Application of Strip Electrode Surfacing Technology

Literature Overview

This 2010 paper published in Electric Welding Machine (Vol. 40, No. 8, pp. 59–63) by Martin Kubenka, Gabriellf Galazzi, and Solveig Rigdal from Esab Welding & Cutting Supplies (Shanghai) Co., Ltd. discusses the application of strip electrode surfacing technology, specifically for depositing stainless steel corrosion-resistant layers onto low-carbon steel or low-alloy steel substrates. The classification number TG455 places this in the general surfacing technology category. The paper provides both technical detail and practical case studies from Italian industrial applications at SICES and Ansaldo Camozzi factories.

Technical Principles of Strip Electrode Surfacing

Strip electrode surfacing is a variant of submerged arc welding (SAW) or electroslag welding (ESW) that uses a continuous metal strip instead of a solid wire as the consumable electrode. The strip electrode is fed into the weld pool at a controlled rate, with the strip serving as both the heat source conductor and the filler metal. The key technical features include:

Two Primary Methods Discussed

The paper discusses two main approaches to strip electrode surfacing:

Method 1: Submerged Arc Strip Electrode Surfacing

In this method, the strip electrode operates under a layer of granular flux, similar to conventional submerged arc welding. The strip is fed from the rear of the welding head, with the flux providing shielding and slag formation. This method is well-suited for planar and cylindrical surfaces and offers excellent bead uniformity.

Method 2: Electroslag Strip Electrode Surfacing

This method utilizes the electroslag welding principle, where the welding process operates in a slag pool rather than under a flux layer. The electroslag process provides even higher deposition rates and better heat input control, making it suitable for thick surfacing builds on large components.

Metallurgical Considerations for Stainless Steel Surfacing

When depositing stainless steel onto carbon steel substrates, several metallurgical challenges must be addressed:

1. Dilution control: Carbon steel base material dilutes the stainless steel deposit, reducing chromium and nickel content. If dilution exceeds approximately 25%, the deposited layer may not achieve the required corrosion resistance. A multi-pass approach with increasing stainless steel alloy content in subsequent passes is recommended.
2. Intermetallic formation: At the interface between the carbon steel base and the stainless steel surfacing, intermetallic compounds may form, particularly if the heat input is excessive. These intermetallics can be brittle and reduce bond strength.
3. Residual stress management: The mismatch in thermal expansion coefficients between carbon steel and stainless steel creates significant residual stresses at the interface. Stress-relief annealing or controlled cooling may be necessary.
4. Sensitivity to impurities: Stainless steel surfacing deposits are sensitive to sulfur, phosphorus, and other impurities that can promote cracking. Base metal cleaning and proper flux selection are critical.

Industrial Application Cases

SICES Application

At the SICES factory in Italy, strip electrode surfacing was applied to large pressure vessels and heat exchanger components in the chemical processing industry. The components required corrosion-resistant stainless steel surfaces but were manufactured from low-cost carbon steel to reduce fabrication costs. The strip electrode process provided:

• High deposition rates suitable for large surface areas
• Consistent bead quality over long weld lengths
• Lower dilution compared to conventional wire SAW
• Reduced welding time and labor costs

Ansaldo Camozzi Application

At the Ansaldo Camozzi factory, strip electrode surfacing was applied to components in the nuclear and power generation sectors. These applications required strict quality control and documentation, and the strip electrode process offered:

• Reproducible weld quality suitable for nuclear-grade applications
• Reduced heat input compared to electroslag welding, minimizing distortion
• Compatibility with existing welding infrastructure
• Ability to deposit multi-layer builds with controlled dilution

Process Optimization and Quality Control

For successful implementation of strip electrode surfacing, the following quality control measures are essential:

1. Pre-weld preparation: Base metal surfaces must be thoroughly cleaned of rust, paint, and contaminants. Edge preparation should ensure adequate penetration of the first surfacing pass.
2. Parameter optimization: Welding current, voltage, travel speed, and strip feed rate must be optimized for the specific alloy system and base material. A parameter matrix approach is recommended to establish the optimal window.
3. Dilution monitoring: Regular dilution analysis of the deposited layer is essential to ensure that the required alloy composition is maintained. Optical emission spectroscopy (OES) provides rapid dilution measurement.
4. Non-destructive testing: Visual inspection, magnetic particle testing, and ultrasonic testing should be performed on each pass to detect defects such as porosity, incomplete fusion, and cracks.
5. Corrosion testing: Potentiodynamic polarization testing or immersion testing should be performed on completed surfacing layers to verify corrosion resistance performance.

Engineering Practice Recommendations

Based on the paper's content and practical experience, the following recommendations are offered:

• For new applications, begin with a comprehensive weldability study including dilution mapping, microstructural analysis, and corrosion testing before full-scale production.
• Establish standardized welding procedures with defined parameter ranges, as strip electrode surfacing is highly sensitive to parameter variations.
• Invest in operator training, as the process requires skill in managing strip feeding stability and maintaining consistent bead profiles.
• Consider the total cost of ownership, including equipment investment, consumable costs, and labor, when evaluating strip electrode surfacing against alternative processes such as laser cladding or thermal spraying.

The paper by Kubenka and colleagues provides a practical and well-documented account of strip electrode surfacing technology application, demonstrating that this process offers a cost-effective solution for depositing corrosion-resistant stainless steel layers onto carbon steel substrates in demanding industrial environments, with proven performance in chemical processing and nuclear power applications.