Investigation of Combined Surfacing Methods for Hydrogenation Reactor Inner Wall Cladding

Literature Overview

This paper by Wang Jinliang, Zhang Shijian, Fu Junhao, Luo Weicong, Liu Yongfa, and Xi Xiaohui from Guangdong Ocean University and Shandong Iron and Steel Co., Ltd. Laizhou Branch was published in 2022 in "Guangzhou Chemical Industry" (Volume 50, Issue 14, pp. 167-169). The research addresses the critical engineering challenge of inner wall surfacing for hydrogenation reactors, which are core equipment in petrochemical enterprises. The study employs a combined surfacing approach using strip electrode electroslag welding (SEESW) followed by flux-cored gas shielded welding (FCGSW) to achieve a dual-layer stainless steel overlay on 2.25Cr-1Mo steel substrate.

Technical Background and Requirements

Hydrogenation reactors operate under extreme conditions involving high temperature, high hydrogen pressure, and corrosive environments containing hydrogen sulfide and other aggressive species. The inner wall cladding must provide:

The base material 2.25Cr-1Mo steel (equivalent to ASTM A387 Gr. 22 or SA-387) provides excellent high-temperature strength and resistance to hydrogen attack, but lacks adequate corrosion resistance for the inner wall environment. The overlay must therefore provide a barrier layer with appropriate composition and microstructure.

Combined Surfacing Methodology

The dual-layer approach combines the high deposition rate of SEESW with the refined microstructure and improved surface quality of FCGSW:

First layer (SEESW): This layer provides the primary transition from base metal to overlay material. Strip electrode electroslag welding offers deposition rates of 10-20 kg/h, making it economically attractive for thick overlay layers. The electroslag process produces a coarse but clean weld with relatively low dilution when properly controlled.

Second layer (FCGSW): This final layer provides the critical surface quality, refined microstructure, and optimized composition for corrosion resistance. The flux-cored wire process offers better gas protection and more precise composition control than SEESW alone.

The combination addresses the inherent limitations of each individual process:

1. SEESW alone produces a coarse microstructure with potential segregation issues at the surface
2. FCGSW alone would be prohibitively expensive for thick overlay layers due to lower deposition rates
3. The combination achieves both economic efficiency and quality requirements

Results Analysis

The study reports comprehensive characterization of the combined surfacing layer:

Chemical composition: The final overlay layer meets the specified composition requirements for the intended stainless steel grade, with adequate Cr, Ni, and Mo content for corrosion resistance. The dilution from the base metal is controlled within acceptable limits through the dual-layer approach.

Ferrite content: The austenitic-ferritic microstructure balance is maintained within the target range. For austenitic stainless steel overlays, a controlled ferrite content of 2-10% is typically desirable to prevent solidification cracking while maintaining adequate mechanical properties.

Hardness and bending performance: The overlay layer exhibits hardness values consistent with the specified stainless steel grade, and bending tests confirm adequate ductility without cracking or delamination.

Intergranular corrosion resistance: The overlay passes standard intergranular corrosion testing, confirming that the welding process does not cause harmful chromium carbide precipitation at grain boundaries.

Engineering Practice Significance

This research has direct relevance to the fabrication of large-diameter hydrogenation reactor shells. The combined surfacing approach represents a practical engineering solution that balances:

• Productivity: SEESW provides the high deposition rate needed for large-scale fabrication
• Quality: FCGSW ensures the critical surface layer meets stringent metallurgical requirements
• Cost: The combination is more economical than using FCGSW or TIG for the entire overlay thickness
• Reliability: The dual-layer approach provides redundancy in terms of defect screening

For engineers involved in reactor fabrication, this work validates the concept of hybrid surfacing processes as a viable approach for meeting the demanding requirements of hydrogenation reactor inner wall cladding. The methodology can be extended to other applications requiring thick corrosion-resistant overlays on high-strength base materials.

Study Insights and Implications

The key insight from this work is that process combination can overcome the limitations of individual surfacing processes. No single process can simultaneously achieve high deposition rate, excellent surface quality, refined microstructure, and precise composition control. The strategic combination of processes, each selected for its specific strengths, provides a path to meeting all requirements simultaneously.

This approach aligns with modern manufacturing philosophy of process integration and hybrid manufacturing. For the fabrication industry, it suggests that the optimal surfacing process selection should consider not just individual process capabilities but also how processes can be sequenced to complement each other's strengths and compensate for their weaknesses.

The practical challenge in implementing such combined processes lies in ensuring proper bonding between the layers and maintaining consistent quality across the entire overlay thickness. Interlayer defects, composition variations, and microstructural incompatibilities between layers must be carefully managed through appropriate interpass temperature control and process parameter optimization.