11.2 Welder Performance Qualification (WPQ) & Continuity per ASME IX

API 653 Aboveground Storage Tank Inspector Exam

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1 Chapter 1: API 653 Scope, Inspector Certification & Roles

1.1 Scope of API 653, Tank Types & Construction Standards 1.2 Inspector Roles, Responsibilities & Certification Requirements 1.3 Inspection Planning, Safety, Confined Space Entry & Preparation

2 Chapter 2: Tank Shell & Roof Components Inspection

2.1 Fixed Roof Types, Structural Supports & Inspection Practices 2.2 Floating Roofs, Seals, Drainage & Operational Issues 2.3 Shell Courses, Welds, Attachments & Wind Girders 2.4 Tank Appurtenances, Nozzles, Manways & Piping Connections

3 Chapter 3: Tank Bottom & Foundation Inspection

3.1 Tank Bottom Types, Annular Plates & Internal Bottom Inspection 3.2 Foundation Types (Concrete Ringwall, Earth, Asphalt) & Inspection 3.3 Leak Detection Systems, Secondary Containment & Under-Tank Monitoring

4 Chapter 4: Corrosion & Damage Mechanisms in Storage Tanks

4.1 Atmospheric Corrosion, Condensation & External Deterioration 4.2 Corrosion Under Insulation (CUI) & Piping/Nozzle Interfaces 4.3 Soil-Side Corrosion, Under-Bottom Pitting & Microbiologically Induced Corrosion (MIC) 4.4 Product-Side Deterioration: Chemical Attack, Ethanol SCC, Concentration Cell & Sulfuric Acid Corrosion

5 Chapter 5: Materials, Toughness & Brittle Fracture Prevention

5.1 Tank Steels, Material Specifications & Historic Standards 5.2 Brittle Fracture Assessment: Figure 5.1 Decision Tree & Exemption Curves (API 653 Section 5) 5.3 Charpy V-Notch Impact Testing & Minimum Design Metal Temperature (MDMT)

6 Chapter 6: Cathodic Protection & Interior Linings

6.1 Cathodic Protection Principles & Systems for Tank Bottoms (API RP 651) 6.2 CP Criteria, Surveys, Potential Measurements & Interference (API RP 651) 6.3 Tank Bottom Interior Linings, Surface Prep & Inspection (API RP 652)

7 Chapter 7: Corrosion Rates, Remaining Life & Inspection Intervals

7.1 Determining Corrosion Rates (Short-Term vs. Long-Term) 7.2 Remaining Life Calculations & Limiting Components 7.3 Establishing In-Service & Out-of-Service Inspection Intervals (API 653 Section 6)

8 Chapter 8: Tank Shell Minimum Thickness Evaluation

8.1 Shell Minimum Thickness Calculations (tmin for Hydrostatic & Operating Levels) 8.2 One-Foot Method, Variable Design Point & Reconstructed-Tank Shell Thickness 8.3 Joint Efficiency (E) Selection, Missing Data & Radiography Factors 8.4 Evaluation of Pitting, Localized Thin Areas (LTA) & Critical Length (L)

9 Chapter 9: Bottom Plate & Annular Ring Thickness Evaluation

9.1 Minimum Bottom Thickness Formulations (MRT, MRTbottom, MRTlinear) 9.2 Annular Plate Evaluation, Stress Criteria & Critical Zones 9.3 Bottom Pitting Evaluation & Remaining Thickness Before Next Inspection

10 Chapter 10: Tank Repairs & Alterations Standards

10.1 Classification: Repair vs. Alteration vs. Reconstruction (API 653 Section 9) 10.2 Shell Plate Replacement, Lapped Patch Plates & Insert Plates 10.3 Shell Penetrations, Door Sheets & Nozzle Additions 10.4 Hot Tapping Requirements, Limitations & Pre-Engineering (API 653 Section 9.15 & API Publ 2201)

11 Chapter 11: Welding Procedures, Qualifications & Quality Control

11.1 Welding Procedure Specification (WPS) & Procedure Qualification Record (PQR) per ASME IX 11.2 Welder Performance Qualification (WPQ) & Continuity per ASME IX 11.3 Essential, Non-Essential & Supplementary Essential Variables 11.4 Preheating, Post-Weld Heat Treatment (PWHT) & Weld Flaw Remediation

12 Chapter 12: Nondestructive Examination (NDE) Methods

12.1 Visual Examination (VT) & Magnetic Particle Testing (MT) per ASME V 12.2 Liquid Penetrant (PT) & Ultrasonic Thickness Measurement (ASME V Article 6 & SE-797) 12.3 Radiographic Testing (RT): Acceptance Criteria, Film Interpretation & ASME V/API 650

13 Chapter 13: Hydrostatic Testing & Post-Repair Examination

13.1 Hydrostatic Test Triggers, Exemption Criteria & Major Alterations (API 653 Section 12.3) 13.2 Leak Testing: Vacuum Box, Tracer Gas, Diesel & Air Pressure Tests 13.3 NDE Examination Requirements for Shell, Bottom, Roof & Nozzle Welds (API 653 Section 12.1)

14 Chapter 14: Relief Devices, Tank Settlement & Nameplate Records

14.1 Pressure & Vacuum Relief Devices, Venting Principles (API RP 576 & API 2000) 14.2 Tank Settlement Types: Uniform, Tilt, Out-of-Plane & Edge Settlement (API 653 Annex B) 14.3 Evaluating Settlement Limits, Cosine Curve Analysis & Remedial Action 14.4 Tank Marking, Nameplates, Inspection Reports & Recordkeeping (API 653 Section 13)

11.2 Welder Performance Qualification (WPQ) & Continuity per ASME IX

Key Takeaways Explain This Topic AI

A Welder Performance Qualification (WPQ) verifies the individual welder's manual dexterity and physical ability to deposit sound, defect-free weld metal, distinct from the PQR's validation of procedure metallurgy.

Essential performance variables under ASME IX QW-350 govern the welder's limits of qualification, including welding process, elimination of backing, filler metal F-number, pipe outside diameter, and welding position.

Qualifying in the 6G inclined pipe test position qualifies a welder for all groove and fillet weld positions on both plate and pipe within the qualified thickness and diameter ranges.

Under ASME IX QW-322.1, a welder's qualification remains active indefinitely provided the specific welding process is used within every 6-month interval; failure to weld using the process causes all qualifications for that process to expire.

API 650 Section 9.4 and API 653 Section 11.2.2 require each welder to be assigned a unique identification symbol to stamp adjacent to production welds, or the repair organization must maintain a comprehensive weld map.

Last updated: September 2026

11.2 Welder Performance Qualification (WPQ) & Continuity per ASME IX

Core Principle of Welder Qualification: While a Procedure Qualification Record (PQR) establishes the mechanical, metallurgical, and structural suitability of a welding procedure, the Welder Performance Qualification (WPQ) evaluates the manual skill, technique, and dexterity of the individual welder. Under ASME Section IX Article III and API 653 Section 11.2 , no welder or welding operator may strike an arc on an aboveground storage tank without documented, active qualification for the specific process, position, consumable, and thickness envelope deployed.

1. Purpose and Philosophy of Welder Performance Qualification (WPQ)

A common misunderstanding in quality assurance is confusing procedure qualification with welder performance qualification:

PQR (The Procedure): Demonstrates that the combination of base metals, filler metals, preheat, and heat input produces a weldment possessing acceptable tensile strength, ductility, and notch toughness. PQR tests the chemistry and physics of the joint.

WPQ (The Welder): Demonstrates that the individual tradesperson has the mechanical ability to deposit sound weld metal free of internal defects such as lack of fusion, slag inclusions, incomplete penetration, porosity, or burn-through. WPQ tests the workmanship and manual dexterity of the person.

Under QW-301.2 , each welder must prepare and weld a standardized test coupon in accordance with an approved, qualified WPS. The test coupon is then examined using non-destructive examination (visual examination plus volumetric radiography or ultrasonic testing per QW-304) or destructive mechanical testing (transverse bend tests per QW-302).

2. Essential Performance Variables (QW-350 & QW-416)

In procedure qualification (QW-250), dozens of variables are tracked. In contrast, welder qualification focuses strictly on essential performance variables listed in QW-350 (for manual/semi-automatic welders) and QW-360 (for machine/automatic welding operators). Non-essential variables do not apply to welders. +-------------------------------------------------------------------------+

| ESSENTIAL PERFORMANCE VARIABLES (QW-350) |
+-----------------------+-------------------------------------------------+
| Variable Type | Code Reference & Operational Impact |
+-----------------------+-------------------------------------------------+
| Welding Process | QW-401.2: A change from one process to another |
| | (e.g., SMAW to GTAW or GMAW) requires full |
| | new qualification. |
+-----------------------+-------------------------------------------------+
| Backing | QW-402.4: Deletion of backing (qualifying with |
| | backing does not qualify open root without |
| | backing; qualifying without backing qualifies |
| | both with and without backing). |
+-----------------------+-------------------------------------------------+
| Filler Metal F-Number | QW-404.15 & QW-433: Grouping of electrodes. |
| | Higher F-numbers qualify lower F-numbers with |
| | backing; F-4 qualifies F-1 through F-4. |
+-----------------------+-------------------------------------------------+
| Base Metal Thickness | QW-452.1(b): Maximum weld metal thickness ($t$) |
| | qualified is $2t$ for $t < 3/4$ in.; $t \ge 3/4$|
| | in. with 3 layers qualifies unlimited ($2t$). |
+-----------------------+-------------------------------------------------+
| Pipe Outside Diameter | QW-452.3: Diameter of test coupon sets minimum |
| | outside diameter qualified for production. |
+-----------------------+-------------------------------------------------+
| Position & Progression| QW-405.1 & QW-405.3: Welding position (1G to |
| | 6G); vertical progression change (uphill vs. |
| | downhill) requires requalification. |
+-----------------------+-------------------------------------------------+
Backing Elimination (QW-402.4)

Welding an open-root groove weld without backing requires significantly greater skill to establish a sound root pass than welding over a permanent steel backing strip, copper shoe, or ceramic tape. Therefore:

Qualifying without backing (open root) qualifies the welder to weld both with and without backing .

Qualifying with backing (or double-welded joints backgouged to sound metal) restricts the welder to production welds with backing only .

Filler Metal Usability F-Numbers (QW-404.15 & QW-433)

ASME Section IX Table QW-432 assigns filler metals to F-Numbers based on their operating characteristics:

F-No. 1: Heavy rutile/iron powder electrodes (e.g., EXX24, EXX27, EXX28).

F-No. 2: High titania potassium electrodes (e.g., EXX12, EXX13, EXX14).

F-No. 3: Cellulosic electrodes (e.g., E6010, E7010) generating a digging, high-penetration arc.

F-No. 4: Low-hydrogen basic electrodes (e.g., E7015, E7016, E7018) providing high toughness and resistance to cracking.

F-No. 5: Austenitic stainless steel electrodes (e.g., E308, E309, E316).

F-No. 6: Solid wire, flux-cored wire, or bare rods for GMAW, GTAW, and SAW.

Under Table QW-433 , qualifying with an F-No. 4 electrode with backing qualifies the welder to deposit F-1, F-2, F-3, and F-4 electrodes with backing . However, to weld open-root F-3 (e.g., E6010 root pass) in production without backing, the welder must explicitly qualify on an open-root F-3 coupon without backing.

Pipe Diameter Qualified Limits (QW-452.3)

Welding around small-diameter cylinders requires continuous manipulation of torch angles and travel speeds. Therefore, test coupon outside diameter ( D D D ) establishes minimum diameter limits:

Coupon OD < 1 in. (25 mm) < 1\text{ in. (25 mm)} < 1 in. (25 mm) : Qualifies from the diameter tested up to unlimited.

Coupon OD 1 in. ≤ D ≤ 2 – 7 / 8 in. (73 mm) 1\text{ in.} \le D \le 2\text{--}7/8\text{ in. (73 mm)} 1 in. ≤ D ≤ 2 – 7/8 in. (73 mm) : Qualifies from 1 in. (25 mm) 1\text{ in. (25 mm)} 1 in. (25 mm) OD up to unlimited .

Coupon OD > 2 – 7 / 8 in. (NPS 2-1/2) > 2\text{--}7/8\text{ in. (NPS 2-1/2)} > 2 – 7/8 in. (NPS 2-1/2) or Plate: Qualifies from 2 – 7 / 8 in. (73 mm) 2\text{--}7/8\text{ in. (73 mm)} 2 – 7/8 in. (73 mm) OD up to unlimited , as well as all plate thicknesses.

3. Welding Positions and Qualification Envelopes (QW-461)

Welding positions present varying gravitational forces on the molten puddle. ASME Section IX defines test positions for plate and pipe groove welds: 1G (Flat) 2G (Horizontal) 3G (Vertical) 4G (Overhead)

-------- +-------------+ | +-------------+
| Weld | | Weld | Weld| | Plate |
| Down | +-------------+ | +-------------+
| | | | Weld ^

5G (Pipe Horizontal Fixed) 6G (Pipe Inclined 45° Fixed)
+-------+ //
/ Weld \ // Weld
| Vertical | // All Positions
\ Seam / //
+-------+ 45°

1G (Flat Position): Plate or pipe horizontal, rotated during welding so the arc deposits weld metal from the top side. Qualifies Flat position only .

2G (Horizontal Position): Plate vertical with the weld seam horizontal; pipe vertical fixed with the seam horizontal. Qualifies Flat and Horizontal positions .

3G (Vertical Position): Plate vertical with the weld seam vertical. Qualifies Flat and Vertical positions .

4G (Overhead Position): Plate horizontal with the weld deposited from the bottom facing upward. Qualifies Flat and Overhead positions .

5G (Pipe Horizontal Fixed): Pipe horizontal with axis fixed (not rotated); the welder must deposit weld metal moving circumferentially through overhead, vertical, and flat positions. Qualifies Flat, Vertical, and Overhead positions .

6G (Pipe Inclined at 45° Fixed): Pipe fixed at a 45° angle without rotation. This is the most comprehensive qualification test. A welder who qualifies in the 6G position is qualified to weld in ALL positions (Flat, Horizontal, Vertical, and Overhead) on both plate and pipe!

Combination 2G + 5G: Qualifying on both a 2G and a 5G test coupon also qualifies the welder for all positions.

Vertical Progression (QW-405.1)

For vertical welding (3G, 5G, 6G), the direction of progression— uphill (progressing from bottom to top) versus downhill (progressing from top to bottom)—is a critical essential performance variable. A change from uphill to downhill, or from downhill to uphill, requires full requalification.

4. Welder Continuity Tracking and Maintenance (QW-322)

Once a welder successfully passes a performance qualification test, the qualification does not remain active permanently without ongoing demonstration of competence.

The 6-Month Continuity Rule (QW-322.1(a))

Under ASME Section IX QW-322.1(a) :

A welder or welding operator's qualification for a specific welding process remains valid indefinitely, provided that no more than six (6) months have elapsed since the welder last welded using that process.

The welder is not required to weld in all qualified positions, diameters, or thicknesses during this 6-month window; striking an arc and depositing sound weld metal with the process (e.g., SMAW, GTAW, GMAW) under any qualified WPS maintains qualification for all positions, diameters, and thicknesses previously earned under that process.

Employer Responsibility and Continuity Records

The employer (the repair organization or tank manufacturer) must maintain a written, verifiable Welder Continuity Log . The log must record:

Welder name and assigned unique identification symbol/stamp.

The specific welding process deployed.

The date the process was used.

Verification reference (e.g., shop traveler number, tank repair seam number, radiographic test report, or supervisory sign-off). +-------------------------------------------------------------------------+

| WELDER CONTINUITY RECORD (EXAMPLE) |
+-----------+-----------+---------+------------+-------------+------------+
| Welder ID | Name | Process | Date Used | Seam / Job | Supervisor |
+-----------+-----------+---------+------------+-------------+------------+
| W-104 | J. Miller | SMAW | 2026-02-15 | TK-101 Door | M. Vance |
| W-104 | J. Miller | GTAW | 2026-03-22 | P-204 Spool | M. Vance |
| W-104 | J. Miller | SMAW | 2026-08-10 | TK-105 Sump | R. Chen |
+-----------+-----------+---------+------------+-------------+------------+
5. Expiration, Renewal, and Revocation for Cause

ASME Section IX and API 653 establish definitive rules for managing lapsed or questioned qualifications:

Expiration and Renewal Protocol (QW-322.2)

Lapse Trigger: If a welder does not use a given process for a period exceeding six (6) months , the qualifications for that specific process expire completely.

Renewal Pathway: Under QW-322.2(a), renewal of a lapsed qualification does not require duplicating all historical test coupons. The welder may renew qualifications for that process by welding a single test coupon of either plate or pipe, of any material, thickness, or diameter , in any position, and successfully completing either radiographic/ultrasonic testing or bend testing. Successful testing immediately reinstates all previous qualifications for that process across all previously qualified positions, diameters, and thicknesses.

Revocation for Cause (QW-322.1(b))

The Revocation Rule: Under QW-322.1(b), whenever there is a specific reason to question a welder's ability to make welds that meet the specification, the qualifications that support that welding must be immediately revoked .

Application: Even if a welder has flawless continuity records, if their production welds on a tank repair show repeated radiographic failures, lack of fusion, or severe crack indications, the Authorized Inspector or owner-user has mandatory authority to stop the welder. Requalification requires welding a new performance coupon and passing full mechanical testing.

6. Verification and Identification Procedures for Authorized Inspectors

Under API 650 Section 9.4 and API 653 Section 11.2.2 , the Authorized Inspector must enforce rigorous quality control oversight:

Pre-Welding Verification: Before any production arc is struck, the inspector must audit the contractor's WPQ records and continuity logs to verify that each assigned welder is actively qualified for the specific process, position, F-number, and thickness range.

Welder Identification Stamps: Each qualified welder must be assigned a unique identification symbol or stamp. The welder must stamp this identification adjacent to completed weld seams at intervals not exceeding 3 ft (1 m) along shell seams, or immediately adjacent to nozzle attachment welds.

Alternative Weld Mapping: In lieu of physically steel-stamping the tank plates (which can create micro-notches in notch-sensitive steels), API 650 Section 9.4.2 and API 653 permit the repair organization to maintain a documented weld map . The weld map records the exact location of every weld seam and lists the unique identification of the welder who completed each pass (root, fill, and cap).

7. Welder Performance Qualification Coverage Matrix

The following matrix summarizes the qualification envelopes earned by specific performance coupon configurations under ASME Section IX:

Test Coupon Configuration Coupon Position Tested Positions Qualified (Groove Welds) Positions Qualified (Fillet Welds) Production Diameter Range Qualified

Plate Groove Coupon 1G (Flat) Flat (1G) only Flat (1F) only Flat plate & pipe ≥ 24 in. OD \ge 24\text{ in. OD} ≥ 24 in. OD (with backing)

Plate Groove Coupon 2G (Horizontal) Flat & Horizontal (1G, 2G) Flat & Horizontal (1F, 2F) Plate & pipe ≥ 24 in. OD \ge 24\text{ in. OD} ≥ 24 in. OD (with backing)

Plate Groove Coupon 3G (Vertical) Flat & Vertical (1G, 3G) Flat, Horizontal & Vertical (1F, 2F, 3F) Plate & pipe ≥ 24 in. OD \ge 24\text{ in. OD} ≥ 24 in. OD (with backing)

Plate Groove Coupon 4G (Overhead) Flat & Overhead (1G, 4G) Flat, Horizontal & Overhead (1F, 2F, 4F) Plate & pipe ≥ 24 in. OD \ge 24\text{ in. OD} ≥ 24 in. OD (with backing)

Pipe Groove Coupon ( > 2 - 7 / 8 in. OD > 2\text{-}7/8\text{ in. OD} > 2 - 7/8 in. OD ) 2G (Horizontal) Flat & Horizontal (1G, 2G) Flat & Horizontal (1F, 2F) Pipe ≥ 2 - 7 / 8 in. (73 mm) OD \ge 2\text{-}7/8\text{ in. (73 mm) OD} ≥ 2 - 7/8 in. (73 mm) OD & plate

Pipe Groove Coupon ( > 2 - 7 / 8 in. OD > 2\text{-}7/8\text{ in. OD} > 2 - 7/8 in. OD ) 5G (Horizontal Fixed) Flat, Vertical & Overhead (1G, 3G, 4G) All Fillet Positions (1F, 2F, 3F, 4F) Pipe ≥ 2 - 7 / 8 in. (73 mm) OD \ge 2\text{-}7/8\text{ in. (73 mm) OD} ≥ 2 - 7/8 in. (73 mm) OD & plate

Pipe Groove Coupon ( > 2 - 7 / 8 in. OD > 2\text{-}7/8\text{ in. OD} > 2 - 7/8 in. OD ) 6G (Inclined 45° Fixed) ALL Positions (1G, 2G, 3G, 4G) ALL Positions (1F, 2F, 3F, 4F) Pipe ≥ 2 - 7 / 8 in. (73 mm) OD \ge 2\text{-}7/8\text{ in. (73 mm) OD} ≥ 2 - 7/8 in. (73 mm) OD & plate

Pipe Groove Coupon ( < 1 in. OD < 1\text{ in. OD} < 1 in. OD ) 6G (Inclined 45° Fixed) ALL Positions ALL Positions From diameter tested up to unlimited & plate