Development and Application of 347 Stainless Steel Wire Electrode Submerged Arc Overlay Welding Materials

Literature Overview

The article by Wang Jinguang, Hu Xihai, Che Hong, Jia Lijuan, Wang Dong, Zou Liwei, Xu Kai, and Zhang Yimei, published in Welding (2011, Issue 6), reports on the development and application of 347 stainless steel wire electrode submerged arc overlay welding materials. The work was conducted jointly by Sinopec Engineering Corporation, Fushun Machinery Equipment Manufacturing Co., Ltd., and the Harbin Welding Research Institute. The developed materials include H309SL and H347SL stainless steel welding wires and matching fluxes SJ661 and SJ667. The study addresses the limitations of conventional SMAW for stainless steel overlay welding—low efficiency, poor surface quality, high cost, and production schedule delays.

Core Technical Findings

The 347 stainless steel is a stabilized austenitic stainless steel containing niobium (Nb) as a stabilizer to prevent chromium carbide precipitation and intergranular corrosion. It is widely used in high-temperature applications in the petrochemical industry, particularly in pressure vessels and heat exchangers operating at temperatures up to 870°C. The overlay welding of 347 stainless steel on carbon steel substrates provides corrosion and oxidation resistance while maintaining structural integrity.

The key technical achievements of this study were: (1) achieving overlay weld performance comparable to strip electrode submerged arc welding (SESAM) using wire electrode submerged arc welding (WSAM), (2) significantly improving deposition rate over SMAW (from 1–2 kg/h to 5–10 kg/h), (3) producing consistent, smooth weld surfaces suitable for subsequent machining or direct use, and (4) reducing production costs and schedule time.

Process Analysis and Engineering Interpretation

The transition from SMAW to WSAM for stainless steel overlay welding represents a significant productivity improvement. SMAW with E309L or E347 electrodes provides excellent weld quality but has inherently low deposition rates, inconsistent bead geometry, and high labor costs. WSAM with the developed H309SL/H347SL wires and matching fluxes offers the advantages of automatic welding—high deposition rate, consistent bead quality, reduced operator skill dependence, and improved cost efficiency—while maintaining the metallurgical quality of the deposited metal.

The two-pass strategy (309L transition layer followed by 347L overlay layer) is a standard practice for overlay welding stainless steel on carbon steel. The 309L transition layer has a higher nickel content than 347L, which reduces the dilution effect of the carbon steel base metal and minimizes the formation of brittle martensitic phases at the interface. The 347L final layer provides the required corrosion and oxidation resistance with niobium stabilization.

The matching fluxes SJ661 and SJ667 were developed to provide the following functions: (1) arc stability and consistent arc length control, (2) deoxidation of the molten pool to reduce inclusion formation, (3) slag protection against atmospheric contamination, (4) appropriate heat input distribution to control solidification microstructure, and (5) easy slag removal for multi-pass welding. The flux composition is critical for achieving the target chemical composition and microstructure in the deposited metal.

Integration with Engineering Practice

In the context of pipe fitting and pressure vessel manufacturing for the petrochemical industry, the developed WSAM materials have direct applicability. Many pressure vessels and heat exchangers require stainless steel overlay welding on carbon steel substrates to provide corrosion resistance in aggressive environments. The following practices are relevant:

1. Process qualification: The WSAM process must be qualified in accordance with ASME Section IX or applicable national codes, including mechanical property testing, corrosion testing (intergranular corrosion per ASTM A262, pitting corrosion per ASTM G48), and microstructural examination.
2. Substrate preparation: The base metal surface must be clean and free of contamination (oil, rust, scale) to ensure proper fusion and avoid contamination of the deposited metal. Machining or grinding to expose clean metal is recommended.
3. Preheat and interpass temperature: For carbon steel substrates, preheat of 100–200°C may be required to control cooling rate and prevent cracking. Interpass temperature should be maintained below 250°C for austenitic stainless steel overlay to prevent sensitization.
4. NDT requirements: Ultrasonic testing (UT) and radiographic testing (RT) are typically required for overlay welds in pressure vessels, per ASME Section VIII or applicable codes. The developed WSAM process should be qualified to produce welds that are amenable to NDT.

Key Questions and Reflections

The study demonstrates that WSAM can achieve performance comparable to SESAM, which is a significant finding. However, a question arises about the scalability of this achievement to different substrate geometries and thicknesses. The study likely focused on flat or slightly curved surfaces typical of pressure vessel shells, but pipe fittings often have complex geometries (elbows, tees, reducers) that may challenge the WSAM process. The ability of WSAM to maintain consistent weld quality on curved surfaces, particularly at tight radii, needs to be evaluated.

Another reflection concerns the long-term performance of the overlay welds in service. The petrochemical industry operates under demanding conditions—high temperatures, corrosive environments, cyclic loading, and thermal cycling. The overlay weld interface, with its inherent microstructural gradient and potential for microcracking, represents a potential failure site. Long-term durability testing, including thermal cycling and corrosion fatigue, should be considered for critical applications.

Study Insights and Implications

This literature represents a successful example of welding materials and process development driven by industrial needs. The systematic approach—identifying the limitations of existing processes, developing new materials to address those limitations, and validating through comprehensive testing—provides a model for technology development in our industry. The key insights are: (1) wire electrode submerged arc welding is a viable alternative to strip electrode submerged arc welding for stainless steel overlay, offering comparable performance with greater flexibility, (2) matching flux development is critical for achieving the target metallurgical properties in the deposited metal, and (3) the transition from manual to automatic welding processes can significantly improve productivity and quality consistency. For engineers in the pipe fitting and pressure vessel industry, this study demonstrates that materials and process innovation can solve practical production challenges, and encourages continued investment in welding technology development.