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What is a Procedure Qualification Record (PQR) in Piping Engineering?
What is a Procedure Qualification Record (PQR) in Piping Engineering?
A Procedure Qualification Record, or PQR, is a formal document that records the actual welding variables used during a test coupon weld and the results of all destructive mechanical testing performed on that coupon. It proves that a specific combination of welding process, base metal, filler metal, and parameters produces a weld with acceptable strength, ductility, and toughness. The PQR forms the technical foundation for the Welding Procedure Specification, or WPS, that production welders follow on the job.
How the PQR Supports the WPS
The WPS tells production welders what parameters to use. However, the WPS cannot exist without a qualifying PQR behind it. The PQR records every essential variable as a single actual value, not a range. Voltage, amperage, travel speed, preheat temperature, base metal grade, filler metal classification, and post-weld heat treatment conditions all appear as exact recorded values. The WPS then derives its allowable ranges from those recorded actuals. Consequently, a PQR cannot be revised after certification. The only permitted correction is a typographical error. Any change to an essential variable beyond code-permitted limits requires a new qualification test entirely.
Governing Codes
ASME Section IX of the BPVC governs PQR requirements for pressure piping and pressure vessels under ASME B31.3 and related codes. It defines essential variables, required test types, acceptance criteria, and documentation requirements. API RP 577 covers welding procedure qualification for petroleum industry piping under API 570. AWS D1.1 governs structural welding qualification separately. Engineers specify which code governs on each project, and the PQR must comply fully with that code before production welding begins.
Applications in Piping Engineering
Qualifying Common Welding Processes
Engineers qualify PQRs for every welding process used on a piping project. SMAW is the most commonly qualified process for field welding of carbon and alloy steel process piping. TIG welding qualifications cover root passes on stainless steel, high-alloy, and small-bore piping where weld quality requirements are highest. FCAW qualifications apply to structural attachments, pipe support welds, and large-bore carbon steel production welds where deposition rate is important. Additionally, orbital welding qualifications apply to small-bore, high-purity, and pharmaceutical piping where consistent automated weld quality is required.
New Construction and Fabrication Shop Qualification
Fabrication shops qualify PQRs before production welding begins on any new piping project. The shop welds a test coupon using the intended process, base metal P-number, and filler metal F-number. A certified testing laboratory then performs the required destructive tests on the coupon. Results must meet the acceptance criteria in ASME Section IX before the shop can write the supporting WPS and assign welders to production work. Furthermore, the completed PQR must be available to the owner’s inspector throughout the project.
Alloy and High-Temperature Service Qualifications
Chromium-molybdenum alloy piping in high-temperature service requires separate PQR qualification from carbon steel. The test coupon must match the P-number group of the production base metal. Impact testing also applies where low-temperature toughness is a design requirement. In these cases, the PQR must record supplementary essential variables in addition to the standard essential variable set. Consequently, alloy piping projects often require multiple PQRs to cover the full range of materials, thicknesses, and welding positions used in the field.
Benefits of Procedure Qualification Records
Proven Weld Mechanical Properties
A PQR demonstrates through physical testing that the welding procedure produces a weld meeting minimum strength and ductility requirements. Tensile tests confirm that the weld metal and heat-affected zone meet the specified minimum tensile strength of the base metal. Guided bend tests confirm adequate ductility. Charpy impact tests confirm adequate toughness at design temperature where required. Therefore, every production weld made to a qualified WPS carries documented assurance of its mechanical properties.
Code Compliance and Traceability
ASME B31.3 requires that all production welds on pressure piping be made to a qualified WPS supported by a valid PQR. Without this documentation, the piping system cannot receive code compliance certification. Additionally, PQR records tied to weld maps and isometric drawings create full traceability from each production weld back to the qualification test that validates the procedure. This traceability supports fitness-for-service assessments, in-service inspection programs, and plant modification projects throughout the operating life of the facility.
Reuse Across Multiple Projects
A single PQR can support multiple WPSs, provided the WPS variables remain within the qualified ranges recorded on the PQR. Consequently, fabrication shops build a library of PQRs over time that covers their standard material grades, thicknesses, and processes. This eliminates the need for a new qualification test every time a new project begins. It also reduces cost and schedule impact for projects with tight timelines.
Limitations to Consider
Essential Variable Changes Require Requalification
Any change to an essential variable beyond the code-permitted range invalidates the existing PQR for that application. Switching base metal P-number, changing filler metal F-number, or increasing material thickness beyond the qualified range all require a new test coupon and a fresh round of destructive testing. This can create schedule delays on projects where late material changes occur after the welding qualification program is already complete.
PQR Does Not Qualify the Welder
A PQR qualifies the procedure, not the individual performing the weld. Each production welder must hold a separate Welder Performance Qualification, or WPQ, demonstrating personal skill in depositing sound welds using the qualified procedure. A valid PQR with no qualified welders assigned to it provides no assurance of production weld quality. Therefore, welding quality programs must manage both procedure qualification and welder qualification as separate parallel requirements.
NDE Complements but Does Not Replace Testing
Ultrasonic testing and mag particle testing on production welds confirm the absence of defects. However, they do not confirm that the welding procedure used was qualified for the material and thickness involved. A production weld can pass all NDE requirements and still be made to an unqualified or incorrectly applied procedure. Consequently, NDE and procedure qualification serve different assurance functions. Both are necessary and neither replaces the other.
Procedure Qualification Record FAQ
What is a Procedure Qualification Record (PQR) in piping engineering? A PQR is a certified document that records the actual welding variables used during a test coupon weld and the results of all required destructive mechanical testing. It proves that a specific welding procedure produces a weld with acceptable strength, ductility, and toughness. ASME Section IX governs PQR requirements for pressure piping under ASME B31.3. The PQR must be complete and certified before the supporting WPS can be written and before any production welding begins on the project.
What is the difference between a PQR and a WPS? The PQR records what actually happened during the qualification test. It contains single actual values for every essential variable and the destructive test results that confirm acceptable mechanical properties. The WPS uses those recorded actuals as the basis for the allowable ranges that production welders follow. Consequently, the WPS cannot exist without a valid supporting PQR. The PQR is the evidence. The WPS is the instruction document derived from that evidence.
What destructive tests does a PQR require under ASME Section IX? ASME Section IX requires tensile tests to confirm that the weld meets the minimum specified tensile strength of the base metal. It also requires guided bend tests to confirm adequate ductility. Where low-temperature service applies or where the construction code requires it, Charpy impact tests confirm adequate toughness at the minimum design metal temperature. Side bend tests replace root and face bend tests for material thicknesses above 19 mm. All tests must be performed by a certified testing laboratory, and results must meet the acceptance criteria in ASME Section IX tables QW-153 and QW-163 before the PQR receives certification.
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