CSWIP 3.2 Summary

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CSWIP 3.2 – Senior Welding Inspector Study Notes

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HEAT TREATMENT

Temperature Classification

• Upper Critical Temperature (880–920°C):

  • Processes: Annealing, Normalizing, Quenching

• Lower Critical Temperature (<730°C):

  • Processes: Preheating, Post Weld Heat Treatment (PWHT), Tempering, Recovery

PWHT (Post Weld Heat Treatment)

• Local PWHT: Heat treatment of a localized section (e.g., weld area)

• Global PWHT: Full-component or equipment-wide heat treatment

• Purpose of Soaking (Holding Time):

  • Reduces yield strength temporarily

  • Reduces residual stresses

  • Enhances ductility and toughness

  • May lead to partial increase in yield strength after cooling

• Effects:

  • Improves toughness

  • Decreases hardness and tensile strength

  • Significantly reduces but does not completely eliminate residual stresses

Tempering

• Always follows quenching

• Aims to reduce brittleness and increase toughness by controlled reheating

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WELDING PROCESSES AND CONSUMABLES

MMAW (Manual Metal Arc Welding) – Process 111

• Electrode Types:

  • Cellulosic (0, 1): No baking required

  • Rutile (2, 3, 4): Dried at 90–120°C

  • Basic (5, 6, 8): Baked at 350°C, then kept at 150°C for up to 4 hours before use

TIG (GTAW) – Process 141

• Lowest hydrogen content process

• Defects:

  • Slope-in: Tungsten inclusions

  • Slope-out: Crater (shrinkage) cracks

• Electrodes:

  • Zirconiated: Used with Aluminum (AC current only)

  • Thoriated: Suitable for Carbon Steel (DCEN)

MIG/MAG (GMAW) – Processes 131/135

• Transfer Modes:

  • Dip Transfer: Thin plate; prone to lack of fusion and spatter

  • Pulse Transfer: Suitable for all positions and small weld pools

  • Spray Transfer: Thick plates in flat/horizontal positions; clean arc

  • Globular Transfer: High distortion and spatter; used with CO₂

SAW (Submerged Arc Welding) – Process 121

• Flux Types:

  • Fused: Hygroscopic; no baking required

  • Agglomerated: Moisture-sensitive; must be baked; allows alloying element additions

• High deposition rate, low distortion, but high dilution

Current and Polarity

• DC Electrode Positive (DCEP): MMAW, FCAW, GMAW, SAW – deepest penetration

• DC Electrode Negative (DCEN): Used in GTAW; lower penetration, high deposition rate

• AC: Balanced arc; commonly used for Aluminum

Arc Blow Control

• Avoid arc blow by switching from DC to AC

• Inverter: Converts DC to AC

• Rectifier: Converts AC to DC

Power Source Characteristics

• Flat Characteristic (Constant Voltage): Wire feed speed controls current; used for MIG, MAG, SAW

• Drooping Characteristic (Constant Current): Manual control of arc length; used in TIG, MMAW

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WELD FRACTURE TYPES

1. Ductile Fracture

   • Large plastic deformation

   • 45° shear surface; rough, torn appearance

2. Brittle Fracture

   • Occurs at low temperature

   • Rapid propagation, smooth and flat fracture surface

   • Crystalline appearance

3. Fatigue Fracture

   • Caused by cyclic loading below yield stress

   • Chevron marks and beach marks visible

   • Initiates from defects, propagates slowly

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DESTRUCTIVE TESTING

Types of Tests

• Quantitative: Tensile, impact, hardness, CTOD

• Qualitative: Bend tests, macro/micro examination

Applications

• WPS Qualification: Transverse tensile, bend, CVN, macro, micro, hardness

• Welder Qualification: Fillet weld fracture, butt weld nick-break

• Consumables Testing: Full tensile tests

Tensile Test

• Measures UTS, YS, elongation (typically over 50mm gauge length)

• Transverse tensile: Strength of weld metal

• Z-direction: Through-thickness properties

Bend Test

• 180° bend over a former (typically 4T)

• Side Bend: ≥13 mm thickness

• Face/Root Bend: <13 mm thickness

Hardness Test

• Rockwell (diamond cone) not permitted on weld metal due to risk of crack initiation

Impact Test

• CVN and CTOD to assess toughness, transition temperature

• CTOD: Quantitative toughness test

Macro & Micro Examination

• Macro: 5x–10x magnification; surface defects

• Micro: 100x–1000x; microstructure and inclusions

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JOINT DESIGN

• Single-Side V/Bevel: High distortion, more filler, requires skilled welder

• Double-Side V/U: Lower distortion, reduced filler

• U/J Grooves: Risk of solidification cracking due to high depth:width ratio

• Set-on Nozzle: Risk of lamellar tearing, poor access for UT

• Set-out Nozzle: Safer design, better UT access

• Narrow groove angle increases risk of lack of fusion

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WELDABILITY – ISO 1011-2

Solidification Cracking (Hot Cracks)

• Occurs along centerline during solidification

• Causes: High tensile stress, high sulfur content, poor joint design

• Detection: VT, PT, UT, RT

Hydrogen Induced Cold Cracking (HICC)

• Occurs in HAZ or weld metal

• Requires:

  • Hydrogen

  • Stress

  • Susceptible microstructure (martensite, high CEV)

  • Temperature

• Austenitic SS not susceptible

Lamellar Tearing

• Base metal only, subsurface cracking

• Common in set-on nozzles and T-joints

• Best detected by UT with 0° probe

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WELD REPAIR

• Cut-out: Required when:

  • Crack defect

  • Second-time repair

  • Affects >25% of weld circumference

• Repair Procedure: Must be reviewed and approved before execution

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