Double-Side Argon Arc Welding Process for Stainless Steel Tanks

1. Summary of double-sided argon arc welding process

Stainless steel storage tanks, characterized by large volumes and thin-walled plates, are typically designed as atmospheric vessels. While manual electrode welding has been the conventional method, it presents several challenges, including significant spatter, internal stress accumulation, and substantial single-sided deformation, making quality control difficult.

To overcome these limitations, argon arc welding has emerged as a superior alternative. This process eliminates spatter and slag formation, addressing the primary drawbacks of manual electrode welding. However, the high oxygen affinity of stainless steel at elevated temperatures introduces additional complexities.

Single-sided argon arc welding, despite its improvements, can still lead to issues such as “slag weld” formation and chromium depletion in the weld joint area. This phenomenon, known as sensitization, can significantly compromise the corrosion resistance of the welded structure, potentially leading to premature failure in aggressive environments. Moreover, single-side welding is highly dependent on groove assembly precision and can result in critical defects like incomplete penetration and inadequate root fusion.

To address these challenges comprehensively, the double-sided argon arc welding process is recommended. This technique involves simultaneous welding on both sides of the joint by two operators. The advantages of this method include:

1. Balanced heat input, minimizing distortion and residual stress
2. Enhanced penetration and fusion, reducing the risk of defects
3. Improved chromium distribution, maintaining corrosion resistance
4. Higher qualification rates in non-destructive testing (NDT)
5. Increased productivity and efficiency in large-scale tank fabrication

By employing inert argon shielding on both sides, this process ensures optimal protection against atmospheric contamination throughout the weld pool and heat-affected zone. The synchronized welding approach also allows for better control of the weld bead profile and microstructure, contributing to superior mechanical properties and long-term performance of the welded joints.

2. Specific process parameters

1. Weld groove type and size

Note: The groove must be machined before welding. Prior to welding, all pollutants on the surface of the groove and within a 100mm radius must be removed. If necessary, the area should be dried with a dry rag. The alignment and misalignment of the inner weld should not exceed 0.5mm.

2. Welding process parameters

3. Recommended Welding Materials

1）Argon must be at least 99.99% pure, and a product certificate must be attached to confirm its purity.

2）The recommended welding materials for various austenitic stainless steels are as follows:

Note: Welding materials must have quality certificates or certificates with red seals.

3. Welding diagram

Note: This process has been successfully piloted by relevant companies.

4. Precautions for the application of this process

1）It is important to strictly control the quality of weld groove processing and weld assembly size, including clearance and unfitness.

2）The groove and heat-affected parts should be cleaned and kept dry.

3）The welding process on the main welding side is the same as that of single-sided argon arc welding. The welder on the auxiliary side must work in coordination with the welder on the main welding side and maintain the same welding speed. The wire feeding speed should be adjusted based on the shape of the weld pool and the welder’s experience to ensure that the inner wall weld looks aesthetically pleasing (on the auxiliary side).

4）The specification of the magnetic nozzle of the argon arc welding gun should be selected reasonably based on the thickness of the base metal and the size of the weld groove. The argon flow should be controlled to ensure that the weld pool and heat-affected zone are fully protected.

5）Both welders should start and extinguish the arc at the same time. After welding and extinguishing, argon should protect the arc crater for 1-2 minutes.

6）The wall panel tack welds must be mechanically cleaned before formal welding.

5. Advantages of this process

1）The welding quality is excellent with a high qualification rate on radiographic testing. The weld on the tank wall is also aesthetically pleasing.

2）The welding deformation is minimal, and the external weld on the tank wall is well-crafted.

3）The work efficiency has significantly improved with an increase in labor force in the same working area.

4）Construction costs have been reduced.

By eliminating the need for back welding for argon filling protection, back gouging, and polishing, argon and labor are saved.

6. Disadvantages of this process

1）The welding process has become more challenging, and it now requires welders to work together as a team to maintain a consistent welding speed.

2）Weld alignment standards are stringent, and the clearance for weld alignment is closely monitored.