CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Domestic Single-Layer Strip Electroslag Welding Consumables in Hydrogenation Reactors
Literature Overview
This study note focuses on the engineering application of domestically produced single-layer strip electroslag welding (ESW) consumables for weld overlay cladding in hydrogenation reactors. Hydrogenation reactors operating under high temperature, high pressure, and hydrogen-rich environments demand exceptional corrosion resistance and mechanical integrity from their internal cladding layers. The adoption of domestically developed consumables represents a significant milestone in reducing dependence on imported materials while maintaining performance standards.
Core Technical Content
The electroslag welding overlay process is particularly suited for large-diameter hydrogenation reactor shells where deposition rates are critical. The single-layer strip ESW approach eliminates the need for multi-pass buildup, simplifying the welding procedure specification (WPS) and reducing total fabrication time. The domestic consumable system typically employs a nickel-based or austenitic stainless steel strip electrode with a matching flux composition designed to produce a fully austenitic weld metal with controlled grain structure.
Key performance requirements for the overlay layer in hydrogenation service include resistance to hydrogen attack (HA), sulfide stress corrosion cracking (SSC), and general corrosion from process fluids. The overlay thickness is typically specified between 3 mm and 6 mm depending on the design code and operating conditions, with bond strength to the base carbon steel or low-alloy steel substrate verified through shear or tensile testing per NB/T 47014 and GB/T 150.
Typical Process Parameters
| Parameter | Typical Range | Notes |
|---|---|---|
| Welding current | 800–1200 A | Dependent on strip thickness |
| Arc voltage | 35–45 V | Monitored continuously |
| Travel speed | 100–200 mm/min | Adjusted for deposition rate |
| Preheat temperature | 100–200 °C | To prevent cold cracking |
| Interpass temperature | ≤ 250 °C | Maintain austenitic structure |
| Post-weld heat treatment | 720–780 °C, 2–4 h | Stress relief and grain refinement |
Standards and Code Compliance
The fabrication of hydrogenation reactor overlay layers must comply with multiple standards simultaneously. GB/T 150 governs pressure vessel design and fabrication requirements, while NB/T 47014 provides qualification procedures for welding procedure specifications. The overlay material specifications typically reference ASTM A263 for Inconel 625 strip or EN 10028-7 for stainless steel clad plate equivalents. The weld qualification follows NB/T 47014 or ASME IX qualification rules.
Engineering Practice and Quality Control
In practice, the single-layer ESW overlay on hydrogenation reactors presents several challenges. The large plate thickness of reactor shells (often 60–120 mm) creates significant thermal gradients during welding, which can lead to distortion and residual stress accumulation. A systematic approach using the PDCA cycle is recommended: Plan the thermal input distribution based on finite element analysis, Do the welding with real-time monitoring of slag pool temperature, Check through ultrasonic testing (UT) and magnetic particle testing (MT) after each pass, and Act by adjusting parameters for subsequent sections.
The bond strength between the overlay layer and the base metal is a critical inspection point. Shear testing per NB/T 47014 typically requires a minimum value of 200 MPa for carbon steel to stainless steel joints. Common defects include lack of fusion at the bond line, slag inclusion, and porosity, all of which are detectable through UT with phased array (PAUT) methods.
Study Insights and Implications
The successful application of domestic single-layer strip ESW consumables demonstrates that Chinese metallurgical capabilities have reached a level comparable to international standards. However, engineers should note that long-term service performance data for domestic consumables in hydrogenation environments is still accumulating. The key takeaway is that material substitution decisions must be supported by comprehensive qualification testing including hydrogen permeation tests, intergranular corrosion resistance evaluation, and accelerated aging studies. The engineering community should continue to document field performance data to build confidence in domestic material systems for critical pressure equipment.