5. Workpiece Preparation
5.1 Pre-weld Cleaning
Before welding, thoroughly remove oil, rust, oxide scale, moisture, paint, and dust from the welding area (groove surface and 20-30mm on both sides). Cleaning methods include mechanical grinding, sandblasting, pickling, alkali washing, or solvent wiping until metallic luster is exposed.
5.2 Groove Processing
Groove form and dimensions must comply with design drawings. Groove surfaces must not have cracks, lamination, or slag inclusions. For thermal cutting, slag and oxide layers must be ground off.
5.3 Assembly and Tack Welding
Assemble workpieces according to drawings. Tack welding materials should match formal welding. Tack weld length, thickness, and spacing should be appropriate. Tack welds must not have cracks, porosity, or slag inclusions.
5.4 Preheating
For materials with poor weldability or thick workpieces, preheat according to process requirements. Preheating temperature should be measured at about 50mm from groove edge.
6. Welding Process Parameter Selection and Control
6.1 Basic Principles
Parameter selection should be based on welding procedure qualification reports, considering welding method, material grade, thickness, groove form, and position.
6.2 SMAW Parameters
- Electrode diameter selected based on material thickness and position
- Welding current determined by electrode diameter and position
- Arc voltage generally 10-20V
- Welding speed moderate to ensure penetration
6.3 GMAW/FCAW Parameters
- Current and voltage must match
- Shielding gas flow adjusted by nozzle diameter and environment
- Wire stick-out length affects current density
6.4 TIG Parameters
- Tungsten diameter and tip shape selected by current and material
- Arc voltage generally 8-15V
- Pulse parameters control heat input for thin plates
7. Welding Quality Control
7.1 Self-inspection and Mutual Inspection
Welders should observe molten pool status at all times and check weld appearance after each pass for porosity, cracks, incomplete fusion, undercut, etc.
7.2 First Article Inspection
For new products, new processes, or important parts, first article inspection must be conducted before batch production.
7.3 Defect Prevention
- Porosity: prevent by drying electrodes, cleaning grooves, ensuring gas purity
- Cracks: control by preheating, low-hydrogen materials, proper heat input
- Incomplete fusion: correct parameters and groove dimensions
- Undercut: adjust current and travel speed
8. Post-weld Treatment
8.1 Cleaning
After welding, promptly remove slag, spatter, and weld beads. For high-requirement welds, grind surfaces smooth.
8.2 Heat Treatment
For materials prone to delayed cracking or important structures under dynamic loads, perform stress relief heat treatment according to process requirements.
8.3 Visual Inspection
100% visual inspection after welding for weld formation, dimensions, and surface defects.
8.4 NDT
Conduct RT, UT, MT, or PT according to design requirements after cleaning and heat treatment.
9. Safety and Health Protection
9.1 PPE
- Welding helmet with proper filter lens
- Heat-resistant leather gloves
- Flame-retardant protective clothing
- Safety shoes with insulation
- Dust mask or respirator in poorly ventilated areas
9.2 Work Environment Safety
- Ventilation: maintain good ventilation to remove fumes and harmful gases
- Fire and explosion prevention: no flammable materials within 10m
- Electric shock prevention: reliable equipment grounding, good cable insulation
- High-altitude work: safety belts required
