CSWIP 3.2 – Senior Welding Inspector Study Notes
🔥 HEAT TREATMENT
Temperature Classification
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Upper Critical Temperature (880–920°C):
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Processes: Annealing, Normalizing, Quenching
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Lower Critical Temperature (<730°C):
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Processes: Preheating, Post Weld Heat Treatment (PWHT), Tempering, Recovery
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PWHT (Post Weld Heat Treatment)
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Local PWHT: Heat treatment of a localized section (e.g., weld area)
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Global PWHT: Full-component or equipment-wide heat treatment
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Purpose of Soaking (Holding Time):
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Reduces yield strength temporarily
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Reduces residual stresses
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Enhances ductility and toughness
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May lead to partial increase in yield strength after cooling
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Effects:
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Improves toughness
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Decreases hardness and tensile strength
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Significantly reduces but does not completely eliminate residual stresses
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Tempering
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Always follows quenching
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Aims to reduce brittleness and increase toughness by controlled reheating
🔧 WELDING PROCESSES AND CONSUMABLES
MMAW (Manual Metal Arc Welding) – Process 111
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Electrode Types:
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Cellulosic (0, 1): No baking required
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Rutile (2, 3, 4): Dried at 90–120°C
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Basic (5, 6, 8): Baked at 350°C, then kept at 150°C for up to 4 hours before use
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TIG (GTAW) – Process 141
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Lowest hydrogen content process
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Defects:
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Slope-in: Tungsten inclusions
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Slope-out: Crater (shrinkage) cracks
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Electrodes:
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Zirconiated: Used with Aluminum (AC current only)
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Thoriated: Suitable for Carbon Steel (DCEN)
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MIG/MAG (GMAW) – Processes 131/135
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Transfer Modes:
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Dip Transfer: Thin plate; prone to lack of fusion and spatter
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Pulse Transfer: Suitable for all positions and small weld pools
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Spray Transfer: Thick plates in flat/horizontal positions; clean arc
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Globular Transfer: High distortion and spatter; used with CO₂
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SAW (Submerged Arc Welding) – Process 121
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Flux Types:
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Fused: Hygroscopic; no baking required
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Agglomerated: Moisture-sensitive; must be baked; allows alloying element additions
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High deposition rate, low distortion, but high dilution
Current and Polarity
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DC Electrode Positive (DCEP): MMAW, FCAW, GMAW, SAW – deepest penetration
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DC Electrode Negative (DCEN): Used in GTAW; lower penetration, high deposition rate
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AC: Balanced arc; commonly used for Aluminum
Arc Blow Control
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Avoid arc blow by switching from DC to AC
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Inverter: Converts DC to AC
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Rectifier: Converts AC to DC
Power Source Characteristics
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Flat Characteristic (Constant Voltage): Wire feed speed controls current; used for MIG, MAG, SAW
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Drooping Characteristic (Constant Current): Manual control of arc length; used in TIG, MMAW
⚙️ WELD FRACTURE TYPES
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Ductile Fracture
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Large plastic deformation
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45° shear surface; rough, torn appearance
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Brittle Fracture
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Occurs at low temperature
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Rapid propagation, smooth and flat fracture surface
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Crystalline appearance
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Fatigue Fracture
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Caused by cyclic loading below yield stress
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Chevron marks and beach marks visible
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Initiates from defects, propagates slowly
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🧪 DESTRUCTIVE TESTING
Types of Tests
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Quantitative: Tensile, impact, hardness, CTOD
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Qualitative: Bend tests, macro/micro examination
Applications
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WPS Qualification: Transverse tensile, bend, CVN, macro, micro, hardness
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Welder Qualification: Fillet weld fracture, butt weld nick-break
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Consumables Testing: Full tensile tests
Tensile Test
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Measures UTS, YS, elongation (typically over 50mm gauge length)
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Transverse tensile: Strength of weld metal
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Z-direction: Through-thickness properties
Bend Test
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180° bend over a former (typically 4T)
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Side Bend: ≥13 mm thickness
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Face/Root Bend: <13 mm thickness
Hardness Test
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Rockwell (diamond cone) not permitted on weld metal due to risk of crack initiation
Impact Test
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CVN and CTOD to assess toughness, transition temperature
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CTOD: Quantitative toughness test
Macro & Micro Examination
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Macro: 5x–10x magnification; surface defects
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Micro: 100x–1000x; microstructure and inclusions
🔩 JOINT DESIGN
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Single-Side V/Bevel: High distortion, more filler, requires skilled welder
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Double-Side V/U: Lower distortion, reduced filler
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U/J Grooves: Risk of solidification cracking due to high depth:width ratio
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Set-on Nozzle: Risk of lamellar tearing, poor access for UT
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Set-out Nozzle: Safer design, better UT access
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Narrow groove angle increases risk of lack of fusion
🧱 WELDABILITY – ISO 1011-2
Solidification Cracking (Hot Cracks)
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Occurs along centerline during solidification
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Causes: High tensile stress, high sulfur content, poor joint design
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Detection: VT, PT, UT, RT
Hydrogen Induced Cold Cracking (HICC)
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Occurs in HAZ or weld metal
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Requires:
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Hydrogen
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Stress
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Susceptible microstructure (martensite, high CEV)
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Temperature
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Austenitic SS not susceptible
Lamellar Tearing
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Base metal only, subsurface cracking
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Common in set-on nozzles and T-joints
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Best detected by UT with 0° probe
🛠 WELD REPAIR
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Cut-out: Required when:
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Crack defect
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Second-time repair
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Affects >25% of weld circumference
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Repair Procedure: Must be reviewed and approved before execution
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