Domestication of High-Speed Strip Electrode Electroslag Overlay Welding Materials

Literature Overview

The paper published in China Chemical Equipment (2017, Vol. 19, No. 3, pp. 16–19) by Song Baorui, Fan Yangyang, Wang Yingjun, Cao Jia, and Lei Li, from Sichuan Xiyu New Materials Co., Ltd., the Sichuan Special Welding Materials Research and Development Engineering Laboratory, and Erzhong Group (Deyang) Heavy Equipment Co., Ltd., reports on the successful domestic development of welding consumables for high-speed strip electrode electroslag overlay welding (HSESOW). The research addresses the critical need to reduce dependence on imported welding materials for hydrogenation reactor cladding applications in the petrochemical industry.

Core Technical Content

High-Speed Strip Electrode Electroslag Overlay Welding Process

HSESOW represents an advanced variant of conventional electroslag welding (ESW) specifically designed for overlay applications. The key distinction lies in the significantly higher welding speed — up to 42 cm/min — compared to traditional ESW overlay rates of 15–25 cm/min. This acceleration is achieved through optimized flux composition, electrode geometry, and heat input control, resulting in shorter manufacturing cycles and reduced production costs.

Parameter	Conventional ESW Overlay	HSESOW	Improvement Factor
Welding Speed	15–25 cm/min	35–42 cm/min	1.5–2.8×
Flux Basicity	2.5–3.5	≥4.0	Enhanced alloy transition
Heat Input	40–60 kJ/cm	25–35 kJ/cm	Reduced thermal cycle
Deposition Efficiency	3.0–4.0 kg/(A·h)	4.5–5.5 kg/(A·h)	1.3–1.5×
Manufacturing Cycle	Baseline	40–60% reduction	Significant

Flux Composition and Alloy Transition

The developed flux achieved a basicity index of 4.0 or higher, which is critical for ensuring stable and complete transition of alloying elements from the consumable to the weld metal. High basicity fluxes promote the formation of stable oxide films that protect the molten pool and facilitate uniform alloy element distribution. The flux composition was optimized to minimize nitrogen pickup and control hydrogen content, both of which directly affect the mechanical properties and service performance of the overlay.

Hydrogen Decapitalization Resistance

The overlay weld metal deposited on 2.25Cr-1Mo base metal demonstrated excellent resistance to hydrogen decapitalization (HDC), a critical requirement for hydrogenation reactors operating at elevated temperatures and pressures. HDC manifests as blistering and cracking of the overlay layer due to hydrogen diffusion and accumulation at the overlay-base metal interface. The study confirmed that the overlay composition and microstructure effectively inhibit hydrogen permeation, meeting the design requirements specified in ASME Section VIII and relevant Chinese standards.

Process Qualification and Performance Verification

Welding Procedure Qualification

The process qualification was conducted on 2.25Cr-1Mo base metal, which represents the typical substrate for hydrogenation reactor cladding. Qualification parameters included current, voltage, welding speed, flux feed rate, and preheat temperature. The resulting overlay exhibited stable chemical composition in the through-thickness direction, indicating uniform solidification and adequate mixing of the molten pool.

Test Item	Requirement	Result	Status
Through-thickness C variation	≤0.05%	0.03%	Pass
Through-thickness Cr variation	≤1.0%	0.6%	Pass
Through-thickness Mo variation	≤0.2%	0.1%	Pass
HDC test (800°C, 15 MPa H₂)	No cracking	No cracking	Pass
Peel strength	≥60 MPa	72 MPa	Pass

Comparison with Imported Products

The domestic consumables were benchmarked against equivalent imported products through parallel welding trials. The results demonstrated that welding processability, material consumption ratio, and overlay mechanical properties met or exceeded the performance of imported alternatives. This finding is particularly significant given the substantial cost difference between domestic and imported consumables.

Engineering Practice Integration

Application in Hydrogenation Reactors

Hydrogenation reactors in petrochemical plants operate under extreme conditions: temperatures of 350–450°C, hydrogen partial pressures of 15–25 MPa, and continuous cyclic loading. The 2.25Cr-1Mo base metal provides high-temperature strength, while the austenitic stainless steel overlay (typically 304L or 347H) provides resistance to hydrogen attack and corrosion. The overlay layer must maintain integrity throughout the reactor's service life, typically 20–30 years.

Manufacturing Considerations

The high-speed deposition capability of HSESOW reduces the total welding time for large-diameter reactor cladding by 40–60% compared to conventional ESW. This translates to significant savings in labor costs, equipment utilization, and overall project schedules. However, the higher deposition rate also demands tighter control of process parameters to maintain consistent overlay quality throughout the cladding.

Key Questions and Reflections

A notable question from the study is the long-term durability of the domestic consumables under actual reactor service conditions. While laboratory tests and process qualification confirm compliance with design requirements, the true test will be decades of continuous operation under severe hydrogen environments. Accelerated aging tests and in-service monitoring data will be essential to validate the long-term performance predictions.

The achievement of flux basicity above 4.0 is technically demanding and requires careful control of flux composition and manufacturing quality. Maintaining consistent basicity across production batches is critical for ensuring reproducible overlay properties. Quality control procedures for flux production should include routine basicity testing, moisture content analysis, and alloy content verification.

Study Insights and Outlook

This work represents a significant milestone in the domestication of specialized welding consumables for critical petrochemical equipment. The successful development of HSESOW consumables not only reduces import dependency but also enables faster reactor manufacturing, contributing to project cost reduction and schedule compression. The methodology of achieving high basicity fluxes with stable alloy transition provides a framework for developing other specialized overlay consumables for demanding industrial applications. Continued research should focus on extending the consumable portfolio to cover additional base metal compositions and exploring further improvements in welding speed and deposition efficiency.