11.1 Welding Procedure Specification (WPS) & Procedure Qualification Record (PQR) per ASME IX

11.1 Welding Procedure Specification (WPS) & Procedure Qualification Record (PQR) per ASME IX

API 653 Core Mandate: Welding integrity is the primary structural safeguard for reconstructed, repaired, or altered aboveground storage tanks. Under API 653 Section 11.1, all welding on tank shells, bottoms, roofs, and attached nozzles must be executed in accordance with qualified Welding Procedure Specifications (WPS) supported by verified Procedure Qualification Records (PQR) that meet the requirements of ASME Boiler and Pressure Vessel Code Section IX and the specific supplementary construction criteria of API Standard 650 Section 9.

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1. Interplay Between ASME Section IX, API 650, and API 653

Storage tank welding quality assurance operates through a tiered regulatory relationship connecting reference codes and in-service repair standards:

+-------------------------------------------------------------------------+
|                   WELDING GOVERNANCE HIERARCHY                          |
|                                                                         |
|   +-----------------------------------------------------------------+   |
|   | API STANDARD 653 (In-Service Inspection, Repair & Alteration)   |   |
|   | - Governs tank repair scopes, insert plates, door sheets        |   |
|   | - Dictates mandatory NDE and hydrotest exemptions               |   |
|   | - Invokes API 650 / ASME Section IX for all welding execution   |   |
|   +-------------------------------+---------------------------------+   |
|                                   | References                          |
|                                   v                                     |
|   +-----------------------------------------------------------------+   |
|   | API STANDARD 650 (New Tank Construction, Section 9)             |   |
|   | - Imposes tank-specific impact test criteria (Section 9.2.2)    |   |
|   | - Restricts consumable selection and preheat baselines          |   |
|   | - Governs welder identification and joint design details        |   |
|   +-------------------------------+---------------------------------+   |
|                                   | Mandates Compliance With            |
|                                   v                                     |
|   +-----------------------------------------------------------------+   |
|   | ASME SECTION IX (Welding, Brazing & Fusing Qualifications)      |   |
|   | - Article I: General Requirements & Mechanical Testing          |   |
|   | - Article II: Welding Procedure Qualifications (WPS & PQR)      |   |
|   | - Article III: Welder Performance Qualifications (WPQ)          |   |
|   | - Article IV: Welding Data (P-Nos., F-Nos., A-Nos., Dimensions)  |   |
|   +-----------------------------------------------------------------+   |
+-------------------------------------------------------------------------+

• ASME Section IX serves as the universal mechanical qualification framework across the pressure vessel and piping industries. It defines the mechanics of procedure testing, the taxonomy of welding variables, and the acceptance thresholds for tensile, bend, and toughness specimens.
• API Standard 650 (Section 9) serves as the parent design and construction code. It incorporates ASME Section IX by reference but introduces industry-specific restrictions, such as minimum toughness requirements for Group IV through Group VI steels, weld spacing rules, and strict limitations on vertical weld joint alignment.
• API Standard 653 (Section 11) governs in-service repairs, alterations, and reconstruction. It mandates that any repair organization performing welding on an aboveground storage tank must maintain qualified WPS documents supported by authenticated PQRs. API 653 takes precedence over original construction codes whenever conflicts arise regarding repair procedures, weld spacing, or non-destructive examination (NDE).

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2. Welding Procedure Specification (WPS): Purpose and Anatomy

Under ASME Section IX QW-200.1, a Welding Procedure Specification (WPS) is a written document that provides detailed direction to the welder or welding operator for making production welds in accordance with code requirements.

The Operational Purpose of a WPS

A WPS is not a theoretical metallurgy treatise; it is a practical, shop-floor and field-level operational instruction sheet. It defines the acceptable envelope of parameters—voltage, amperage, travel speed, joint design, shielding gas, and preheat—within which a welder must operate to produce sound welds matching the mechanical integrity demonstrated during initial procedure qualification.

Mandatory Contents of a WPS

Per QW-200.1(b), a completed WPS must explicitly address every essential variable, non-essential variable, and (when notch toughness testing is required) supplementary essential variable listed in the applicable QW-250 table for each welding process deployed. Key technical elements include:

1. Joint Design (QW-402): Groove types (single-V, double-V, square, bevel, U, or J), backing type (metal backing, weld metal backing, or open root), root opening dimensions, root face lands, and bevel groove angles.
2. Base Metals (QW-403): Assigned ASME P-Number and Group Number groupings (e.g., P-No. 1 Group 1 or 2 for carbon steels such as ASTM A36, A283-C, A516-70, or A573-70), base metal thickness range qualified ($T$), and diameter limits for nozzle penetrations.
3. Filler Metals (QW-404): Specification (SFA number), AWS classification (e.g., E7018, ER70S-6), ASME F-Number (usability grouping), ASME A-Number (deposited weld metal chemical composition), electrode diameter, and deposited weld metal thickness ($t$).
4. Position (QW-405): Approved welding positions (1G Flat, 2G Horizontal, 3G Vertical, 4G Overhead) and the direction of vertical progression (uphill vs. downhill).
5. Preheat and Interpass Temperature (QW-406): Minimum preheat temperature, continuous preheat maintenance, and maximum allowable interpass temperature.
6. Post-Weld Heat Treatment (PWHT) (QW-407): Temperature range, soaking time per unit thickness, heating and cooling rates, or explicit confirmation that no PWHT is applied.
7. Shielding Gas (QW-408): Gas composition, percentages (e.g., 75% Argon / 25% $\text{CO}_2$), flow rate (CFH or L/min), backing gas, and trailing gas requirements.
8. Electrical Characteristics (QW-409): Current type (AC or DC), polarity (DCEP or DCEN), amperage range, arc voltage range, wire feed speed, travel speed range, and maximum calculated heat input.
9. Technique (QW-410): Stringer versus weave bead application, multi-pass versus single-pass per side, orifice size, cleaning method (grinding, wire brushing, chipping), and backgouging method.

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3. Procedure Qualification Record (PQR): Evidentiary Proof & Certification

Under ASME Section IX QW-200.2, a Procedure Qualification Record (PQR) is a certified record documenting the actual welding variables recorded during the welding of a test coupon, along with the subsequent quantitative results of destructive mechanical tests.

The Relationship Between WPS and PQR

The relationship between a WPS and a PQR is foundational to welding quality assurance:

+-------------------------------+       +-------------------------------+
|   PQR-001 (Actual Data)       |       |   PQR-002 (Actual Data)       |
| - Welded on 0.500 in. plate   |       | - Welded on 1.000 in. plate   |
| - Actual Amps: 135 A          |       | - Impact Tested @ -20°F       |
| - Actual Volts: 24 V          |       | - Actual Preheat: 200°F       |
| - Tension: 76.4 ksi (Pass)    |       | - Tension: 78.2 ksi (Pass)    |
| - Bends: 4 Side Bends (Pass)  |       | - Bends: 4 Side Bends (Pass)  |
+---------------+---------------+       +---------------+---------------+
                |                                       |
                +-------------------+-------------------+
                                    |
                                    v
+-----------------------------------------------------------------------+
|                   WPS-101 REV. 2 (Operational Ranges)                 |
| - Base Metal Thickness Range Qualified: 0.1875 in. to 2.000 in.       |
| - Amperage Range: 115 A - 165 A                                       |
| - Voltage Range: 22 V - 26 V                                          |
| - Preheat Minimum: 200°F                                              |
| - Toughness: Qualified for service down to -20°F                       |
+-----------------------------------------------------------------------+

• Evidentiary Baseline: The PQR records actual, discrete values observed during coupon fabrication (e.g., "142 Amperes, 23.5 Volts, 4.2 in/min travel speed"), whereas the WPS lists qualified operational ranges (e.g., "120–160 Amperes, 22–26 Volts, 3.5–5.5 in/min").
• Combinations: One PQR can support multiple WPS documents (e.g., separate WPSs for flat fillet welds and out-of-position groove welds). Conversely, multiple PQRs can be combined to support a single composite WPS (e.g., a PQR for a GTAW root pass combined with a PQR for SMAW fill passes).
• Certification Mandate: Per QW-200.2(d), the PQR must be formally certified by an authorized representative of the repair organization or tank manufacturer. The certification attests that the test coupons were prepared, welded, and mechanically tested in full compliance with ASME Section IX. The PQR is a permanent legal record; unlike the WPS, it cannot be arbitrarily revised or edited, except to correct typographical errors or incorporate official ASME code errata.

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4. Mechanical Testing Protocol: Tension Testing (QW-150)

Tension tests demonstrate the ultimate tensile strength of the groove-welded joint, confirming that the weld metal and the heat-affected zone (HAZ) match or exceed the minimum strength requirements of the parent base material.

Test Specimen Preparation (QW-151 & QW-462.1)

• Specimen Types: Reduced-section specimens are prepared by machining or grinding the weld reinforcement flush with the base metal surface on both sides. This eliminates stress concentrations caused by weld crown geometry, ensuring that tensile stress is distributed uniformly through the joint cross section.
• Quantity Required: Per Table QW-451.1, a standard plate or pipe procedure qualification test coupon requires a minimum of two (2) reduced-section tension specimens.
• Cross-Sectional Area Calculation: The cross-sectional area ($A$) is determined by measuring the machined width ($w$) and thickness ($t$) of the reduced section using a calibrated micrometer: $A = w \times t$
• Tensile Strength Determination: The test specimen is pulled in a calibrated tensile machine until rupture occurs. The ultimate tensile strength ($S_u$) is calculated as: $S_u = \frac{P_{\text{max}}}{A}$ where $P_{\text{max}}$ is the maximum breaking load recorded in pounds-force (or Newtons).

Acceptance Criteria (QW-153)

To pass procedure qualification, both tension test specimens must satisfy one of the following conditions:

1. Weld or Fusion Zone Failure: If the specimen breaks in the weld metal or along the weld interface, the calculated tensile strength must be equal to or greater than the Specified Minimum Tensile Strength (SMTS) of the base metal (or the weaker of two base metals if joining dissimilar materials).
2. Base Metal Failure (The 95% Rule): If the specimen breaks in the base metal outside of the weld and weld interface, the test is acceptable provided the calculated tensile strength is not more than 5% below the Specified Minimum Tensile Strength of the base metal: $S_{\text{actual}} \ge 0.95 \times S_{\text{SMTS}}$ Engineering Rationale: The heat input of welding can cause minor thermal softening in adjacent base metal that is structurally inconsequential. A rupture in the base metal proves that the weld joint itself was stronger than the failure location.

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5. Mechanical Testing Protocol: Guided-Bend Testing (QW-160)

Guided-bend tests evaluate the ductility, soundness, and structural consolidation of the weld metal and heat-affected zone, detecting lack of sidewall fusion, slag entrapment, porosity, and micro-fissuring under severe mechanical deformation.

Specimen Types and Thickness Regimes (QW-161 & Table QW-451.1)

ASME Section IX defines four primary transverse guided-bend specimen configurations:

+-------------------------------------------------------------------------+
|                   GUIDED-BEND SPECIMEN SELECTION                        |
+-----------------------+-------------------------------------------------+
| Coupon Thickness (T)  | Mandatory Bend Specimens (Table QW-451.1)       |
+-----------------------+-------------------------------------------------+
| T < 3/8 in. (10 mm)   | 2 Transverse Face Bends + 2 Transverse Root     |
|                       | Bends (Side bends permitted for 3/8 in.)        |
+-----------------------+-------------------------------------------------+
| 3/8 in. <= T < 3/4 in.| 4 Transverse Side Bends OR                      |
| (10 mm <= T < 19 mm)  | 2 Face Bends + 2 Root Bends                     |
+-----------------------+-------------------------------------------------+
| T >= 3/4 in. (19 mm)  | 4 Transverse Side Bends (Mandatory)             |
+-----------------------+-------------------------------------------------+

• Transverse Face Bend (QW-462.3(a)): Specimen bent such that the weld face surface becomes the outer, convex, stretched tension surface.
• Transverse Root Bend (QW-462.3(a)): Specimen bent such that the weld root surface becomes the outer, convex, stretched tension surface.
• Transverse Side Bend (QW-462.2): Specimen cross-sectioned through its full thickness (standard width 3/8 in. / 10 mm) and bent such that the entire side profile of the weld, including both fusion lines and all weld passes, is stretched in tension.

Bend Test Tooling and Mechanics (QW-162)

Specimens are placed across a standardized guided-bend test jig (plunger and die, wrap-around roller, or wrap-around jig). The plunger forces the specimen into the die cavity until it achieves a full U-bend geometry (180° curvature). The diameter of the bending plunger is calculated based on the base metal nominal ductility and elongation characteristics per ASME IX Table QW-466.1.

Acceptance Criteria (QW-163)

Following bending, the convex tension surface of the curved specimen must be visually inspected under magnification. The specimen passes if:

1. The weld metal and heat-affected zone exhibit no open discontinuities exceeding 1/8 in. (3.2 mm) measured in any direction on the convex surface.
2. Corner Cracks Exception: Open cracks that originate at the specimen corners during bending are disregarded, unless visual evidence confirms that the crack initiated from lack of fusion, slag inclusions, internal porosity, or other mechanical weld flaws.
3. Corrosion-Resistant Overlays: For cladding or weld overlays, open discontinuities in the cladding itself must not exceed 1/16 in. (1.6 mm), and along the fusion line must not exceed 1/8 in. (3.2 mm).

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6. Code Acceptance Criteria Matrix for Procedure Qualification

The following table consolidates the mechanical testing requirements, specimen counts, and code pass/fail thresholds under ASME Section IX for procedure qualification:

Exam Scope: What the WPS/PQR Review Will and Will Not Contain

API's API 653 Body of Knowledge narrows the weld procedure review sharply. Knowing the boundary saves time on exam day:

Included:

• SMAW or GMAW only, and no more than one process on a single WPS, PQR, or WPQ.
• The WPS will be supported by a single PQR, and that PQR will be the supporting PQR for the WPS.
• Filler metals limited to one per process.
• Base metals limited to P-No. 1.
• The WPQ test coupon will have been welded in accordance with a qualified WPS.
• You must determine whether the records comply with ASME BPVC and any additional API 653 requirements, whether all required essential and non-essential variables are properly addressed, whether the number and type of mechanical tests on the PQR are correct and the results acceptable, and whether the welder is qualified to make a production weld according to the WPS.
• The WPS must reference the applicable PQR, and the PQR must be signed and dated.

Specifically excluded:

• Dissimilar base metal joints.
• Supplemental powdered filler metals and consumable inserts.
• Special weld processes such as corrosion-resistant weld metal overlay, hard-facing overlay, and dissimilar metal welds with buttering.
• Charpy impact requirements and supplementary essential variables.
• Any PQR or WPS on the exam will not include heat treatment requirements.
• Brazing is not covered at all.

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API RP 577, Welding Processes, Inspection, and Metallurgy

API RP 577 is a full reference publication on the API 653 effectivity sheet, and the Body of Knowledge lists fourteen topic areas from it. Most overlap with ASME Section IX and API 650 Section 9; the items below are the ones API 577 uniquely owns.

1. The Two Processes the Exam Cares About

API's Body of Knowledge restricts the weld procedure review to SMAW or GMAW only, so those are the two processes to know cold:

Short-circuiting transfer warning. GMAW short-circuiting transfer runs cold and is notorious for cold lap / incomplete fusion on heavy sections. API 577 flags it, and an inspector seeing short-circuit GMAW proposed on a thick shell insert should ask for a fill-and-cap procedure that runs in spray transfer or a different process.

2. Terminology and Weld Symbols

API 577 catalogues the welding terminology and the AWS A2.4 symbol set an inspector must read off a repair drawing:

• The reference line carries the weld symbol. A symbol placed below the reference line means the weld goes on the arrow side of the joint; a symbol above the line means the other side. Symbols on both sides mean welds on both sides.
• The tail of the symbol carries the specification, process, or WPS number.
• A flag at the kink of the arrow means field weld; a circle at the kink means weld all around.
• Fillet weld size is written to the left of the symbol; length and pitch to the right.
• Key joint vocabulary: root opening, root face (land), groove angle, bevel angle, weld reinforcement, weld toe, throat, leg, fusion line, heat-affected zone.

3. Guide to Common Filler Metal Selection

The governing principle is to match or slightly overmatch the base metal strength while minimizing hydrogen:

• For P-No. 1 carbon steels — the only base metal group in the exam's WPS review scope — the standard SMAW choice is an E70XX electrode.
• E7018 is the low-hydrogen workhorse: basic (lime) covering, iron powder, all-position, high toughness, low crack sensitivity. It must be kept dry — stored in a rod oven, and exposed rod re-baked or discarded per the manufacturer's limits, because the covering reabsorbs atmospheric moisture and reintroduces diffusible hydrogen.
• E6010 / E6011 are cellulosic, deep-penetrating, and not low-hydrogen; they are chosen for open-root passes where penetration matters more than hydrogen control.
• Suffixes carry meaning: -1 denotes improved impact properties; H4 / H8 / H16 denote maximum diffusible hydrogen in mL per 100 g of deposited weld metal (H4 = the lowest, 4 mL/100 g).
• For GMAW on carbon steel, ER70S-3 and ER70S-6 are the common solid wires; ER70S-6 carries higher silicon and manganese deoxidizers and handles mill scale and rust better.

4. Actions to Address Improperly Made Production Welds

API 577 sets out what an inspector does when a production weld does not conform:

1. Stop the work on the affected joint and document the nonconformance — location, weld number, welder identification, and the specific requirement not met.
2. Determine the root cause. Distinguish between a welder performance problem (wrong technique, lapsed qualification), a procedure problem (the WPS itself is inadequate or an essential variable was exceeded), and a material or fit-up problem.
3. Check the scope of the defect. If an essential variable was violated, every weld made under that condition is suspect — not just the one that was examined.
4. Act on the welder's qualification. ASME Section IX QW-322.1(b) requires that where there is specific reason to question a welder's ability to make welds meeting the specification, the qualifications supporting that welding be revoked.
5. Repair or replace per a qualified procedure, then re-examine by the same method that found the flaw plus any supplementary methods the referencing code requires.
6. Expand the examination. Where a rejectable indication is found in a spot radiograph, the referencing code typically requires two additional radiographs at the same weld — and if either of those fails, full radiography of that weld.

5. Example Report of Radiographic Results

API 577 includes a model RT report, and the inspector's job is to confirm that the report is complete enough to be auditable years later. A conforming report identifies:

• Job, tank, and weld identification, with a weld map locating each radiograph;
• Welder identification for each weld radiographed;
• The procedure, radiation source and strength, source-to-film distance, exposure time, and film type and screens;
• IQI type, set, and placement (source side or film side), and the essential hole or wire actually resolved;
• Measured film density;
• Interpretation of each film — the specific discontinuity type, its length, and the accept/reject decision against the named acceptance standard;
• Reshoots and repairs, with repaired-weld radiographs marked "R";
• The examiner's name, level, and certification, and the date.