Welding Processes Guide
A complete welding reference: MIG/MAG, TIG/GTAW, SMAW/Stick, FCAW/SAW, special processes (laser, EBW, FSW, resistance, plasma), AWS weld symbols, edge preparation, preheat and PWHT, defects and NDT, welding by material, and a full process comparison guide.
⚡Welding — Welding Processes
Welding — joining metals with heat/pressure. 50+ processes. Correct prep + correct filler + correct process = quality weld.
MIG/MAG — GMAW
Most CommonFastSemi-Automatic
StandardAWS A5.18 / ISO 14341
CurrentDCEP — 60-350A
Voltage15-32V
Wire Speed3-15 m/min
MIG GasAr / Ar+2%O2 (Al, SS)
MAG GasCO2 / Ar+15-25%CO2 (steel)
WireER70S-6 (steel) / ER308L (SS) / ER4043 (Al)
MIG = Metal Inert Gas (Ar). MAG = Metal Active Gas (CO2)
Transfer Modes: Short Circuit / Globular / Spray / Pulse
✓ Fast. Convenient. High volume
✓ Semi-auto + robot welding
✗ Sensitive to wind (indoors only). Spatter with CO2
▶ YouTubeTransfer Modes: Short Circuit / Globular / Spray / Pulse
✓ Fast. Convenient. High volume
✓ Semi-auto + robot welding
✗ Sensitive to wind (indoors only). Spatter with CO2
Transfer Modes
Short ArcSprayPulse
Short Circuit15-21V, <200A. ↓heat. For thin sections. Spatter↑
Globular22-26V. Unstable. CO2 only. Not recommended
Spray>26V, >200A. Ar↑. Excellent finish. Not for thin sections
PulsePeak+base current. ↓heat input. ↓spatter. All-position
CMTCold Metal Transfer — ↓↓ heat. Al+SS with zero spatter!
✓ Pulse = all-position + ↓distortion + ↑quality
✓ CMT = a revolution for Al + zero spatter
✗ Spray = not all-position
▶ YouTube✓ CMT = a revolution for Al + zero spatter
✗ Spray = not all-position
Wire & Shielding Gas — Selection Guide
MaterialGas
C-SteelER70S-6 + 75%Ar/25%CO2 (C25)
SS 304/316ER308L/316L + 98%Ar/2%O2
Al 5xxxER5356 + 100%Ar
Al 6xxxER4043 + 100%Ar
CuSi/CuAlMIG brazing: CuSi3 + 100%Ar
DuplexER2209 + 98%Ar/2%N2
+OK+ ER70S-6 = the most common. Si+Mn = ↓porosity
✗ Al: never CO2! Not MAG — pure Ar only
▶ YouTube✗ Al: never CO2! Not MAG — pure Ar only
TIG/GTAW — Gas Tungsten Arc Welding
AWS A5.12DCENMaximum Precision
StandardAWS A5.12 / ISO 6848
CurrentDCEN (steel/SS/Ti) / AC (Al/Mg)
W ElectrodeEWTh-2 (2%Th) / EWG (WL15 lanthanated)
Gas100% Ar / Ar+He / He
Filler WireManual / automatic (hot wire)
Thickness0.3mm to 10mm as a single pass
DCEN: ↑penetration, ↑electrode life. AC: oxide cleaning for Al!
✓ Perfect finish. Maximum control
✓ Any metal: SS, Ti, Al, Cu, Ni
✗ Slow. ↑skill required. Not for thick sections
▶ YouTube✓ Perfect finish. Maximum control
✓ Any metal: SS, Ti, Al, Cu, Ni
✗ Slow. ↑skill required. Not for thick sections
TIG — Tungsten Electrodes
WL15EWThTip
EWP (green)Pure. AC for Al. Balled tip
EWTh-2 (red)2% thorium. ↑↑ emission. DCEN
EWG/WL15 (gold)Lanthanum. A replacement for Th. RoHS!
EWCe-2 (gray)Cerium. Any polarity. Easy start
Tip ShapeDCEN=pointed 15-30° / AC=balled
WL15/WL20 = the modern choice: ↑emission without radioactive Th
✓ WL15 = a complete replacement for EWTh in every application
▶ YouTube✓ WL15 = a complete replacement for EWTh in every application
TIG — Special Variants: Orbital, Hot Wire, Plasma
OrbitalPlasma
Orbital TIGAutomatic 360° pipe TIG. Aerospace, semiconductor, medical
Hot Wire TIGPreheated wire ← ↑↑ deposition rate x3
Plasma GTAWConcentrated arc↑ → keyhole welding → single-pass full penetration
KeyholeSS pipes 10-25mm thick — a single pass!
✓ Orbital = perfect repeatability for piping
✓ Plasma keyhole = single pass, ↓cost
▶ YouTube✓ Plasma keyhole = single pass, ↓cost
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SMAW/MMA — Stick Electrode Welding
E7018AC/DCField
StandardAWS A5.1 / ISO 2560
Diameter2.0 / 2.5 / 3.2 / 4.0 / 5.0 mm
CurrentDCEP (most) / DCEN / AC (certain)
E7018RM=70ksi. Low-H. DCEP. ↑toughness
E6013Easy start. AC. Cosmetic. Beginners
E6010Deep penetration. DCEP. Root pass. Pipeline
E ####XX: RM / position / coating type
E7018: low-hydrogen — bake at 300-350°C/1h before use!
✓ Self-sufficient. Field-friendly. Any position. Not wind-sensitive
✗ Slow. ↑slag. Not for Al
▶ YouTubeE7018: low-hydrogen — bake at 300-350°C/1h before use!
✓ Self-sufficient. Field-friendly. Any position. Not wind-sensitive
✗ Slow. ↑slag. Not for Al
Low-Hydrogen — E7018 Control
H4/H8BakingAWS
Diffusible HH4 (<4ml/100g) / H8 / H16
ReasonHydrogen cracking (HAZ/weld) — dangerous!
Storage120°C holding oven — after opening
Baking300-350°C/1h after moisture exposure
HY-80E11018-M. ↑↑ toughness
✗ Moisture → H↑ → hydrogen cracking → failure risk!
✓ Baking + holding oven = complete prevention
▶ YouTube✓ Baking + holding oven = complete prevention
Pipeline Welding — E6010 Root
PipelineDCEPAPI 1104
Root PassE6010 — deep penetration + drag technique
Hot PassE8010-P1 / E7010
Fill+CapE8018 / E7018
StandardAPI 1104 / ASME B31.3
Down vs UpDownhill=fast. Uphill=↑penetration
✓ E6010 root = the global pipeline standard
✓ Pipeline 5G/6G position
▶ YouTube✓ Pipeline 5G/6G position
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FCAW — Flux-Cored Arc Welding
E71T-1FastAll-Pos
StandardAWS A5.20 / ISO 17632
TypesFCAW-S (self-shielded) / FCAW-G (gas-shielded)
E71T-1CCO2 gas. All-position. ↑speed vs. SMAW
E71T-8Self-shielded. Outdoor without gas. AWS D1.8 Seismic
Sizes1.2 / 1.6 / 2.0 / 2.4 mm
UseThickening, bridges, construction, shipbuilding
FCAW = MIG speed + SMAW independence
✓ ↑↑ deposition rate vs. SMAW/MIG
✓ FCAW-S = outdoor without gas — bridges, thickening
✗ ↑fume. Slag removal. FCAW-G: gas mandatory
▶ YouTube✓ ↑↑ deposition rate vs. SMAW/MIG
✓ FCAW-S = outdoor without gas — bridges, thickening
✗ ↑fume. Slag removal. FCAW-G: gas mandatory
SAW — Submerged Arc Welding
↑↑ FastFluxBeams
StandardAWS A5.17 / ISO 14171
Current300-1500A! (higher than any other process)
Deposition15-45 kg/h — the highest!
UseSteel beams, thick plates, shipbuilding, pipes
PositionFlat + horizontal only
Tandem SAW2 electrodes → x2 speed!
SAW: arc beneath a flux layer → ↓fume + ↑deposition
✓ ↑↑↑ deposition. ↑quality. ↓fume
✗ Flat-only. Not for small pipes
▶ YouTube✓ ↑↑↑ deposition. ↑quality. ↓fume
✗ Flat-only. Not for small pipes
MCAW + Metal-Cored Wire
E70C-6M↓Spatter↑Speed
PrincipleA tubular wire with metal powder inside (not flux)
Gas75%Ar/25%CO2 (C25)
Advantage↓spatter vs. FCAW. ↑speed vs. ER70S-6
E70C-6MMetal-core. Robot welding
UseRobot lines, automotive, industrial structure
✓ ↑deposition + ↓spatter = perfect for robot welding
✗ More expensive than solid wire
▶ YouTube✗ More expensive than solid wire
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Laser Beam Welding — LBW
Keyhole↓DistortionFast
SourceCO2 / Nd:YAG / Fiber / Disk laser
DepthUp to 25mm single pass!
Speed1-20 m/min
Heat Input↓↓ → ↓↓ distortion
UseAutomotive (tailored blanks), aerospace, medical
ManufacturersTRUMPF, IPG, Coherent
Keyhole mode: laser ↑↑ → plasma → vapor cavity → deep penetration
✓ ↓↓ distortion + ↑↑ speed + precision
✗ Expensive. Precise fit-up mandatory. Fume
▶ YouTube✓ ↓↓ distortion + ↑↑ speed + precision
✗ Expensive. Precise fit-up mandatory. Fume
Electron Beam Welding — EBW
Vacuum↑↑ DepthAerospace
PrincipleElectron beam in vacuum → ↑↑ energy density
DepthUp to 300mm single pass!
Vacuum10-4 mbar — ↓↓ oxidation
Heat Input↓↓↓ — ↓↓↓ distortion
UseGas turbines, weapons, nuclear components
✓ ↑↑↑ single-pass weld depth
✓ ↓↓ distortion + ↓↓ oxidation
✗ Huge, expensive equipment. Vacuum = batch
▶ YouTube✓ ↓↓ distortion + ↓↓ oxidation
✗ Huge, expensive equipment. Vacuum = batch
Friction Stir Welding — FSW
No Melting!AlNASA
PrincipleA rotating tool → friction → plasticization → solid-state weld
MaterialsAl, Cu, Mg — no melting!
UseShinkansen trains, Boeing 777X, SpaceX
Advantage↓↓ distortion. ↓porosity. ↑fatigue
LimitationLinear joints only (almost)
✓ Al welding ← a high-quality solution
✓ ↓porosity + ↑fatigue vs. MIG Al
✗ Linear joint. High force. Tool wear
▶ YouTube✓ ↓porosity + ↑fatigue vs. MIG Al
✗ Linear joint. High force. Tool wear
Resistance Welding — RSW/RSEW
SpotFastAutomotive
RSW SpotCu electrodes → current → nugget. 100-400 ms
RSEW SeamA continuous weld strip — tanks, radiators
ProjectionA pre-defined projection → ↑consistency
Force1000-15000 A · 200-800 ms · 200-800 daN
UseAutomotive: 4000-6000 spots per car!
✓ ×100 faster than TIG. Fully automatic
✓ Every modern car = RSW-primary
✗ Spot joint only. Cu tool wear
▶ YouTube✓ Every modern car = RSW-primary
✗ Spot joint only. Cu tool wear
Plasma Arc Welding — PAW
KeyholePrecisionSS/Ti
PrincipleArc concentrated through an orifice → ↑↑ energy density
Keyhole Mode↑current → full penetration. SS up to 8mm single pass
Melt ModeLike TIG but ↑focus
GasPlasma: Ar | Shield: Ar / Ar+H2
UseSS, Ti piping — orbital PAW
✓ ↑↑ penetration vs. TIG. Keyhole = full pen.
✗ Nozzle wear. More complex than TIG
▶ YouTube✗ Nozzle wear. More complex than TIG
Laser-MIG Hybrid — LAHW
Hybrid↑↑ SpeedShipbuilding
PrincipleLaser + MIG ← synergistic interaction
Advantage↑deposition rate + ↑speed + ↑gap tolerance
Gap ToleranceUp to 2mm (vs. laser <0.5mm)
UseShipbuilding, high-speed trains, thick plates
✓ ↑↑ speed vs. laser-only + ↑gap tolerance
✓ Large-scale shipbuilding structures
▶ YouTube✓ Large-scale shipbuilding structures
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📐 Weld Symbols — AWS/ISO
| Symbol | Name | Use | Edge Prep | Penetration |
|---|---|---|---|---|
| △ | Fillet | T/perpendicular joint — most common | Not required | Partial |
| V | V-Groove | Plates 6-25mm | Chamfer 60-70° | Full |
| ⋀ | Double-V | Plates >16mm | Both sides | Full |
| U | U-Groove | Minimal distortion | CNC milling | Full |
| J | J-Groove | One-sided access | J profile | Full |
| Square | Square | Thin plates <3mm | Straight | Partial/Full |
| ▲ | Surfacing | Cladding/restoration | — | — |
| C | Back/Backing | Root run | Back strip | Full |
📏 Reading a Weld Symbol — AWS A2.4
Reference Line — the horizontal base line
Arrow — points to the weld side
Weld Symbol — below the line = arrow side | above = other side
Tail — process/WPS specifications
Flag — field weld
Circle — weld all around
Size — left of symbol | Length-Pitch = right
▶ YouTubeArrow — points to the weld side
Weld Symbol — below the line = arrow side | above = other side
Tail — process/WPS specifications
Flag — field weld
Circle — weld all around
Size — left of symbol | Length-Pitch = right
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Edge Preparation
AWS D1.1Angle
V-Groove 60°Steel 6-25mm. 1.6mm root gap + 1.6mm root face
Double-VSteel >16mm. Two-sided access. ↓distortion
U-Groove↓filler vs. V. ↓distortion. CNC required
Bevel 45°T-joint. Partial pen. Fast
Square Butt≤3mm. No prep. Full pen with laser/TIG
GTAW Root1-2mm root face + 2-4mm gap → complete pen
✓ Root face: prevents burn-through
✓ Root gap: ensures full penetration
✗ Mismatch >1mm → lack of fusion
▶ YouTube✓ Root gap: ensures full penetration
✗ Mismatch >1mm → lack of fusion
Interpass Temperature
AWS D1.1SSCr-Mo
C-SteelInterpass max: 250°C (typical)
SS AusteniticMax 175°C! ↓sensitization
SS DuplexMax 150°C! Critical!
Cr-Mo (P91)300°C + PWHT 760°C mandatory
HY-80Interpass max 175°C. HIC risk
MeasurementContact thermometer / temp crayon
✗ SS: interpass>175°C → sensitization → IGA!
✗ Duplex: >150°C → sigma phase → brittleness
▶ YouTube✗ Duplex: >150°C → sigma phase → brittleness
Weld Sequence
Back-StepSymmetric↓Distortion
Back-StepA reverse sequence opposite the direction of travel → ↓distortion
SymmetricAlternating ↑↓ welding → cancels stresses
SkipJumping forward and back → ↓heat input
Pre-SetA pre-set angle before welding → ↓distortion
✓ Back-step + symmetric = ↓↓ distortion
✓ Pre-set = simple and effective
▶ YouTube✓ Pre-set = simple and effective
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Preheating
CECETAWS D1.1
Purpose↓cooling rate → ↓martensite → ↓hydrogen cracking
CE (IIW)CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15
CETCET = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40
CE<0.4No preheat needed (usually)
CE 0.4-0.6100-200°C
CE>0.6200-300°C min.
CE = the basic tool for determining preheat!
4340: CE≈1.0 → preheat 200-300°C mandatory
✓ Preheat = prevents cold cracking in HAZ
✗ Low preheat + HRC>35 = HAZ cracking
▶ YouTube4340: CE≈1.0 → preheat 200-300°C mandatory
✓ Preheat = prevents cold cracking in HAZ
✗ Low preheat + HRC>35 = HAZ cracking
PWHT — Post Weld Heat Treatment
AWS D10.10ASMEP91
Carbon Steel580-620°C / 1h per 25mm thickness
Low Alloy Cr-Mo700-760°C. P11,P22,P91
P91 (9Cr-1Mo)760°C / 2h min. — critical!
SS 304/316Annealing 1050°C + quench (no standard PWHT)
StandardASME B31.3 / AWS D10.10 / BS PD 5500
Result↓residual stress + ↑toughness + ↓HIC
P91: missing PWHT = creep failure in service!
✓ PWHT = mandatory for Cr-Mo pressure parts
✗ SS: PWHT = sensitization → IGA!
▶ YouTube✓ PWHT = mandatory for Cr-Mo pressure parts
✗ SS: PWHT = sensitization → IGA!
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Welding Defects
ISO 6520AWS D1.1
PorosityGas bubbles. Cause: moisture/contamination. Prevention: drying+cleaning
Lack of FusionIncomplete fusion. Cause: ↑speed / wrong angle
UndercutA groove at the edge. Cause: ↑amperage / ↑speed
Crack HotSolidification crack. ↑S+P. ↓crater
Crack ColdHAZ/weld. ↑H + ↑CE + stress. Preheat!
OverlapWeld metal on base metal with no fusion
ISO 6520: Group 1=cracks / 2=cavities / 3=solid inclusions / 4=lack of fusion
✗ Cracks = rejected almost always!
▶ YouTube✗ Cracks = rejected almost always!
NDT — Non-Destructive Testing
VT/PT/MT/UT/RTISO 17635
VT VisualAlways first. ISO 17637. Tool: weld gauge
PT Dye PenSurface cracks. ISO 3452. SS/Al/Ti
MT Mag ParticleSurface + near-surface. Magnetic steel only!
UT UltrasonicInternal. ISO 17640. 100% volume
RT RadiographyX-Ray/gamma. ISO 17636. Porosity+cracks
TOFD/PAUTPhased array UT — ↑↑ resolution. An RT replacement
Sequence: VT → PT/MT → UT/RT (per criticality)
✓ PAUT = an RT replacement in many cases
✗ MT = not for austenitic SS / Al / Ti (non-magnetic). Martensitic/duplex SS — yes!
▶ YouTube✓ PAUT = an RT replacement in many cases
✗ MT = not for austenitic SS / Al / Ti (non-magnetic). Martensitic/duplex SS — yes!
Weld Qualification — WPS/PQR/WPQ
AWS D1.1ASME IXISO 15614
WPSWelding Procedure Specification — the instructions
PQRProcedure Qualification Record — WPS approval
WPQWelder Performance Qualification — welder qualification
ASME IXPressure vessels, piping. P-Number grouping
AWS D1.1Steel structures. Prequalified WPS possible
ISO 15614Europe. Part 1=fusion / Part 5=TIG tube
✓ PQR = mandatory basis for a WPS! Cannot be skipped
✓ Prequalified (AWS D1.1) = ↓cost
✗ ASME: every essential variable change = a new PQR
▶ YouTube✓ Prequalified (AWS D1.1) = ↓cost
✗ ASME: every essential variable change = a new PQR
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Steels — Weldability
CEHRC
Carbon <0.25%CExcellent. ER70S-6. No preheat
Low Alloy 4130/4140Good. CE→preheat. ER80S-D2 / E7018-A1
4340Difficult. CE≈1.0 → preheat 200°C. E12018-M
H13 Tool SteelVery difficult. Preheat 300°C. H13 filler. ↑PWHT
Maraging 300TIG. ER18Ni300. Solution HT afterward
✓ <0.25%C = free welding
✗ CE>0.6 = preheat + PWHT + low-H electrodes
▶ YouTube✗ CE>0.6 = preheat + PWHT + low-H electrodes
Stainless Steel — Welding SS
L GradeInterpass
304/316ER308L/316L. EWG TIG. Ar+2%O2. Interpass<175°C
Duplex 2205ER2209. Interpass<150°C! N2 in shielding gas
PH 17-4PHER630. Solution HT after welding. No standard PWHT
Martensitic 410Preheat 200°C. PWHT 675°C. ER410
SS→CS309L / 309LMo — butter layer!
✓ L Grade (ER308L): ↓C = ↓sensitization
✗ Duplex: gas+interpass are critical!
▶ YouTube✗ Duplex: gas+interpass are critical!
Aluminum — Welding Al
4043/5356AC TIG
6061-T6ER4043 MIG/TIG. ↓cracking. Afterward: re-age to T6
5083/5086ER5356 — ↑weld strength
2024Very difficult to arc-weld — susceptible to hot cracking
7075Not possible! — FSW only
TIG ACOxide cleaning in AC. HF start. Gas lens!
✗ 2024 + 7075 = not for arc welding! FSW only
✓ 6061: ER4043. ↓crack sensitivity
▶ YouTube✓ 6061: ER4043. ↓crack sensitivity
Special Materials — Ti/Ni/Cu
TiInconelCu
TitaniumTIG only. 100% Ar. Trailing shield! ↓O2
Inconel 625ERNiCrMo-3. Low heat input. ↑interpass control
CopperCuSi3 MIG braze / TIG. ↑preheat
Duplex+TiPlasma PAW. Laser. ↑inert gas
✓ Ti: trailing shield mandatory! O2=blue oxide=reject
✗ Ti: ↑contamination = immediate reject
▶ YouTube✗ Ti: ↑contamination = immediate reject
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📊 Welding Process Comparison
| Process | Speed | Heat Input | All-Position | Finish | Main Use |
|---|---|---|---|---|---|
| TIG/GTAW | Low | ↓ | Yes | Excellent | SS, Ti, Al, thin sections |
| MIG/MAG GMAW | High | Medium | Yes | Good | C-Steel, Al, SS |
| SMAW/MMA | Medium | High | Yes | Medium | Maintenance, field |
| FCAW-G | Very high | High | Yes | Medium | Structure, shipbuilding |
| SAW | Very high | Very high | Flat only | Excellent | Thick plates |
| Laser LBW | Very high | ↓↓ | Limited | Excellent | Automotive, aerospace |
| FSW | High | N/A | Limited | Excellent | Al, Cu — no melting |
| RSW Spot | Very high | N/A | — | Excellent | Automotive, sheet metal |
| EBW | High | ↓↓↓ | Limited (vacuum) | Excellent | Aerospace, precision |
📌 Process Selection Guide
Thin SS/Ti/Al — perfect finish? TIG/GTAW
Volume, C-Steel, semi-auto? MIG/MAG
Field, maintenance, all-position? SMAW
Heavy structure, high deposition? FCAW / SAW
↓Distortion, high speed? Laser / hybrid
Al/Cu — no melting? FSW
Automotive sheet metal, full automation? RSW Spot
Volume, C-Steel, semi-auto? MIG/MAG
Field, maintenance, all-position? SMAW
Heavy structure, high deposition? FCAW / SAW
↓Distortion, high speed? Laser / hybrid
Al/Cu — no melting? FSW
Automotive sheet metal, full automation? RSW Spot