for cellulosic, F-No. 4 for low-hydrogen and F-No. 5 for stainless electrodes, while steel wires fall under F-No. 6. A-numbers classify the chemical composition of ferrous weld metal.

3. Essential, supplementary essential and nonessential variables

• Essential variables affect the mechanical properties of the joint. A change outside the range, such as a different P-number or F-number, a thickness outside the range or a change in PWHT, requires a new PQR.
• Supplementary essential variables apply only when the construction code requires impact testing, for example an increase in heat input or a different group number within the same P-number.
• Nonessential variables, such as groove design, cleaning method or, in many cases, electrode size, can be changed by revising the WPS without new testing.

The QW-250 tables show which variable falls into which category per process. Welders have their own essential variables; notably, position is usually nonessential for the procedure but essential for the welder.

4. WPS, PQR and WPQ: three documents, three jobs

• The PQR records what was actually used to weld the test coupon and what testing showed. It is a historical record and is not revised in substance.
• The WPS is the working instruction, with ranges derived from one or more PQRs under the rules of ASME IX. One PQR can support several WPSs, and one WPS can rest on several PQRs.
• The WPQ records that a welder welded a coupon to a qualified WPS, and the range this qualifies.

The organisation is responsible for all three. The coupon must be welded under its own supervision; material preparation, specimen machining and testing may be subcontracted. Taking over another company's PQR is not permitted, except in specific cases such as a change of ownership. See our article on the procedure qualification record (PQR).

5. Testing for procedures and welders

A groove weld PQR requires tension tests and guided bend tests, with side bends above a certain thickness. Impact tests are added only when the construction code requires them. A fillet-only PQR is assessed by macro examination. The WPS thickness range follows from coupon thickness and deposited weld metal thickness.

For a WPQ, bend tests or volumetric examination suffice: radiography, or ultrasonic testing under conditions. Short-circuit GMAW (GMAW-S) still requires bend tests. The welder's range follows from coupon thickness, diameter and position, from 1G to 6G.

6. ASME IX, Section VIII and B31.3

ASME IX says how to qualify; the construction code says when and with what additions. Where they conflict, the construction code governs.

• Section VIII Division 1 (pressure vessels) refers to ASME IX in UW-28 and UW-29. Impact requirements follow from UG-84 and UCS-66, PWHT from UCS-56, and the Authorized Inspector reviews qualifications.
• ASME B31.3 (process piping) requires ASME IX qualification in paragraph 328, with its own additions, including rules for qualifications made by other employers or organisations, reviewed by the owner's Inspector.
• Section I, B31.1 and several API standards also refer to ASME IX.

For pressure equipment placed on the EU market under PED 2014/68/EU, ASME qualifications are not automatically valid; the notified body assesses them case by case. Projects combining both worlds benefit from aligning qualifications early through WPS and WPQR qualification.