Comparative Study of Band Electrode Electroslag and Submerged Arc Surfacing for Thick-Walled Pressure Vessel Stainless Steel Lining

Literature Overview

The study by Wang Jiachun and Sun Dunwu from the Harbin Welding Research Institute, published in Welding (1997, No. 7, pp. 12-14), presents a comprehensive comparative investigation of band electrode electroslag surfacing (BESS) and band electrode submerged arc surfacing (BESAS) for stainless steel lining of thick-walled pressure vessels. The research addresses a critical engineering challenge in pressure vessel manufacturing, where corrosion-resistant stainless steel linings must be applied to carbon steel base metals with significant wall thickness, and the surfacing process must achieve low dilution, excellent metallurgical quality, and high productivity.

Core Technical Content

The comparison was conducted across multiple dimensions including surfacing process characteristics, weld bead formation, base metal dilution rate, surfacing layer properties, and fusion zone features. The study concluded that band electrode electroslag surfacing outperforms band electrode submerged arc surfacing and can replace the latter for inner wall surfacing of thick-walled pressure vessels.

Process Mechanisms and Fundamental Differences

Band electrode electroslag surfacing operates on the principle of electroslag welding, where the heat source is the resistance heating of a slag pool rather than direct arc heating. The band electrode and a consumable strip electrode (or the base metal itself) form the electrical circuit, and the molten slag pool provides both the heat source and the protective atmosphere. In contrast, band electrode submerged arc surfacing relies on arc heating between the band electrode and the base metal, with flux providing protection and fluxing.

The fundamental difference in heat generation mechanisms leads to distinct thermal cycles, which in turn affect dilution, microstructure, and mechanical properties of the surfacing deposit. Electroslag surfacing produces a slower cooling rate due to the thermal mass of the slag pool, while submerged arc surfacing generates a more concentrated heat input with faster cooling.

Dilution Rate Comparison

Dilution is the most critical parameter for stainless steel surfacing on carbon steel, as excessive dilution can compromise the corrosion resistance of the surfacing layer by introducing carbon and alloying elements from the base metal. The study demonstrated that band electrode electroslag surfacing achieves significantly lower dilution rates compared to band electrode submerged arc surfacing.

Fusion Zone Characteristics

The fusion zone is the most critical region for evaluating surfacing quality, as it represents the metallurgical interface between the base metal and the surfacing deposit. In band electrode electroslag surfacing, the slower cooling rate and lower dilution result in a fusion zone with a more gradual compositional gradient, reduced residual stresses, and lower susceptibility to cracking. The microstructure of the fusion zone in electroslag surfacing typically shows a more uniform distribution of phases with reduced segregation.

In band electrode submerged arc surfacing, the faster cooling rate and higher dilution lead to a steeper compositional gradient at the fusion line, increased residual stresses, and higher susceptibility to solidification cracking and hydrogen-induced cracking. The microstructure may show increased segregation of alloying elements at grain boundaries, which can compromise corrosion resistance.

Surfacing Layer Properties

The surfacing layer properties, including chemical composition, hardness, corrosion resistance, and mechanical strength, were evaluated for both processes. The electroslag surfacing deposits exhibited more consistent chemical composition with lower carbon content, resulting in better corrosion resistance in aggressive environments. The hardness was slightly lower in electroslag deposits due to the slower cooling rate, but this was acceptable for most pressure vessel lining applications where corrosion resistance is the primary requirement.

Engineering Application and Selection Criteria

The study provides clear guidance for process selection based on specific application requirements. Band electrode electroslag surfacing is recommended for thick-walled pressure vessels where low dilution is critical, high productivity is desired, and the equipment investment can be justified. The process is particularly suitable for large diameter vessels with wall thicknesses exceeding 30 mm, where the thermal mass of the base metal significantly affects the surfacing quality.

Key Process Parameters for Electroslag Surfacing

Quality Assurance Considerations

Quality assurance for band electrode electroslag surfacing of pressure vessels requires attention to several critical aspects. The slag composition must be carefully controlled to ensure proper fluidity, deoxidation, and minimal inclusion formation. The band electrode chemistry must be compatible with the flux to produce a stable slag pool with appropriate electrical resistance. Surface preparation of the base metal is essential to ensure proper fusion and prevent contamination of the surfacing deposit.

Non-destructive testing of the surfacing layers should include magnetic particle testing for surface and near-surface defects, ultrasonic testing for subsurface defects and lack of fusion, and hardness testing to verify the mechanical properties of the surfacing layer. Corrosion testing, including intergranular corrosion tests and immersion tests, should be performed to confirm the corrosion resistance of the surfacing deposit.

Study Insights and Reflections

This comparative study provides valuable engineering guidance for pressure vessel manufacturers and welding engineers involved in stainless steel lining applications. The clear demonstration that band electrode electroslag surfacing achieves lower dilution, better fusion zone quality, and higher productivity establishes a strong technical basis for process selection. The systematic approach of comparing processes across multiple quality dimensions rather than focusing on a single parameter reflects best practices in welding process evaluation.

The findings of this study have direct implications for cost-benefit analysis in pressure vessel manufacturing. While band electrode electroslag surfacing requires more sophisticated equipment and process control, the reduced dilution, improved quality consistency, and higher productivity can result in lower total costs when accounting for rework, inspection, and service life. The study also highlights the importance of considering the entire surfacing system—electrode, flux, parameters, and post-weld treatment—rather than evaluating individual components in isolation.

From a contemporary perspective, the principles established in this 1997 study remain highly relevant. Modern pressure vessel manufacturing continues to face the challenge of applying corrosion-resistant linings to thick carbon steel base metals, and band electrode electroslag surfacing remains a preferred process for many applications. Advances in equipment automation, process monitoring, and consumable development have further enhanced the capabilities of electroslag surfacing, but the fundamental metallurgical principles governing dilution, fusion zone quality, and surfacing layer properties remain unchanged. The study's emphasis on dilution rate as the primary quality indicator for stainless steel surfacing continues to be the cornerstone of surfacing process optimization.