6.2 Welder Performance Qualification (WPQ) & Testing

Welder Performance Qualification (WPQ) & Testing

While a Welding Procedure Specification (WPS) and its supporting Procedure Qualification Record (PQR) prove that a specific combination of materials, consumables, and heat treatments can produce sound metallurgical and mechanical properties, they do not guarantee that an individual craftsman possesses the manual dexterity to execute those welds cleanly in production.

Welder Performance Qualification (WPQ), governed by ASME Section IX Article III (QW-300) and API 577 Section 6, is the formal testing mechanism used to verify that a welder or welding operator can manipulate the arc, control the puddle, achieve complete fusion, and deposit sound, defect-free weld metal in accordance with a qualified WPS.

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1. Purpose & Philosophy of Welder Performance Qualification

The fundamental philosophy of ASME Section IX separates procedure qualification from performance qualification:

+-----------------------------------------------------------------------------+
|                        PQR VS. WPQ PHILOSOPHICAL SPLIT                      |
|                                                                             |
|   [PROCEDURE QUALIFICATION (PQR)]           [WELDER QUALIFICATION (WPQ)]    |
|   - "Can this weld recipe work?"            - "Can this person weld?"       |
|   - Tests metallurgical compatibility       - Tests manual dexterity        |
|   - Tension tests & bend tests              - Bend tests or volumetric NDE  |
|   - Qualifies base metal chemistry & heat   - Qualifies positions & skills  |
|   - Permanent company record                - Expired if inactive 6 months  |
+-----------------------------------------------------------------------------+

Core Rules Governing WPQ:

1. WPS Adherence: A welder must weld the qualification coupon following the essential parameters of a qualified WPS.
2. Performance vs. Procedure Variables: Welder qualifications have far fewer essential variables than procedure qualifications. For example, changes in base metal P-Number (e.g., welding on P-1 vs. P-8) or preheat temperature do not affect welder qualification because they do not alter the welder's physical manipulation of the puddle (with minor alloy exceptions).
3. Volumetric NDE Option: Unlike a PQR (which requires destructive mechanical tension and bend tests), a welder qualification coupon (except GMAW short-circuiting mode) may often be examined and passed using Radiographic Examination (RT) or Ultrasonic Testing (UT) under QW-304.

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2. Welder Essential Variables (ASME Section IX QW-350 Series)

Paragraphs QW-352 through QW-357 establish the Welder Essential Variables for each welding process. Any change in an essential variable beyond the limits qualified requires immediate performance requalification.

+-----------------------------------------------------------------------------+
|                   ASME SECTION IX WELDER ESSENTIAL VARIABLES                |
|                                                                             |
|   1. WELDING PROCESS      ---> Deleting or changing process (e.g., SMAW->GTAW)|
|   2. BACKING DELETION     ---> Deleting backing (welding open root)         |
|   3. FILLER METAL F-NUMBER---> Changing to higher or non-qualified F-Number |
|   4. DEPOSIT THICKNESS (t)---> Exceeding max qualified thickness (Table 452)|
|   5. PIPE DIAMETER        ---> Welding on pipe smaller than qualified OD    |
|   6. WELDING POSITION     ---> Welding in positions not qualified by coupon |
|   7. VERTICAL PROGRESSION ---> Changing vertical uphill to downhill (or rev)|
|   8. GMAW TRANSFER MODE   ---> Changing spray/globular to short-circuit (S) |
+-----------------------------------------------------------------------------+

Detailed Variable Descriptions for Welder Qualification

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3. Position Qualification Matrix & Progression (QW-461.9)

Welding positions are standardized based on the orientation of the weld axis and the plate/pipe face:

+-----------------------------------------------------------------------------+
|                        STANDARDIZED WELDING POSITIONS                       |
|                                                                             |
|   [PLATE POSITIONS]                                                         |
|   - 1G : Flat position (weld on top)                                        |
|   - 2G : Horizontal position (plate vertical, weld axis horizontal)         |
|   - 3G : Vertical position (plate vertical, weld axis vertical: Up/Down)    |
|   - 4G : Overhead position (plate horizontal, weld from underneath)         |
|                                                                             |
|   [PIPE POSITIONS]                                                          |
|   - 1G : Horizontal pipe ROTATED during welding (flat position)             |
|   - 2G : Vertical pipe FIXED axis (horizontal circumferential weld)         |
|   - 5G : Horizontal pipe FIXED axis (vertical circumferential weld: Up/Down)|
|   - 6G : Pipe inclined at 45° FIXED axis (The Universal Qualification Test) |
+-----------------------------------------------------------------------------+

Position Qualification Matrix (ASME Table QW-461.9)

[!TIP] The Universal 6G Test: In refining and vessel maintenance, testing welders on a 6G pipe coupon (nominal $2\text{ in.}$ Schedule 80 or Schedule 160 pipe) is standard practice because this single coupon qualifies the welder for all positions on both plate and pipe (down to $1\text{ in. OD}$ or $2-7/8\text{ in. OD}$ depending on pipe size tested).

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4. Filler Metal F-Number Qualification Hierarchy (QW-433)

Filler metal F-Numbers represent operator skill. ASME Table QW-433 defines which filler metals a welder is qualified to use based on the test coupon filler metal:

+-----------------------------------------------------------------------------+
|                   TABLE QW-433: F-NUMBER QUALIFICATION HIERARCHY            |
|                                                                             |
|   Tested With:            Qualifies With Backing:    Qualifies Without Backing|
|   ------------            -----------------------    -------------------------|
|   F-4 (Low Hydrogen) ---> F-1, F-2, F-3, F-4         F-4 (Only if tested w/o) |
|   F-3 (Cellulosic)   ---> F-1, F-2, F-3              F-3 (Only if tested w/o) |
|   F-2 (Rutile)       ---> F-1, F-2                   F-2 (Only if tested w/o) |
|   F-1 (Heavy Rutile) ---> F-1                        F-1 (Only if tested w/o) |
|   F-5 (Stainless)    ---> F-5                        F-5 (Only if tested w/o) |
+-----------------------------------------------------------------------------+

Key F-Number Rules for the Exam:

1. F-4 Backing Rule: A welder who qualifies with F-4 (e.g., E7018) on a coupon with backing is qualified to weld with F-1, F-2, F-3, and F-4 with backing. They are NOT qualified to weld open-root (without backing) with any electrode.
2. The Open-Root F-3 / F-4 Combination: In piping and vessel repairs, welders frequently qualify by depositing F-3 (E6010) open-root followed by F-4 (E7018) fill and cap. This single test qualifies the welder to weld:
   • F-3 without backing (open root)
   • F-1, F-2, F-3, and F-4 with backing (since the F-3 root serves as backing for the F-4 fill passes).

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5. Diameter & Thickness Range Qualification Rules (Table QW-452)

Deposited Weld Metal Thickness ($t$) Limits (Table QW-452.1(b))

Unlike procedure qualifications where base metal thickness $T$ dictates the limits, welder qualifications are governed by the thickness of weld metal deposited ($t$) by that welder:

+-----------------------------------------------------------------------------+
|              WELDER DEPOSITED THICKNESS LIMITS (TABLE QW-452.1(b))          |
|                                                                             |
|   Weld Metal Deposited in Coupon (t)    Max Thickness Qualified to Weld     |
|   ----------------------------------    -------------------------------     |
|   t < 1/2 in. (13 mm)                   2t                                  |
|   t >= 1/2 in. (13 mm) [>= 3 layers]    UNLIMITED (Maximum to be welded)    |
+-----------------------------------------------------------------------------+

Pipe Diameter Qualification Limits (Table QW-452.3)

• Test on Plate: Qualifies plate and pipe with outside diameter $\ge 24\text{ in.} (610\text{ mm})$ only.
• Test on Pipe $\text{OD} \ge 2-7/8\text{ in.} (73\text{ mm})$: Qualifies pipe outside diameters from $2-7/8\text{ in.} (73\text{ mm})$ to unlimited, plus plate in all positions qualified.
• Test on Pipe $\text{OD} \ge 1\text{ in.} \text{ to } < 2-7/8\text{ in.}$: Qualifies pipe from $1\text{ in.} (25\text{ mm}) \text{ to unlimited}$, plus plate.
• Test on Pipe $\text{OD} < 1\text{ in.} (25\text{ mm})$: Qualifies size tested down to minimum tested diameter.

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6. Examination & Testing Methods: Guided Bend vs. Volumetric NDE (QW-304)

To qualify a welder, the completed test coupon must be evaluated by either mechanical bend testing or volumetric examination:

+-----------------------------------------------------------------------------+
|                      WELDER QUALIFICATION TESTING OPTIONS                   |
|                                                                             |
|   [OPTION 1: GUIDED BEND TESTS]               [OPTION 2: VOLUMETRIC NDE]    |
|   - Table QW-452.1(a)                         - Radiography (RT) or UT      |
|   - Plate or pipe coupons                     - Minimum 6 in. length        |
|   - 2 specimens (root/face or 2 side)         - Pipe: entire circumference  |
|   - Acceptance: open defect <= 1/8 in.        - GMAW-S EXCLUDED from RT/UT  |
+-----------------------------------------------------------------------------+

Mechanical Guided Bend Tests (Table QW-452.1(a))

• Coupons $t < 3/8\text{ in.} (10\text{ mm})$: 1 Transverse Root Bend + 1 Transverse Face Bend.
• Coupons $3/8\text{ in.} \le t < 3/4\text{ in.}$: Either 1 Root + 1 Face Bend OR 2 Transverse Side Bends.
• Coupons $t \ge 3/4\text{ in.} (19\text{ mm})$: 2 Transverse Side Bends are mandatory.
• Acceptance Criteria (QW-163): No open discontinuity in weld or HAZ exceeding $1/8\text{ in.} (3.2\text{ mm})$ in any direction.

Volumetric NDE (RT and UT per QW-304)

A welder testing on plate or pipe may be qualified by volumetric radiography or ultrasonic examination with specific rules:

1. Length Requirement: Minimum coupon length of $6\text{ inches } (150\text{ mm})$ for plate, or the entire circumference for pipe coupons (or combined coupons for small pipe to total 6 inches).
2. GMAW-S Limitation: Welder performance qualification using Gas Metal Arc Welding in the short-circuiting transfer mode (GMAW-S) CANNOT be qualified by volumetric NDE alone. Mechanical guided bend tests are mandatory due to the extreme risk of undetected side-wall lack of fusion ("cold lap") which radiography frequently misses.

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7. Expiration, Continuity Logs, and Requalification (QW-322)

Unlike a PQR which remains permanently valid for a company, a Welder Performance Qualification is subject to strict activity tracking:

+-----------------------------------------------------------------------------+
|                   WELDER QUALIFICATION EXPIRATION RULES                     |
|                                                                             |
|   [6-MONTH INACTIVITY RULE (QW-322.1(a))]                                   |
|   - Welder must weld with the qualified process at least once every 6 mos   |
|   - Monitored and signed off on a Welder Continuity Log                     |
|   - If 6 months elapse with NO welding using that process ---> EXPIRED!     |
|                                                                             |
|   [REASON TO QUESTION ABILITY (QW-322.1(b))]                                |
|   - If inspector observes unacceptable defects in production welds,         |
|     qualifications for that process may be IMMEDIATELY REVOKED!             |
|                                                                             |
|   [RENEWAL / REQUALIFICATION (QW-322.2)]                                    |
|   - Weld a single test coupon (plate or pipe) of any thickness, diameter,   |
|     or position using that process, and pass bend test or RT/UT.            |
|   - Restores qualification for all previously qualified ranges!             |
+-----------------------------------------------------------------------------+

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8. Common Exam Traps in Welder Qualification

[!WARNING] Trap 1: Plate Coupon Qualified for Pipe Diameter: A welder passes a performance test on a 1/2 in. flat plate coupon. Can they weld a 12-inch diameter pressure vessel shell girth seam? NO. A plate test qualifies the welder only on plate and on pipe with outside diameter $\ge 24 ext{ inches}$. For a 12-inch pipe/vessel, the welder must qualify on pipe.

[!IMPORTANT] Trap 2: PQR Tension Tests vs. WPQ Bend Tests: Tension tests are NEVER required for Welder Performance Qualification (WPQ). Tension tests are strictly for Procedure Qualification (PQR). A WPQ requires only guided bend tests or volumetric NDE.

[!TIP] Trap 3: 6-Month Inactivity Renewal Scope: When a welder's qualification lapses after 6 months of inactivity, they do not need to re-weld every position, thickness, and diameter previously held. Welding a single test coupon of any thickness or position with that process renews all previous qualification ranges for that process.