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Backside Protection Methods for Stainless Steel Welding

With the rapid development of the petrochemical industry, stainless steel materials are widely used, demanding higher standards for pipeline and plate welding. Traditional arc welding for root passes has been phased out in favor of TIG welding (argon arc welding), which offers cleaner and faster root passes. However, challenges arise as the backside of stainless steel TIG welds is prone to oxidation defects. Effective backside protection is critical to ensure weld mechanical properties and corrosion resistance. Below are common backside protection methods for stainless steel welding:

01

Backside Argon Shielding Methods

> Common shielding gases include pure argon or mixed gases (e.g., argon-nitrogen blends), which enhance welding performance for austenitic stainless steel. Some inert gases are excluded due to high costs.

> Argon purging is a traditional and reliable method, offering excellent protection, ease of operation, cleanliness, and high pass rates. Techniques include:

1. Protective Hood Argon Purging

> Used for large plates or wide-diameter pipes. A hood connected to an argon hose is placed over the weld’s backside. An operator slides the hood along with the welding torch, ensuring continuous argon coverage. Advantages: focused protection, minimal argon waste.

2. Local Argon Purging

> Suitable for small or short pipelines. Seal the weld area with tape, block pipe ends with sponges/rubber/paper, and insert an argon hose. A small vent hole on the opposite end prevents internal pressure buildup. Remove tape incrementally during welding to reduce argon loss. Disadvantages: slower purging, higher cost.

3. Direct Weld Joint Argon Purging

> Ideal for long or large-diameter pipes where local purging is inefficient.

> Create two sponge plugs slightly larger than the pipe diameter, connected by a wire. Position plugs 150-200mm from the weld joint. Insert a flattened argon tube into the joint for purging. Remove plugs post-welding using the wire.

> Apply water-soluble paper 150-200mm from the weld joint before alignment. After welding, the paper dissolves during hydrostatic testing.

4. Argon Shielding Quality Assessment

> Evaluate protection effectiveness by observing the weld’s internal color: white/golden indicates optimal shielding; gray/black signifies poor protection. Adjust argon flow accordingly.

5. Key Considerations for Backside Protection

> - Purge with sufficient argon flow before welding, then reduce gradually.

> - Maintain argon flow throughout welding; disconnect only after completion.

> - Position argon inlet at the lowest point and vents at higher points (argon is heavier than air).

> - Tape weld gaps to minimize argon loss; remove tape incrementally during welding.

02

Self-Shielding Flux-Cored Wire Method

> Self-shielding flux-cored wires contain flux coatings that generate protective slag during welding, preventing backside oxidation. The slag detaches post-cooling and is removed during testing.

Advantages:

- Simplifies setup,not limited by welding conditions.

- Suitable for root passes.

Challenges:

- Requires skilled operators to avoid defects like concave roots.

- Higher cost; imported brands offer better quality and adaptability.