Wide Strip Electrode Single-Layer High-Speed Electroslag Surfacing for Hydrogenation Reactor Inner Wall

Literature Overview and Industrial Significance

This paper by Liu Baojian and colleagues from Qingdao Lanshi Heavy Machinery Co., Ltd., published in the journal Pressure Vessel in 2019, addresses a critical manufacturing challenge in the fabrication of high-pressure hydrogenation reactors used in the petroleum refining industry. These reactors typically consist of a carbon steel shell lined with a corrosion-resistant stainless steel layer on the inner wall to resist hydrogen attack and high-temperature corrosion. The conventional multi-layer electroslag welding (ESW) process is energy-efficient but requires multiple passes to achieve the required lining thickness, resulting in long cycle times and potential interpass defects. The researchers investigated whether single-layer high-speed electroslag surfacing using wide strip electrodes could meet the stringent technical requirements for hydrogenation reactor inner wall stainless steel linings.

Technical Approach and Welding Specification Comparison

The study compared three configurations of single-layer strip electrode electroslag surfacing on a hydrogenation reactor shell:

Configuration	Strip Dimensions	Process Type	Notes
Configuration A	90 mm x 0.5 mm steel strip	Conventional single-layer ESW	Baseline reference
Configuration B	75 mm x 0.4 mm steel strip	Single-layer high-speed ESW	Reduced strip width and thickness
Configuration C	90 mm x 0.5 mm steel strip	Single-layer high-speed ESW	Full width with high-speed parameters

The welding specifications were optimized for each configuration to achieve adequate penetration, uniform thickness, and controlled heat input. The high-speed variant involves increased travel speed and adjusted current and voltage parameters to compensate for the reduced strip dimensions or to increase productivity. The deposited layers were evaluated for thickness uniformity, chemical composition, mechanical properties, ferrite content stability, and hydrogen-induced blistering resistance.

Key Performance Results and Metallurgical Assessment

The critical requirement for hydrogenation reactor linings is resistance to hydrogen blistering and hydrogen attack under high-temperature hydrogen service conditions. The researchers confirmed that both Configuration B (75 mm x 0.4 mm high-speed) and Configuration C (90 mm x 0.5 mm high-speed) produced surfacing layers that met the technical requirements. The deposited layers exhibited acceptable chemical composition within the specified range for the stainless steel lining material, typically a 304L or 316L grade austenitic stainless steel. The ferrite content was stable across the layer thickness, which is important for avoiding phase instability under thermal cycling. The mechanical properties, including tensile strength and elongation, were within acceptable limits. Most importantly, no hydrogen-induced blistering was observed under the specified testing conditions.

The single-layer approach eliminates the need for interpass cleaning and inspection between layers, significantly reducing fabrication time. The wide strip electrode provides a broad, uniform weld bead that covers large areas efficiently. The high-speed variant further improves productivity by increasing the deposition rate without compromising quality.

Engineering Practice Considerations and Risk Analysis

Implementing single-layer high-speed electroslag surfacing on large-diameter reactor shells introduces several technical risks that must be managed. First, the thermal gradient between the hot weld zone and the cold base metal can cause distortion and residual stress. Preheating and controlled cooling are essential. Second, the uniformity of the deposited layer across the entire circumference of the shell must be maintained, which requires precise control of the welding torch speed, strip feed rate, and alignment. Third, the interface between the stainless steel lining and the carbon steel base metal is a potential site for intermetallic compound formation, which can embrittle the joint. The dilution rate must be carefully controlled to prevent excessive carbon steel mixing into the austenitic lining.

Risk Factor	Potential Consequence	Mitigation Strategy
High thermal gradient	Shell distortion, residual stress	Preheating to 100-150°C, post-weld stress relief
Excessive dilution	Loss of austenitic corrosion resistance	Control current density, limit penetration depth
Ferrite instability	Phase transformation under thermal cycling	Monitor delta ferrite content, maintain <10%
Hydrogen blistering	Loss of lining integrity under H2 service	Control hydrogen content, ensure full austenite
Layer thickness variation	Localized thinning, stress concentration	Real-time thickness monitoring, process parameter adjustment

Study Insights and Reflections

This research demonstrates that single-layer high-speed electroslag surfacing is a viable and productive alternative to conventional multi-layer ESW for hydrogenation reactor linings. The key advantage is the reduction in fabrication time while maintaining the metallurgical quality required for high-temperature hydrogen service. For engineers involved in pressure vessel manufacturing, this technology offers a pathway to cost reduction and schedule compression without compromising safety. The selection between the 75 mm and 90 mm strip configurations depends on the specific reactor geometry, available equipment, and the required lining thickness. Future development should focus on further increasing deposition rates while maintaining tight control over ferrite content and hydrogen resistance, as these remain the critical quality indicators for hydrogenation reactor applications.