The welding of stainless steel pipes typically involves three stages: root (backing) welding, fill welding, and cap welding. Among these, backing welding is the most critical step, as it directly influences both weld quality and construction progress. Currently, two primary backing welding approaches are used: argon-protected root welding and non-argon root welding. Each includes various sub-methods with distinct technical characteristics and field suitability.
1. Argon-Backed Root Welding with Plugging Plates (Solid Wire + TIG)
In prefabrication environments, where the pipe welds can be rotated and ventilation is easy, this method is commonly used.
Process: Install plugging plates on both sides of the weld to create a sealed chamber. Apply adhesive cloth externally to prevent argon leakage. Begin with pre-purging, and delay argon cutoff after welding.
Materials: Plugging plates are typically made of rubber and tinplate, providing good durability and air-tightness.
Advantages: Ensures high argon purity and effectively prevents oxidation of the weld root, leading to reliable weld quality.
2. Combined Use of Water-Soluble Paper and Plugging Plates (Solid Wire + TIG + Soluble Paper)
Used primarily when welding fixed ports where interior ventilation is limited or access is restricted.
Method A: For one-sided limited access, block the easy side with a plugging plate and the difficult side with double-layered water-soluble paper; seal externally with adhesive cloth.
Method B: When neither side can be vented, block both with soluble paper and ventilate from the weld center. After purging, quickly remove the gas line and complete the weld using the remaining argon.
Precautions:
Soluble paper must be securely affixed to prevent displacement or failure during welding.
Insufficient protection can lead to oxidation, requiring costly rework.
Welders must strictly inspect sealing integrity before starting.
Despite its technical challenges, this method has shown excellent weld quality in practical site applications, particularly in complex installations.
3. Flux-Cored Wire Backing without Argon (Flux-Cored Wire + TIG)
This technique omits argon purging and uses flux-cored wire for root pass welding, offering practical advantages in field applications.
Materials: E308T1-1, E308LT1-1, E309T1-1, E316LT1-1, 347T1-1, etc.
Benefits:
No internal purging required
Cost-effective and efficient
Ideal for construction sites and repair welding
However, due to its fast wire feed speed and high operator sensitivity, this method requires highly skilled and trained welders to ensure consistency.
Successfully applied in projects such as Nanjing Yangba and international sites, especially where argon supply is limited or impractical.
4. Self-Protecting Flux-Coated Wire + TIG (No Argon Protection)
In this approach, protection is achieved through the slag and alloy reaction from the flux-coated wire, while the front side is still shielded with TIG and argon gas.
Process Key Points:
Maintain correct torch angle (70°–80°) and wire angle (15°–20°)
Adjust welding speed and torch tilt to control molten pool temperature
Use slightly higher current than with solid wire
Swing the torch gently to ensure good slag separation and observation of weld pool
Feed wire into half of the molten pool, applying slight pressure to ensure penetration
Keep the wire tip under continuous argon protection to avoid oxidation
Carefully manage arc start and termination to avoid defects like arc pits
Advantages:
No need for back-side argon filling
High efficiency and low cost
Consistent weld quality with proper technique
Simplified operation, especially suited for base layer welding
Summary and Process Selection
Each of the four stainless steel root welding methods has its own advantages and limitations. The appropriate process should be selected based on:
Welding quality requirements
Site conditions
Construction cost
Project timeline
A rational process selection not only ensures welding reliability and safety but also helps to optimize construction efficiency and economic performance.
United Steel Industry As the most important steel pipe manufacturer and exporter in China, in the past 20 years, we have completed more than 100 projects, with partners in more than 100 countries, and established relationships with oil and gas and EPC companies in many countries business relationship.
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please consult:Email:Sales@usisteels.com
