Application of ESAB Strip Cladding Technology

Literature Overview

This paper provides a comprehensive overview of strip cladding technology as applied by ESAB, a leading manufacturer of welding consumables and equipment. Strip cladding, also known as strip cladding welding or electroslag strip cladding, is a specialized welding process that uses a strip of cladding material (typically stainless steel or nickel-based alloy) fed through an electroslag bath to deposit a corrosion-resistant or wear-resistant layer onto a base material. The process combines the advantages of electroslag welding (high deposition rate, low dilution, low hydrogen) with the compositional precision of strip feed, making it one of the most efficient and reliable methods for producing clad plate and clad components.

Process Description and Mechanism

Strip cladding operates on the principle of electroslag welding. A direct current (DC) arc is established between the strip (which serves as the electrode) and the base metal, creating a pool of molten flux on top of the workpiece. The flux is typically a water-cooled copper nozzle that melts a granular flux (such as a rutile-type or basic-type flux) to create a stable slag pool. The strip is continuously fed through the slag pool, and the electroslag effect melts both the strip and a small portion of the base metal, creating a weld pool that solidifies beneath the slag.

The electroslag process provides several inherent advantages for cladding applications. The large slag pool provides excellent shielding of the weld pool from atmospheric contamination, resulting in very low porosity. The high thermal input and slow cooling rates produce a coarse but uniform microstructure with minimal hardening in the heat-affected zone. Most importantly, the dilution ratio is typically very low (5-15% depending on process parameters), which is critical for maintaining the corrosion resistance of the cladding layer.

Typical Strip Cladding Process Parameters

Common Strip Materials and Applications

ESAB offers a wide range of strip materials for cladding applications. For stainless steel cladding, common strip grades include 308L (AWS A5.9), 309L, 316L, 321, 347, and 310. The 308L strip is the most widely used for general corrosion resistance on carbon steel and low-alloy steel substrates. The 316L strip provides enhanced resistance to chlorides and sulfuric acid. The 321 and 347 strips contain titanium or niobium stabilizers for applications requiring resistance to intergranular corrosion.

For nickel-based alloy cladding, ESAB strips include Inconel 625, Inconel 600, Monel 400, and Hastelloy C276. These strips are used for severe corrosion environments such as chemical processing, pulp and paper, and offshore oil and gas applications. The high cost of nickel-based strips makes them economically viable primarily for high-value components where corrosion failure would result in significant downtime or safety risks.

Quality Control and Inspection

Quality control in strip cladding is critical due to the high cost of the cladding material and the importance of the cladding layer for component performance. The primary inspection methods include:

1. Visual inspection: Checking for surface defects such as cracks, porosity, undercut, and insufficient overlap between adjacent weld passes. The strip cladding process typically produces a very smooth, uniform surface, and any deviation from this uniformity indicates a potential defect.
2. Magnetic particle testing (MT): Used for surface and near-surface defect detection in ferromagnetic cladding materials. MT is particularly effective for detecting cracks and lack of fusion at the base-cladding interface.
3. Ultrasonic testing (UT): Used for detecting lack of fusion, cracks, and other volumetric defects at the base-cladding interface. The dilution ratio and bond strength at this interface are critical for the structural integrity of the clad component.
4. Hardness testing: Verifying that the cladding layer hardness is within the specified range and that the heat-affected zone has not been excessively hardened. For austenitic stainless steel cladding, hardness should typically be below 200 HV to ensure adequate corrosion resistance.
5. Corrosion testing: Including intergranular corrosion tests (ASTM A263/A264), ferric chloride tests, and other application-specific corrosion tests to verify the corrosion resistance of the cladding layer.

Engineering Practice and Process Optimization

In my experience with bimetal pressure vessel fabrication, strip cladding is the preferred process for producing clad plate used in hydrogenation reactors, heat exchangers, and storage tanks. The key to successful strip cladding lies in maintaining consistent process parameters throughout the entire cladding operation. Any variation in strip speed, travel speed, current, or voltage can result in variations in dilution ratio, which directly affects the corrosion resistance of the cladding layer.

A common challenge in strip cladding is maintaining the correct dilution ratio, particularly at the start and end of each weld pass. At the beginning of a pass, the dilution ratio may be higher due to the initial melting of the base metal, and at the end, it may be lower as the slag pool cools and the electroslag effect diminishes. To address this, experienced operators use start and stop plates and carefully control the strip entry and exit angles. Some modern strip cladding systems incorporate automatic process monitoring and feedback control to maintain consistent parameters throughout the pass.

Another critical aspect is the management of the heat-affected zone (HAZ). In strip cladding of stainless steel onto carbon steel, the HAZ in the base metal can experience sensitization if the cooling rate is too fast or if the carbon content is too high. This can lead to intergranular corrosion in the HAZ, which is as detrimental as corrosion in the cladding layer itself. The low dilution and slow cooling rates of the electroslag process help mitigate this risk, but careful selection of the base material (preferably with carbon content below 0.06%) and appropriate post-weld heat treatment are still recommended.

Study Insights and Implications

The ESAB strip cladding technology represents a mature, well-established process for producing high-quality clad plate and clad components. Its key advantages—high deposition rate, low dilution, excellent shielding, and consistent quality—make it the process of choice for many critical applications in pressure vessel and chemical processing industries. The technology has been refined over decades of industrial practice, and the availability of a wide range of strip materials allows engineers to select the optimal cladding material for virtually any corrosion environment. However, the process requires significant capital investment in specialized equipment and skilled operators, which limits its application to high-volume or high-value production. For smaller-scale or repair applications, alternative cladding processes such as multi-pass submerged arc welding or gas tungsten arc welding may be more practical. The key takeaway for engineers is that strip cladding, when properly executed with rigorous process control and quality inspection, provides the highest level of confidence in cladding layer performance and component longevity.