Stainless Steel Bypass Diversion MIG-TIG Double-Sided Arc Welding Process Characteristics

Literature Overview

This paper, published in the Journal of Welding in 2013 by researchers from Harbin Engineering University, investigates the process characteristics of double-sided arc welding combining MIG and TIG methods for stainless steel bypass diversion pipelines in marine and underwater engineering applications. The work was supported by the National Natural Science Foundation of China (Grant No. 51005049) and conducted at the Key Laboratory of Underwater Robot Technology. The study addresses a critical fabrication challenge in submarine pipeline systems where stainless steel piping must be joined with high integrity under demanding service conditions.

Core Technical Content

The research focuses on the hybrid application of Gas Metal Arc Welding (GMAW/MIG) for the root and fill passes combined with Gas Tungsten Arc Welding (GTAW/TIG) for the cap pass on stainless steel bypass pipelines. This approach leverages the high deposition rate of MIG welding for bulk material buildup while utilizing the superior surface finish and weld appearance achievable through TIG welding for the final exposed surface. The double-sided configuration allows full-penetration welds without backing rings, which is essential for applications requiring internal smoothness such as fluid transport systems in underwater vehicles.

Process Parameters and Configuration

Parameter	MIG Pass	TIG Pass
Current range	140–220 A	100–160 A
Voltage	20–26 V	10–14 V
Travel speed	300–500 mm/min	200–350 mm/min
Shielding gas	98% Ar + 2% CO₂	100% Ar
Wire diameter	1.0 mm	2.5 mm tungsten
Nozzle diameter	14–16 mm	12–14 mm

The key innovation in this work lies in the coordinated control of heat input between the two welding methods. When MIG is applied from one side and TIG from the opposite side simultaneously, the thermal interaction creates a complex heat-affected zone (HAZ) morphology that requires careful parameter optimization to avoid excessive grain growth or residual stress concentration.

Process Analysis and Engineering Relevance

For engineers working with clad or bimetal pressure vessels, this study provides valuable insights into multi-process welding strategies that can be adapted for weld-overlay cladding applications. The MIG-TIG combination mirrors the philosophy used in many cladding procedures where high-deposition-rate processes (such as SAW or FCAW) are employed for the build-up layers while precision processes (such as GTAW or PTA) are reserved for the final overlay layer that contacts the corrosive medium.

The bypass diversion application is particularly relevant to hydrogenation reactor fabrication and chemical processing equipment where stainless steel cladding layers must be deposited on carbon steel or low-alloy steel substrates. The residual stress management techniques discussed in this paper—particularly the use of sequential heating from both sides to minimize angular distortion—can be directly transferred to the welding sequence planning for large-diameter clad vessels.

Key Defect Considerations

Undercut at the TIG cap: When transitioning from MIG fill to TIG cap, thermal mismatch can produce undercut along the weld toe. Preheating the transition zone to 150–200°C before applying the TIG cap pass reduces this tendency significantly.
Porous defects in MIG root: In stainless steel, hydrogen porosity is less common than in aluminum alloys, but nitrogen pickup during MIG with inappropriate shielding can lead to subsurface voids. Maintaining gas flow rates above 15 L/min and ensuring adequate gas coverage during the root pass is essential.
Intermetallic compound formation: In bimetallic configurations where stainless steel overlays carbon steel, the HAZ on the base metal side may develop a diffusion layer of chromium carbides. This is mitigated by limiting interpass temperature to below 150°C and controlling the dilution ratio to less than 30%.

Study Insights and Implications for Cladding Practice

The fundamental lesson from this research is that combining welding processes with different thermal characteristics requires systematic parameter interaction studies rather than simply optimizing each process independently. In cladding applications, where the overlay material and base metal often have vastly different thermal properties, this principle is amplified. For example, when performing GTAW overlay of Inconel 625 on carbon steel, the dilution from the base metal into the overlay is typically 15–25%, which fundamentally changes the composition and properties of the resulting weld metal.

The paper's approach to evaluating weld quality through both macrostructural examination and mechanical testing (hardness traverse, tensile strength, impact toughness) provides a methodology template that can be applied to weld-overlay qualification under NB/T 47014 or ASME IX. The emphasis on balancing deposition rate against weld quality is directly transferable to the economic optimization of cladding procedures, where minimizing the number of layers while maintaining metallurgical integrity is always a key design objective.

This literature demonstrates that even seemingly simple process combinations carry deep metallurgical implications, and that rigorous experimental methodology remains the cornerstone of reliable welding technology development in pressure vessel and cladding applications.