E347L Stainless Steel Welding Strip Design and Submerged Arc Surfacing Layer Performance

Literature Overview

The paper by Zhang Xinbao from the Technical Center of Taiyuan Stainless Steel Co., Ltd., published in China Surface Engineering (Vol. 24, Issue 6, pp. 92-97, 2011), presents a comprehensive study on the design, production, and performance evaluation of E347L stainless steel welding strip for submerged arc strip surfacing applications. This work was driven by the need to replace imported EQ347 surfacing strip material, which is used in critical applications such as hydrogenation reactors in the chemical industry.

Technical Background and Design Philosophy

E347L is a low-carbon, stabilized austenitic stainless steel that is resistant to intergranular corrosion (IGC) due to the addition of niobium (Nb), which preferentially forms NbC rather than allowing Cr₂C₃ to form at grain boundaries. The "L" designation indicates a low-carbon grade (C ≤ 0.03%), which provides additional resistance to sensitization. This alloy is particularly suitable for applications involving:

• High-temperature hydrogen service (hydrogenation reactors, hydrocrackers)
• Sulfidic environments (sour service)
• High-temperature oxidation and corrosion
• Resistance to chloride stress corrosion cracking (SCC)

The design of E347L welding strip for submerged arc strip surfacing presents unique challenges:

Production Process Details

The authors described a production process that involved several critical steps:

1. Melting and refining: The steel was melted in an EAF (Electric Arc Furnace) and refined using AOD technology. AOD is essential for achieving the ultra-low carbon content required for the "L" grade. The AOD process allows precise control of carbon and nitrogen levels through controlled oxygen injection and argon stirring.
2. Hot forging and hot rolling: The hot working temperatures were controlled below 1250°C to prevent excessive grain growth and to maintain proper NbC formation. Excessive hot working temperatures can cause NbC dissolution and subsequent grain boundary chromium depletion upon cooling.
3. Cold rolling: The final cold rolling produced a strip with dimensions of 0.5 mm × 50 mm with dimensional tolerances of ±0.01 mm. This level of dimensional accuracy is critical for submerged arc strip surfacing, as variations in strip thickness directly affect the overlay thickness and dilution rate.
4. Heat treatment: The strip was solution annealed to dissolve any precipitated carbides and achieve a homogeneous austenitic structure.

Surfacing Performance Results

The submerged arc strip surfacing trials produced the following results:

The FN value of 5-7 is particularly significant. In austenitic stainless steel surfacing, a small amount of delta ferrite (typically 3-10 FN) is desirable because it:

• Reduces hot cracking susceptibility during welding.
• Improves resistance to solidification cracking.
• Provides a slight increase in strength without compromising ductility.

The IGC test result (no cracking after intergranular corrosion attack and subsequent 180° bending) confirms the effectiveness of the Nb stabilization and low carbon design. This is a critical requirement for hydrogenation reactor applications, where the weld overlay must resist sensitization during prolonged exposure to elevated temperatures.

Engineering Practice Integration

For engineers specifying E347L surfacing strips for industrial applications, the following considerations are important:

1. Application selection: E347L is ideal for applications requiring resistance to both high-temperature corrosion and hydrogen damage. It is particularly suitable for:

• Hydrogenation reactor internals (tube bundles, heat exchangers)
• Hydrocracker reactor linings
• Sulfidic environment equipment (refinery sour water strippers)
• High-temperature furnace components

1. Welding process selection: Submerged arc strip surfacing is the preferred process for E347L because it provides:

• Low dilution rates (typically 5-15%)
• High deposition rates
• Excellent surface finish
• Controlled heat input

1. Welding parameter optimization: The following parameters are critical for achieving optimal surfacing quality:

• Arc voltage: 25-35 V (adjust based on strip thickness)
• Welding current: 300-500 A
• Travel speed: 200-400 mm/min
• Shielding flux: Low-hydrogen, basic flux with appropriate Mn and Si content
• Preheating: Typically not required for austenitic stainless steel, but may be needed for thick base plates to control residual stress

1. Quality assurance: The surfacing layer should be inspected for:

• Chemical composition verification (spectroscopic analysis)
• Ferrite number measurement (Magnetic Ferrite Meter)
• Hardness testing (Vickers or Rockwell)
• Intergranular corrosion testing (ASTM A262 Practice E or ASTM G48)
• Non-destructive testing (PT for surface defects, UT for subsurface defects)

Comparative Analysis with Imported EQ347

The domestic E347L strip was developed to replace imported EQ347 material. The comparison reveals:

The successful replacement of imported material with domestically produced E347L strip represents a significant achievement in terms of supply chain security and cost reduction. For large-scale applications such as hydrogenation reactor refurbishment, where thousands of meters of strip may be required, the cost savings are substantial.

Key Questions and Reflections

The paper does not provide detailed information on the long-term performance of the E347L surfacing layer under actual service conditions in hydrogenation reactors. Long-term exposure to high-temperature hydrogen can cause hydrogen embrittlement, and the resistance of the surfacing layer to this degradation mechanism should be evaluated.

Additionally, the paper does not discuss the effects of multiple surfacing passes on the microstructure and properties of the overlay. In practice, multiple passes are often required to achieve the desired overlay thickness, and each subsequent pass experiences a different thermal history that can affect the final microstructure.

The study also does not address the compatibility of the E347L overlay with different base materials. In hydrogenation reactor applications, the base material may be a low-alloy steel (such as Cr-Mo steel) or a higher-alloy austenitic stainless steel. The dilution and metallurgical compatibility of the overlay with different base materials should be evaluated.

Study Insights and Implications

This research demonstrates the successful development and production of a high-quality E347L stainless steel welding strip that meets international standards and can replace imported material in critical industrial applications. The combination of advanced metallurgical processing (AOD refining, controlled rolling temperatures) and precision manufacturing (tight dimensional tolerances) results in a surfacing strip that delivers excellent performance in terms of corrosion resistance, mechanical properties, and weldability. For engineers working on hydrogenation reactor projects and other high-temperature, high-pressure applications requiring corrosion-resistant overlays, the domestic E347L strip offers a reliable and cost-effective solution. The successful replacement of imported material also highlights the importance of developing domestic capabilities in specialized welding consumables, reducing supply chain vulnerabilities and enabling faster project execution.