Study guide
11.1 Welding Procedure Specification (WPS) & Procedure Qualification Record (PQR) 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)
11.1 Welding Procedure Specification (WPS) & Procedure Qualification Record (PQR) per ASME IX
Key Takeaways Explain This Topic AI
API 653 Section 11.1 mandates that all welding procedure qualifications for storage tank repairs, alterations, and reconstruction comply with ASME Section IX and the supplementary rules of API 650 Section 9.
A Welding Procedure Specification (WPS) is the written guide defining acceptable ranges for essential, non-essential, and supplementary essential variables, while the Procedure Qualification Record (PQR) is the certified record of the actual variables used on the test coupon and the measured destructive-test results.
PQR mechanical testing under ASME Section IX covers tension tests (QW-150), which accept base-metal failures no more than 5% below the specified minimum tensile strength, and guided-bend tests (QW-160), which reject specimens with open discontinuities exceeding 1/8 in. (3.2 mm) on the convex surface.
API's Body of Knowledge limits the exam's WPS/PQR/WPQ review to a single SMAW or GMAW process on P-No. 1 base metal with one filler metal and one supporting PQR, and expressly excludes dissimilar-metal joints, consumable inserts, overlays, heat treatment, and Charpy/supplementary essential variables.
API RP 577 supplies the welding-inspection material that ASME Section IX does not: process characteristics of SMAW and GMAW, AWS A2.4 weld symbols and terminology, common filler metal selection including E7018 hydrogen control and the H4/H8/H16 suffixes, the actions required when a production weld is made improperly, and the content of a conforming radiographic report.
Last updated: September 2026
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 .
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).
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:
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.
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 T T ), and diameter limits for nozzle penetrations.
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 t t ).
Position (QW-405): Approved welding positions (1G Flat, 2G Horizontal, 3G Vertical, 4G Overhead) and the direction of vertical progression (uphill vs. downhill).
Preheat and Interpass Temperature (QW-406): Minimum preheat temperature, continuous preheat maintenance, and maximum allowable interpass temperature.
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.
Shielding Gas (QW-408): Gas composition, percentages (e.g., 75% Argon / 25% CO 2 \text{CO}_2 CO 2 ), flow rate (CFH or L/min), backing gas, and trailing gas requirements.
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.
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.
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.
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 A A ) is determined by measuring the machined width ( w w w ) and thickness ( t t t ) of the reduced section using a calibrated micrometer: A = w × t A = w \times t A = w × t
Tensile Strength Determination: The test specimen is pulled in a calibrated tensile machine until rupture occurs. The ultimate tensile strength ( S u S_u S u ) is calculated as: S u = P max A S_u = \frac{P_{\text{max}}}{A} S u = A P max where P max P_{\text{max}} P 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:
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).
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 actual ≥ 0.95 × S SMTS S_{\text{actual}} \ge 0.95 \times S_{\text{SMTS}} S actual ≥ 0.95 × S 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.
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:
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.
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.
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).
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:
Mechanical Test Primary Purpose Required Specimen Count (Plate/Pipe QW-451.1) Code Acceptance Criteria (ASME IX) Failure Implications
Reduced-Section Tension Test (QW-150) Quantifies ultimate tensile strength of weld and HAZ 2 specimens minimum per test coupon S u ≥ SMTS S_u \ge \text{SMTS} S u ≥ SMTS ; if break is outside weld in base metal, S u ≥ 0.95 × SMTS S_u \ge 0.95 \times \text{SMTS} S u ≥ 0.95 × SMTS Low strength requires modifying filler metal, heat input, or preheat/PWHT; full requalification mandatory
Transverse Side Bend (QW-160) Evaluates soundness and ductility across full weld thickness 4 specimens (for T ≥ 3 / 4 in. T \ge 3/4\text{ in.} T ≥ 3/4 in. , or optional for 3 / 8 in. ≤ T < 3 / 4 in. 3/8\text{ in.} \le T < 3/4\text{ in.} 3/8 in. ≤ T < 3/4 in. ) No open discontinuity > 1 / 8 in. (3.2 mm) > 1/8\text{ in. (3.2 mm)} > 1/8 in. (3.2 mm) in any direction on convex face; corner cracks excluded unless flaw-induced Slag, lack of sidewall fusion, or lack of penetration; requires joint re-design, cleaning changes, or re-welding
Transverse Face Bend (QW-160) Tests ductility and fusion along weld face crown 2 specimens (for T < 3 / 4 in. T < 3/4\text{ in.} T < 3/4 in. ) No open discontinuity > 1 / 8 in. (3.2 mm) > 1/8\text{ in. (3.2 mm)} > 1/8 in. (3.2 mm) on convex surface Surface porosity, lack of interpass fusion, undercut, or embrittlement; rejects procedure
Transverse Root Bend (QW-160) Tests ductility and complete penetration at root pass 2 specimens (for T < 3 / 4 in. T < 3/4\text{ in.} T < 3/4 in. ) No open discontinuity > 1 / 8 in. (3.2 mm) > 1/8\text{ in. (3.2 mm)} > 1/8 in. (3.2 mm) on convex surface Lack of root penetration, burn-through, root suck-back, or heavy root slag inclusions
Charpy V-Notch Impact Test (QW-170 / API 650) Quantifies dynamic notch toughness at design temperature 1 set of 3 weld metal + 1 set of 3 HAZ specimens (when invoked) Governed by API 650 Table 4.4 / Section 9.2.2 (typically ≥ 15 – 30 ft-lbf \ge 15\text{--}30\text{ ft-lbf} ≥ 15 – 30 ft-lbf average depending on steel grade) Coarse grain microstructures, high heat input; triggers supplementary essential variable redesign
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.
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:
- SMAW (Shielded Metal Arc Welding, "stick") GMAW (Gas Metal Arc Welding, "MIG")
- Electrode Consumable flux-covered stick electrode Continuous solid wire fed through a gun
Shielding Gases produced by the decomposing flux covering Externally supplied shielding gas (argon, CO₂, or mixtures)
Slag Yes — must be removed between passes None (solid wire)
Field suitability Excellent; tolerant of wind, rust, and out-of-position work Sensitive to wind, which strips the shielding gas
Typical tank use Shell butt welds, door sheets, bottom repairs, hot taps Shop prefabrication, high-deposition fill on heavy sections
Transfer modes n/a Short-circuiting, globular, spray, pulsed spray
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:
Stop the work on the affected joint and document the nonconformance — location, weld number, welder identification, and the specific requirement not met.
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.
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.
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 .
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.
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.