16.1 PQR versus WPS Hierarchy, Qualification Workflow & Standard Procedures
Key Takeaways
- A Procedure Qualification Record (PQR) is a certified historical record documenting actual welding variables recorded during test coupon fabrication and subsequent destructive mechanical test results; it never specifies operating ranges.
- A Welding Procedure Specification (WPS) is a written production instruction providing qualified operating ranges for welders and quality inspectors, mathematically and metallurgically derived from one or more supporting PQRs.
- Under ASME Section IX QW-103 and AWS B2.1 Clause 4, the qualifying manufacturer maintains non-delegable operational responsibility; coupon welding cannot be subcontracted, though specimen machining and mechanical testing may be performed by accredited independent laboratories.
- Standard Welding Procedure Specifications (SWPSs) per AWS B2.1 and ASME IX Appendix E eliminate coupon welding only when the adopting organization successfully conducts a documented demonstrative test per QW-500.
- Multiple PQRs may support a single production WPS, and conversely, a single PQR may support multiple WPSs across different joint configurations, processes, and thickness combinations per QW-200.2.
16.1 Procedure Qualification Record (PQR) & WPS Generation Workflows
Quick Answer: A Procedure Qualification Record (PQR) is a permanent, certified factual record documenting the actual welding variables (single values, not ranges) recorded during the welding of a test coupon and the resulting destructive test data (tension, bend, impact, macroetch). The Welding Procedure Specification (WPS) is a qualified written direction providing operational parameter ranges to welders and quality personnel for production fabrication. Under ASME Section IX (Article II, QW-200.1/QW-200.2) and AWS B2.1, a preliminary WPS (pWPS) guides test coupon fabrication. The manufacturer holds non-delegable organizational responsibility: while specimen machining and mechanical testing can be subcontracted to accredited testing laboratories, coupon welding must be performed under the direct operational control of the manufacturer by their own personnel. Standard Welding Procedure Specifications (SWPSs) per AWS B2.1 and ASME IX Appendix E exempt the user from standard PQR coupon testing only upon completion of a documented demonstrative test per QW-500.
The Dual-Document Hierarchy: PQR vs. WPS Engineering Philosophy
In pressure vessel, structural, and piping fabrication governed by the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (BPVC) Section IX and the American Welding Society (AWS) B2.1/B2.1M (Specification for Welding Procedure and Performance Qualification), welding is recognized as a special process. The internal metallurgical soundness, mechanical strength, ductility, and fracture toughness of a completed weldment cannot be fully verified through nondestructive surface or volumetric examination alone. Consequently, quality assurance relies on rigorous a priori qualification of the welding procedure.
This regulatory philosophy establishes a strict two-tier documentation hierarchy consisting of the Procedure Qualification Record (PQR) and the Welding Procedure Specification (WPS).
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| THE DUAL-DOCUMENT QUALIFICATION ARCHITECTURE |
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| Document Parameter | Procedure Qualification Record (PQR) | Welding Procedure Spec (WPS)|
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| Governing Clauses | ASME IX QW-200.2 / AWS B2.1 Cl. 4 | ASME IX QW-200.1 / AWS B2.1 |
| Fundamental Purpose | Historical record of test coupon | Working shop instruction |
| Parameter Representation | Exact actual values recorded | Qualified operational ranges|
| Base & Weld Metal Thickness | Exact coupon thickness T and weld t | Qualified range per QW-451 |
| Modifiability & Revisions | Immutable historical document | Dynamic engineering revision|
| Organizational Certification | Signed certification mandatory | Technical approval required |
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The Procedure Qualification Record (PQR)
Per ASME Section IX QW-200.2, the PQR is a record of the variables recorded during the welding of the test coupon. It also contains the test results of the tested specimens. Crucially, the PQR is a factual, historical document:
- Exact Actuals Only: The PQR records single values observed during coupon fabrication (e.g., "125 A, 24 V, 8.2 in/min travel speed, 225°F preheat"). It never contains operational tolerance ranges.
- Destructive Test Results: It records numerical tensile breaking loads, calculated ultimate tensile stresses, failure locations (e.g., "base metal ductile fracture"), guided bend results (e.g., "no open defects"), and absorbed Charpy V-notch energy values.
- Immutability: Because it documents a completed historical physical event, a PQR cannot be altered or updated over time. The only permitted changes are editorial or typographical corrections, provided the underlying factual testing data is substantiated by original laboratory records.
The Welding Procedure Specification (WPS)
Per ASME Section IX QW-200.1, a WPS is a written qualified welding procedure prepared to provide direction for making production welds to Code requirements. Unlike the PQR, the WPS is an operational instruction document:
- Qualified Ranges: It provides practical operating envelopes (e.g., "110–140 A, 22–26 V, 6–10 in/min") within which a welder or welding operator can maintain arc stability and deposit sound weld metal.
- Boundary Conditions: The parameter ranges on the WPS are bounded by the essential, supplementary essential, and nonessential variables established by the supporting PQR(s) and governed by Section IX tables (e.g., QW-451 for thickness, QW-250 for process variables).
The Preliminary WPS (pWPS)
Before a test coupon can be welded, the welding engineer must formulate a preliminary Welding Procedure Specification (pWPS) or draft procedure. The pWPS outlines the proposed base metals, filler metal specifications, joint geometry, preheat, shielding gas composition, and target electrical parameters intended to achieve the desired metallurgical properties. The welder follows the pWPS during coupon assembly while quality personnel record the actual parameters that will populate the final PQR.
Standardized Procedure Qualification Workflow
The standardized workflow for developing, qualifying, and certifying a welding procedure per ASME Section IX Article II and AWS B2.1 follows an eight-stage engineering cycle.
STANDARDIZED WPS / PQR DEVELOPMENT PIPELINE
[1. Design Intent] ----> [2. Formulate pWPS] ----> [3. Assemble & Weld Coupon]
- Design Code Mandates - Select P-No, F-No - Clean & Fit Joint
- Material & Service - Target Volts/Amps - Log Real-Time Variables
- Toughness Reqs - Establish Preheat - Direct Manufacturer Control
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v
[6. Certify PQR] <------ [5. Destructive Tests] <-- [4. Nondestructive Exam]
- Verify Code Compliance - Reduced-Section Tensile - Visual Inspection (VT)
- Match SMTS & 5% Rule - Guided Bends (QW-160) - Volumetric NDE (RT/UT)
- Sign Certification - Charpy V-Notch (QW-170) - Confirm Defect-Free
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v
[7. Generate Production WPS] ---------------------> [8. Production Deployment]
- Apply Table QW-451 Thickness Multipliers - Welder Direction in Shop
- Establish Essential & Nonessential Ranges - Quality Surveillance
Multiplicity Rules: Supporting Relationships
ASME Section IX QW-200.2 explicitly codifies flexible documentation relationships between WPSs and PQRs:
- Multiple PQRs Supporting One WPS: A fabricator may combine multiple PQRs to create a single versatile production WPS. For example, a multi-process WPS for Gas Tungsten Arc Welding (GTAW) root combined with Shielded Metal Arc Welding (SMAW) fill and cap can be supported by two distinct PQRs—one qualifying GTAW on a thin coupon and another qualifying SMAW on a heavy-wall coupon.
- One PQR Supporting Multiple WPSs: A single robust PQR may support several distinct production WPSs. For example, a single PQR welded on 1.0 in (25.4 mm) thick plate qualifies base metals from 3/16 in (5 mm) up to 2.0 in (50 mm). The fabricator can generate separate WPSs for flat groove welds, vertical fillet welds, and diverse joint groove preparations, all cross-referencing the single PQR.
Standard Welding Procedure Specifications (SWPS)
Both AWS B2.1 and ASME Section IX recognize that qualifying proprietary welding procedures via test coupons represents a significant financial and administrative commitment. To support standard manufacturing applications, the American Welding Society publishes Standard Welding Procedure Specifications (SWPSs) under AWS B2.1. ASME Section IX adopts selected SWPSs through Mandatory Appendix E.
SWPS Architecture and Adoption Prerequisites
An SWPS is a pre-tested, pre-qualified procedure published by AWS consensus committees covering common carbon and austenitic steel combinations, thicknesses, and processes (e.g., AWS B2.1-1-016 for SMAW of carbon steel, 1/8 through 1-1/2 inch thick). However, adopting an SWPS is not simply a paperwork exercise. ASME Section IX Article V (QW-500) establishes mandatory technical and organizational prerequisites:
- Formal Organizational Adoption: The manufacturer's quality assurance system must officially adopt the SWPS by recording the company name, entering internal procedure numbers, and obtaining the dated signature of the responsible engineering authority.
- Mandatory Demonstrative Testing (QW-500): Prior to production welding, the fabricator must execute a demonstration test coupon using the welding parameters, consumables, and joint configurations specified in the SWPS. The demonstrative coupon must be welded by the manufacturer's employee and subjected to:
- Visual examination per QW-194; and
- Either mechanical testing (two transverse tension specimens and four guided bend specimens per Table QW-451.1) or volumetric nondestructive examination (RT or UT) as permitted by QW-520.
- Prohibition of Technical Alteration: The manufacturer is strictly forbidden from altering any essential or supplementary essential variable printed on the SWPS. If any parameter (e.g., shielding gas composition, base metal P-Number, or electrical parameter range) must be changed to suit shop operations, the entire SWPS is voided, and the procedure must be qualified independently from scratch under Article II.
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| SWPS VS. PROPRIETARY ASME IX QUALIFICATION |
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| Technical Parameter | Proprietary PQR Qualification | SWPS per Mandatory Appendix E |
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| Coupon Welding | Mandatory (Article II) | Demonstration Coupon (QW-500) |
| Mechanical Destructive Testing | Full Tension + Guided Bends | Permitted RT/UT in lieu of Mech |
| Variable Flexibility | Full engineering control | Zero modification permitted |
| Supported Materials | Any weldable alloy | Limited to published standards |
| Development Cost | High initial qualification cost | Low adoption cost |
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A contractor constructing piping under ASME B31.3 elects to adopt an AWS B2.1 Standard Welding Procedure Specification (SWPS) listed in ASME Section IX Mandatory Appendix E. What administrative and technical action must the contractor perform before the SWPS can be legally utilized in production?