Single-Layer Strip Electrode Electroslag Cladding Technology for Hydrogenation Refining Reactor Manufacturing

Literature Overview

This paper, published in Chemical Engineering and Machinery (2020, Vol. 47, No. 3, pp. 393-396), authored by Liu Yan, Ma Xiaobing, Wang Junjie, Li Fufu, An Tianyou, and Wang Xiping from Xinjiang Lanshi Heavy Energy Engineering Co., Ltd., presents a systematic study on single-layer strip electrode electroslag cladding (SS-ESCl) technology applied to hydrogenation refining reactors. The work covers the welding procedure qualification (WPQ) for 12Cr2Mo1R stainless steel cladding on carbon steel substrate, followed by comprehensive performance evaluation including ferrite content, chemical composition, bend testing, corrosion resistance, and hydrogen blistering resistance.

Core Technical Content and Process Parameters

The authors established a qualified single-layer strip electrode electroslag cladding process for overlaying 12Cr2Mo1R stainless steel onto the interior surfaces of reactor shells and heads. This is a critical technology for hydrogenation refining service, where the vessel interior is exposed to high-temperature, high-pressure hydrogen environments that demand exceptional resistance to hydrogen damage, hydrogen blistering, and high-temperature oxidation.

Performance Evaluation Results

The study conducted five key performance assessments on the cladding layer:

1. Ferrite Content: The delta ferrite content in the cladding layer was maintained within the acceptable range of 5-30% (per ASME Section IX, QW-451), which is essential for preventing cracking in austenitic and duplex-type welds. The single-layer approach provides uniform ferrite distribution without the dilution gradient issues common in multi-pass cladding.
2. Chemical Composition: The cladding layer composition met the requirements of 12Cr2Mo1R specifications, with controlled carbon content (typically below 0.10%) to minimize carbide precipitation and maintain hydrogen resistance. Chromium and molybdenum contents were verified to be within specification limits for high-temperature hydrogen service.
3. Bend Testing: Side-bend tests were performed per ASME Section IX requirements, demonstrating the ductility and soundness of the cladding layer and the cladding-to-base metal fusion zone. No cracks or defects exceeding acceptance criteria were observed.
4. Corrosion Resistance: The cladding layer exhibited satisfactory resistance to high-temperature oxidation and hydrogen-induced degradation, which are the primary failure mechanisms in hydrogenation refining reactors operating at temperatures above 350°C and pressures exceeding 10 MPa.
5. Hydrogen Blistering Test: The hydrogen blistering resistance test, which simulates the actual hydrogen environment in the reactor, confirmed that the single-layer SS-ESCl cladding provides adequate protection against hydrogen blistering and hydrogen cracking. This is a critical qualification requirement for vessels operating in sour hydrogen service.

Engineering Practice and Technical Insights

The single-layer strip electrode electroslag cladding process offers several distinct advantages over conventional multi-pass cladding methods:

• Efficiency: A single pass achieves the full required cladding thickness, significantly reducing production time compared to multi-pass GTAW or SAW cladding. This is particularly important for large-diameter reactor shells where surface area is extensive.
• Uniformity: The electroslag process provides consistent heat input and cooling rates, resulting in uniform microstructure and mechanical properties across the entire cladding surface.
• Porosity Control: The slag cover in electroslag welding acts as a natural gas shield, virtually eliminating porosity defects that are common in multi-pass arc welding processes.
• Fusion Zone Quality: The controlled dilution ratio between the strip electrode and the base metal ensures a consistent cladding composition, avoiding the compositional variation that can occur with manual or semi-automatic multi-pass cladding.

However, the single-layer approach also presents challenges that must be managed. The high heat input inherent in electroslag welding can lead to coarse grain structure in the heat-affected zone (HAZ) of the base metal if not properly controlled. The authors addressed this through careful preheating and post-weld heat treatment (PWHT) protocols, typically normalizing the entire vessel at 760-790°C for stress relief and grain refinement.

From an FMEA perspective, the critical failure modes for this application include: hydrogen blistering and cracking at the cladding-to-base metal interface, cracking in the HAZ during PWHT due to excessive carbon content in the base metal, and loss of cladding integrity under cyclic thermal loading. The qualification testing described in this paper provides the basis for mitigating these risks through process control.

Study Insights and Implications

This work demonstrates that single-layer strip electrode electroslag cladding is a viable and reliable technology for hydrogenation refining reactor manufacturing. The key insight is that the process, when properly qualified and controlled, can deliver cladding layers with consistent performance characteristics that meet the demanding requirements of high-temperature hydrogen service. For engineers involved in pressure vessel manufacturing, this paper provides a practical reference for WPQ development and process optimization. The emphasis on hydrogen blistering testing as a qualification criterion reflects the industry's growing recognition of hydrogen damage as a primary failure mechanism in hydrogenation reactors, and the importance of material selection and cladding technology in ensuring long-term vessel integrity.