I. Pre-Welding Preparation
Base Metal Preparation
Thoroughly remove oil, rust, moisture, and other impurities from the groove and the 20mm range on both sides of the groove. This prevents hydrogen-induced cracking and porosity.
For thick plates or high-constraint structures, perform pre-cleaning (e.g., mechanical grinding or chemical cleaning) to ensure no oxide scale remains on the surface.
Electrode Drying and Storage
Before use, dry the electrodes at 350~400℃ for 1 hour, then store them in a 100~150℃ heat-insulated container and take them as needed to prevent moisture absorption.
The number of re-drying cycles should not exceed 2 to avoid cracking of the electrode coating.
Preheating Control
Preheating temperature should be adjusted based on the type of base metal:
P92/T91 heat-resistant steel: Preheat to 150℃ for GTAW (Gas Tungsten Arc Welding) backing, and preheat to 220℃ before SMAW (Shielded Metal Arc Welding).
Q460 high-strength steel: Preheating temperature ranges from 100~200℃, adjusted according to plate thickness and ambient temperature.
The preheating range covers 3 times the plate thickness (and not less than 100mm) on both sides of the weld. Use an infrared temperature gun for monitoring.
II. Welding Process Control
Power Source and Polarity
Adopt DC electrode positive (DCEP) to ensure stable arc, low spatter, and good slag detachability.
Current and Voltage Parameters
Electrode diameter and current range:
φ3.2mm: 100~120A for flat welding, 90~110A for vertical/overhead welding.
φ4.0mm: 140~180A for flat welding, 130~160A for vertical/overhead welding.
Voltage should match the current, usually ranging from 22~26V. Avoid excessive arc length, which may cause porosity.
Electrode Manipulation and Interpass Cleaning
Use short arc operation; the arc length should not exceed 1 time the electrode diameter, and the oscillation amplitude should be ≤ 3 times the electrode diameter.
For multi-layer multi-pass welding, the thickness of each layer should be ≤ the electrode diameter (e.g., ≤3.2mm for φ3.2mm electrodes). Maintain the interpass temperature above the preheating temperature (e.g., 200~300℃ for P92 steel).
Thoroughly clean slag between each weld pass with a grinder to prevent slag inclusion.
Argon Purging Protection (for Heat-Resistant Steels)
When welding materials with high alloy content (such as P92/T91), argon purging is required for the root. The argon flow rate is 15~30L/min to ensure no oxidation on the backside.
III. Post-Welding Treatment
Post-Heating and Hydrogen Relief Treatment
Immediately perform post-heating at 200~350℃ after welding, with heat preservation for 0.5~2 hours to accelerate hydrogen diffusion.
For thick plates or high-constraint structures, conduct isothermal tempering at 750~770℃ (e.g., for P92 steel, the isothermal time is 5 minutes/mm and not less than 3 hours) to eliminate stress and improve microstructural properties.
Slow Cooling and Cooling Control
Avoid rapid cooling; wrap the weld with asbestos cloth to cool it slowly to room temperature.
IV. Prevention of Common Defects
Porosity
Causes: Moisture-absorbed electrodes, contaminated base metal, excessive arc length.
Measures: Strictly dry electrodes, clean the groove, and use short arc operation.
Slag Inclusion
Causes: Inadequate interpass cleaning, excessively fast welding speed.
Measures: Grind each weld pass with a grinder and control the welding speed.
Incomplete Penetration
Causes: Insufficient current, inadequate groove angle.
Measures: Adjust the current to the recommended range and ensure the groove dimensions meet requirements.
Cold Cracking
Causes: Excessively high hydrogen content, excessively fast cooling rate.
Measures: Strictly control preheating/interpass temperature and perform timely post-heating after welding.
V. Safety and Environmental Requirements
Personal Protection
Wear welding goggles, fire-resistant gloves, and protective clothing to prevent arc burns and spatter scalds.
Weld in a well-ventilated environment; use fume extraction equipment if necessary to avoid inhaling fumes containing chromium and molybdenum.
Environmental Control
Ensure the ambient temperature is ≥5℃, relative humidity ≤60%, and wind speed ≤2m/s. If not, take measures such as heating, dehumidification, or wind shielding.
VI. Other Precautions
Electrode Matching: Select electrodes of corresponding models based on the strength and alloy composition of the base metal (e.g., match E9015-G with P92 steel); avoid mixed use.
Welding Procedure Qualification (WPQ): Conduct WPQ before first use or when welding critical structures to verify the rationality of parameters.
Performance Variations: The performance of E9015G electrodes from different manufacturers may vary slightly; refer to specific technical data sheets.
By strictly implementing the above measures, the strength, toughness, and crack resistance of E9015G welded joints can be ensured, meeting the strict requirements of scenarios such as pressure vessels and power station pipelines. In practical operations, it is recommended to further optimize process parameters based on base metal characteristics, structural forms, and relevant standards (e.g., AWS A5.5).
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