Single-Layer High-Speed Electroslag Surfacing Technology Study Note

Literature Overview

The paper by Zhou Bingfeng from Nanjing Chemical Machinery Co., Ltd. (Sinopec) investigates single-layer high-speed strip-electrode electroslag surfacing (SS-ESS) technology applied to SA387 Gr.22 Cl.2 base material. The study employs imported SOUDOTAPE 24.12.LNB strip electrode paired with RECORD EST129 flux. This technology is relatively unexplored in China and has not yet achieved widespread industrial adoption, making the research findings particularly valuable for engineers seeking to improve production efficiency in high-alloy pressure vessel and heat exchanger manufacturing.

Core Technical Content

The fundamental principle of single-layer high-speed electroslag surfacing relies on a strip electrode fed at high speed through an electroslag pool, creating a single pass with significantly reduced heat input compared to conventional multi-pass electroslag surfacing. The key advantages identified include:

High deposition rate: Single-layer completion eliminates interpass grinding and re-preparation.
Reduced heat input: Faster welding speed limits the thermal cycle, minimizing the heat-affected zone width.
Deep penetration: The electroslag process inherently provides deep fusion, enabling single-pass coverage of thicker repair zones.

Process Parameters and Equipment Requirements

The study emphasizes that SS-ESS technology imposes stringent demands on welding equipment stability and power source capacity. Based on the experimental findings, the following parameter considerations are critical:

Parameter	Typical Range	Effect on Process
Welding current	600–900 A	Higher current increases deposition rate but raises dilution
Welding speed	300–600 mm/min	Higher speed reduces heat input and HAZ width
Strip electrode feed rate	Synchronized with travel speed	Must maintain stable slag pool geometry
Flux coverage thickness	15–25 mm	Ensures proper arc shielding and slag fluidity
Preheat temperature	100–200°C	Controls cooling rate and reduces cracking susceptibility

Dilution Rate Analysis

A critical finding of the study is the quantification of elemental dilution rates for key alloying elements (C, Cr, Ni, Nb) across different base metal thicknesses. The dilution rate in SS-ESS is slightly higher than conventional single-layer normal-speed electroslag surfacing due to the deeper penetration achieved at higher speeds. For SA387 Gr.22 Cl.2, which requires specific Cr-Ni-Nb compositions to achieve low-temperature toughness, dilution control is paramount.

The study reveals that as base metal thickness increases, the dilution rate of Cr and Ni decreases because the thicker base contributes more thermal mass but less relative dilution per unit of deposited metal. Conversely, carbon dilution tends to be more sensitive to thickness variations due to the high carbon content in the base steel relative to the strip electrode.

Engineering Practice Implications

For pressure vessel and heat exchanger manufacturers working with Cr-Mo-V steels such as SA387 Gr.22 Cl.2, this technology offers a pathway to reduce manufacturing time by 40–60% compared to multi-pass conventional surfacing. However, several practical considerations must be addressed:

Equipment investment: The power source must deliver stable, high-current output with precise current regulation (±2%) to maintain slag pool stability at high travel speeds.
Strip electrode quality: The SOUDOTAPE 24.12.LNB strip electrode requires consistent thickness, flatness, and chemical composition to prevent process interruptions.
Flux management: RECORD EST129 flux must be properly dried and maintained at controlled moisture levels to prevent hydrogen-induced cracking.
Post-weld heat treatment: Given the dilution characteristics, PWHT may be required to achieve the specified low-temperature impact properties per ASTM A387 requirements.

Key Questions and Reflections

The paper raises several important questions for further investigation:

How does the SS-ESS process affect the grain structure at the fusion boundary, particularly regarding grain coarsening in the HAZ?
What is the effect of SS-ESS on residual stress distribution compared to multi-pass conventional electroslag surfacing?
Can this technology be adapted for other Cr-Mo-V grades such as SA387 Gr.91 or P91/P92 steels?
What are the long-term fatigue and creep properties of SS-ESS deposits under cyclic thermal loading conditions?

The dilution rate data provided in this study serves as an essential baseline for process qualification. Engineers should note that the slightly elevated dilution rate compared to normal-speed single-layer electroslag surfacing must be factored into material selection calculations. If the dilution rate exceeds acceptable limits for a given application, intermediate alloy compositions or multi-layer strategies may be necessary.

Study Insights and Implications

This research represents a significant advancement in electroslag surfacing technology for high-alloy steel applications. The single-layer high-speed approach addresses the longstanding challenge of balancing deposition efficiency with metallurgical quality in Cr-Mo-V steel surfacing operations. For engineers involved in pressure vessel repair and manufacturing, this technology could substantially reduce production cycle times while maintaining acceptable metallurgical properties, provided that the equipment stability requirements are met and the dilution characteristics are properly managed through careful parameter selection and post-weld treatment.