Application of Domestic Single-layer Strip Electrode Electroslag Surfacing in Hydrogenation Reactors

Literature Overview

The paper by Liu Baojian, Kong Fanhong, Wang Tianxian, and Fan Xibin from Qingdao Lanshi Heavy Machinery Equipment Co., Ltd., published in Pressure Vessel Technology in 2019 (Volume 36, Issue 9, pages 70-77), documents the application of domestically produced single-layer strip electrode electroslag surfacing (EES) consumables in hydrogenation reactor manufacturing. The work is classified under TG455 and represents a significant engineering achievement in the domestication of critical surfacing technology for hydrogen-containing pressure vessels.

Core Technical Content

Hydrogenation reactors in petroleum refining and chemical processing operate under severe conditions involving high temperatures, high pressures, and hydrogen-containing atmospheres. These conditions create susceptibility to hydrogen-induced cracking (HIC), sulfide stress cracking (SSC), and hydrogen blistering, necessitating the application of corrosion-resistant overlay layers on the reactor inner walls. The study reports the use of domestically produced 75 mm × 0.4 mm steel strip electrodes with matching flux for single-layer electroslag surfacing.

Process Parameters and Specifications

The single-layer electroslag surfacing approach was selected over multi-layer alternatives to reduce production cycle time and minimize the risk of interpass cracking and hydrogen-induced defects. The 75 mm strip width provides efficient deposition rates while the 0.4 mm thickness ensures adequate heat input for proper slag-metal interaction and dilution control.

Welding Procedure Qualification Analysis

The welding procedure qualification (WPQ) process followed standard practices including:

1. Pre-qualification review: Verification of consumable specifications, equipment capabilities, and operator qualifications.
2. Coupon preparation: Fabrication of test coupons representative of the production geometry and thickness.
3. Welding execution: Application of the qualified procedure to produce surfacing layers on test coupons.
4. Non-destructive testing: Application of radiographic testing (RT) and/or ultrasonic testing (UT) to detect internal defects such as slag inclusions, porosity, and lack of fusion.
5. Destructive testing: Mechanical property evaluation including tensile strength, hardness profiling, and macrograph examination.
6. Corrosion testing: HIC and SSC resistance evaluation per NACE MR0175/ISO 15156 or equivalent standards.

The successful qualification and subsequent product acceptance demonstrate that domestic consumables can meet the stringent requirements for hydrogen-containing pressure vessel applications, which have historically relied on imported materials.

Engineering Practice Integration

The successful application of domestic EES consumables in hydrogenation reactors has several important implications for the Chinese pressure vessel manufacturing industry:

1. Supply chain security: Reducing dependence on imported electroslag surfacing consumables mitigates supply chain risks and reduces lead times for critical pressure vessel manufacturing.
2. Cost reduction: Domestic consumables typically offer lower unit costs compared to imported alternatives, contributing to improved project economics for hydrogenation reactor manufacturing.
3. Technical standardization: The WPQ process documented in this paper can serve as a reference for similar applications, facilitating the broader adoption of domestic EES consumables across the industry.
4. Quality assurance: The acceptance of the product for shipment confirms that the domestic consumables produce surfacing layers with adequate metallurgical quality, corrosion resistance, and mechanical integrity.

Key Questions and Reflections

A critical question that arises from this study is the long-term performance validation of the domestic EES consumables under actual service conditions. While the WPQ and product acceptance demonstrate compliance with specified requirements, the true test of corrosion resistance and hydrogen damage resistance occurs during extended service in hydrogenation reactors. Post-service inspection programs should be established to track the performance of reactors surfaced with domestic consumables over their operational lifetime.

Another reflection concerns the generalizability of this qualification to other reactor types and operating conditions. Hydrogenation reactors vary significantly in terms of operating temperature, pressure, hydrogen partial pressure, and corrosive medium composition. The qualification performed here may not be directly transferable to reactors operating under more severe conditions, and additional WPQs may be required for each specific application.

Study Insights and Implications

This paper documents a significant milestone in the domestication of electroslag surfacing technology for hydrogen-containing pressure vessels in China. The successful qualification and application of 75 mm × 0.4 mm domestic strip electrodes and flux in hydrogenation reactor manufacturing demonstrates that domestic consumables can meet the demanding requirements of critical pressure vessel applications. For pressure vessel manufacturers and surfacing engineers, this study provides confidence in the availability and quality of domestic EES consumables, while highlighting the importance of rigorous WPQ and product acceptance procedures to ensure long-term service reliability. The broader implication is that domestic consumable development can reduce industry dependence on imported materials while maintaining or improving product quality, contributing to the competitiveness of the domestic pressure vessel manufacturing sector.